CIAT The International Center for Tropical Agriculture (CIAT) – a member of the CGIAR Consortium – develops technologies, innovative methods, and new knowledge that better enable farmers, especially smallholders, to make agriculture eco-efficient – that is, competitive and profitable as well as sustainable and resilient. Eco-efficient agriculture reduces hunger and poverty, improves human nutrition, and offers solutions to environmental degradation and climate change in the tropics. Headquartered near Cali, Colombia, CIAT conducts research for development in tropical regions of Latin America, Africa, and Asia. www.ciat.cgiar.org CGIAR is a global research partnership for a food secure future. Its science is carried out by the 15 research centers of the CGIAR Consortium in collaboration with hundreds of partner organizations. www.cgiar.org CLAYUCA The Latin American and Caribbean Consortium to Support Cassava Research and Development (CLAYUCA, Consorcio Latinoamericano y del Caribe de Apoyo a la Investigación y al Desarrollo de la Yuca) is a network operating through collaborative agreements between its members, public and private entities. The membership of CLAYUCA includes as of 2012, Colombia, Costa Rica, Ecuador, Guyana, Mexico, Nicaragua, Panama, Trinidad and Tobago, and Venezuela, as well as Ghana, China, and the United States. www.clayuca.org CTA The Technical Centre for Agricultural and Rural Cooperation (CTA) is a joint international institution of the African, Caribbean and Pacific (ACP) Group of States and the European Union (EU). Its mission is to advance food and nutritional security, increase prosperity and encourage sound natural resource management in ACP countries. It provides access to information and knowledge, facilitates policy dialogue and strengthens the capacity of agricultural and rural development institutions and communities. CTA operates under the framework of the Cotonou Agreement and is funded by the EU. www.cta.int ISBN (CIAT): 978-958-694-112-9 ISBN (CTA): 978-92-9081-503-7 Cassava in the Third Millennium Modern Production, Processing, Use, and Marketing Systems Compilation and direction: Bernardo Ospina, Agr. Eng., M.Sc. Hernán Ceballos, Ph.D. © CIAT, CTA. 2012 ISBN (CIAT): 978-958-694-112-9 ISBN (CTA): 978-92-9081-503-7 Apartado Aéreo 6713 Cali, Colombia Phone: +57 2 4450000 Fax: +57 2 4450073 E-mail: b.ospina@cgiar.org / h.ceballos@cgiar.org Website: www.ciat.cgiar.org CIAT Publication No. 377 Press run: 1250 Printed in Colombia June 2012 Cassava in the third millennium : modern production, processing, use, and marketing systems / Compiled and directed by: Bernardo Ospina and Hernán Ceballos. -- Cali, Colombia : Centro Internacional de Agricultura Tropical (CIAT) ; Latin American and Caribbean Consortium to Support Cassava Research and Development (CLAYUCA) ; Technical Centre for Agricultural and Rural Cooperation (CTA), 2012. 574 p. -- (CIAT publication no. 377) ISBN (CIAT): 978-958-694-112-9 ISBN (CTA): 978-92-9081-503-7 Original version in Spanish under the title La Yuca en el Tercer Milenio: Sistemas Modernos de Producción, Procesamiento, Utilización y Comercialización. © CIAT. 2002 This book is accompanied by the Practical Handbook for Managing Cassava Diseases, Pests, and Nutritional Disorders / Elizabeth Álvarez, Anthony Bellotti, Lee Calvert, Bernardo Arias, Luis Fernando Cadavid, Benjamín Pineda, Germán Llano, and Maritza Cuervo (115 p.). ISBN (CIAT): 978-958-694-113-6 ISBN (CTA): 978-92-9081-504-4 Descriptors in English: 1. Manihot esculenta. 2. Cultivation. 3. Fertilizer application. 4. Soil conservation. 5. Weed control. 6. Disease control. 7. Pest control. 8. Genetic resources. 9. Plant breeding. 10. Harvesting. 11. Postharvest technology. 12. Byproducts. 13. Marketing. 14. Cassava. Descriptors in Spanish: 1. Manihot esculenta. 2. Cultivo. 3. Aplicación de abonos. 4. Conservación de suelos. 5. Escarda. 6. Control de enfermedades. 7. Control de plagas. 8. Recursos genéticos. 9. Fitomejoramiento. 10. Cosecha. 11. Tecnología postcosecha. 12. Subproductos. 13. Mercadeo. 14. Yuca. I. Tit. II. Ospina, Bernardo. III. Ceballos, Hernán. IV. Alvarez, Elizabeth. V. Bellotti, Anthony. VI. Calvert, Lee. VII. Arias, Bernardo. VIII. Cadavid, Luis Fernando. IX. Pineda, Benjamín. X. Llano, Germán. XI. Cuervo, Maritza. XII. Centro Internacional de Agricultura Tropical. XIII. Latin American and Caribbean Consortium to Support Cassava Research and Development. XIV. Technical Centre for Agricultural and Rural Cooperation. AGRIS subject category: F01 Cultivation LC classification: SB 211. C3 C3774 Contents Page Foreword vii Preface ix Chapter 1 Cassava in Colombia and the World: New Prospects for a Millennial Crop Hernán Ceballos 1 Part a The Plant 2 Cassava Taxonomy and Morphology Hernán Ceballos and Gabriel de la Cruz 15 3 Cassava Productivity, Photosynthesis, Ecophysiology, and Response to Environmental Stresses in the Tropics: A Multidisciplinary Approach to Crop Improvement and Sustainable Production Mabrouk A. El-Sharkawy, Sara M. de Tafur, and Yamel López 29 Part B The Crop 4 Cassava Planting Materials Javier López 91 5 Soils and Fertilizers for the Cassava Crop Luis Fernando Cadavid L. 113 6 Conservation of Soil under Cassava Cultivation Luis Fernando Cadavid L. 138 7 Weed Control in Cassava Fernando Calle and Hernán Ceballos 157 Part C Pest and Disease Management 8 Cassava Diseases Elizabeth Álvarez, Germán Alberto Llano, and Juan Fernando Mejía 165 9 Cassava Bacterial Blight, Caused by Xanthomonas axonopodis pv. manihotis Valérie Verdier, Camilo López, and Adriana Bernal 200 iii Cassava in the Third Millennium: … Page Chapter 10 Insects and Mites that Attack Cassava, and their Control Anthony C. Bellotti, Bernardo Arias V., Octavio Vargas H., Jesús A. Reyes Q., and José María Guerrero 213 11 Insects and Mites Causing Yield Losses in Cassava Anthony C. Bellotti, Bernardo Arias V., Octavio Vargas H., and Jorge E. Peña 251 12 Cassava Pest Management Anthony C. Bellotti, Bernardo Arias V., and Jesús A. Reyes Q. 265 13 Potential for Biological Control in the Management of Cassava Pests Elsa Liliana Melo and Carlos Alberto Ortega 277 14 Cassava’s Natural Defense against Arthropod Pests Paul-André Calatayud and Diego Fernando Múnera 295 15 Biotechnology for Cassava Improvement: Genetic Modification and Clean-Seed Production Paul Chavarriaga, Roosevelt H. Escobar, Danilo López, Jesús Beltrán, William Roca, and Joe Tohme 300 16 Cassava Viral Diseases of South America Lee Calvert, Maritza Cuervo, and Iván Lozano 309 Part D Improvement and Technification 17 Manihot Genetic Resources at CIAT (Centro Internacional de Agricultura Tropical) Gustavo Jaramillo O. 321 18 Cassava Genetic Improvement Hernán Ceballos, Nelson Morante, Fernando Calle, Jorge Iván Lenis, Gustavo Jaramillo O., and Juan Carlos Pérez 342 19 Methodology for Hardening Large Numbers of In Vitro Cassava Plants Roberto J. Segovia, Armando Bedoya, William Triviño, Hernán Ceballos, Martin Fregene, Guillermo Gálvez, and Bernardo Ospina 369 20 Mechanized Systems for Planting and Harvesting Cassava (Manihot esculenta Crantz) Bernardo Ospina Patiño, Luis Fernando Cadavid L., Martha García, and César Alcalde 374 Part E Technologies for the Postharvest Management of Cassava 21 Natural Cassava Drying Systems Bernardo Ospina Patiño, Rupert Best, and Lisímaco Alonso 397 22 Artificial Cassava Drying Systems Lisímaco Alonso, Miguel Angel Viera, Rupert Best, Sonia Gallego, and José Alberto García 427 iv Contents Page Chapter 23 Production and Uses of Refined Cassava Flour José Alberto García, Lisímaco Alonso, Sonia Gallego, Johanna A. Aristizábal, Sergio Henao, Ana Milena Bonilla, and Andrés Giraldo 442 24 Producing Hydrated Bioethanol from Cassava Bernardo Ospina, Sonia Gallego, Harold Patiño, and Jorge Luis Gil 463 25 Conserving and Treating Fresh Cassava Roots Teresa Sánchez and Lisímaco Alonso 479 26 Sour Cassava Starch in Colombia Freddy Alarcón M. and Dominique Dufour 496 27 The Use of Cassava Products in Animal Feeding Julián Buitrago A., Jorge Luis Gil, and Bernardo Ospina 526 Appendix 1 Acronyms, Abbreviations, and Technical Terminology 569 v Foreword When CIAT published La Yuca en el Tercer Milenio The cassava industry was once based almost (Cassava in the Third Millennium) in 2002, new cassava entirely on general-purpose starch and animal feed. In technologies were on the verge of making remarkable recent years, however, market demand has begun to impacts on the lives of small producers who rely on the diversify – especially with respect to starch functional crop for income and food security. In Africa, research properties and nutritional factors – and this is creating had already resulted in successful biological control of opportunities for improvement through crop genetics the devastating mealybug and green mite (through the and postharvest processing. CIAT’s 2006 discovery use of natural enemies introduced from the Americas), of an amylose-free (waxy) starch has created the thus preventing widespread hunger and huge economic possibility of niche markets for cassava starch and has losses. In Asia, new cassava varieties were demonstrating prompted investment in the development of high- significant yield and quality advantages over local yielding waxy varieties. In addition, a small-granule landraces on a large scale, especially in Thailand. starch resulting from induced mutation shows potential These developments generated benefits whose value is for more efficient hydrolysis in ethanol production. estimated in the tens of billions of dollars. Meanwhile, yellow cassava with high beta-carotene content is attracting donor interest as a possible But the benefits have not been evenly distributed, solution for vitamin A deficiency, especially in parts of and this has taught us important lessons about Africa where this is a major health problem. technology development, particularly the need for continuously readjusting priorities. Invariably, farmers One of the great challenges for cassava, as for have benefited most where three conditions exist: many crops, has to do with environmental sustainability. (1) expanding markets (e.g., for starch or animal feed), The problem is especially serious with cassava because (2) government policies that favor cassava research of its well-known adaptation to fragile marginal and extension, and (3) an interdisciplinary research environments characterized by acid soils, low soil approach, which has long-term financial and technical fertility, and low or erratic rainfall. Though technologies support. are available for reversing land degradation in cassava production and for keeping productivity high through For many years, cassava research was financed improved management of soil fertility, much more almost exclusively by the public sector. Vegetative must be done to make these technologies accessible propagation of cassava has posed a significant barrier to farmers and provide better information about the to private sector participation, offering little scope for benefits. profitable marketing of new varieties. Nonetheless, processing industries have begun to recognize the Further challenges will result from ongoing advantage of supporting public research or at least expansion of cassava within current production areas assisting in the multiplication of new varieties with and into new ones. Given the crop’s long production superior quality traits. While private investment still cycle, more intensive culture will create more favorable accounts for only a small part of the total effort aimed conditions for pests and diseases. Over the longer term, at improving technology for cassava production, climate change will worsen drought stress in some this portion is growing and should continue to grow, areas and flooding in others. Changes in temperature as science brings new value-added traits to the and rainfall could have a strong effect on pest and marketplace. pathogen distribution and severity. vii Cassava in the Third Millennium: … In the face of new opportunities and challenges, CIAT, the Latin American and Caribbean Consortium cassava’s good adaptation to difficult agricultural to Support Cassava Research and Development environments should enable it to thrive in the coming (CLAYUCA), and many partner organizations over decades. The crop has much potential to enter a wide more than 40 years. It is impossible for a single volume array of markets, but it is also vulnerable to a wide to cover all the relevant developments, so extensive range of biotic and abiotic constraints. Substantial effort references are included that point the reader to will be required to ensure cassava’s market success additional reading. and also ward off disease and pest threats. Research capacity must be renewed; research must be targeted This book will be a valuable resource for scientists, more appropriately; and policies must be put in place extension workers, cassava growers and processors, that enable farmers to adopt improved practices, which manufacturers of machinery, and policy makers. The sustainably increase their cassava productivity and world of cassava research and development is rising incomes. quickly on the foundation of previous accomplishments. This volume is essential for understanding what has This volume summarizes the accumulated been achieved so far and for defining how best to knowledge and experience gained by scientists with address future challenges and opportunities. Clair H. Hershey Leader, CIAT Cassava Program viii Preface The International Center for Tropical Agriculture (CIAT), Producers. With the aim of facilitating information established in 1967 with headquarters near Cali, access and exchange, the book documented a wide Colombia, works to combat hunger, poverty, and natural range of cassava technologies, some of which were resource degradation through agricultural research for new while others had been tested and proven through development in tropical regions of Latin America, Africa, years of experience. The book was distributed to a wide and Asia. Within the Center’s portfolio of technology audience within the cassava sector of Latin America and options, cassava, a versatile and rugged root crop, the Caribbean (LAC) and rapidly proved its value as a figures importantly because of its role as the main resource for technological change across the region. source of sustenance for hundreds of millions of people. While helping strengthen food security for these people, Since then, further challenges and opportunities the crop also provides many of them with opportunities for cassava have emerged, as familiar problems have for income and employment, particularly in marginal grown worse and new ones have arisen while demand areas, where smallholder farmers predominate and and uses for the crop have continued to expand in LAC growing conditions are typically harsh, characterized by as well as in the dynamic cassava sectors of Africa and poor soils and frequent drought. Asia. For this reason, CIAT researchers decided it was time to provide an update on recent advances, so that CIAT’s Cassava Program consists of a our partners can more easily stay abreast of innovative multidisciplinary scientific team, which generates a solutions and alternative strategies. continuous flow of improved technologies for the production, processing, marketing, and use of cassava. Another factor that influenced the decision To make the products of this research widely available, consisted of important developments in international the Program works with partner organizations engaged agricultural research for development. As a result of in technology transfer, training, and other activities major reforms in the CGIAR, of which CIAT forms a that promote the adoption and adaptation of new part, new global programs are being created – including technologies by farmers and other end users. one on roots, tubers, and bananas – which provide a useful framework for integrating research across One of the most effective ways in which CIAT can disciplines and regions. promote the uptake of research results is to provide technical information in print and electronic form. Against this background, it seemed necessary not Combining scientific content with practical guidance, only to update La Yuca en el Tercer Milenio but to this material enables our partners to enrich and translate the new version into English together with the strengthen the knowledge and abilities needed to field handbook that accompanies it. The final product transfer improved cassava technologies more effectively. of this effort represents an important contribution to the exchange of experience and knowledge between Among the most successful examples of this cassava-producing regions of the developing world in approach at CIAT is the book titled La Yuca en el support of cassava modernization. Tercer Milenio (Cassava in the Third Millennium), which was published in 2002 with financial support We are grateful to the Technical Centre for from Colombia’s Ministry of Agriculture and Rural Agricultural and Rural Cooperation (CTA), based in the Development and the National Federation of Poultry Netherlands, for the generous financial support that ix Cassava in the Third Millennium: … enabled us to undertake this work. We also wish to in updating the scientific and technical content of the thank scientific staff at CIAT, colleagues with the Latin publication. Thanks are due as well to CIAT’s Corporate American Consortium to Support Cassava Research Communications team for its enthusiastic support in the and Development (CLAYUCA), and other partners in editing, design, and production phases. various institutions and countries for their assistance Bernardo Ospina, M.Sc. Hernán Ceballos, Ph.D. CLAYUCA CIAT Cassava Program x CHAPTER 1 Cassava in Colombia and the World: New Prospects for a Millennial Crop Hernán Ceballos1 Introduction Currently, cassava is a very important crop in the tropics, that is, at latitudes of less than 30 degrees, and Cassava (Manihot esculenta Crantz), together with from sea level to 1800 m above sea level. Although, the maize, sugarcane, and rice, constitutes the most principal economic product are its roots, cassava leaves important source of energy in the tropics. Native to also have excellent potential and are extensively used in South America (Olsen and Schaal 2001), cassava was Africa and Asia, as either human food or animal feed. domesticated about 5000 years ago and has since been Cassava is the fourth most important commodity after extensively cultivated in the tropics and subtropics of rice, wheat, and maize, and is a basic component in the the continent. The first European travelers quickly diet of many millions of people (FAO and IFAD 2000). recognized this crop’s virtues and distributed it throughout the colonies that European countries held According to Scott et al. (2000), for the period in Africa and Asia. 1995 to 1997, world annual cassava production was 165.3 million tons, with an approximate value of In South America, particularly in Brazil, cassava is US$8800 million. known as mandioca (or “manioc” in English). The English name “cassava” may have derived from the word In addition to the economic value of the products casabi, which, among the Arawak Indians, signifies and byproducts obtained from cassava, this crop offers “root” (FAO and IFAD 2000), or else came from the other recognized advantages: tolerance of drought, word cazabe, which is a cake or dry biscuit produced by capacity to produce in degraded soils, resistance to the indigenous populations of the Amazon Basin (Cock pests and diseases, tolerance of acid soils (which are 1989). In English, cassava is also known as “tapioca”. predominant in most of the world’s tropical plains), and flexibility in planting and harvesting times. Until a few decades ago, cassava and its products were little known outside the tropics, where it had been In preparing this Chapter, the author formally cultivated for many years. This crop received little recognizes three papers on which many of the sections interest in other regions, partly because its products here developed were based. These are, first, the 1989 were not exported, and because the species does not Spanish version of Cassava: new potential for a adapt to temperate climates. However, the Centro neglected crop by James H Cock (1985). Many of the Internacional de Agricultura Tropical (CIAT)2, in concerns and observations presented here were first Colombia, and the International Institute of Tropical mentioned by Cock in his book. Agriculture (IITA), in Nigeria, were created around 1970. For the first time, efforts were coordinated to improve Second, The world economy of cassava: facts, the scientific bases of the crop (Cock 1989). Numerous trends, and outlook, published in Spanish. It was one of countries have since developed successful cassava numerous publications prepared for the Validation programs. Forum on the Global Cassava Development Strategy, held in April 2000, in Rome, Italy, by the Food and 1. Breeder, Cassava Program, CIAT, Cali, Colombia. Agriculture Organization of the United Nations (FAO) E-mail: h.ceballos@cgiar.org and the International Fund for Agricultural Development 2. For an explanation of this and other acronyms and abbreviations, (IFAD). Many of the statistical data presented here see Appendix 1: Acronyms, and Abbreviations, Technical Terminology, this volume. appear in this publication. 1 Cassava in the Third Millennium: … Finally, Roots and tubers for the 21st century: continent’s high productivity (Table 1-3). In fact, India trends, projections, and policy options by GJ Scott, has the highest yields in the world, producing, in the MW Rosegrant, and C Ringler. This document is the period 1993/95, about 24.0 t/ha (FAO and IFAD 2000). source of numerous data that were very useful for the Latin America and the Caribbean (LAC) possess about preparation of this Chapter. 16% of the world’s area planted to cassava, but produces a little less than 19% of the total. World production statistics The annual growth of world cassava production in Much of cassava is grown on small farms and in the period 1961 to 1997 was 2.35% per year (Scott et marginal agricultural areas. As a result, a significant al. 2000). This is comparable with that of other crops proportion of production is inadequately recorded and such as wheat (4.32%), potato (4.00%), maize (3.94%), specified in statistics. The best statistics available are yam (3.90%), rice (2.85%), and sweet potato (1.07%). those of the FAO reports, but even so, errors in Increase in productivity on a worldwide scale is estimates can be still quite large (Cock 1989). estimated to be 1.1% per year for the period 1994– 2005, although this value, as in the case of LAC, is only Africa holds almost 62% of the total world area 0.7% (Table 1-3). This implies that the yields observed (Table 1-1) where cassava is planted, but only about for the period 1993–1995 (11.9 t/ha) will reach, in 2005, 50% of the world’s harvest (Table 1-2). In contrast, Asia 12.8 t/ha (Table 1-4). For the specific case of Colombia, produces 30% of the world’s cassava in an area that forecasts suggest that yields will increase at a rate of represents almost 23% of the total, thus indicating that about 0.8% per year, that is, slightly more than the Table 1-1. Area (thousands of hectares) planted to cassava in the world, by region, 1973 to 1995. Region Planted area Growth (annual percentage) 1973/75 1983/85 1993/95 1973/75 to 1983/85 1983/85 to 1993/95 Africa 7,030 7,518 10,158 9.7 3,1 LACa 2,722 2,592 2,593 -0.5 0 Asia 2,928 3,730 3,775 2.5 0.1 World 12,693 13,855 16,450 0.9 1.8 a. LAC refers to Latin America and the Caribbean. SOURCE: FAO and IFAD (2000). Table 1-2. Production (thousands of tons) of cassava roots (or equivalent) in the world, by region, 1973 to 1995. Region Production Growth (annual percentage) 1973/75 1983/85 1993/95 1973/75 to 1983/85 1983/85 to 1993/95 Africa 43,378 55,207 83,062 2.4 4.2 LACa 31,628 28,690 30,804 -1.0 0.7 Asia 30,262 47,371 49,740 4.6 0.5 World 105,400 131,424 163,746 2.2 2.2 a. LAC refers to Latin America and the Caribbean. SOURCE: FAO and IFAD (2000). Table 1-3. Yield (tons per hectare) of the cassava crop in the world, by region, 1973 to 1995. Region Yield Growth (annual percentage) 1973/75 1983/85 1993/95 1973/75 to 1983/85 1983/85 to 1993/95 Africa 6.2 7.3 8.2 1.6 1.2 LACa 11.6 11.1 11.9 -0.4 0.7 Asia 10.3 12.7 13.2 2.1 0.4 World 8.3 9.5 9.9 1.4 0.4 a. LAC refers to Latin America and the Caribbean. SOURCE: FAO and IFAD (2000). 2 Cassava in Colombia and the World: … Table 1-4. Forecasts for the year 2005 on cassava area, production, and yield in the world, by region. Region Period 1993/95 Forecast for 2005 Area Production Yield Area Production Yield (ha × 103) (t × 103) (t/ha) (ha × 103) (t × 103) (t/ha) Africa 10,158 83,062 8.2 11,961 114,202 9.5 LACa 2,593 30,804 11.9 2,777 35,590 12.8 Asia 3,775 49,740 13.2 3,836 57,572 15.0 World 16,540 163,746 9.9 18,595 207,556 11.2 a. LAC refers to Latin America and the Caribbean. SOURCE: FAO and IFAD (2000). average for the region (FAO and IFAD 2000). These conserve their flavor after cooking and, in addition, can values coincide overall with what is observed for the still be toxic. period 1983–1995 (Table 1-3). Cassava is also consumed fried. An interesting Uses of Cassava industry of precooked and frozen croquettes has recently been developed. This alternative solves the problem of Cassava is characterized by its great diversity of uses. the roots’ fast perishability, thereby adding value through Both its roots and leaves can be consumed by processing. This, in its turn, enables urban areas to humans and animals in many varied ways. Cassava access cassava, as the problems mentioned above make products, particularly starch and its derivatives, can marketing fresh roots in these areas difficult. also be used by industry. A brief description of the principal uses of cassava is presented below. Cassava can also be consumed as flours, which are either fermented or unfermented. Unfermented flour is Human food prepared by milling peeled roots or cutting them into small pieces. The resulting material is then dried and Both cassava roots and leaves are suitable for human ground to form flour (Cock 1989). consumption. The first constitute an important source of carbohydrates, and the second of proteins, In Brazil, much of the cassava is consumed as minerals, and vitamins (particularly carotenes and farinha (toasted cassava meal) in the preparation of vitamin C). various typical plates. Farinha is obtained primarily by peeling, grating, and pressing the roots, thus ultimately The presence of cyanogenic glucosides in both eliminating cyanogenic glucosides. Various alternatives roots and leaves determine the use of harvested exist to press the mass of grated roots, from the cassava. Many so-called “sweet” varieties have low traditional tipití to more sophisticated methods such as levels of these glucosides and can be consumed safely filter-presses. The pulp or mass is immediately grated after normal cooking processes. Other so-called again, then baked, dried, and ground. It is then packaged “bitter” varieties, however, have such high levels of and marketed. Once the mass of the roots is pressed, it these substances that a more sophisticated process is can be kneaded until it forms a flat cake, similar to a needed to make them suitable for human large tortilla, which is toasted on a plate to obtain a type consumption. These varieties are usually used for of bread or biscuit called cazabe. It is commonly eaten in industrial purposes. The inhabitants of the American the Caribbean islands, Venezuela, and Colombia. hemisphere identified, a long time ago, the problem of cyanogenic glucosides and have developed several Another alternative for the human consumption of methods for eliminating cyanide from bitter cassava. cassava, and which is creating its own interesting market, is as fried cassava chips, similar to the potato snacks, Humans consume cassava in numerous ways. In but with the advantage that the product absorbs less oil Colombia, cassava is traditionally boiled 10 to 40 min to cook. This makes it more attractive from the viewpoint in the preparation of sancochos (type of stew), soups, of human health. This product is produced commercially and gruels. The boiling time required depends on the in Colombia, Venezuela, Brazil, and other countries. It is variety, which thus becomes a factor to take into also exported to those areas of USA where Latin account in selecting varieties for this purpose. Only populations are predominant. sweet varieties should be used, as bitter varieties 3 Cassava in the Third Millennium: … In other regions of the world, cassava is consumed Starches in highly diverse ways. Variants of traditional flours exist such as the gaplek of Indonesia or the kokonte of Without a doubt, a major use of cassava is starch Ghana. production. Numerous sources of starch exist to meet humanity’s growing demands: in addition to cassava, In countries such as Nigeria, gari is a very popular these are maize, potato, and wheat (Ellis et al. 1998). cassava product. Roots are washed, peeled, and grated, much as for farinha production in Brazil, but Starch extraction can be carried out in artisanal with the difference that the resulting mass is placed in plants with capacities of only a few tons per month, or bags and then pressed down with weights (stones or in enormous plants with capacities of up to logs) placed on top of them. The process is slow with 400,000 t/year. In both cases, the process is essentially the mass remaining for several days, during which it the same: roots are washed, peeled, and macerated ferments. The mass is then toasted or fried (often with finely. Immediately, the starch, together with the water palm oil), until it dries. It is then packed in bags for that carries it, is separated from root fibers and proteins storage or marketing. by means of different filtrate systems. The water and starch are then separated from each other by gravity or Animal feed centrifuging. Finally, the starch is dried and ground for packaging and marketing. Because of its high energy value, cassava offers excellent opportunities for animal feed. One way, As with the alternatives of normal and fermented perhaps the best known on a worldwide scale, is to dry cassava flours, starch can also be either unfermented cassava pieces or chips, an activity for which Thailand (or native) or fermented (sour). Production of the latter is world leader. Alternatively, cassava pieces may be type of starch is very popular in the rallanderos processed into pellets. (artisanal starch extraction plants) of northern Cauca, Colombia. As either dried pieces or pellets, cassava may be incorporated into the formulation of balanced feed for Cassava starch has particular properties that make poultry, swine, farmed fish, and other domesticated it especially suitable for certain industrial processes. animals. In Asia, drying is carried out on patios, Among the properties that define a starch’s exposing the material to air and sun, meaning that the characteristics are the amylose-to-amylopectin ratio process is totally natural. This drying method employs and granule size. These characteristics are described in many people, but the costs of construction of patios more detail in Chapter 2 on taxonomy and morphology, are currently exorbitant for most cases. Furthermore, a this volume. relatively prolonged period without rains is needed, which is not possible in many areas of Colombia. Demand for modified starches is growing. These Along the Caribbean coast, however, particularly in the are used for very specific purposes. Cassava starch departments of Sucre, Córdoba, and Magdalena, offers opportunities, as, in some cases, chemical considerable infrastructure for this type of drying modification is simpler and less expensive than it is with exists, having been regularly exploited since the 1980s. starches from maize or potato. We point out that, recently, cassava is increasingly being used for starch Cassava can also be used for animal nutrition production in countries such as Brazil and Thailand. without first being dried. In many places of the world, This trend is expected to continue in coming years. both roots and leaves are ensiled. This process allows Taking into account these opportunities, major efforts the product to be stored over long periods and, at the have been made recently to develop or identify cassava same time, reduces the levels of cyanogenic cultivars whose starch offers special morphological glucosides, even if these are initially very high. This characteristics, biochemical, or functional properties. As alternative benefits the significant swine production a result, cultivars are now available that have starch with industry in Asia. It has the additional advantage of no amylose or else with small granules and increased combining the energy source from the roots with the amylose contents (Ceballos et al. 2007, 2008). leaves’ high protein content. Fresh broken pieces of cassava can be left out in the open for a few hours and Alcohol then offered to swine and cattle, with excellent results (Buitrago 1990). Cock (1989) gives an interesting account of cassava’s potential to produce alcohol. After the 1970s oil crisis, 4 Cassava in Colombia and the World: … Brazil planned to partly replace gasoline with alcohol Lack of cultivars specifically developed for derived from sugarcane or cassava. Despite initial industry. Frequently, the objectives of genetic skepticism, results demonstrated that the Brazilian improvement programs and development of cassava approach to resolve the energy crisis deserved varieties aim at “dual purpose” materials, that is, those considerable support. For example, in 1980, Brazil genotypes that could be used either for human produced sufficient alcohol to replace 20% of the consumption or for industry. If fresh-root market prices gasoline needed for its cars (Cock 1989). are high, then farmers sell their products to this market. If not, then the roots are sold to industry, usually at The drop in oil prices during the 1980s and 1990s considerably lower prices. reduced interest in this strategy, until 2000, when another crisis developed through high prices. This This strategy has, in fact, interfered with the crisis generated interest in establishing numerous industrial use of cassava because it does not permit ethanol production centers based on cassava roots. constant and reliable supplies of raw materials. Although interest in producing alcohol as a substitute for oil (as described) may oscillate, it is nevertheless In addition, the search for dual purpose varieties has inevitable: as supplies of petroleum derivatives become resulted in materials that were not optimal for either one more difficult to obtain, demand for substitutes will or the other end use. From the genetic viewpoint, making become stronger and more constant. strides when too many goals are imposed is very difficult. In the past, most alcohol produced for these Maize presents a good example of a case that purposes came from sugarcane. In the future, however, contrasts with the situation for cassava. Two very different it is likely to come increasingly from cassava because and totally independent activities with this crop exist: of its capacity to grow in marginal soils, which common maize and sweet maize. The former is destined sugarcane is unable to do. In this regard, the to provide, efficiently and competitively, for the needs for technologies generated in developed countries to various agroindustries, which means productivity is the reduce costs of hydrolyzing maize starch in the principal objective. The latter is basically a horticultural production of bioethanol have directly facilitated these crop and the varieties or hybrids developed mostly seek processes carried out with cassava starch. culinary quality and product appearance rather than productivity. Improvement programs and seed Problems of crop development companies dedicate themselves to one or the other type of maize, and are completely independent, having Despite its enormous production potential, its relatively little interaction among them. noteworthy adaptation to a great diversity of environments, its recognized tolerance of biotic and This volume emphasizes the changes that have been abiotic constraints to production, and its diversity of implemented recently, with a view to developing varieties uses, cassava has not yet managed to fully develop its to meet specific needs of different industries. potential in tropical agriculture. Numerous factors explain this delay. Lengthy selection cycles and low reproduction rate. The genetic improvement of cassava is slow. Where Influence of temperate-region technologies. a full-sib recurrent selection cycle of any grain can be The evolution of agriculture and of different completed in less than one year, cassava requires five. agroindustries of tropical countries have frequently Two factors influence this: cassava is usually harvested benefited from developments achieved in temperate 10–12 months after planting, and the reproduction rate is regions. Maize has been, and continues to be, a major relatively low. For example, one hectare of maize source of energy and starch for these latter regions. produces sufficient seed to plant 100 or more hectares. Most of the technology, machinery, industrial For cassava, the ratio is much smaller, with one hectare processes, and formulations for concentrated feed producing seed for about 7 to 10 ha. Most of the time adopted by tropical countries were originally adjusted required for variety selection is used basically to obtain to those crops and processes predominant in sufficient seed to conduct evaluations with replications temperate regions. This situation, without a doubt, and across several sites to complete each selection cycle. favored the cereal sector of tropical countries, but This situation also affects the rate of adoption of new resulted in a disincentive for the development of varieties once the latter are officially released. technologies appropriate to crops specifically adapted to the tropics such as cassava. 5 Cassava in the Third Millennium: … Governmental policies. Because of a Governmental policies are also and inevitably conjunction of several factors, governments of reflected in the private sector, which invested similarly, developing countries have usually paid little attention favoring grains and either ignoring root and tuber crops to the cassava crop. Between the 1970s and 1990s, or relegating them to a lesser importance than they the policies of most governments in tropical and deserved. subtropical regions were oriented towards promoting grain production, following the successful experiences Root bulk and rapid perishability. Cassava roots of the Green Revolution (FAO and IFAD 2000). present two important constraints to extensive and dynamic marketing. The first is its bulk water content Data on investments in research in these (nearly 65%), which make transportation costs of fresh countries, according to crop, are extremely difficult to roots high in terms of the dry matter they contain. obtain. However, Judd and co-workers demonstrated Hence, cassava production should be located near in a detailed study (1987) that “several staple crops, processing centers. The second problem is the roots’ specifically cassava, sweet potato, and coconut palm short life after harvest. They need to be consumed or have received very little attention in every region of the processed no later than 7 days after harvest, as they world.” From the data, Cock published (1989), undergo a process known as postharvest physiological investment in cassava research has obviously been deterioration (PPD). Various sources of tolerance of PPD low, unjustly so, and in disproportion with other crops have recently been identified. These are described in (Table 1-5). later chapters of this volume. These data continue to be in effect 2 decades Root characteristics also affect processing costs. later. For example, according to CIMMYT (1994), in According to Cock (1989), traditional cassava processing 1992 a total of 372 scientists worked in the genetic methods are so laborious that probably more work is improvement of maize (224 and 148 in the public and invested in processing than in cultivating and harvesting private sectors, respectively). In contrast, no more the crop. than three full-time breeders dedicated their activities to cassava (C Iglesias 1999, pers. comm.) in that same Limited market development. A problem, similar period. In other words, the region dedicated less than to the egg and chicken paradox, has always existed in 1% of human resources to cassava, compared with the industrial use of cassava: markets for the industry do maize. not exist because no guaranteed availability of raw material exist, and roots are not produced for these For this period (Scott et al. 2000), the relationship markets because they do not exist. between the value of maize production and that for cassava on a worldwide scale was about 3:1, that is, Marketing problems are more pronounced for 32,500 million versus 8800 million dollars, cassava than for other crops, as it is cultivated mostly by respectively. small farmers, and thus demanding greater coordination for use in industrial processes. Production areas are also usually located in areas with poor or deficient Table 1-5. Investments made by developing countries in research on amylaceous foods in 1975. infrastructures. Product Product Research Cost-to- value cost value ratio In addition, the low-input technologies that (US$106) (US$106) (%)a characterize most cassava cultivation imply increased Sorghum 1500 12 0.77 environmental variability, which has the effect of varying Maize 3000–4000 29 0.75 root quality. The crop’s low rate of multiplication creates Potato 1000 8 0.68 difficulties in accelerating and up-scaling production. Wheat 5000–6000 35 0.65 The absence of credit is a problem that rice, maize, or Sugarcane 5000–6000 30 0.50 sugarcane farmers do not have. Rice > 13000 34 0.26b Sweet potato 3000–4000 3 0.09 New opportunities for cassava in tropical agriculture Cassava 5000–6000 4 0.07 a. Proportion of research costs with respect to product value. b. In “shallow-flooding” rice, the ratio is 0.40. Despite all the above-mentioned difficulties that prevent SOURCE: Adapted by Cock (1989) from data of the National cassava reaching the most relevant ranking, it remains a Academy of Sciences (1977). crop of world importance. Steps are being made to 6 Cassava in Colombia and the World: … quickly solve some of the inherent problems, as briefly f. Poor farming practices, limited resources, described below. inadequate application of inputs, and delayed technology transfer. Cassava will be more relevant to agriculture of the 21st century. The clearest and widespread economic Many of the factors that reduce the competitiveness trend during the 1990s has been, without a doubt, of maize in tropical areas are clearly very difficult or globalization of economies. Markets for agricultural impossible to overcome. Hence, if the trend towards products have been a part of this trend. As a result, market aperture continues, still fewer opportunities will commercial tariffs and other protectionist barriers exist in the future for local competitive production, have been gradually reduced. For example, Colombia which needs be carried out in optimal areas with imported an insignificant quantity of maize adequate soil fertility, reliable heavy rainfall, appropriate (32,000 tons) in 1990 but, in 2000, this figure was infrastructure, and efficient mechanization of close to 2 million tons. This represents an annual production. growth of 79.5% for imports. This situation is repeated in many other tropical countries, where local maize Also obvious is that many weaknesses of tropical production is not competitive with that of temperate maize production are, precisely, the strengths of cassava regions. production. Indeed, cassava is characterized by the stability of its production. It has an innate tolerance of The annual growth of maize imports in African and low soil fertility and water deficiencies. Its physiological Asian countries was, respectively, 5.53% and 4.58% metabolism is not as severely affected by the (FAO and IFAD 2000) during the past decade. Maize is relationship between day and night temperatures as it is a building block for animal feeds and an important raw for maize. It is naturally tolerant of the typical edaphic material for the starch industry. This means that maize conditions of acid soils. The stability of cassava competes directly with cassava. It also implies that the production and the crop itself was proven during the future of cassava production and use in tropical 1983–1985 droughts that affected Africa, when grains countries depends largely on local grain production deteriorated critically. Likewise, more recently, in Asia and on the possibility of importing grain. and South America, cassava has played a role of great importance in food security on the occasion of the Numerous reasons explain the limited maize scarcity of grains derived from the meteorological competitiveness in the tropics. Pandey and Gardner anomalies that occurred in 1997 and 1998, as a (1992) suggested that “maize yields in the tropics are consequence of El Niño and La Niña, respectively (FAO mainly limited by the quotient between intercepted and IFAD 2000). radiation and heat units. This quotient is much lower in lowlands comparative with higher areas and is smaller As a result of this evolution, the Colombian in the tropics than in temperate regions. Relatively, a Government is vigorously supporting cassava research smaller quantity of light is intercepted during the rainy and development through the Ministry of Agriculture and season in the tropics, which coincides with the period Rural Development. Numerous highly relevant projects of grain filling for the crop. The interception of light is have been supported and many of their initial results will reduced even more by low planting densities. The be presented throughout this volume. Coinciding with extreme climatic variations, erratic precipitations, high changes in governmental policies, a similar situation is temperatures, particularly during the night, and low being observed with the processing sector, which is also temperatures in high areas also reduce yields.” vigorously supporting this initiative to recover lost time. Other factors that limit maize productivity in the Strategies for Making the Cassava Crop tropics are: Even More Competitive a. Low fertility of most soils in the region. Cultivars specifically oriented towards meeting various b. Low yield potential of tropical cultivars. demands of the processing sector are being actively c. High pest pressure and less-than-optimal developed, while cultivar production for the fresh-root availability of water. market is being maintained. This does not mean that the d. Diseases that frequently reduce production by needs of the more traditional cassava markets are being as much as 30%–40%. put aside. Instead, a genotype is not ruled out when, for e. Weeds that, in low-input production systems, example, root appearance does not conform to these reduce yields by as much as 50%. markets’ criteria. 7 Cassava in the Third Millennium: … The productive potential of these varieties are these problems by combining step-wise plantings and detailed in Chapter 18, which considers cassava identifying materials that can be harvested at different genetics. Here, it is enough to mention that, in the ages to thus facilitate a more continuous product Department of Córdoba, Colombia, variety SM 1433-3, supply in those regions where this situation can be an industrial clone, had a commercial yield of more problematic, as for the Colombian North Coast. than 80 t/ha of fresh roots in an area of almost 10 ha. Those steps needed to make economic use of In addition to redefining the improvement project’s foliage are also being taken, first by developing objectives, the scheme used was also modified to methods for mechanically harvesting the product. The improve its efficiency. This new improvement scheme, development of varieties and cultural practices for on the one hand, permits substantial shortening of the high-density plantings exclusive to foliage production is duration of each selection cycle; and, on the other, being considered. The possibility of taking advantage improves the reliability of data on which selection is of foliage residues when roots are harvested in normal based. With these changes, those genetic materials crops is also being evaluated. This would add greater that are available and fully competitive in most of the value to farmers’ harvests, with an increase, albeit environments where cassava is cultivated can be proportionately smaller, in production costs (derived expected to be replaced in the medium term by from the additional activity of harvesting the foliage). varieties that are genetically superior and more For this operation, a mechanical harvester for foliage specifically adapted to meet the needs to which they was designed, built, and evaluated. are destined. Strengthening and creating new markets Genetic improvement will be very much favored by the implementation of new biotechnology tools. CIAT Interest in cassava has been growing recently in has developed a molecular genetic map of the species Colombia, leading to highly creative solutions for some and has managed to identify molecular markers of the crop’s typical problems. For example, PPD and associated with traits of agronomic interest. In addition, the difficulties of marketing fresh roots in urban areas the technology now exists for transferring genes from can be overcome by producing precooked and frozen either within the cassava species or wild species, not croquettes. These food products have become very through sexual crosses, but through genetic popular and are now consolidated as a value-added transformation. This permits faster transfer of useful cassava product for consumption in large urban genes from one cultivar to another. centers. This is a good example of establishing and consolidating a production chain, from production in In vitro culture techniques help solve problems the field to distribution to end consumers. The market associated with cassava’s low reproduction rate. for fried cassava chips, as part of the snacks sector, has Although the costs per plant increase with these followed the same road in the recent past. techniques, they make possible the mass reproduction of large volumes of seedlings whenever this should be For other cases, to strengthen a given market, necessary or advisable. technological innovations are needed such as artificial drying of cassava. As mentioned above, the best known Advances in genetic potential will be accompanied, way of drying cassava destined for animal feed is in parallel, by other strategies to improve the crop’s through drying patios. This technology, however, is competitiveness. Mechanization of planting and unsuitable for regions where no relatively long rainless harvesting has been introduced, resulting in, on the one periods exist. As a result, the public and private sectors hand, reduced costs and, on the other, higher yields. have invested resources to develop a solution that is This machinery is being adapted to the needs of economically viable and compatible with environmental different regions in Colombia where cassava is conservation to artificially dry roots and foliage. The cultivated and where mechanization can be introduced first step was to construct a pilot plant in which without harming the environment. different variables were adjusted to measure their effects on product quality and drying costs. The One problem that the cassava-processing sector construction of this pilot plant was made possible frequently meets is the seasonal nature of the product. through an association of public and private sectors In some situations, this implies that processing plants collaborating actively on different aspects related to (drying patios, starch extraction plants, etc.) remain cassava use and processing. inactive for relatively long periods. The goal is to solve 8 Cassava in Colombia and the World: … The economic feasibility of artificial cassava Practical methods are being actively developed to drying is important to organizations with a vertical integrate these biological control methods into current integration of production such as the cassava drying practices of crop care. In addition to reducing plant or “trapiche” (a Spanish name borrowed from production costs, these alternatives offer the advantage small sugarcane processing facilities). These of being usually durable and contributing to organizations would use a centralized production environmental health by reducing or eliminating the model, similar to that of sugar plantations and their need for agricultural chemicals. associated trapiches. A cassava plantation, ranging from 600 to 6000 ha in size, would provide a drying Similarly, genetic improvement programs are plant (or refinery) with raw materials in a more or less continually selecting against the principal diseases of continuous manner throughout the year. each ecoregion to develop resistant or tolerant cultivars. In cases where genetic resistance is not Associates of these drying centers may include sufficient, other methods for pathogen control like that poultry or pork industries that would consume the of thermotherapy are developed to “clean” cuttings of product of these centers and return fertility to the diseases such as cassava bacterial blight. system in the form of manure. A fundamental concept of this system is the short distances that the products As with other activities, biotechnology offers tools involved would travel. Cassava roots would be that facilitate these efforts. At present, it is being used produced within a radius of about 30 km of the drying to identify molecular markers associated with genes for plant and would be transported in bulk. Dried cassava resistance to whiteflies. This methodology is also being would also be transported in bulk to the poultry- or used to better understand the population dynamics of pig-raising centers that would also be located relatively the bacterial blight pathogen. Biotechnology also close by. permits the development of serological diagnostic tests based on the polymerase chain reaction (PCR). This proposal would therefore help solve the problem of cassava roots’ bulkiness—resulting from Adding value to the crop and increasing its their high water content—by minimizing their profitability transport. In developing new varieties, the possibility of selecting Taking advantage of and increasing the crop’s for specific markets is also considered. For example, hardiness the cassava genome carries genes for orange-fleshed roots, so colored for possessing high carotene Cassava is recognized for its hardiness, that is, for its contents. Although this color may not be desirable for excellent tolerance of different biotic and abiotic certain markets, it offers advantages for other uses, stresses. It is particularly tolerant of low fertility soils, particularly poultry feed. Apparently, this component water deficiencies, and acid soils. It can also grow in also delays the beginning of PPD. Such yellow-rooted moist tropical environments with rains that exceed or “egg yolk” cassava varieties would also be very 3 M/year. All these characteristics confer cassava with useful for producing fried cassava chips because, significantly stable production. Moreover, these according to preliminary studies, the product has a very valuable characteristics can be improved even more. appealing presentation. Techniques of integrated pest-and-disease CIAT holds genetic capital of enormous management (IPDM) have significantly contributed to importance: the World Cassava Germplasm Bank, stability of production. Genetic resistance or tolerance which carries about 6000 accessions that contain to principal pests and diseases has been incorporated practically the crop’s entire genetic variability. Studies into most improvement programs of the crop are currently being carried out to evaluate starch throughout the world. For example, resistance properties and traits, and other agronomically relevant (reported to be antibiosis) to whiteflies properties of roots and leaves in each accession. One (Aleurotrachelus socialis) of the local variety M Ecu 72 possible result of this arduous effort would be the is the first reported for any commercial crop. In those finding of genotypes that present new starch types with few cases in which genetic resistance or tolerance specific industrial applications. does not offer adequate protection, numerous alternatives of biological control are available. 9 Cassava in the Third Millennium: … Uniting research, production, and processing than during the previous decade, when it grew at a rate of 1.7%. Expansion in area planted was the main way in A common factor runs through all those cases of which production increased (1.7% versus only 0.3% for successful cassava initiatives: close and active increases in productivity). Projections for the period interaction between farmer, researcher, and 1993–2020 estimate a similar growth rate as observed processor. Similarly, when this “triangle of success” is so far, ranging between 1.93% and 2.15% per year, but not well established, failure was frequent. Cassava’s with a substantial change in terms of productivity current situation in Colombia is showing numerous increases (higher than 1%), with respect to planted area, positive cases where achievement entails such a which may range between 0.74% and 0.95% (CGIAR paradigm. 1999). Research has been favored, at very much the Tables 1-6 and 1-7 present other projections right time, by vigorous institutional support from the extracted from Scott et al. (2000). Table 1-6 presents Ministry of Agriculture and Rural Development that, statistics derived from a base scenario, whereas data in with the support of different trade associations, was Table 1-7 were obtained by assuming high demand for an unconditional promoter for the creation of the agricultural products. In general terms, these projections Latin American and Caribbean Consortium to coincide with the ones described above: that, annually, Support Cassava Research and Development production will increase between 1.74% and 1.95% per (CLAYUCA, its Spanish acronym). year, yields will increase about 1% per year, and planted area will increase between 0.73% and 0.94%. This Consortium is the clearest instance where interaction between processors, farmers, and References researchers is harmonious and productive. The presence of the private sector and trade associations Buitrago A, JA. 1990. La yuca en la alimentación animal. (particularly FENAVI and ACOPOR), promoting the Centro Internacional de Agricultura Tropical (CIAT), crop with appropriate technologies, has been Cali, Colombia. 450 p. fundamental in bringing cassava closer to the position of importance that it deserves in tropical Ceballos H; Sánchez T; Morante N; Fregene M; Dufour D; agriculture. In this interaction, the public sector has Smith AM; Denyer K; Pérez JC; Calle F; Mestres C. also contributed through CORPOICA’s technical and 2007. Discovery of an amylose-free starch mutant in logistical capability and ICA’s continuous and timely cassava (Manihot esculenta Crantz). J Agric Food intervention, when the situation so merited it. Chem 55(18):7469–7476. Ceballos H; Sánchez T; Denyer K; Tofiño AP; Rosero EA; Predicting the Future for Cassava Dufour D; Smith A; Morante N; Pérez JC; Fahy B. 2008. Induction and identification of a small-granule, World cassava production grew at an annual rate of high-amylose mutant in cassava (Manihot esculenta 2% between 1987 and 1997, which was slightly more Crantz). J Agric Food Chem 56(16):7215–7222. Table 1-6. Projections of the planted area, production, and yield of cassava for the year 2020. Region Planted area Production Yield Year Exchange rate Year Exchange rate Year Exchange rate 1993 2020 (%/y ear) 1993 2020 (%/ye ar) 1993 2020 (%/year) (ha in millions) (t in millions) (t/ha) China 0.3 0.3 0.08 4.8 6.5 1.18 15.1 20.2 1.10 India 0.2 0.2 0.02 5.8 7.0 0.71 23.6 28.4 0.69 Asia 3.9 3.9 0.25 42.0 48.2 0.51 12.1 13.7 0.46 LACa 2.7 2.7 -0.01 30.3 41.7 1.19 11.3 15.6 1.21 Africa 11.9 15.9 1.09 87.8 168.6 2.45 7.4 10.6 1.34 World 18.8 22.9 0.73 172.7 275.1 1.74 9.2 12.0 1.00 a. LAC refers to Latin America and the Caribbean. SOURCE: Adapted from Scott et al. (2000). 10 Cassava in Colombia and the World: … Table 1-7. Projections (based on a scenario of high demand) of planted area, production, and yield for the year 2020. Region Planted area Production Yield Year Exchange rate Year Exchange rate Year Exchange rate 1993 2020 (%/year) 1993 2020 (%/year) 1993 2020 (%/year) (ha in millions) (t in millions) (t/ha) China 0.3 0.3 0.09 4.8 6.6 1.21 15.1 20.3 1.12 India 0.2 0.2 0.03 5.8 7.1 0.76 23.6 28.7 0.73 Asia 3.5 3.5 0.03 42.0 48.2 0.51 12.1 13.8 0.49 LACa 2.7 2.7 -0.01 30.3 42.0 1.22 11.3 15.7 1.23 Africa 11.9 17.2 1.39 87.8 183.8 2.77 7.4 10.7 1.36 World 18.8 24.2 0.94 172.7 290.8 1.95 9.2 12.0 1.00 a. LAC refers to Latin America and the Caribbean. SOURCE: Adapted from Scott et al. (2000). CGIAR (Consultative Group on International Agricultural Judd MA; Boyce JK; Evenson RE. 1987. Investment in Research). 1999. Annual report 1999: science for the agriculture. In: Ruttan VW; Pray CE, eds. Research poor and environment. Washington, DC. and extension policy for agricultural research. Westview Press, Boulder, CO, USA. p 7–38. CIMMYT (International Maize and Wheat Improvement Center). 1994. World maize facts and trends—maize Olsen KM; Schaal BA. 2001. Microsatellite variation in seed industries revisited: emerging roles of the public cassava (Manihot esculenta, Euphorbiaceae) and its and private sectors. Mexico, DF. wild relatives: further evidence for a southern Amazonian origin of domestication. Am J Bot Cock JH. 1989. La yuca, nuevo potencial para un cultivo 88(1):131–142. tradicional. Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia. 240 p. (Also Pandey S; Gardner CO. 1992. Recurrent selection for available in English as Cock JH. 1985. Cassava: population, variety, and hybrid improvement in new potential for a neglected crop. Westview Press, tropical maize. Adv Agron 48:1–87. Boulder, CO, USA.) Scott GJ; Rosegrant MW; Ringler C. 2000. Roots and Ellis RP; Cochrane MP; Dale MFB; Duffus CM; Lynn A; tubers for the 21st century: trends, projections, and Morrison IM; Prentice RDM; Swanston JS; Tiller SA. policy options. International Food Policy Research 1998. Starch production and industrial uses. J Sci Institute (IFPRI); Centro Internacional de la Papa Food Agric 77:289–311. (CIP), Washington, DC. 64 p. FAO; IFAD (Food and Agriculture Organization of the United Nations and International Fund for Agricultural Development). 2000. La economía mundial de la yuca: Hechos, tendencias y perspectivas. Rome, Italy. 59 p. (Also available in English as The World Economy of Cassava: Facts, Trends, and Outlook.) 11 Part a The Plant CHAPTER 2 Cassava Taxonomy and Morphology Hernán Ceballos1 and Gabriel de la Cruz2 Introduction Taxonomy In preparing this chapter, advantage was taken of the Cassava belongs to the Euphorbiaceae family, which is knowledge base provided by other authors whose made up of about 7200 species, characterized for their valuable contributions should be recognized. Of the notable development of lactiferous vessels, themselves publication Cassava: research, production, and made up of secretory cells called lacticifers. These utilization (edited by Carlos E Domínguez [1983]), the produce the milky secretion, or “latex”, that chapters used were written by Carlos E Domínguez, characterizes the plants of this family. Plant architecture Luis F Ceballos, and Cilia Fuentes (“Morphology of the varies enormously within this family, ranging from cassava plant”); Clair Hershey and Alvaro Amaya arboreal types such as rubber (Hevea brasiliensis) to (“Genetics, cytogenetics, floral structure, and shrubs, also of economic importance, such as the techniques of hybridization in cassava” and “Cassava castor-oil plant (Ricinus communis). Also representing germplasm: evolution, distribution and collection”); this family are numerous weeds, ornamental plants, and James H Cock (“Physiological aspects of the and medicinal plants. A highly significant genus of this growth and development of the cassava plant”). Of the family is Manihot to which cassava belongs. book Cassava in the face of hunger in the tropical world (edited by Alvaro Montaldo 1996), information The Manihot genus is native only to the Americas, was extracted from the chapters written by Jocelyne with species being distributed from southwestern USA Ascencio (“Some aspects related to the physiology of (33º N) to Argentina (33º S). Although all species of the the cassava plant”); and JJ Castilloa, A Castillo, and LT genus can cross with each other, evidence suggests Pino (“Notes on leaf and root histology of cassava”). that, in nature, they are reproductively isolated. About 98 species have been described as belonging to this All 98 species of the Manihot genus are native to genus, of which only cassava (Manihot esculenta the Neotropics from where cassava was introduced to Crantz) has economic importance and is cultivated. other regions of the world (Rogers and Appan 1973). Perhaps more than 100 common names now exist for The origin of cultivated cassava is still unclear. Three this species, owing to its spread throughout the tropical relevant questions were raised by Allem (2002): its world by early traders. In Latin America, it is usually botanical origin (parental wild species that eventually known either as yuca (Spanish) or as mandioca led to the emergence of M. esculenta), the geographic (Portuguese). In Brazil, sweet cassava (aipim) is area where this emergence took place, and the region distinguished from bitter cassava (mandioca). Other where it was domesticated (agricultural origin). The names in different languages include manioc, manioca, prevailing hypothesis is that cultivated cassava tapioca, and mhogo (Cock 1989). originated in South America (Olsen and Schaal 2001; Allem 2002), but many questions remain unanswered. Cassava’s scientific name was first given by Cranzt in 1766. It was then reclassified by Pohl (1827) and Pax (1910) as two different species, depending on whether it was bitter (M. utilissima) or sweet (M. aipi). However, 1. Breeder, Cassava Program, CIAT, Cali, Colombia. E-mail: h.ceballos@cgiar.org the Italian R Ciferri (1938) recognized that, for 2. Formerly Vice-Rector, UN–Palmira. E-mail: gacruza@unal.edu.co cassava’s scientific name, priority should be given to 15 Cassava in the Third Millennium: … Crantz’s work in which he had proposed its current The stem name of M. esculenta. Allem (1994) proposed that the species M. esculenta be divided into three Stems are particularly important in cassava, as they are subspecies: M. esculenta subsp. esculenta, subsp. the means by which the species propagates vegetatively flabellifolia, and subsp. peruviana. The author also or asexually. Lignified parts of the stem, commonly suggests that the last two subspecies are wild forms called stakes or cangres (cuttings), serve as “seed” for of the cultivated version M. esculenta subsp. the crop’s commercial production. The mature stem is esculenta. cylindrical, with a diameter that varies from 2 to 6 cm and coloring that may be silvery gray, purple, or yellow. Cytogenetics Both stem diameter and color vary significantly with plant age and, obviously, with variety. Very little is known of either cassava genetics or cassava cytogenetics. The basic chromosome Stems are formed by the alternation of nodes and number in the Euphorbiaceae family is usually 8, internodes. The oldest parts may show protuberances, although this may vary between 6 and 11. About 50% which mark, within the nodes, the position that leaves of euphorbia species are polyploid (Martin 1976). had initially occupied. The node is that place where a leaf joins the stem, and the internode is that part of the Although cassava is frequently considered as a stem between two successive nodes. Inserted into the polyploid species, analyses conducted during node are the leaf petiole, an axillary bud protected by a diakinesis and metaphase I indicate the presence of scale, and two lateral stipules. The length of internodes 18 small and similar bivalents in cassava (Hahn et al. in the principal stem is highly variable and depends, not 1990). Univalents, trivalents, and late bivalent only on the variety, but also on other factors such as pairings have also been observed in cassava. This plant age, drought, thrips attacks, and available soil plant is therefore a functional diploid, that is, fertility. In a certain sense, the stem provides a lasting 2n = 2x = 36 (Jennings 1963; De Carvahlo and record of the history of the plant’s development, Guerra 2002; Nassar and Ortiz 2008). Magoon et al. enabling one to deduce the conditions and events that (1969) have suggested that certain portions of the had influenced it. genome may be duplicated and, therefore, cassava may in fact be a segmental allotetraploid. The presence of axillary buds in each node is important as, from these, a stake can produce a new Describing the Plant plant. In theory, a stake can produce the shoot of a new primary stem from the bud in each node. However, the Every botanical description is based on the analysis number of stems produced depends heavily on the way of morphological characters that, where these are in which a given stake is planted. For example, when the constant, typify the species. However, many stake is planted horizontally, all nodes tend to emerge, characteristics are expression in a variable fashion but if the stake is planted in a vertical position, usually and are profoundly influenced by environment. The only the apical bud is activated. The number of shoots effect of the variety-by-environment interaction is from a stake also depends on the apical dominance that most notable in the case of cassava. For example, a characterizes each variety. When it is strong, only the given variety’s architecture, known to be typical in a upper bud generates a primary stem. General specific environment, will change drastically when conditions of the stake, particularly of the axillary buds, that variety is grown in another site with different also determine the number of stems a stake will environmental conditions. This variety-by- produce. environment interaction hinders both the morphological and varietal description of the species. The typical phyllotaxis observed in cassava stems is 2/5. This means that the leaves are located in spiral Cassava is a perennial shrub. It is monoecious, fashion around the stem. If leaves are counted that is, a single plant may carry both male and female successively upwards from a given leaf (number 1), the flowers, but these are separated from each other. The sixth leaf will be exactly in the same position as leaf cassava plant has sympodial branching and variable number 1, but farther up the stem. The fraction 2/5 also plant height, ranging between 1 and 5 m, although implies that two turns have to be taken around the stem maximum height usually does not exceed 3 m. before finding a leaf that perfectly overlaps leaf number 1 and that, in the process, five leaves are counted. 16 Cassava Taxonomy and Morphology The primary stem, after a certain growing period, The number and promptness with which such ultimately produces branches that may be either branching occurs notably influence plant architecture. reproductive (producing inflorescences) or vegetative Early flowering results in the primary branches being (producing lateral branches). The “reproductive” located in relatively lower positions in the plant. Hence, branches are important, as they constitute a very stable early and multiple branching will therefore tend to characteristic for varietal description. They also produce a short plant that hinders the cleaning and determine, to a great extent, the architecture that is care of the crop. However, it rapidly covers the soil, characteristic of each variety. The latter, as will be seen protecting it from, particularly, hydric erosion. Reduced in other chapters of this volume, is significant for and/or late branching tends to produce erect plants, defining the agronomic value of each material, as it with good stake production, that facilitate crop care, influences the quantity of planting material or “stakes” but leaves the soil exposed to erosion. that the plant produces, and other factors such as ease in carrying out tasks of cleaning and general care of In addition to the number of reproductive the crop. branches, the angle of these also greatly affects the plant’s general architecture (Figure 2-2). The greater Although the reproductive lateral branch is induced the angle of incidence of the branches, the more open by flowering of the principal axis (hence its name), the plant architecture and the shorter it is. In general, reproductive branching may also occur without the this type of architecture is undesirable from the presence of inflorescences. What factors determine the agronomic standpoint. moment in which reproductive branches will be produced are not yet clear, as this event is very strongly Lateral branches from the same node (called influenced by the environment. Reproductive branching chupones in Spanish) are sporadic and depend on may give rise to two, three, and even four secondary planting density, climatic conditions, soil fertility, and branches, which, in their turn, may ultimately produce cultivar. They stem from the axillary buds of the tertiary branches, and so on (Figure 2-1). principal stem, and are usually thinner than this stem, with long internodes and smaller leaves. Wounds or damage in the apical area (e.g., from lancefly [Silba pendula] or thrips) will also induce lateral buds into producing branches that will assume the role of the principal stem, replacing it. Fourth The internal structure of the cassava stem is branching typically dicotyledonous. The outermost layer in young Third stems is the epidermis, followed by (going towards the branching interior) cortical tissue. Pigmentation in these two layers will define the color that the stem ultimately assumes. Internally, the layer is ligneous. The center of the stem is occupied by a prominent pith, composed of Second branching parenchymatous cells. As stem diameter increases, large quantities of xylem accumulate, giving the mature stem a ligneous consistency and generating the suber or cork that replaces the epidermis. First The leaf branching Leaves are the organs in which photosynthesis mostly occurs, transforming radiant energy into chemical energy. Leaves are caducous, that is, with age they senesce, and fall from the plant as it develops. The total number of leaves produced by the plant, their longevity, and photosynthetic capacity are varietal characteristics, which are profoundly influenced by Figure 2-1. Plant stripped of leaves to show branching. environmental conditions. 17 Cassava in the Third Millennium: … Figure 2-2. Variations in branching angle and number of branches. Leaves are simple, consisting of the leaf blade and Leaf color is also a varietal characteristic but may petiole. The blade is palmate with variable number of vary with plant age. Mature leaves may be purple, dark lobes, usually, odd, ranging between 3 and 9. Lobes green, or light green. Purple buds may, as the leaves measure between 4 and 20 cm long and between grow and develop, ultimately become greenish in 1 and 6 cm wide. The central lobes are larger than the coloring. Bud color is a very useful characteristic for lateral ones. Lobe shape can be classified in different varietal identification, as it is relatively constant. The ways, with a variable number of categories. A simple color of the nervure ranges between green and purple, classification distinguishes three types of lobes: linear and may also be used for varietal description. This or straight, obovate, and pandurate. But intermediate color may be the same or different for the two sides of types also exist, encouraging the development of other the leaf blade. classification systems to qualify such characteristics (Figure 2-3). The leaf petiole may be between 9 and 20 cm long. It is thin, with variable pigmentation (green to purple), Leaf size is a typical characteristic of each cultivar, depending on variety. Petiole color does not always although it depends heavily on environmental coincide with that of the nervure. conditions. Leaves produced in the first 3 to 4 months of the plant’s life are larger than those produced after Mature leaves are always glabrous, that is, they lack the fourth month. For example, in variety M Col 72, the pubescence. Leaves of buds, however, may or may not average leaf area at 4 months old is about 250 cm2; at be pubescent—a relevant feature as pubescence in bud 7 months, it is 130 cm2; and at 10 months (harvest), leaves is closely related to resistance to thrips. The only about 90 cm2. upper surface of the leaf is covered by a brilliant waxy 18 Cassava Taxonomy and Morphology cuticle, while the lower surface is opaque. Most stomata are found on the lower surface, although, in some varieties, abundant stomata may also appear on the upper surface. At the petiole’s point of insertion in the stem, two stipules, 0.5 to 1.0 cm long, can be found. These stipules may or may not remain adhered to the stem once the leaf is fully developed. Although the principal economic product of cassava is the root, leaves are also important. In several regions of Africa and Asia, leaves are processed for human consumption. Cassava leaves have a valuable nutrient content with high protein levels that range between 18% and 22%, dry weight (Buitrago A 1990). Young cassava foliage also has several vitamins and minerals. Table 2-1 shows ascorbic acid and carotene contents for cassava roots and leaves. Data are based mostly on evaluations of more than 500 genotypes belonging to the core collection held by the cassava germplasm bank at the Centro Internacional de Agricultura Tropical (CIAT)3. Information on contents of principal minerals is also presented from the viewpoint of human and animal nutrition (Table 2-2), extracted from a representative sample of 20 varieties. Table 2-1. Contents of ascorbic acid and carotenes in leaves and roots of more than 500 cassava varieties from the germplasm bank at CIAT. Ascorbic acid Carotenes (mg/100 g fw)a (mg/100 g fw)a In leaves In roots In leaves In roots Minimum value 0 0 23.28 0.100 Maximum value 419.25 37.52 86.22 1.040 Median 109.30 8.09 47.72 0.190 Average 120.16 9.48 48.26 0.230 SD 84.14 6.50 8.61 0.137 a. fw = fresh weight. SOURCE: CIAT (1999). The inflorescence Not all cassava varieties flower under the same environmental conditions. Those that do show marked differences in flowering times and quantities of flowers produced. The environment greatly influences the induction of flowering. As with all plants of the Manihot genus, cassava is a monoecious plant, that is, it bears 3. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, Abbreviations, and Figure 2-3. Two types of leaf lobes. Technical Terminology, this volume. 19 Cassava in the Third Millennium: … Table 2-2. Concentration of mineral elements in leaves and roots of 20 cassava clones evaluated at CIAT (unpublished data). Element Concentration Concentration in leaves in roots (mg/100 g dw)a (mg/100 g dw)a Average SD Average SD Rachis Fe 94.4 37.8 9.6 2.49 Mn 67.9 10.5 1.2 1.00 Axis of secondary B 66.1 7.7 2.4 0.51 raceme Flowers (♂) Cu 7.3 0.6 2.2 0.35 Bracteole Zn 51.6 11.8 6.4 1.35 Flowers (♀) Ca 12,324.0 1761.0 590.0 120.00 Pedicel Mg 7,198.0 888.0 1153.0 147.00 Pedicelar or secondary bract Na 11.4 3.0 66.4 27.00 K 10,109.0 903.0 8903.0 882.00 Peduncle Primary bract P 3,071.0 236.0 1284.0 113.00 S 2,714.0 145.0 273.0 40.00 a. dw = dry weight. Figure 2-4. Diagrammatic representation of an inflorescence (from Domínguez et al. [1983]). unisexual flowers, with some being male and others female, with both usually found on the same Male an d female flowers inflorescence. The evolution of flower structures in the Euphorbias is, Cassava u ndergoes cross pollina tion, which means compared with other flowering plants, remarkable. that it is a heterozygous plant, with each individual Cassava flowers are in fact apetalous, having no petals being a hybrid. Pollinati on is typ ically carried out by or sepals. They are also monoecious, that is, male and insects. Self-poll ination is prevented b y the female female flowers are separately found on the same flowers of a raceme opening first before the male inflorescence. Female flowers are single, and are flowers of that same raceme. This phenomenon is reduced to a pistil that is protected by petal-like bracts. known as protogyny. However, oc casionally, the male Male flowers are also reduced—to a single stamen— and female flowers of different racemes on a single but, unlike female flowers, they form inflorescences of plant may open simultaneously. When this happens, 10 single-stamen flowers. These inflorescences, known self-pollination may naturally occur. as cyathia (sing. cyathium), are also protected by bracts. Together, the female flowers and male cyathia Cassava “ flowers” are produced in inflorescences. form inflorescences of a secondary order known as The basic arrangement of flowers is the ra ceme panicles. (Figure 2-4), where the female flowers occupy basal positions and the male the distal ones. The latte r are What are commonly called tepals (i.e., petal-like smaller and usually more numerous than the female sepals) in cassava flowers are actually bracts. In this ones. Frequentl y, pa nicles are also produced, that is, volume, the male cyathia will be treated as if they are from the botanical viewpoint, a raceme of racemes single flowers, as the distinction is only relevant from develops. In such c as es, a principal raceme exists, the botanical point of view. which is composed of secondary racemes. The mal e “flower” is about half the size of the Each flo w er, whether male or female, has a primary female. It posses ses a straight and very short pedicel, bract and a bracteole. These foliaceous organs appear while th at of the female flower is thicker and longer in the inflorescences and may either remain or drop off (Figures 2-4 and 2-5). Inside th e male flower is a basal once the flowers develop. disk that is divided into 10 lobes. In the center of this disk a r ud imentary ovary can be seen. At the po ints of In most c ases, inflorescences are formed from separation of the lobes of the basal disk, arranged in buds at the point of insertion of reproductive branches. two series, are the 10 stamens that support anthers. Of Occasiona lly, inflorescences may develop from buds in these stamens, t he 5 outer ones are separate and leaf axils in the plant’s upper parts. longer than the 5 inner ones. Together, they form the 20 Cassava Taxonomy and Morphology 3 months to complete. The fruit is a dehiscent capsule that is trilocular, and ovoid to globate, with a diameter of 1.0 to 1.5 cm and six longitudinal, narrow, and prominent ridges (Figure 2-6). Cross-sections of the developing fruit show a series of clearly discernible tissues: epicarp, mesocarp, and endocarp. As the seed matures, the epicarp and mesocarp dry up. The endocarp, which is ligneous, opens abruptly when the fruit is mature and dried, releasing and dispersing seeds to a certain distance. During dehiscence tissues separate both, throughout the mid-vein of each fruit loculus and between the separations themselves. The seed The seed is the medium for the plant’s sexual reproduction. While it is not important in reproduction and commercial multiplication, it has incalculable value for plant breeding, as only through sexual reproduction can new, genetically superior, cultivars be developed. The seed is ovoid-ellipsoid in form and measures Figure 2-5. Cassava flowers: female (top) and male (bottom). about 1 cm long, 6 mm wide, and 4 mm thick. The seed coat is smooth, coffee-colored, and mottled gray. In the upper part, especially of new seed, the caruncle is found. set of anthers. On each stamen is an elongated anther This structure is lost once the seed falls to the ground. that inclines towards the central part of the flower. The At the other end of the seed, opposite the caruncle, a anthers open along longitudinal apertures. Pollen small cavity is found. A slender suture leaves from the release begins 2 or 3 h before the flower opens and may caruncle and finishes in this basal cavity. Figure 2-7 even end before the flower completely opens. Pollen shows the typical structure of a cassava seed. grains are large and spherical, and only a few are produced in each sac. They are also sticky, which The seed coat is the outermost part of the seed. facilitates pollination by insects. Pollen remains viable Immediately inside the seed coat is the endosperm, for up to 6 days. A detailed description of which is formed of polyhedral parenchymatous cells that microsporogenesis in cassava has been recently protect and nourish the embryo, itself located in the published (Wang et al. 2010). central area of the seed. Within the endosperm are found the cotyledons and embryonic axis that will give Because cassava can reproduce vegetatively, rise to the new plant after germination. The embryo is reproductive dysfunction is not, from an evolutionary viewpoint, as negative as it would be in crops that have exclusively sexual reproduction. As a result, cases of male-sterility, for example, can be frequently found. Such cases are of two types: one where the flowers abort before reaching maturity, and the other when flowers mature but the anthers do not produce pollen. Genetics of such sterility, however, has not yet been fully studied. The fruit Once the female flower has been pollinated, fruit begins to form from the ovary. Fruit maturation requires about Figure 2-6. Cassava fruit. 21 Cassava in the Third Millennium: … (A) (B) Apparently the primary root always evolves into a tuberous root, and is the first to do so. If the plant grows Endosperm from a stake, the roots are adventitious, forming at Seed coat (1) the lower end o f the stake, which produces a callosity, an d (2) from buds in that part of the stake that is buried in the soil. These roots i nitially form a fibrous system but, later, some (usually <10) begin thickening and become tu berous roots. The number of tuberous roots is determined, in most cases, by the plant’s early growth. Cotyledons Plumule Although root density is low, penetration into the Hypocotyl soil is deep. This is a highly relevant characteristic, as it Radicle c ontributes to the plant having the capacity to endure prolonged droughts. Fibrous cassava roots can reach Caruncle depths of up to 2.5 m. The plant absorbs water an d Figure 2-7. Diagram of two longitudinal sections of botanical nutrients through the fibrous roots, a capacity that is cassava seed (from Domínguez et al. [1983]). lost w hen t hey become tuberous. (A) Cross-section cut across suture; (B) cross- section cut through suture. Morphologically and anatomically no d if ferences are found among fibrous and tuberous roots. What happens made up of the two cotyledonous le aves, plumule, is that, as starch accumulation begins, the directio n o f hypocotyl, and radicle. The cotyledonous leaves and root growth changes from longitudinal to radial. endosperm occupy almost the entire interior of the Howeve r, this does not necessarily mean that the root seed; they are white, elliptical, and carnose. absolutely stops longitudinal growth. As mentioned above, tuberous r oots co me from secondary Although currently see d does not play a enlargement of fibrous roots. This means that the root predominant role in cassava multiplication, it may well system first pene trates the soil while roots are thin and do so in the future. A phenomenon in n ature, especially only after such penetration, do roots begin thickening. among grasses, known as apomixis, consists of producing botanical seed without th e usual sexual Externally, the parts that are disting ui shable of reproduction. In other words, the seed embryo tuberous roots of an adult cassava plant are the produced by apomixis is genetically ide ntical to t he tuberous portion proper; its dist al extreme, which may mother plant. This means that, when the embryo grows still retain its fibrous character (Figure 2-8); and its into a plant, it will also produce an individual p lant that is i dentical to its mother. Apomixis has been reported for the Manihot genus (Nassar et al. 2000). It could be incorporated into commercial systems because of its a ppreciable advantages: it would enable seed storage for more than the month or 2 months that stems can be Stem kept and the rate of multiplication of a material could be increased significantly. Also th ey ar e less likely to carry Peduncle pathogens than stem cuttings. Neck The root system Tuberous root The principal characteristic of cassava roots is their Fibrous root capacity for starch storage, which is the reason wh y, so far, it is the plant organ that has the greatest economic value. However, not all roots produced ultimately become storage organs. Fibrous roots Figure 2-8. Drawing showing the components of the cassava When t he plant grows from sexual seed, a primary root system (from Domínguez et al. [1983]). Ideally, root develops and then , several seconda ry on es. with either short or long peduncles. 22 Cassava Taxonomy and Morphology upper or proximal extreme, or neck or “peduncl e” , which stake’s lower extreme. Some roots growing from lateral also remains fibrous and joins the tuberous section to buds on the stake may also become tuberous roots. the stem. N eck size ranges from being absent or very Tuberous roots tend to explore and be located in short (<1 cm) to being longer than 8 cm. The depth at d eeper strata of the soil. When the stake’s position is at which t he stake is buried affects peduncle length, which an angle to the soil’s surface, tuberous roots again tends to be longer as stake depth is greater. Neck length tend to f or m at the callosity and, as in the previous is a characteristic of commercial interest. When it is very case, other roots may emerge from t ho se lateral buds short it hinders separation of tuberous roots from their that are under the soil. If the stake is placed ste m s, resulting in injuries to the tuberous area and horizontally, then tuberous roots are distri bu ted along accelerating postharvest physiolog ic al deterioration the stake, as they are formed at both the lateral buds (PPD). When the peduncle is too long, it results in higher and the two extremes of the stake. Roots location also losses, as the peduncle breaks more ea sily during tends to be closer to the surf ac e and more disperse, harve st, leaving roots of commercial interest in the thus facilitating harvest. ground. The tissues that compose a tuberous root are, Roots may be highly variable i n shape and size, successively from ou ts ide in, the peel, pulp, and central depending on both variety and the environmental fibers (Figure 2-10). A highly relevant aspect in cassava conditions under which the plants grow (Figure 2-9). use is the presence of a cyanogenic glucoside called However, when varie ti es are evaluated over numerous linamarin. This glucoside, in the pres ence of an experiments, clear differences do appear, with some enzyme (mainly linamarase) and acids, is hydrolyzed to varieties tending to produce large roots and others produce hydroc yanic acid in dosages that range from having consistently smalle r roots than the rest. The innocuous, through poisonous, to lethal. This reaction roots may be cylindrical, fusiform, or conical in shape, occurs spontaneously in decompose d plant tissues or with intermediate forms such as cylindrical-conical in the digestive tract of animals. Hydrocyanic acid frequently occu r ring. production is particularly hi gh in root peel. Other plant tissues (including leaves) also have cyanogenic The distribution of roots in the soil depends on both potential. Depending on cyanogenic glucoside levels, genetic and cultural factors. Varieties that tend to some publications will classify sweet cassava (low produce roots with long necks or peduncles also have cyanoge ni c potential) as M. utilissima, while their roots distributed in a scattered fashio n, covering a classifying bitter cassava (high cyanogenic potential) greater area of soil than those varieties with “sessile” as M. esculenta. roots (i.e., with absent or very short necks). The way st akes are planted also affects the pattern in which roots The cyanogenic potential of di fferent tissues of a will be distributed. When a s take is planted vertically, it cassava plant is greatly affected by the environmental produces roots around the callosity that forms at the conditions under which i t grows and its age at harvest. Roots of a given cultivar can be sweet in a particular site, but bitter in other locations. Usually, however, the cyanogenic potential of bitter varieties tends to be Periderm Sclerenchyma Parenchyma Xylem vessels Phloem and Cambium fibers Storage parenchyma Xylem vessels Peel Pulp Figure 2-9. Different shapes of cassava roots (conical, Figure 2-10. Cross-section of a tuberous cassava root (from cylindrical, and long) with and without constrictions. Domínguez et al. [1983]). 23 Cassava in the Third Millennium: … consistently higher (to as much as 1000 mg of acid per et al. 1982). Starch granule size is variable, and is, to kg of fresh roots) across numerous evaluations than for some degree, determined genetically according to the sweet varieties (20 mg/kg of root). Apparently, there are variety. Starch granule shape and size are characteristics no cyanogen-free cassava varieties. of great practical relevance to industry, as described below. Root peel. This tissue comprises the periderm and cortex. The periderm consists of dead cork cells (suber Central fibers. These fibers, forming the center of or phellem) that envelop the root surface. As the root the root, comprise rows of parenchyma and xylem increases in diameter, the continuity of cellular layers sclerenchyma vessels, whose hardness, length, and breaks, causing longitudinal fissures that characterize width are varietal characteristics of economic the surface of the cassava root. The way in which these importance, as they affect the culinary quality and fissures are produced, and the resulting appearance, appearance of roots cooked for human consumption. are frequently used to identify cultivars for marketing purposes. Underneath these fissures, new cork cells are About 80% of root fresh weight corresponds to pulp. formed from the phellogen, re-establishing the Dry matter content of cassava roots ranges between continuity of this type of tissue over the root’s entire 30% and 40%, although this range can sometimes be surface. In addition to the periderm’s texture, which can exceeded. The dry matter found in the parenchyma be rugose to more or less smooth, external color is also mostly (90% to 95%) constitutes the non-nitrogenous used to identify cultivars, as it is a highly stable fraction, that is, carbohydrates such as starch and morphological characteristic. Root color may range sugars. The rest of the dry matter corresponds to fiber from white or cream, through pale coffee-colored, to (1% to 2%), fats (0.5% to 1.0%), ashes or minerals (1.5% dark brown. to 2.5%), and protein (about 2%). Finally, we point out that starch comprises most of the carbohydrates (96%) Below the periderm is the cortex or cortical layer and is, therefore, the principal component of dry matter (phelloderm). This tissue is 1 to 5 mm thick (Pérez et al. in the root. 2011), with a color of its inner layer ranging from white, through cream, to pink. This characteristic is also used, Nutritional value of the roots. Without a doubt, even by housewives, to identify cultivars. Within the the principal economic value of the cassava crop lies in cortex, compressed phloem tissues are found, its roots. Cassava roots, being storage organs for containing the highest concentrations of cyanogenic energy, have various uses as human food, animal feed, glucoside. In this layer, lactiferous canals can also be and starch extraction. Table 2-3 summarizes the seen, especially in young roots. principal chemical characteristics of cassava roots that have been chipped, dried, and processed into dry flour. Pulp. This tissue constitutes the usable part of the root and is therefore the tissue of greatest economic Most of the root content constitutes available interest. It appears as a solid mass, composed mainly of carbohydrates. Compared with other energy sources secondary xylem tissue derived from the cambium, the such as maize, cassava roots have less protein (2% to 3% cells of which contain starch in abundance and in the versus 8% to 10% for maize). This difference in protein form of round granules of unequal sizes. Pulp is also formed by parenchymatous cells that, in the case of Table 2-3. Chemical composition of cassava flour from whole cassava, develops to such a magnitude that the root and from root without peel (dry weight). conductive xylem tubes remain reduced to small Component Contents (%) isolated groups scattered throughout the reserve Root with Root without parenchyma. The cambium from which pulp tissues are peel peel derived is found in the pulp’s outermost part, separating Dry matter 100.00 100.00 the pulp from the cortex. This cambium also generates Available carbohydrates 83.80 92.40 secondary phloem cells towards the exterior. Crude protein 3.05 1.56 Ether extract 1.04 0.88 The parenchyma cells that form most of the Ash 2.45 2.00 cassava root pulp contain one to numerous Neutral detergent fiber 6.01 3.40 amyloplasts. Within these, starch is accumulated as Acid detergent fiber 4.85 1.95 more or less spherical often truncated granules, Hemicellulose 1.16 1.45 although a great diversity of shapes exists such as Data extracted from Buitrago A (1990). cupuliform, biconcave-convex, and mitriform (Castilloa 24 Cassava Taxonomy and Morphology content justifies cassava flour having a cost of about Table 2-4. Qualitative characteristics of cassava roots. 70% that of maize, when it is used to formulate animal Trait Average Minimum Maximum feed. Dry matter content (%) 33.50 14.30 48.10 Cyanogenic glucosides Postharvest physiological deterioration in (ppm) 325.00 14.00 3274.00 cassava roots Starch (% of dry weight) 84.50 65.00 91.00 Cassava roots undergo rapid deterioration once Amylose content (% total starch) 20.70 15.20 26.50 harvested, a process mentioned above as “postharvest Starch granule size (μm) 16.29 13.97 18.73 physiological deterioration” (PPD). As a result, cassava Total sugars roots must be consumed within a few days of harvest (% of dry weight) 3.75 0.20 18.80 because, during the first 3 days, bluish spots begin Reducing sugars appearing, concentrating on the root’s periphery. The (% of dry weight) 1.31 0 15.70 spots then extend to the entire tissue, turning it coffee- Amylose (% of starch) 20.70 15.10 26.50 colored or brown and, in longitudinal sections of the Total carotenoids roots, appearing as vascular streaks (Wheatley et al. (μg/g fresh root) 8.84 3.39 18.87 [1983]). While little is known about PPD, its occurrence SOURCES: Chávez et al. (2005); Ceballos et al. (2008); Morante et is directly associated with any mechanical damage that al. (2009); Sánchez et al. (2009). occurred during harvest and also on variety. Some evidence suggests that varieties with less dry matter characteristics of cassava starch differ from that content are more tolerant of PPD. Roots with high obtained from maize or potato, thus creating a niche carotene content (the so-called “egg yolk” cassava) also whereby certain industrial processes may prefer the use tend to suffer less from PPD (Morante et al. 2010). of one starch over another. Two mutations affecting functional properties, granule morphology, and/or One cultural practice that does reduce the incidence biochemical characteristics of cassava starch have also of PPD or delay its appearance is to prune plants several been reported (Ceballos et al. 2007, 2008). days in advance of harvesting the roots (van Oirschot et al. 2000). However, pruning also notably reduces dry The principal physicochemical properties of a starch matter content and, as a result, starch content, while are proximal composition; granule characteristics (size increasing total sugars content. These results illustrate and shape); crystalline nature; molecular weight; the way in which these variables can be affected swelling power; solubility; relative amylose content; and according to the conditions under which the plant grows characteristics of the starch paste. and the cultural practices to which it is subjected. The protein content of cassava starch (0.1%) is very Cassava starch and its properties low, compared with that of rice (0.45%) or maize starch (0.35%). Residual protein can impart a floury flavor and Starch is one of the dominant reserve substances in give these starches a tendency to foam. nature and is found as small granules deposited in seeds, tubers, and roots of different plants. Starch is a Potato and cassava starch granules contain mixture of two polymers: amylose, which is linear, and negligible amounts of fatty substances, compared with amylopectin, which is branched. Table 2-4 lists some of cereal starches such as maize (0.6%) and rice (0.8%). the most relevant qualitative characteristics of cassava Such a composition favors cassava starch, as these roots, with emphasis on starch. These results were lipids form a complex with amylose that tends to prevent consolidated, based on information published in several starch granules from swelling and solubilizing, therefore articles (Chávez et al. 2005; Ceballos et al. 2008; requiring high temperatures (>125 oC) to break the Morante et al. 2009; Sánchez et al. 2009). amylose-lipid structure and dissolve the amylose fraction. The presence of fatty substances can also The relative proportion of the polymers amylose to create problems of rancidity during storage. amylopectin in any starch, and their specific molecular weight, determines the physicochemical properties of Cassava starch granules are round, with truncated the starch and its industrial properties (Sánchez et al. terminals and a well-defined nucleus (thread). Size varies 2010). Analysis of these properties is fundamental to from 5 to 35 μm, with averages between 15 and 18 μm. achieving an exact use of the existing genetic variability A mutation that severely affects granule size has recently within the Manihot genus. Furthermore, the typical been reported (Ceballos et al. 2008; Figure 2-11). Starch 25 Cassava in the Third Millennium: … (A) granules of rice, maize, and waxy maize have a polyhedral form, while potato starch granules are ovoid and larger, with sizes ranging between 5 and 100 μm, with an average of 33 μm. The granule size for maize and waxy maize starches is intermediate, between 3 and 26 μm, with an average of 15 μm, and similar to that of cassava starch granules. Rice starch granules are smaller, varying between 3 and 8 μm. They are regarded as more resistant to high-temperature processes such as sterilization and to be more digestible. X-ray diffraction patterns of native cassava starch granules have been reported as intermediate (type C) between the characteristic patterns of cereal starches (type A) and fruit and tuber starches (type B). Crystallization levels in cassava starch are about 38% (Rickard et al. 1991). Granule crystallinity is essentially due to amylopectin. The small granule mutation of (B) cassava affects crystallinity, branching pattern, and amylose content (Rolland Sabaté et al. 2012). When an aqueous starch suspension is subjected to heating, granules slowly begin absorbing water and increasing in size. They initially hold their optical properties, including the ability to refract polarized light (birefringence), which is due to the alignment of molecules with no starch granules. Birefringence in cassava starch granules declines at temperatures between 58 and 64 oC, compared with that in maize starch granules, which declines between 62 and 68 oC. Starch granules, as mentioned, are composed of two polysaccharides with glucan links: amylose and amylopectin. Amylose is basically a linear polymer of α (1-4) units. Amylopectin comprises the greater component and consists of a branched polymer of α (1-4) and α (1-6) units. In some starches, granule size is related to the amylose-to-amylopectin ratio (Delpeuch and Favier 1980). The average amylose content in the following starches are: for cassava, 20.9%; maize, 26%; potato, 24%; rice, 17%; and waxy maize, <1%. Amylose content of starches is very strongly related to some of their properties. For example, starches with high amylose content retrograde very quickly. In contrast, waxy maize, which is 100% free of amylose, is highly stable and resistant to retrogradation (i.e., the reorganization of amylose and amylopectin molecules in a crystalline structure Figure 2-11. Scanning electron microscope photographs of when starch pastes are cooled). A mutation in cassava, (A) normal and (B) mutant cassava starch granules. resulting in amylose-free starch, has recently been reported (Ceballos et al. 2007). 26 Cassava Taxonomy and Morphology Although varietal differences are found for Castilloa JJ; Ogura M; Quintero F. 1982. Vacuum drying: rheological or functional properties of cassava starches, a fast and reliable SEM processing method to study Brabender amylogram curves for cassava starch follow starch grain racemes and morphology in fresh edible a similar pattern to that of starches with a high tropical roots and tubers. 10th International Congress amylopectin content. Cassava starch gelatinizes, as do of Electron Microscopy, vol. 3. Hamburg, Germany. rice and waxy maize starches, at relatively low p 507–508. temperatures (60–67 oC), rapidly reaching the maximum peak. This implies that it is an easy starch to Ceballos H; Sánchez T; Morante N; Fregene M; Dufour cook, requiring less energy for cooking. Furthermore, it D; Smith AM; Denyer K; Pérez JC; Calle F; Mestres has a low tendency towards retrogradation, and C. 2007. Discovery of an amylose-free starch mutant produces a very clear and stable gel. in cassava (Manihot esculenta Crantz). J Agric Food Chem 55(18):7469–7476. Cassava starch gelatinizes in water at temperatures of more than 60 oC but, at more than 90 oC, although Ceballos H; Sánchez T; Denyer K; Tofiño AP; Rosero EA; paste viscosity is initially high, it declines abruptly, with Dufour D; Smith A; Morante N; Pérez JC; Fahy B. continuous solubilizing and agitation, and no gel is 2008. Induction and identification of a small-granule, formed with subsequent cooling. Such behavior in high-amylose mutant in cassava (Manihot esculenta cassava starch makes it technologically convenient as a Crantz). J Agric Food Chem 56(16):7215–7222. substrate for hydrolytic processes, but inappropriate as a substitute for cereal starches in processes requiring Chávez AL; Sánchez T; Jaramillo G; Bedoya JM; Echeverry retrogradation. J; Bolaños EA; Ceballos H; Iglesias CA. 2005. Variation of quality traits in cassava roots evaluated in The cassava starch’s properties of clarity and low landraces and improved clones. Euphytica retrogradation can be used in many food products. Its 143:125–133. rheological characteristics closely resemble that of waxy maize starch. CIAT. 1999. Improved cassava for a developing world— Annual report [of] Project IP-3. Cali, Colombia. 127 p. Quality properties of starch pastes are modified during freezing, with the paste structure usually Ciferri R. 1938. Saggio de classificazione delle razze deteriorating through increased exudation of water or di manioca (Manihot esculenta Crantz). Relaz. “syneresis”. Some native starches like those of cassava Monografie Agrar.-Colon. 44:1-59. and oca (Oxalis tuberosa) are regarded as resistant to this process (Rurales 1995; Sánchez et al. 2010). Cock JH. 1989. La yuca, nuevo potencial para un cultivo tradicional. CIAT, Cali, Colombia. 240 p. (Also Cassava starch pastes are stable in acid media available in English as Cook JH. 1985. Cassava: where pH < 2.4. Normally, such acidity would destroy new potential for a neglected crop. Westview Press, starch granules and the paste’s physical aspect through Boulder, CO, USA.) partial or total hydrolysis. Crantz. 1766. Institutiones Rei Herbariae; nutum naturae References digestae ex habitu. Vol. 1, p 167. To save space, the acronym “CIAT” is used instead of De Carvalho RD; Guerra M. 2002. Cytogenetics of “Centro Internacional de Agricultura Tropical”. Manihot esculenta Crantz (cassava) and eight related species. Hereditas 136:159–168. Allem AC. 1994. The origin of Manihot esculenta Crantz (Euphorbiaceae). Genet Resour Crop Evol 41:133–154. Delpeuch F; Favier JC. 1980. Caracteristique des amidons de plantas alimentaires tropicales: action de l’alpha- Allem AC. 2002. The origins and taxonomy of cassava. amylase, gonflement et solubilité. Ann Technol Agric In: Hillocks RJ; Thresh JM; Bellotti AC, eds. Cassava: 29(I):53–57. biology, production and utilization. CABI Publishing, Wallingford, UK. p 1–16. Domínguez CE; Ceballos LF; Fuentes C. [1983]. Morfología de la planta de yuca. In: Domínguez CE, Buitrago A, JA. 1990. La yuca en la alimentación animal. ed. Yuca: Investigación, producción y utilización. CIAT, Cali, Colombia. 446 p. CIAT; United Nations Development Programme (PNUD), Cali, Colombia. p 29–49. 27 Cassava in the Third Millennium: … Hahn SK; Bai KV; Asiedu R. 1990. Tetraploids, triploids, Rickard JE; Asoka M; Blanshard MV. 1991. The physico- and 2n pollen from diploid interspecific crosses with chemical properties of cassava starch. Trop Sci cassava. Theor Appl Genetics 79:433–439. 31:189–207. Jennings DL. 1963. Variation in pollen and ovule fertility Rogers DJ; Appan SG. 1973. Manihot and manihotoides in varieties of cassava, and the effect of interspecific (Euphorbiaceae): a computer-assisted study. Flora crossing on fertility. Euphytica 12:69–76. Neotropica, Monograph No. 13. Hafner Press, New York. Magoon ML; Krishnan R; Bai KV. 1969. Morphology of the pachytene chromosomes and meiosis in Manihot Rolland-Sabaté A; Sánchez T; Buléon A; Colonna P; esculenta Crantz. Cytologia 34:612–626. Jaillais B; Ceballos H; Dufour D. 2012. Structural characterization of cassava, maize and potato Martin FW. 1976. Cytogenetics and plant breeding of starches with low and high amylose contents. Food cassava. Commonwealth Bur Plant Breed Genet Hydrocolloids 27:161–174. 46:909–916. Rurales J. 1995. Caracterización de las propiedades Montaldo A, ed. 1996. La yuca frente al hambre del mundo reológicas y nutricionales del almidón nativo y tropical. Universidad Central de Venezuela. Anauco gelatanizado de achira (Canna edulis). Conferencia Ediciones, C.A. Caracas, Venezuela. 570 p. Internacional en Biodisponibilidad de Nutrientes, March, 1995. Escuela Politécnica Nacional (EPN), Morante N; Sánchez T; Ceballos H; Calle F; Pérez JC; Egesi Quito, Ecuador. p 179–188. C; Cuambe CE; Escobar AF; Ortiz D; Chávez AL. 2010. Tolerance to post-harvest physiological deterioration in Sánchez, T; Mafla G; Morante N; Ceballos H; Dufour cassava roots. Crop Sci 50:1333–1338. D; Calle F; Moreno X; Pérez JC; Debouck D. 2009. Screening of starch quality traits in cassava (Manihot Nassar NA; Dos Santos E; David SRO. 2000. The esculenta Crantz). Starch/Stärke 61:12–19. transference of apomixis genes from Manihot neusana Nassar to cassava, M. esculenta Crantz. Sánchez T; Dufour D; Moreno IX; Ceballos H. 2010. Hereditas 132:167–170. Pasting and gel stability of waxy and normal starches from cassava, potato, maize, and rice under thermal, Nassar NMA; Ortiz R. 2008. Cassava genetic resources: chemical and mechanical stress. J Agric Food Chem manipulation for crop improvement. Plant Breed Rev 58:5093–5099. 31:247–275. van Oirschot QEA; Quirien EA; O’Brien GM; Dufour D; Olsen KM; Schaal BA. 2001. Microsatellite variation in El-Sharkawy MA; Mesa E. 2000. The effect of pre- cassava (Manihot esculenta, Euphorbiaceae) and harvest pruning of cassava upon root deterioration its wild relatives: further evidence for a southern and quality characteristics. J Sci Food Agric Amazonian origin of domestication. Am J Bot 80:1866–1873. 88(1):131–142. Wang C; Lentini Z; Tabares E; Quintero M; Ceballos H; Pax, F. 1910. Manihot Adans. In: Engle Pflanzenreich IV Dedicova B; Sautter C; Olaya C; Zhang P. 2010. 147(Heft 44):21-111. Microsporogenesis and pollen formation in cassava. Biol Plant 55(3):469–478. Pérez JC; Lenis JI; Calle F; Morante N; Sánchez T; Debouck D; Ceballos H. 2011. Heritability of root peel thickness Wheatley C; Lozano C; Gómez G. [1983]. Deterioración and its influence in extractable starch from cassava postcosecha de raíces de yuca. In: Domínguez CE, (Manihot esculenta Crantz) roots. Plant Breed ed. Yuca: Investigación, producción y utilización. 130:688–693. CIAT; United Nations Development Programme (PNUD), Cali, Colombia. p 493–510. Pohl J. 1827. Plantarum Brasiliae Icones et Descriptiones 1:17–56. 28 CHAPTER 3 Cassava Productivity, Photosynthesis, Ecophysiology, and Response to Environmental Stresses in the Tropics: A Multidisciplinary Approach to Crop Improvement and Sustainable Production Mabrouk A. El-Sharkawy1, Sara M. de Tafur2, and Yamel López3 Introduction Balagopalan 2002; Westby 2002). Cassava roots are highly perishable once harvested (van Oirschot et al. Cassava (Euphorbiaceae: Manihot esculenta Crantz) is 2000), and must be used immediately or processed into also called manioc, yuca, or mandioca. It is widely grown dried products. Sometimes, however, pruning the crop for its starchy roots, which are used as a staple food and 3 weeks before harvest can reduce deterioration. animal feed. Crops are cultivated throughout the tropics and subtropics of Africa, Asia, and Latin America, Regardless of its attributes and potential productivity, between latitudes 30° N and 30° S, and from sea level to the cassava crop has received little attention from more than 2000 m above sea level (masl)4. Growers are policymakers or researchers in the developing countries mostly farmers who live in areas of marginal where it is widely grown. Even so, limited work was environments that characteristically possess highly carried out in parts of Africa, Asia, and Latin America eroded, low-fertility, acidic soils. Farmers are usually too until late 20th century (Verteuil 1917, 1918; Nijholt 1935; resource-poor to afford applications of agrochemicals Cours 1951; James 1959; Hunt et al. 1977; Cock 1985), (El-Sharkawy 1993, 2004; Ruppenthal et al. 1997; when cassava research increased exponentially. Fermont 2009). Cassava is the most important source of dietary Because cassava has an inherent tolerance of carbohydrates after rice, sugarcane, and maize for over various edaphoclimatic stresses, the crop is expanding 500 million people in the developing countries of the into more marginal lands, particularly in sub-Saharan tropics and subtropics. Yet, the crop was overlooked by Africa (Romanoff and Lynam 1992), where other staple the so-called “Green Revolution” created through the food crops yield poorly (El-Sharkawy 1993; de Tafur et efforts of international agricultural research centers in the al. 1997b; Cadavid et al. 1998; Flörchinger et al. 2000). 1960s. These centers aimed to improve major cereal crops such as wheat, rice, and maize with the help of and Cassava storage roots are used as a source of funding by a few international agricultural development carbohydrates (protein is less than 3% in dried roots), and research agencies. In 1971, the Consultative Group mainly for human consumption. It is prepared fresh, as on International Agricultural Research (CGIAR) was in the case of sweet cultivars, which have low contents of established under the sponsorship of the World Bank, the cyanogenic glucosides. It is also processed, particularly United Nations Development Programme (UNDP), and in the case of bitter cultivars, which are high in the Food and Agriculture Organization of the United cyanogenic glucosides into dried products such as flour, Nations (FAO) (Wortman 1981). This Group gave high starch, or animal feed (Dufour 1988; Essers 1995; priority to research on other crops, including cassava, and on production ecosystems in the humid tropics of Africa 1. Plant Physiologist, formerly of CIAT, Cali, Colombia. Present (through the International Institute of Tropical Agriculture address: A.A. 26360, Cali, Colombia. [IITA], based in Nigeria) and South America (through the E-mail: mabrouk99@hotmail.com Centro Internacional de Agricultura Tropical [CIAT], based 2. Plant Physiologist, Associate Professor of UN–Palmira, Colombia. E-mail: msmejiat@unal.edu.co in Colombia). 3. Plant Physiologist, Emeritus Professor of UN–Palmira. E-mail: lopezyamel@yahoo.com Given the necessary financial support, international 4. For an explanation of this and other abbreviations and acronyms, see Appendix 1: Acronyms, Abbreviations, and Technical multidisciplinary teams of scientists were able, for the first Terminology, this volume. time, to conduct extensive research on cassava. They 29 Cassava in the Third Millennium: … collaborated with the few, already existing, national germplasm that was more broadly adapted to the various research programs to improve germplasm collection and environments prevailing in the tropics and subtropics of characterization, breeding, agronomy, cropping systems both Latin America and Asia. management, pest-and-disease control, and crop use. These activities were based on increased understanding At first, breeding objectives were directed towards of the physiological processes involved. Various developing high-yielding cultivars for favorable conditions researchers reviewed results on many aspects of cassava where biotic and abiotic stresses were absent (Kawano et research in Africa, Asia, and Latin America over the last al. 1978; Cock et al. 1979). This strategy focused on 3 decades. These authors include Kawano (2003) and selecting for high yield per unit land area and comparing others, working on different continents, who contributed with traditional vigorous cultivars and/or landraces chapters to the book entitled Cassava: biology, suitable for intercropping. Another trait selected for was production and utilization, edited by Hillocks et al. high dry matter content (i.e., high starch content) in (2002). storage roots. Harvest indexes (HI, where HI = root yield/total plant biomass) were selected to be higher than In this chapter, we review research, both published those (<0.5) usually found in low-yielding traditional and unpublished, conducted at CIAT during more than varieties and landraces (Kawano 1990, 2003). This early 15 years on cassava productivity, physiology, and work showed that cassava germplasm is genetically ecophysiology in response to environmental stresses diverse, with potential for high productivity in near- normally encountered in the tropics. The review optimal environments and as having sufficient genetic addresses a need to assemble and integrate this resources for tolerating a range of pests and diseases. dispersed information for scientists in general and for Thus, the need to transfer traits from wild relatives those concerned with cassava in particular. Focus is on (advocated even as recently as 2010 by Nassar and Ortiz) the strategy adopted to improve the crop, taking into is largely obviated. account the conditions faced by cassava growers who lack the resources to use high-production inputs. This However, most cassava production occurs in approach contrasts with the capital-intensive practices environments with varying degrees of stresses and with used in the Green Revolution crops. little, or no, production inputs from resource-poor farmers. Hence, later breeding strategy goals centered Original results were regularly documented and on selecting and developing cultivars with adequate and reported in progress annual reports that were exchanged stable yields, and able to adapt to a wide range of biotic across countries (CIAT Reports 1983 to 1998), and and abiotic stresses (Hershey 1984; Hershey et al. 1988; published in peer-reviewed technical journals, reviews, Hershey and Jennings 1992; Kawano et al. 1998; students’ theses, proceedings, and books (Porto 1983; Jennings and Iglesias 2002; Kawano 2003). This strategy El-Sharkawy and Cock 1984, 1986, 1987a, 1987b, 1990; was stimulated by cassava’s inherent capacity to tolerate El-Sharkawy et al. 1984a, 1984b, 1984c, 1984d, 1985, adverse environments, particularly those where other 1990, 1992a, 1992b, 1993, 1998a, 1998b, 2008; Cock et major staple food crops such as cereals and grain al. 1985, 1987; Veltkamp 1985; Cock and El-Sharkawy legumes would fail to produce. The strategy also aimed 1988a, 1988b; Guzman 1989; El-Sharkawy 1990, 1993, to avoid and/or reduce the negative consequences on the 2004, 2005, 2006, 2010; Bernal 1991; Hershey and environment caused when high-input (agrochemicals) Jennings 1992; Caicedo 1993; López et al. 1993; Pellet production systems are adopted (El-Sharkawy 1993). and El-Sharkawy 1993a, 1993b, 1994, 1997; Tenjo et al. 1993; Tscherning et al. 1995; Cayón et al. 1997; de Tafur The strategy took advantage of the wide genetic et al. 1997a, 1997b; Cadavid et al. 1998; El-Sharkawy diversity found within more than 5000 accessions that and Cadavid 2000, 2002; Flörchinger et al. 2000; de were conserved at the time at CIAT headquarters (CIAT Tafur 2002; El-Sharkawy and de Tafur 2007, 2010). HQ). These accessions were mostly of Latin American origin, or originated in the 7 or 8 edaphoclimatic Cassava Research Strategy at CIAT ecozones in Colombia, each of which was also characterized by high pest and disease pressures. These The multidisciplinary cassava program at CIAT was ecozones represent most cassava production ecosystems established in the early 1970s. Having a global mandate in the tropics and subtropics (Hershey and Jennings for cassava, the Center focused its research strategy on 1992; El-Sharkawy 1993). collecting, conserving, and characterizing worldwide available germplasm (most of it coming from Latin In light of this environmentally sound breeding America). The program also selected and bred strategy, research on cassava physiology has focused on 30 Productivity, Photosynthesis, Ecophysiology, … both basic and applied aspects of the crop under Exchange of Gas between the prevailing environments. The goal was to better Cassava Leaf and the Environment understand and elucidate the characteristics and mechanisms underlying productivity and tolerance of Responding to air humidity and water stress stresses (Cock and El-Sharkawy 1988a, 1988b; El-Sharkawy 1993, 2004). Pingali (2010) suggested Under controlled laboratory conditions, leaves, still that molecular biology tools would certainly help in attached to their plants, were sampled from both achieving this goal, as would a deeper understanding well-watered and water-stressed cassava grown in large of the agricultural systems and biology of tropical pots left outdoors. The leaves’ central lobes were crops (including cassava plant physiology). He pointed inserted into clip-on chambers connected to an out that temperate-zone research laboratories in infrared gas exchange system and then exposed to countries belonging to the Organisation for Economic high air humidity. This was followed by a short period Co-opreation and Development (OECD) are currently of low humidity. Rates of CO2 uptake at saturating not investing in such knowledge. photons and normal air declined sharply. The response was more pronounced in stressed plants (Figure 3-1; Objectives included (1) characterizing materials El-Sharkawy and Cock 1984). This effect of short from a core collection of cassava germplasm held at exposure to dry air was totally reversible. This reaction CIAT for tolerance of extended water shortages, was also observed in several woody species (Davies either natural or imposed, and of low-fertility soils; and Kozlowski 1974), but was only partially reversible (2) studying leaf photosynthetic potential in relation to after a much longer exposure to dry air. It resulted in productivity under various edaphoclimatic conditions; about an 80% reduction in leaf photosynthesis. and (3) identifying plant traits that may be useful in breeding programs. The multidisciplinary and Terminal leaf water potential was measured with a interinstitutional research approach adopted was pressure chamber and compared with that of the free pivotal in achieving these objectives. lobes of the same leaves. The lobes tested in both 20 ΨL = -0.75 MPa (lobe of same leaf) 18 Watered No watering 16 Humid (VPD = 0.8 kPa) Dry (VPD = 3 kPa) 14 12 10 8 ΨL = -0.8 MPa ΨL = -1.1 MPa 6 (lobe of same leaf) ΨL = -1.2 MPa 4 2 0 0 1 2 3 4 5 6 Humid Dry Humid Dry Humid Time (h) Figure 3-1. Response of leaf photosynthesis (Pn) to changes in air humidity, using plants of cassava cultivar M Col 88 grown in 40-liter pots (El-Sharkawy and Cock 1984). 31 Pn ( m mol CO2 per m2/s) Cassava in the Third Millennium: … well-watered and water-stressed plants remained (A) 30 unchanged during several hours of gas exchange monitoring. Results indicated that cassava stomata 25 directly responded to changes in air humidity. This response was previously termed a feed-forward reaction 20 (Cowan 1977; Farquhar 1978). It differs from the feed-backward response to changes in bulk leaf water potential. However, we did not determine abscisic acid 15 (ABA) levels in leaves in this case. It was therefore not clear if ABA played a role in stomatal closure during this 10 short exposure to dry air without changes in leaf water potential (Henson 1984). 5 When leaves were exposed to stepwise rises in leaf-to-air vapor pressure deficits (VPD), CO2 uptake 0 rates remained stable in the range of 1 to 1.5 kPa, and 0 1 2 3 4 5 then rapidly declined above that range (Figure 3-2A). Transpiration initially increased with rising VPD up to (B) 5 2 kPa, and then leveled off or declined with further increases in VPD (Figure 3-2B; Berg et al.1986; 4 El-Sharkawy 1990). Leaf conductance also declined sharply at VPD greater than 2 kPa (Figure 3-2C). 3 These observations clearly showed that cassava is 2 sensitive to changes in atmospheric humidity, irrespective of plant- or soil-water status. Furthermore, 1 compared with several woody and herbaceous species, cassava was more sensitive to changes in air humidity 0 (El-Sharkawy et al. 1984d, 1985; El-Sharkawy and Cock 0 1 2 3 4 5 1986; Cock and El-Sharkawy 1988b). The response was (C) 7 related to stomatal density and maximum leaf conductance (El-Sharkawy et al. 1984d, 1985; El- Sharkawy and Cock 1986). Cassava leaves possess 6 large numbers of stomata on the abaxial epidermis (>400 stomata/mm2; Pereira 1977; Connor and Palta 5 1981; El-Sharkawy et al. 1984b; Guzmán 1989), which may underlie its strong response to humidity 4 (El-Sharkawy et al. 1985; El-Sharkawy and Cock 1986). The phenomenon of direct stomatal response to air 3 humidity was observed since the last century (Haberlandt 1914; Thoday 1938; El-Sharkawy and Cock 2 1986). Numerous reports showed that several herbaceous and woody plant species tended to close their stomata in response to dry air, whether within 1 plant communities, attached leaves, or isolated epidermal strips (Hoffman and Rawlins 1971; Hoffman 0 et al. 1971; Lange et al. 1971; Schulze et al. 1972; Aston 0 1.2 2.0 2.8 3.6 4.4 1976; Hall and Hoffman 1976; Lösch 1977, 1979; VPD (kPa) Rawson et al. 1977; Sheriff and Kaye 1977; Lösch and Figure 3-2. Responses of leaf photosynthesis (Pn) (A), Schenk 1978; Ludlow and Ibaraki 1979; Tibbitts 1979; transpiration (T) (B), and leaf conductance to water Farquhar et al. 1980; Hall and Schulze 1980; Jarvis vapor (C) to stepwise increases in leaf-to-air vapor pressure deficit (VPD) in cassava cultivar M Col 90 1980; Tazaki et al. 1980; Bunce 1981, 1982, 1984; (El-Sharkawy and Cock 1984). Leverenz 1981; Lösch and Tenhunen 1981; Fanjul and refers to no watering; to well watered. 32 Leaf conductance (mm/s) T (mmol H2O per m2/s) Pn ( m mol CO2 per m2/s) Productivity, Photosynthesis, Ecophysiology, … Jones 1982; Kaufmann 1982; Meinzer 1982; Schulze and Sheriff (1977, 1979, 1984) suggested that the Hall 1982; Gollan et al. 1985; Körner 1985; Körner and mechanism underlying direct stomatal response to low Bannister 1985; Jarvis and McNaughton 1986; Schulze humidity involves both evaporation from the epidermis 1986; Ward and Bunce 1986; Bongi et al. 1987; and a lower hydraulic conductivity within the leaf that Hirasawa et al. 1988; Pettigrew et al. 1990; Held K 1991; probably accelerates water stress in the epidermis, Kappen and Haeger 1991; Tinoco-Ojanguren and regardless of leaf water content. Recently, Pieruschka et Pearcy 1993). al. (2010) reported that the water balance in the epidermis is very sensitive to differences between the This apparently widespread phenomenon indicated transpiration rate and the rate at which absorbed the need for detailed studies and for its consideration radiation produces water vapor inside the leaf. These when modeling plant community/environment authors suggested that leaf heat load is tightly linked to ecosystems (Jarvis and McNaughton 1986). water transport from mesophyll cells, through the epidermis, to the leaf’s environs. Mechanisms underlying stomatal response to air humidity This important finding further explains why cassava leaves orient themselves towards the sun in early Stomatal movement is controlled by (1) stomata sensing morning and late afternoon (also called heliotropism or changes in air humidity and (2) the so-called sun tracking) when VPD is lowest, and droop at mid-day “peristomatal transpiration”, first hypothesized by (sun avoidance) when VPD is highest (El-Sharkawy and Seybold (1961/1962), where water is lost from the cuticle Cock 1984; Berg et al. 1986), thus optimizing water-use of the guard and subsidiary cells and their adjacent efficiency. epidermal cells. The possible mechanisms underlying these activities were reviewed and discussed by many Tyree and Yanoulis (1980) used physical models of workers (Meidner and Mansfield 1968; Lange et al. 1971; substomatal cavity to calculate water vapor diffusion Meidner 1976; Sheriff 1977, 1979, 1984; Lösch and patterns. They concluded that, because of high Schenk 1978; Maier-Maercker 1979a, 1979b, 1983; evaporation from guard cells, stomata could close in Tyree and Yianoulis 1980; Lösch and Tenhunen 1981; direct response to low humidity. They suggested that Zeiger 1983). localized water stress or dehydration in guard cells may take place because of high leaf resistance to flow of Support for Seybold’s hypothesis on the role of water from minor leaf veins to guard cells. peristomatal transpiration was demonstrated through extensive research by German workers who used intact A strong association between stomatal density leaves and isolated epidermal strips systems without (i.e., exposed epidermal areas) and the degree of water stress (Lange et al. 1971; Maier-Maercker 1979a, sensitivity to changes in air humidity was observed in 1979b, 1983; Lösch and Tenhunen 1981). Meidner and well-watered plants across many herbaceous and woody Mansfield (1968) argued that stomatal movements are species (El-Sharkawy et al. 1985). Such an association unlikely to be affected by changes in atmospheric may indicate the occurrence of localized dehydration in humidity, but instead by the water status of mesophyll the stomatal apparatus and adjacent exposed epidermal tissue (feedback reaction). cells. Hence, it supports a role for peristomatal transpiration in controlling stomatal movement. Kramer (1983) cautioned against the hypothesized Moreover, the poor physical connection between the role of peristomatal transpiration until more information numerous stomatal areas (where evaporation may take became available on the degree of cutinization of the place) and the mesophyll tissue observed in cassava leaf mesophyll tissue (where most evaporation presumably (El-Sharkawy and Cock 1986) may accelerate water takes place), and the inner and external walls of guard stress in the epidermis and stomatal apparatus. Hence, cells. Appleby and Davies (1983) demonstrated possible the striking sensitivity to changes in atmospheric sites of evaporation from cuticle-free areas in the walls humidity without any noticeable decrease in bulk leaf of guard cells of oak (Quercus robur), poplar (Populus water potential (Figures 3-1 to 3-3; Connor and Palta nigra), and Pinus sylvestris, when these areas were 1981; Porto 1983; El-Sharkawy et al. 1984d, 1992b; exposed to the outside of the leaf during stomatal El-Sharkawy and Cock 1986; El-Sharkawy 1990; Cayón closure in dry air. Körner and Cochrane (1985) also et al. 1997; de Tafur et al. 1997a). reported relatively less cutinization of the external walls of guard cells in Eucalyptus pauciflora, which may underlie This conclusion was further substantiated by the its stomatal sensitivity to changes in air humidity. closure of stomata in field-grown cassava in response to 33 Cassava in the Third Millennium: … high wind speed, despite conditions of high soil high moisture content at two sites: the mid-altitude, moisture and high bulk leaf water potential Palmira experiment station at CIAT HQ, Department of (El-Sharkawy 1990). Bunce (1985) also reported Valle del Cauca; and the low-altitude Carimagua ICA– greater water loss from the outer surface of epidermis CIAT station, Department of Meta (Figure 3-3A; Cock of herbaceous species under high wind speed, thus et al. 1985; Berg et al. 1986; El-Sharkawy 1990). providing further evidence to support peristomatal transpiration. An array of cultivars, representing the core collection of cassava germplasm from different Responses of field-grown cassava to air habitats, was grown at a third site: CIAT’s mid-altitude humidity, and implications for breeding for experiment station at Santander de Quilichao, different edaphoclimatic zones and ecosystems Department of Cauca. The cultivars showed significant differences in stomatal sensitivity to humidity Cassava stomatal sensitivity to atmospheric humidity (Figure 3-3C; El-Sharkawy 2004). Furthermore, total was also observed in field-grown cassava in soils with biomass and storage root yield were greater in high (A) 30 No misting Misted plants (B) 3 No misting Misted plants 2.5 25 2 20 1.5 1 15 y = 8.82 + 0.1793x 0.5 R2 = 0.64 10 0 28 38 48 58 68 78 0 5 10 RH (%) Weeks of misting (C) 2.4 2.0 1.6 y = 1.57 + 9.9/VPD 1.2 humid environments (cvs. CG 996-6 and CM 305-41) seasonally dry environments (cvs. M Bra 191 and CG 927-12) 0.8 y = 1.06 + 18.9/VPD semi-arid environments (cvs. M Col 2215 and CM 4617-1) 0.4 y = 0.69 + 24.3/VPD 0 0 2 4 VPD (kPa) Figure 3-3. (A) Response of leaf photosynthesis (Pn) in cassava cultivar M Col 1684 to changes in air humidity in the field, with or without misting (Cock et al. 1985; El-Sharkawy and Cock 1986). (B) Oven-dried storage root yield of cv. M Col 1684 at periodic harvests after 3, 6, and 9 weeks of misting. Ages of plants at harvest were 65, 85, and 105 days, respectively. The differences in yield between the two crops were significant for all harvests (P < 0.01). Top biomass and leaf area index did not differ, whereas total biomass was significantly higher after 6 and 9 weeks of misting (Cock et al. 1985; El-Sharkawy and Cock 1986). (C) Response of leaf water-use efficiency (WUE) to vapor pressure deficit (VPD) in field-grown cassava in a mid-altitude, warm, subhumid climate. Levels of VPD progressively increased from morning to mid-day. Thirty-three clones were evaluated and were grouped according to humid, subhumid/seasonally dry, and semi-arid habitats. Sensitivity to VPD increased from humid to semi-arid habitats. Differences between plant groups illustrate the genetic diversity within cassava germplasm for response to changes in atmospheric humidity. Adapted from El-Sharkawy 2004; MA El-Sharkawy, MC Amézquita, HF Ramírez, and G Lema 1991, unpublished. 34 WUE (mmol CO2 /mol H2O) Pn ( m mol CO2 per m2/s) Dry root yield (t/ha) Productivity, Photosynthesis, Ecophysiology, … humidity environments, particularly when enhanced by to imposed prolonged water stress (>2 months) in misting, leading to higher leaf photosynthesis. These subhumid zones had 40% of the net photosynthesis findings indicated that stomatal sensitivity to changes in found in well-watered plants. Yet, they were capable of VPD was translated into growth at the canopy level completely recovering once the stress ended (CIAT (Figure 3-3B; Cock et al. 1985; El-Sharkawy and Cock Reports 1987 to 1994; El-Sharkawy 1993). Selecting for 1986). Recent research on whole-plant-water relations of longer leaf life span helps save dry matter already field-grown cassava under prolonged natural water invested in leaf canopy formation (Chabot and Hicks deficit in Ghana (West Africa) showed that both canopy 1982). More assimilates would therefore be diverted conductance and transpiration declined with increasing towards storage roots, resulting in the crop having higher VPD (Oguntunde 2005; Oguntunde and Alatise 2007). HI and harvestable yield (Cock and El-Sharkawy 1988a; El-Sharkawy 1993). These findings have important practical implications for cassava breeding and improvement for different For seasonally dry zones, de Tafur et al. (1997b) ecosystems and edaphoclimatic zones. For example, reported a wide range of variation in net leaf less sensitive cultivars should be selected and bred to photosynthesis among rainfed cassava, as measured in maximize productivity in wet or humid zones such as the the field during the driest months. The photosynthetic Amazon Basin, equatorial western Africa, and western rate (Pn) ranged from 27 to 31 µmol CO2 per m2/s, with Java in Indonesia; and in zones with short intermittent significant differences among cultivars. In semi-arid water deficits. For these cases, optimizing water-use zones, Pn ranged from 7 to 20 µmol CO2 per m2/s, with efficiency is not of importance (El-Sharkawy and Cock significant differences among cultivars. Such variation 1986; El-Sharkawy 2004). could be exploited to breed improved genotypes. Host-plant tolerance or resistance to pests and diseases Less sensitive cultivars are those with must also be incorporated in cultivars targeted for hypostomatous leaves, that is, possessing lower seasonally dry and semi-arid zones to maintain, as much stomatal density on leaf undersurfaces, and/or as possible, a functioning leaf canopy over an extended amphistomatous leaves, which possess equal time (Byrne et al. 1982; Hershey and Jennings 1992; conductance on both sides of the leaf blade. For more Bellotti 2002; Calvert and Thresh 2002; Hillocks and information on (1) leaf ontogenesis; (2) the impact on Wydra 2002). photosynthesis of stomatal density, size, and distribution patterns on both leaf sides; and (3) the comparative Within cassava germplasm, a wide genetic diversity, adaptive advantages of amphistomatic versus useful for breeding programs, also exists for stomatal hypostomatic leaf characteristics, see Parkhurst 1978; density, with a percentage of materials possessing Pospisilová and Solárová 1980; Mott et al. 1982; Tichá amphistomatous leaves. Several accessions with a 1982; Gutschick 1984. significant number of stomata on upper leaf surfaces have been identified. These, however, comprised less However, in subhumid or seasonally dry and than 5% of more than 1500 landraces and cultivars that semi-arid zones that characteristically have 3 months or were screened in the field. The techniques used were the more of water deficits, breeding and selecting for more transient porometer and microscopic observations of sensitive cultivars is more advantageous. Such cultivars leaf-surface replicas that were made by spraying leaves can conserve and deplete limited soil-water supplies with collodion solution (El-Sharkawy et al. 1984b, 1985; more slowly. Thus, they optimize water-use efficiency, Guzmán 1989). rather than maximize productivity, over a longer period during the growth cycle. Both porometry (Kirkham 2005) and leaf-surface replicas, combined with microscopic observation, are Because new leaf formation is highly restricted easy to handle in screening large numbers of breeding under prolonged drought (Connor and Cock 1981; Porto materials in the field for stomatal characterization. The 1983; El-Sharkawy and Cock 1987b; El-Sharkawy et al. leaf-replica method, however, has some limitations where 1992b), higher degrees of stomatal sensitivity should be leaves are hairy and stomata sunken (North 1956; Slávik combined with greater leaf retention. That is, leaves 1971). The leaf-surface replica method was effective, both live and last longer (El-Sharkawy 1993, 2004). Leaf using tissue-cultured young seedlings (El-Sharkawy et al. retention was recently found, over a wide range of 1984b). It may facilitate early screening of larger cultivars and breeding lines, to be positively correlated populations. Zelitch (1962) described a similar technique with productivity under naturally extended water deficits for obtaining stomatal impressions, using silicon rubber, (Lenis et al. 2006). Moreover, leaves of plants subjected combined with cellulose acetate solution. 35 Cassava in the Third Millennium: … Response to Temperature 3-4B). Leaves that had developed first in the cool climate and were then acclimated for 7 days in the Responses of potted cassava grown outdoors warm climate partially recovered their photosynthetic in a high-altitude cool climate and in a mid- capacities. Rates, however, remained much lower than altitude warm climate those of the leaves developed in the warm climate. Cassava requires a warm climate for both optimal In the hot-climate cultivar (M Bra 12), maximum growth and productivity. However, it is also cultivated rates in all sets of leaves were higher than those in the in cool climates at high altitudes in the tropics cool-climate cultivar (M Col 2059). This trend was also (>1700 m) and at low altitudes in the subtropics (Irikura observed over the wide range of leaf temperatures et al. 1979). Growth and productivity depend largely on tested. A wide temperature optimum of 25–40 oC and the leaf canopy’s capacity to intercept solar radiation peaks at 30–35 oC were observed in the hot-climate during most of the growth cycle. They also depend cultivar for all sets of leaves. In the cool-climate on leaf photosynthetic potential and performance cultivar, there was an apparent upward shift in optimal under prevailing field conditions (Cock et al. 1979; temperature in both the acclimated and warm-climate El-Sharkawy et al. 1990; de Tafur et al. 1997a, 1997b; leaves. In contrast, a wide plateau occurred for the El-Sharkawy 2004). We therefore studied the effects of non-acclimated cool-climate leaves. In both cultivars temperature on leaf photosynthesis during growth. and in all sets of leaves, rates declined rapidly at temperatures higher than 40 oC, reaching zero at To obtain temperature differences under natural 50 oC. conditions, we took advantage of the nearness of a high-altitude site (2000 m; 17 oC mean annual During the 7 days of acclimation in the warm temperature), located 18 km from CIAT HQ, itself climate, changes in non-stomatal components of located at about 965 masl, with a mean annual photosynthesis (photosystems I and II, and CO2 temperature at 24 oC. Several cultivars, representing fixation reactions) were more likely than changes in several habitats, were grown in large pots (>40 L), physical stomatal characteristics (Berry and Björkman which contained a mixture, by weight, of 40% top soil, 1980). Moreover, the photosynthetic rates in cool- 33% compost, 27% sand, and sufficient fertilizer. The climate leaves were much lower at all photon levels and potted plants were left outside and kept well-watered had less saturation irradiance than either the throughout their growth at the two sites. Solar radiation acclimated or warm-climate leaves (Figure 3-4C). at the high-altitude location was similar to that of CIAT HQ in terms of duration and intensity (El-Sharkawy et The differences in radiant energy saturated rates al. 1992a, 1993). among these sets of leaves may be attributed mainly to differences in CO2 fixation capacity (Björkman et al. Measurements of leaf gas exchange were 1980). Warm-climate leaves were not photon-saturated conducted under controlled conditions in the at 1800 µmol per m2/s. The same phenomenon was physiology laboratory at CIAT. An open-ended, observed in several field-grown cassava cultivars in a infrared, CO2 analyzer was used to test responses to warm climate when leaf photosynthesis was measured both leaf temperature at saturating photons levels during the high rainfall period (Figure 3-5; El-Sharkawy (>1800 µmol per m2/s) and to light intensity. and Cock 1990; El-Sharkawy et al. 1992a, 1993). Figures 3-4A to 3-4C (El-Sharkawy et al. 1984c, Pereira (1977) also reported increases in cassava leaf 1992a, 1993; El-Sharkawy and Cock 1990) illustrate net photosynthesis with rising photon flux density up to responses of leaves grown in the cool climate and then 2000 µmol per m2/s. Maximum photosynthetic rates of acclimated for 7 days to the warm climate. They also several cultivars of field-grown cassava were more than show responses of leaves of the same plants that were 40 µmol CO2 per m2/s, with a mean Ci /Ca ratio of later developed in the warm climate. The two cultivars 0.42 (Table 3-1). These values are comparable with were adapted to contrasting habitats: M Col 2059 from those observed in C4 species and much less than those a cool, humid, high-altitude zone (Colombia) and obtained in C3 species. M Bra 12 from a hot, humid, low-altitude zone (Brazil). These data indicate that cassava possesses high In both cultivars, net leaf photosynthetic rates were photosynthetic capacity, which is fully expressed only substantially lower in leaves that had developed in the in hot humid climates with high solar radiation. Thus, cool high-altitude climate than for those that developed when grown in environments, either natural or artificial, in the mid-altitude warm climate (Figures 3-4A and that deviate from these fundamental climatic 36 Productivity, Photosynthesis, Ecophysiology, … (A) 30 M Col 2059 (B) 40 M Bra 12 Cool humid Hot humid 24 32 Cool, 7-d warm , 7-d warm Warm Warm Cool 18 24 12 16 6 8 Cool Cool 0 0 0 15 20 25 30 35 40 45 50 0 15 20 25 30 35 40 45 50 Leaf temperature (oC) Leaf temperature (oC) (C) 35 M Col 2059 Warm Cool humid 30 25 Cool, 7-d warm 20 15 10 Cool 5 0 300 600 900 1200 1500 1800 -5 Photon flux density ( m mol per m2/s) Figure 3-4. Response in terms of net photosynthetic rate (Pn) of cassava to leaf temperature. (A) Cultivar M Col 2059 in a cool habitat; (B) cv. M Bra 12 in a hot humid habitat; (C) response in terms of net photosynthetic rate (Pn) to PAR irradiance in cv. M Col 2059. refers to leaves developed in a cool climate; to leaves developed in a cool climate and then acclimated for 1 week in a warm climate; to newly developed leaves in a warm climate. Note that (1) an apparent upward shift in optimal temperature is observed from cool to warm-acclimated and warm-climate leaves; (2) the lack of light saturation in warm-climate leaves, compared with cool-and-warm-acclimated leaves; and (3) the higher maximum photosynthetic rates in all sets of leaves of cv. M Bra 12 from the hot-humid habitat, compared with the cool-climate cv. M Col 2059. References: CIAT Report 1992; El-Sharkawy et al. 1992a, 1993. requirements, its photosynthetic capacity is not fully controlling the overall photosynthetic process expressed (Gleadow et al. 2009). (El-Sharkawy and Cock 1987a; El-Sharkawy et al. 1992a, 1993; El-Sharkawy 2004). Studies of plants grown in the greenhouse or growth chamber showed much lower photosynthetic Lower photosynthetic rates of potted cassava rates (from 15 to 20 µmol CO2 per m2/s), lower grown in growth chambers or greenhouses probably saturation radiation, lower optimal temperatures, and resulted from lower activities of photosynthetic lower photosynthetic enzyme activity (Aslam et al. enzymes. Such results have been long observed in 1977; Mahon et al. 1977a, 1977b; Edwards et al. 1990; other plant species. Other factors may have also played Angelov et al. 1993; Ueno and Agarie 1997; Gleadow et a part such as changes in leaf anatomy because of al. 2009). These studies are of limited value if their exposure to suboptimal irradiance and air temperatures results are to be interpreted in relation to cassava’s during leaf development; imbalances in source-sink real potential and to the underlying mechanisms relations in the whole plant system; and pot size, which 37 Pn ( m mol CO2 per m2/s) Pn ( m mol CO2 per m 2/s) Cassava in the Third Millennium: … (A) 50 CG 927-12 30 10 (D) 50 CM 523-7 0 30 (B) 50 CG 996-6 30 10 0 10 0 (E) 50 CM 3456-3 (C) 50 CM 507-37 30 30 10 10 0 0 0 500 1000 1500 2000 500 1000 1500 2000 Photon flux density ( m mol per m2/s) Figure 3-5. Responses in terms of leaf photosynthesis (Pn) to PAR irradiance in upper-canopy leaves of five cultivars of field-grown cassava during the rainy season (CIAT Report 1992; El-Sharkawy et al. 1992a, 1993). may have encouraged feed-back inhibition of leaf collected under the conditions in which plants or crops photosynthesis because of restricted root sinks for are normally grown must be taken into account for assimilates (Nösberger and Humphries 1965; these purposes. Humphries 1967; Neales and Incolls 1968; Moss and Musgrave 1971; Nobel 1976, 1980; Boardman 1977; This conclusion on the invalidity of data obtained Björkman et al. 1980; Herold 1980; Nobel and with plants inappropriately grown was further Hartsock 1981; Sesták 1985; Bunce 1986; Ho 1988; substantiated by recent findings in a wide range of Wardlaw 1990; Evans 1993; Pellet and El-Sharkawy long-term CO2-enrichment field trials (Long et al. 1994; Gleadow et al. 2009). 2006). In these trials, the degree of enhancement in both leaf photosynthetic rate and yield of various crops El-Sharkawy (2005) recently reviewed and by elevated CO2 (as compared with crops grown at discussed the problems of plant acclimation/adaptation ambient CO2) were much less than those previously to environments that are normally encountered but observed with plants grown in greenhouses, growth bewilder scientists in general and plant photosynthesis chambers, or field enclosures, where air humidity and researchers in particular. He pointed out the limited temperatures were probably also elevated. Such value of data collected on plants grown in findings confirmed the limitations of using data from environments that are inappropriate for optimal inappropriately grown plants for crop modeling or growth. He also emphasized their invalidity for use in predicting anticipated effects of rising atmospheric crop modeling or extrapolating and predicting CO2 levels and air temperature on plant photosynthesis responses in natural environments if the necessary and productivity (i.e., the effects of global climate calibration is not carried out, that is, field data change) (Gleadow et al. 2009). 38 Pn ( m mol CO2 per m2/s) Pn ( m mol CO2 per m2/s) Pn ( m mol CO2 per m2/s) Productivity, Photosynthesis, Ecophysiology, … Table 3-1. Net leaf photosynthesis (Pn) of field-grown cassava at Santander de Quilichao, Department of Cauca, Colombia (warm subhumid), during the 1990/91 season. Maximum photosynthetic rates were obtained during wet periods and high air humidity. Note the Ci/Ca values, which are comparable with those of C4 species and much lower than those of C3 species, indicating cassava’s high photosynthetic capacity, as expressed in near-optimal environments. In this group of cultivars, the average seasonal Pn was correlated with final root yield. Cultivar Maximum net photosynthesis Ci/Ca Seasonal average net photosynthesis (n = 6) (n = 6) (n = 30) µmol CO2 per m2/s µmol CO2 per m2/s CG 996-6 49.7 0.37 33.8 M Bra 191 47.4 0.37 35.5 CM 4864-1 45.1 0.39 34.0 CM 4145-4 43.9 0.40 31.7 CM 3456-3 43.7 0.43 31.9 CM 507-37 43.7 0.38 28.7 CM 4716-1 43.6 0.42 31.8 M Col 1684 43.0 0.42 30.9 CM 4575-1 42.8 0.39 33.2 CM 4617-1 42.8 0.46 31.4 CM 523-7 42.3 0.45 30.1 CMC 40 42.3 0.44 30.3 CM 4701-1 42.2 0.45 30.9 CM 4711-2 41.3 0.45 30.9 CG 927-12 39.3 0.43 26.2 Mean of all cultivars 43.5 0.42 31.4 LSD0.05 1.70 0.08 1.80 Ci/Ca = intercellular CO2 divided by atmospheric CO2. This ratio is commonly used to differentiate plant species according to their photosynthetic capacities, that is, the lower the ratio, the higher the capacity. SOURCES: El-Sharkawy et al. (1992a, 1993). Screening Cassava Germplasm for diseases (Hershey and Jennings 1992; Jennings and Leaf Photosynthesis Iglesias 2002). Field evaluation of cassava germplasm for leaf photosynthesis in subhumid, high-altitude, This objective was justified by our previous research cool climates, and mid-altitude warm climates at different sites in subhumid, seasonally dry, and semi-arid environments. We measured photosynthesis Once we ascertained the importance of field research in the field, using portable infrared gas analyzers across and the need to assess cassava’s potential a wide range of germplasm and edaphoclimatic photosynthesis under representative environments, we conditions. studied photosynthesis in recently matured upper- canopy leaves. The germplasm used was selected from Results showed significant correlations between a core collection of the cassava genebank held at CIAT. upper-canopy leaf photosynthesis and total biomass and Materials comprised groups of cultivars, landraces, and storage root yields (Figure 3-6; CIAT Reports 1987 to improved CIAT breeding materials grown at three sites 1995; El-Sharkawy and Cock 1990; El-Sharkawy et al. used by CIAT’s cassava breeding program to evaluate 1990, 1993; Pellet and El-Sharkawy 1993a; de Tafur et genetic performance. We wanted to identify, in the al. 1997b; de Tafur 2002; El-Sharkawy 2004, 2006). field, those cultivars and lines with high photosynthetic Moreover, the findings at CIAT were corroborated by potential. They would then be used as parental later research at IITA (Nigeria), where photosynthetic materials in crosses and breeding procedures to rates of upper-canopy leaves were correlated with improve productivity (El-Sharkawy 1993) in storage root yields across diploid, triploid, and tetraploid combination with other major breeding objectives such cassava cultivars (Ekanayake et al. 2007). as yield stability; broad adaptation; and tolerance or resistance to edaphoclimatic stresses, pests, and Tables 3-2 to 3-4 present data on upper-canopy leaf photosynthesis measured in two climates: (1) the 39 Cassava in the Third Millennium: … Santander de Santander de 2.0 Quilichao (A) (B) Quilichao Yield (kg/m2) = -0.54 + 0.06 Pn r = 0.853 (P < 0.001) Yield (kg/m2) = 3.03 - 9.58 internal CO2 1.5 r2 = 0.73 (P < 0.001) r = 0.90 (P < 0.001) r2 = 0.81 (P < 0.001) 1.0 Santo Tomás Santo Tomás 0.5 Riohacha Riohacha 0 0 10 20 30 40 100 150 200 250 300 350 400 Pn ( m mol CO 2 2 per m /s) Internal CO2 ( m mol/mol) Figure 3-6. Relationships between dry root yield and upper-canopy leaf photosynthesis (Pn) (A) and intercellular CO2 (B) for 38 cassava cultivars grown at three sites in Colombia: Santander de Quilichao (subhumid, 15 varieties), Santo Tomás (seasonal dry, 10 varieties), and Riohacha (semi-arid, 13 varieties) (El-Sharkawy et al. 1993; de Tafur et al. 1997b; de Tafur 2002; SM de Tafur and MA El-Sharkawy 1995, unpublished). Table 3-2. Net leaf photosynthesis (Pn; µmol CO2 per m2/s), applications of fertilizer. Measurements were made on stomatal conductance (mmol per m2/s), and internal several occasions, mainly during dry periods, and CO2 (µmol CO2/mol) for some cassava clones with relatively high photosynthetic capacity. Note that, for averaged. Chambers enclosing central leaf lobes or part this group of clones, the Pn rates are higher, and the thereof (depending on the type of equipment and leaf stomatal conductance and internal CO2 are lower chambers used) were always directed towards the sun than the trial means. The values indicate the between 09:00 and 12:00 local time when photon flux importance of non-stomatal factors (i.e., biochemical densities were greater than 1000 µmol per m2 and anatomical) in selecting for enhanced photosyn- /s. The thetic capacity. This group of clones will improve the plants used were 4 to 6-month-old plants, that is, of an genetic base of cassava for the cooler ecosystems of age when leaf canopies nearly close (i.e., high leaf high-altitude tropics and subtropics. capacity source) and rates of storage root bulking are at Clone Pn Stomatal Internal their highest (high root sink demand). conductance CO2 SM 1061-1 17.3 196 98 At all sites, average leaf photosynthesis varied SM 526-12 16.7 320 154 significantly among screened cultivars and landraces, SM 1054-4 16.6 225 114 but with rates greatly reduced in the high-altitude cool M Per 501 16.4 391 166 climate, thus confirming results and patterns observed SM 1053-9 15.7 225 122 with potted cassava grown in a high-altitude cool climate (Tables 3-2 to 3-4 and Figure 3-4). The Mean of all accessions (n = 107) 12.3 312 183 accessions evaluated in the high-altitude cool climate were local traditional cultivars or landraces collected LSD0.05 1.3 32 14 from cool-climate regions in several countries. They SOURCE: CIAT Report (1994). also included improved CIAT materials bred and selected for better adaptation to high-altitude cool climates. high-altitude cool climate of Cajibío, Department of Cauca (about 1800 m; mean annual temperature at The materials with rates (15.7 to 17.3 µmol CO2 per about 19 oC); and (2) the mid-altitude warm climate at m2/s) that ranked higher than the overall mean two sites (CIAT Quilichao experiment station, Cauca, photosynthetic rate (12.3) were four CIAT improved and CIAT Palmira station at HQ, Valle del Cauca), clones and a Peruvian cultivar (M Per 501) (Table 3-2). where altitudes range between 965 and 1000 m, and This finding indicates a narrow genetic base for this the mean annual temperature is about 24 oC. Crops ecosystem. It also shows the relative effectiveness of the were grown under rainfed conditions with minimal CIAT cassava program’s strategy to breed for specific 40 Dry root yield (kg/m2) Productivity, Photosynthesis, Ecophysiology, … Table 3-3. Net leaf photosynthesis (Pn; µmol CO2 per m2/s) in the upper-canopy leaves of cultivars from the core collection of cassava germplasm and grown at Santander de Quilichao in 1993/94. Measurements were carried out 5 to 6 months after planting, using portable infrared gas analyzers. Values are means of 7 to 11 measurements made during the dry period. Compare these higher Pn values, obtained within a warm subhumid habitat, with those obtained in the cool subhumid habitat shown in Table 3-2. Cultivar M Mal 48, from Malaysia, had the highest Pn rate and the highest dry root yield in this trial. Clone Pn Clone Pn M Mal 48 27.6 M Tai 1 24.4 M Bra 900 27.6 M Pan 51 24.3 M Bra 12 26.8 M Bra 383 24.2 M Bra 191 26.7 M Ind 33 24.1 M Mal 2 26.4 CM 849-1 23.6 HMC-1 26.0 M Col 1684 23.4 CMC 40 25.8 M Mex 59 23.2 M Col 2061 25.4 M Ven 25 23.2 M Gua 44 25.4 M Bra 885 23.1 M Chn 1 25.3 M Cub 51 22.8 M Col 22 25.1 M Col 2215 22.3 M Arg 13 25.0 M Cub 74 22.3 M Ven 45A 24.8 M Per 205 22.0 M Col 1505 24.8 M Ptr 19 21.3 M Bra 110 24.6 M Ecu 82 21.0 LSD0.05 4.8 SOURCE: CIAT (1994). edaphoclimatic zones and ecosystems. It also points Most of the materials evaluated at CIAT–HQ out the importance of including leaf photosynthesis comprised cultivars and landraces from Brazil, with as a selection criterion for parental materials when eight accessions from Argentina and one accession enhancing productivity (El-Sharkawy and Cock 1990; each from Colombia (HMC-1) and Bolivia (M Bol 1). El-Sharkawy et al. 1990; El-Sharkawy 2004). The mean photosynthesis rate was significantly higher in the smaller group of germplasm materials from The enhanced photosynthesis in these few clones Argentina (26 µmol CO2 per m2/s) than in the could not be attributed to stomatal control because germplasm from Brazil (Table 3-4), many accessions of their average stomatal conductance (271 mmol per which had lower rates than their original overall mean m2/s) was significantly lower than the overall mean of of 22 µmol CO2 per m2/s. Even so, several Brazilian accessions (312 mmol per m2/s; Table 3-2). However, accessions fell into the highest photosynthesis range, the intercellular CO2 concentration was much particularly M Bra 12 (Figure 3-4B) and M Bra 110. reduced in these clones, thus indicating possible control by non-stomatal factors such as leaf anatomy These two materials could be used for crossing and biochemistry (e.g., enzyme activity). As leaf and breeding for warm-climate ecosystems. In formation is much slower but leaf life much longer in contrast, the accessions from Argentina, presumably high-altitude cool climates than under warm-climate more adapted to subtropical ecosystems, better conditions (Irikura et al. 1979), selection for tolerated low winter temperatures than the warm- enhanced photosynthesis and tolerance of low climate germplasm from tropical ecosystems. They temperature becomes even more important in this could therefore be used in crossing and breeding for case. In the mid-altitude warm-climate sites, enhancing photosynthesis in germplasm for high- particularly at CIAT–HQ, average photosynthesis altitude cool-climates. rates were much higher than in the cool-climate site (Tables 3-3 and 3-4). Measurements were all made The Pn of this group of accessions was highly and during the dry period, when rates were lower than the negatively correlated with intercellular CO2 (Figure 3-7). maximum rates observed under wet conditions As Pn was measured in normal air, the calculated (Table 3-1). intercellular CO2 concentration represents the balance 41 Cassava in the Third Millennium: … Table 3-4. Net leaf photosynthesis (Pn; µmol CO2 per m2/s) of upper-canopy leaves and intercellular CO2 (µmol CO2/mol) for 53 accessions from the core collection of cassava germplasm and grown at CIAT headquarters, Palmira, Colombia, in the 1991/92 season. Measurements of 4-month-old plants were made, using portable infrared CO2 analyzers during dry periods. Compare these higher Pn rates in the warm subhumid habitat with those obtained in the cool subhumid habitat, as shown in Table 3-2. Note that most accessions from Argentina and Brazil had relatively high Pn rates, compared with trial means. Note that, in this group of clones, Pn was highly negatively correlated with intercellular CO2 (r 2 = 0.90, P < 0.0001), indicating that differences in Pn were caused by non-stomatal factors, that is, anatomical and/or biochemical factors such as enzyme activity and leaf anatomy. Regression: intercellular CO2 = 315 - 7.83 Pn. Accession Pn Intercellular Accession Pn Intercellular CO2 CO2 Accessions with high Pn M Arg 11 32 73 M Bra 85 26 112 M Bra 12 30 82 M Arg 9 26 110 M Bra 110 30 74 M Bra 190 26 97 HMC-1 29 87 M Bra 124 26 100 M Arg 2 28 95 M Bra 403 25 131 M Bra 132 28 88 M Bra 162 25 108 M Bra 172 27 83 M Arg 5 25 115 M Arg 13 27 105 M Bra 242 24 133 M Bra 359 27 127 M Bra 299 24 133 M Bra 71 26 111 M Bra 165 24 114 M Arg 7 26 119 Accessions with intermediate to low Pn M Bra 243 23 132 M Bol 1 21 147 M Bra 405 23 143 M Bra 309 21 148 M Bra 73 23 134 M Bra 453 21 159 M Bra 217 23 140 M Bra 400 21 169 M Bra 404 23 151 M Bra 329 20 159 M Bra 125 23 129 M Bra 435 20 173 M Bra 258 22 143 M Bra 337 19 177 M Bra 273 22 128 M Bra 158 19 137 M Bra 77 22 145 M Bra 325 18 169 M Bra 233 22 144 M Bra 237 17 173 M Arg 12 22 146 M Bra 355 17 195 M Bra 416 22 151 M Bra 450 17 196 M Arg 15 22 139 M Bra 328 17 182 M Bra 356 22 156 M Bra 311 16 188 M Bra 191 21 145 M Bra 315 16 191 M Bra 383 21 162 M Bra 335 14 187 LSD0.05 6.2 23 SOURCE: CIAT Report (1992). between the supply from outside air via stomata and The accessions screened at Quilichao were a mix the demand from carboxylation reactions within the of cultivars and landraces, mostly from Latin America, mesophyll. The lower intercellular CO2 in accessions but also from Asia (Table 3-3). Again, average with high Pn indicates a faster carboxylation rate, photosynthesis rates varied widely among cultivars, probably because of higher rubisco activity inside the with several high-ranking accessions from Brazil, chloroplasts and/or higher activity of Colombia, and Malaysia. The highest ranking accession phosphoenolpyruvate carboxylase (PEPC) in the from Malaysia (M Mal 48) also had the highest dry root cytosol of mesophyll cells. This finding indicates the yield (15.6 t/ha versus the overall mean for the trial at need to select and breed for higher activity of key 10.6 t/ha). This clone has already been used for photosynthetic enzymes. crossing and breeding at CIAT. 42 Productivity, Photosynthesis, Ecophysiology, … 250 group of clones, were also reported as being among the highest ranked clones (fourth and fifth, respectively, 200 among 33 clones evaluated) for tolerance of soils low in 150 phosphorus (CIAT Report 1990; El-Sharkawy 2004). 100 In this group of accessions, standing shoot 50 y = 315.4 - 7.8293x biomass correlated with root yield (r = 0.7; P < 0.001). r2 = 0.90 This finding confirms previous findings, and suggests 0 the use of this trait as a proxy for leaf area formation 10 15 20 25 30 35 and duration when evaluating large breeding Pn ( m mol CO2 m2/s) populations (CIAT Report 1990; El-Sharkawy et al. Figure 3-7. Relationships between Pn and intercellular CO2 1990; El-Sharkawy 2004). In this group of clones, dry concentration (Ci) in 53 cassava accessions root yield also correlated with seasonal leaf area index (Table 3-4). Note the negative correlation between Pn and Ci, which indicates that the association was (Figure 3-8; r = 0.65; P < 0.001), further corroborating caused by non-stomatal factors (i.e., biochemical earlier reports (Pellet and El-Sharkawy 1993a). It also and/or anatomical mesophyll traits) (SM de Tafur supports the concept of breeding for longer leaf life and MA El-Sharkawy 1995, unpublished). and optimal leaf area duration to maximize productivity under favorable conditions and to ensure sustainable yields in stressful environments (El-Sharkawy and Evaluating cassava germplasm for leaf area Cock 1987b; Cock and El-Sharkawy 1988a, 1988b; duration (seasonal average leaf area index) and El-Sharkawy et al. 1992b; El-Sharkawy 1993, 2004; productivity in a mid-altitude warm climate Lenis et al. 2006). To complement the joint physiology/breeding efforts to In conclusion, although leaf photosynthesis can be characterize cassava germplasm from the core used as a selection criterion in cassava improvement collection and identify useful yield-determinant traits, a programs, it may be difficult to handle when evaluating field trial was conducted at the CIAT–Quilichao large breeding populations. It should be included at experiment station (mid-altitude warm climate). Thirty least in the evaluation and selection of parental clones were evaluated for leaf duration across the materials in combination with other important yield- growth cycle (seasonal average leaf area index as related traits, particularly relatively high HI (>0.5; measured with a leaf canopy analyzer). Table 3-5 Kawano 1990, 2003), large root sink (using root (CIAT Report 1995) presents data on yield, shoot and number per plant as a criterion; Cock et al. 1979; Pellet total biomass, seasonal average leaf area index, and and El-Sharkawy 1993a, 1994), and longer leaf life root dry matter content. (greater leaf retention and duration over the growth cycle; El-Sharkawy and Cock 1987b; Cock and Wide variations among clones were found for El-Sharkawy 1988a, 1988b; El-Sharkawy et al. 1992b; standing shoot (i.e., top biomass, excluding dropped El-Sharkawy 1993, 2004; Lenis et al. 2006). Recent leaves) and total biomass, yield, dry matter content in advances in molecular biology and the development roots, and seasonal leaf area index. Notably, several and manufacture of more precise techniques, accessions from Brazil were among the highest ranked methods, and equipment can only enhance and speed in terms of yield, total biomass, and dry matter up the elucidation of fundamental mechanisms contents in storage roots, thus highlighting the underlying photosynthetic potential and associated importance of Brazilian germplasm (El-Sharkawy and beneficial traits, and their controlling genes. de Tafur 2010). Responses to Extended Water Shortages CIAT, to diversify the genetic base of the cassava Imposed at Different Growth Stages genebank, has incorporated many of these accessions in the Field for their useful plant traits. Outstanding among these is clone M Bra 12, with its high leaf photosynthesis under Unlike grain crops, cassava does not have specific both potted (grown outdoors in a mid-altitude warm water-stress sensitive growth stages beyond crop climate) and field-grown conditions (Table 3-4; establishment. It is therefore highly tolerant of Figure 3-4B), high yield, and resistance to mites (Byrne prolonged drought in areas that typically have low et al. 1982). Two other accessions of Brazilian origin, (<600 mm annually) and erratic precipitation, dry air M Bra 383 and M Bra 191, which ranked high in this and high temperatures (i.e., potential for high 43 Intercellular CO2 ( m mol/mol) Cassava in the Third Millennium: … Table 3-5. Seasonal average leaf area index (LAI), dry root yield, top and total biomass, and root dry matter content of 30 clones from the core collection of cassava germplasm. Plants were grown at Santander de Quilichao, Colombia, in the 1994/95 season. Leaf area duration, as estimated by seasonal average LAI, was significantly correlated with root yield (Figure 3-8), indicating the importance of this trait in selecting and breeding for improved cultivars (Lenis et al. 2006). Clone Seasonal Dry top Dry root Total Root dry average biomass (t/ha) biomass matter LAI (m2/m2) (t/ha) (t/ha) (%) M Bra 383 1.3 6.0 15.5 21.5 41.7 M Bra 12 1.0 5.3 15.3 20.6 38.2 M Pan 51 1.8 10.2 14.7 23.9 40.8 CM 849-1 1.4 6.3 14.1 20.4 41.7 M Bra 191 1.5 5.7 14.0 19.7 41.3 M Mal 48 1.9 4.2 13.9 18.1 41.0 M Bra 885 1.6 5.4 13.8 19.2 41.6 M Ven 25 1.1 4.9 12.6 17.5 40.0 HMC-1 1.6 4.8 12.2 17.0 38.5 M Ind 33 1.6 5.9 11.6 17.5 36.6 M Bra 100 1.9 6.4 11.3 17.7 40.6 M Gua 44 1.2 4.6 11.2 15.8 38.9 M Cub 74 0.9 3.9 10.8 14.7 39.8 M Tai 1 1.2 5.6 10.6 16.2 37.5 M Mex 59 1.6 6.8 10.3 17.1 40.7 M Arg 13 0.9 2.4 9.3 11.7 39.1 M Mal 2 1.8 6.9 8.4 15.3 36.2 M Chn 1 1.0 1.9 8.0 9.9 36.2 M Col 22 1.4 1.7 7.8 9.5 37.8 M Ven 45A 1.0 5.1 7.7 12.8 37.4 M Col 1684 0.8 2.2 7.0 9.2 34.6 M Ecu 82 0.8 3.4 6.7 10.1 38.6 M Ptr 19 1.1 4.0 6.1 10.1 40.0 M Col 2215 0.7 2.4 5.9 8.3 40.3 CMC 40 0.9 1.9 5.6 7.5 36.7 M Col 2061 0.9 3.5 5.3 8.8 30.7 M Per 205 1.0 3.8 5.3 9.1 38.7 M Col 1505 0.7 2.1 5.1 7.2 40.6 M Cub 51 0.7 3.1 4.9 8.0 39.9 M Bra 900 0.9 1.3 4.7 6.0 31.4 Mean of all clones 1.2 4.4 9.7 14.0 39.6 LSD0.05 0.5 2.0 3.5 4.6 3.6 SOURCE: CIAT Report (1996). evapotranspiration), low-fertility soils, and high pest- Indeed, Allem (2002) suggests that cassava may, in and-disease pressure. Examples of areas with such fact, have originated in the open savanna forests of conditions include Northeast Brazil, Colombian Brazil. This inherent capacity to withstand drought is North Coast, the Peruvian coastal regions, some also behind the crop’s expansion into more marginal areas of sub-Saharan Africa, and parts of Thailand lands across many parts of Africa, Asia, and Latin (El-Sharkawy 1993). America, where it is grown by resource-poor farmers. Under these conditions, other staple food crops We have already mentioned some inherent plant such as grain cereals and legumes, will rarely survive mechanisms that may underlie such tolerance. Most and produce. That cassava can grow in such areas is notable among them is the cassava plant’s striking contrary to the common assumption that it originated sensitivity to both changes in atmospheric humidity in the hot humid climates of the Amazon forests. and soil-water deficits. It reacts by partly closing its 44 Productivity, Photosynthesis, Ecophysiology, … 18 refilled with the same soil layers (El-Sharkawy and 16 Cock 1987b). We also used adjacent undisturbed larger areas. 14 Water stress was always initiated by covering soil 12 with high moisture content with caliber-6 white 10 plastics, which were manually kept free of rainwater and of ruptures or leaks during stress periods. Soil 8 water was periodically monitored by sampling or by y = 2.34 + 6.07x using a calibrated neutron meter at a 1.8–2 m depth. 6 r = 0.65 (P < 0.001) Leaf water potential was assessed with the standard 4 pressure chamber technique (Kirkham 2005). Leaf gas 0.5 1 1.5 2 exchange was measured with portable infrared gas LAI analyzers, and leaf area coverage/index was measured Figure 3-8. Relationships between final dry root yield of with a solar-irradiance sensing analyzer (leaf canopy 30 clones from the core collection of cassava analyzer; LI-COR Biosciences, Inc., Lincoln, NE, USA). germplasm and seasonal average leaf area index Periodic harvests were also conducted to determine (LAI). The significant correlation indicates the importance of leaf area duration for yield formation. yield and biomass (CIAT Reports 1987 to 1995; Because of the small leaf area canopy in the first El-Sharkawy and Cock 1987b; El-Sharkawy et al. 3 months and in the final 8 to 12 months, the 1992b, 1998b; Cayón et al. 1997; de Tafur et al. 1997a, seasonal average canopy area still limits yield. It 1997b; El-Sharkawy and Cadavid 2002). indicates the need to select and breed for a higher and more sustainable canopy that would last most of the growth cycle, combined with enhanced leaf Evaluating Germplasm under Mid-Season photosynthesis, high harvest index, and strong root Water Stress in a Field Drainage sink (larger storage root number/plant). Cultivar M Bra 12 had a notably higher yield with an LAI Lysimeter that was less than the overall average of the trial, indicating its high leaf photosynthetic potential Relationship between productivity and (CIAT Report 1995; El-Sharkawy 2006). hydrocyanic acid (HCN) levels Sixteen cultivars from a core collection of cassava stomata and restricting water losses, once it is exposed germplasm were evaluated across two cropping cycles to dry air and/or dry soils. Thus, the leaf is protected in a field drainage lysimeter. For each cycle, at 90 to from severe dehydration. Such sensitivity is also 100 days after planting, 3 months of water stress was coupled with the leaf’s ability to partly retain its initiated (mid-season stress). Figure 3-9 illustrates dry photosynthetic capacities under prolonged water root yield accumulation patterns for four representative shortages (El-Sharkawy et al. 1992b; El-Sharkawy accessions affected by stress during the growth cycle. 1993; Caýon et al. 1997; de Tafur et al. 1997a, 1997b). Water stress significantly reduced yield and shoot Moreover, the cassava plant, despite its sparse biomass in all accessions at the end of the stress (data fine-root system, is able to penetrate soil layers at 2 m not shown; CIAT Reports 1991, 1992; El-Sharkawy et or deeper, unlike other crops such as cereals and al. 1992b). On recovery from stress, however, final tropical grasses (Tscherning et al. 1995). Thus, the yields of some accessions were equal to those of plant can endure long periods of drought. Moreover, it well-watered plants, while final yields in others were is slow to deplete the deeper stored water, resulting in reduced (Table 3-6; El-Sharkawy 1993). Significant higher seasonal crop water-use efficiency, although at differences for final root yield were also found among reduced productivity (Connor et al. 1981; El-Sharkawy cultivars, with the hybrid CM 489-1 having the highest and Cock 1986, 1987b; El-Sharkawy et al. 1992b; yield under both stress (18 t/ha oven-dried roots) and El-Sharkawy 1993, 2004). non-stress (19 t/ha) conditions. Also noteworthy is CM 489-1, which showed high PEPC activity in leaf We report here on further research with diverse extracts under extended field water shortages. germplasm that was exposed at various growth stages to long periods (3–6 months) of water shortages. We In a group of cultivars, high PEPC activity used a large field drainage lysimeter (30 × 15 × 2.3 m correlated with leaf photosynthesis (Pn) (El-Sharkawy deep) at CIAT–Quilichao, which was excavated and 2004). The parameter Pn also correlated with high 45 Dry root yield (t/ha) Cassava in the Third Millennium: … 25 cv. CM 489-1 20 24 cv. CM 922-2 19 15 14 10 9 5 4 0 -1 0 4 8 12 0 4 8 12 25 cv. CM 1335-4 25 cv. CM 2136-2 20 20 15 15 10 10 5 5 0 0 0 4 8 12 0 4 8 12 Age of plant (months) Age of plant (months) Figure 3-9. Dry root yield in a group of clones affected by 3 months of water stress, starting 90 days after planting (mid-season stress). Yield was significantly lower at the end of stress, but recovered rapidly with watering, so that final yields were approaching those of the controls. There were differences among cultivars, with cv. CM 489-1 having the highest yield in both water regimes (CIAT Report 1992; El-Sharkawy 2006). refers to unstressed clones; to stressed clones. values for yield, nutrient-use efficiency in terms of When exposed to extended water deficits, most root production, radiation-use efficiency in terms of cassava cultivars show increased HCN content (which total biomass production, and many harvestable indicates cyanogenic potential) in their storage roots. storage roots per plant across a range of phosphorus Thus, the roots become less suitable for human fertilizer levels in acidic soils in subhumid warm consumption if they not properly processed to climates (Pellet and El-Sharkawy 1993a, 1993b, 1994, eliminate most, if not all, HCN (Dufour 1988; Rosling 1997). 1994; Essers 1995). Some crop management practices can greatly reduce HCN in cassava roots, for Across accessions, reductions as a result of water example, where moderate amounts of N-P-K fertilizers stress were much higher for shoot biomass (28%) and/or plant residues such as mulch are applied to than for roots (9%). However, HI increased about 6%, low-fertility sandy soils in zones with long dry periods thus indicating cassava’s potential to tolerate (Cadavid et al. 1998). Another practice is to apply K to prolonged mid-season stress in subhumid zones and clayey acidic soils low in K in subhumid zones its ability to recover and compensate for possible (El-Sharkawy and Cadavid 2000). Selection for low losses in productivity. This is an advantage over other HCN cultivars, however, remains a major objective of staple food crops (El-Sharkawy and Cock 1987b; most breeding programs, particularly those targeting CIAT Reports 1991, 1992; El-Sharkawy et al. 1992b). germplasm for stressful environments (El-Sharkawy The genetic variability existing for stress tolerance 1993). should be exploited in breeding and improving cassava germplasm for dry environments (CIAT In our case, those less sensitive genotypes with Reports 1991 to 1995; Hershey and Jennings 1992; low HCN that we identified (Table 3-6) offer adequate El-Sharkawy 1993). genetic sources for breeding sweet cultivars. Nassar (1986) also reported some wild species with low HCN 46 Dry root yield (t/ha) Productivity, Photosynthesis, Ecophysiology, … Table 3-6. Yield, top biomass (dry, t/ha), and hydrocyanic acid (HCN) content in roots at final harvest (11 months after planting) after 3 months of mid-season water stress, starting 90–100 days after planting. Averages are from the 1987/88 and 1988/89 seasons at Santander de Quilichao, Colombia. Note the increase in HCN contents due to stress and the differences among cultivars. Clones with lower HCN under stress are good genetic sources for selecting and breeding materials suitable for fresh consumption by humans, particularly in dry and semi-arid zones. Clone Unstressed Stressed Roots Tops Total HCN Roots Tops Total HCN (mg/kg dry root) (mg/kg dry root) CM 489-1 19.1 7.2 214 18.0 7.1 401 CM 922-2 14.8 7.6 142 15.0 5.9 190 CM 1335-4 18.1 7.8 107 16.5 5.1 123 CM 2136-2 19.3 12.4 166 15.5 7.3 338 Average 17.8 8.8 157 16.2 6.4 263 % change due to stress -9 -28 +68 SOURCES: CIAT Report (1991); El-Sharkawy (1993). and high protein in storage roots. In addition to on bitter cassava, particularly in soils with high traditional breeding, transgenic approaches have moisture content, even though several sweet cultivars been used to produce cassava with reduced HCN were determined as having potential resistance or levels (i.e., >90% reduction in cyanogenic contents in tolerance of the bug (Riis 1997). One mechanism that storage roots) in transformed cv. M Col 22 (Jørgensen may deter or prevent the bug from feeding on sweet et al. 2005). “Acyanogenic” (i.e., cyanogen-free) cassava is high HCN content in the storage root peel clones have also been generated (Siritunga and Sayre instead of the parenchyma tissue (Riis 1997). The first 2003). However, the role of cyanogenesis in cassava, two nymphal instars have short stylets, thus confining as a potential deterrent to pests that feed on leaves feeding mainly to the root peel (Riis 1990; Riis et al. and roots, needs to be assessed in the developed 1995). Hence, selection for sweet cultivars having high “acyanogenic” materials before they are released (Riis HCN in the thicker root peel may be advantageous in et al. 1995, 2003). this case. Pereira (1977) and Poulton (1990) have argued Some cultural practices such as intercropping that high levels of HCN in plants may function as a cassava with sunn hemp (Crotalaria sp.), which defensive mechanism to protect crops against possesses natural insecticidal substances, was found predators, herbivores, and rodents. HCN may also to effectively reduce bug attack and damage to serve as a source of stored nitrogen, particularly for cassava roots. However, cassava yield was reduced seeds. The presumably defensive role of HCN against because of competition and crowding by the pests and diseases has not been observed Crotalaria (Bellotti et al. 1988; Bellotti 2002). (Brekelbaum et al. 1978). Despite normally higher elevations of leaf HCN levels in most cultivars, A social study was recently conducted on the water-stressed cassava crops in Northeast Brazil and Tukano Indians in northwestern Amazon Basin, Brazil. North Colombia (which typically have several The Tukano cultivate more bitter cultivars, which are months of water shortages) showed higher rates of high in HCN, than they do sweet cultivars, perhaps infestation by mites than did non-stressed crops because they are more prevalent rather than because (MA El-Sharkawy 1992, pers. comm.). of any inherent adaptive advantages. That is, no consistent relationships or patterns were Thrips also fed on cassava, regardless of HCN demonstrated to exist for the Tukanos’ preferring levels in leaves (Schoonhoven 1978). Other pests with bitter cultivars over sweet ones, whether for resistance different feeding habits, whether on shoots or roots, to predators, particularly pests and diseases, or other may present different responses. Recent work at CIAT reasons (Wilson 2003). However, Wilson and Dufour (Bellotti et al. 1988; Bellotti and Arias V 1993; Bellotti (2002) suggest that higher yields, often observed in and Riis 1994; Bellotti 2002) showed that the bitter cultivars grown in that region, form the Amazon subterranean burrower bug (Cyrtomenus bergi) Basin Indians’ likely criterion for choosing high-HCN preferred to feed on cassava roots low in HCN than cassava. 47 Cassava in the Third Millennium: … However, to our knowledge, no conclusive Table 3-7. Activity of C4 phosphoenolpyruvate carboxylase (PEPC) carboxylase in leaf extracts. Values are means evidence, based on sound research, exists as to of four leaves; ± are standard deviations. Note the whether bitter cultivars do, in fact, have an inherent much higher activity in cassava, compared with and superior potential for productivity than sweet beans, a C3 species, and the very high activity in wild ones. That no consistent relationship exists between Manihot (about 30% to 40% of activity in maize, a C4 species). In a group of field-grown cultivars under productivity and HCN contents in roots is prolonged water stress, Pn was significantly correlated furthermore supported by data in Table 3-6 and with the PEPC activity measured in the same leaves findings of trials with 14 other cultivars. These (El-Sharkawy 2004), indicating the importance of materials were tested across five consecutive growth selecting and breeding for elevated PEPC activity. Note that wild Manihot also possesses an additional cycles under different application rates of K fertilizer short-palisade layer beneath the lower leaf surface and in acidic clayey soils in subhumid zones of Colombia numerous stomata on both leaf surfaces—two traits (El-Sharkawy and Cadavid 2000). advantageous for enhancing photosynthesis (El-Sharkawy 2004). Moreover, several tested clones, including Species PEPC activity HMC-1, HMC-2, M Cub 74, M Pan 70, M Col 1505, (µmol NADH) CM 91-3, CM 523-7, CMC 40, CM 1585-13, and those gfw/min mg Chl/min shown in Table 3-6, have high yields and moderate Maize (cv. CIMMYT 346) 15.0 ± 1.8 7.0 ± 3.6 to low HCN levels in root parenchyma. Most of these Common beans 0.2 ± 0.07 0.3 ± 0.1 clones are improved materials that indicate (cv. Calima G 4494) compatibility of selection and breeding for high yield Cassava cultivars: with low HCN. Álvarez and Llano (2008) have M Mex 59 3.2 ± 0.6 2.2 ± 1.0 suggested that the bread-making quality of bitter M Nga 2 1.3 ± 0.1 0.4 ± 1.0 cultivars is different and possibly better than that of Wild Manihot species: sweet cultivars. This might be a reason why the M. grahamii 4.0 ± 0.9 2.8 ± 1.2 Indians grow bitter cultivars, that is, for culinary, not M. rubricaulis 5.8 ± 0.6 3.4 ± 1.3 agronomic, purposes. More research is needed to SOURCES: El-Sharkawy and Cock (1990); El-Sharkawy (2004); uncover other possible reasons why bitter cassava is MA El-Sharkawy, L Bernal, and Y López (1988, chosen in the Amazon Basin and elsewhere. unpublished). Photosynthesis and the C3-C higher than in C3-C4 plants with a C4-like kranz 4 Intermediate Characteristics of Cassava anatomy, as found in Panicum milioides (Ku et al. 1983; Brown and Bouton 1993). Previous research on cassava photosynthesis shows that several cassava cultivars and wild species exhibit The presence of a C4 PEPC protein in cassava activity of the C4 enzyme PEPC, ranging from 1.5 to was further determined immunologically >5 µmol per mg Chl/min. This is 15% to 25% of (Figure 3-10; CIAT Report 1991). In cassava, PEPC activities of C4 species such as maize and sorghum. appears to be of at least two different forms The research also demonstrated the importance of (isoenzymes), compared with PEPC from maize. The elevated PEPC activity, which may partly underlie presence of the enzyme, however, does not cassava’s high photosynthetic capacity and which necessarily mean it is active. When we used the correlates with productivity across environments and stain Fast Violet BB, which is relatively specific for genotypes (Table 3-7; Cock et al. 1987; El-Sharkawy oxaloacetate (i.e., the initial C4 product), we could and Cock 1987a, 1990; CIAT Reports 1990 to 1994; demonstrate that the PEPC is, indeed, active in El-Sharkawy et al. 1990, 1992a, 1993, 2008; Bernal cassava (Figure 3-10, at left, lanes 2 and 3 for 1991; López et al. 1993; Pellet and El-Sharkawy cassava cultivar M Col 22, lane 1 for maize, and lane 1993a; de Tafur et al. 1997b; El-Sharkawy 2004). 4 for beans). Thus, we quantitatively confirmed activity in centrifuged leaf extracts (Table 3-7). The PEPC activity observed in cassava and its wild relatives are much higher than those observed in More recent research on the biochemical and C3 species such as field bean. Instead, they are molecular characteristics of cassava photosynthetic comparable with activities found in several C3-C4 enzymes showed that a maize PEPC-specific intermediate Flaveria species, which have a limited antiserum (maize ppc probe, received from functional C4 cycle. They are also two to three times T. Nelson, Yale University, USA) cross-reacted with 48 Productivity, Photosynthesis, Ecophysiology, … Maize Cassava Cassava Beans Figure 3-10. At right, immunological detection of phosphoenolpyruvate carboxylase (PEPC) in leaf extracts: upper right, shows a double immunodiffusion, with wells 1, 3, and 8 for beans; wells 2, 4, and 5, for purified maize PEPC; well 6 for cassava cultivar M Col 22; well 7 for maize; AB = antiserum containing anti-PEPC. Lower right, shows immunoelectrophoresis in 1.2% agarose gel, where well 9 is for purified maize PEPC; well 10 is for cassava; AB = antiserum containing anti-PEPC. At left, simple PAGE patterns for PEPC in maize, cassava, and beans; the two forms of PEPC (isoenzymes) in cassava are apparent (Y López, MA El-Sharkawy, JH Cock, and H Ramírez 1987, unpublished; CIAT 1991; El-Sharkawy 2006). cassava PEPC. The reaction indicated the presence CO2 in light and in CO2-free air (Figure 3-13; of homologous antigenic determinants (CIAT Report El-Sharkawy and Cock 1987a). Complete or partial 1993; López et al. 1993). This was also shown at the apparent refixation and/or recycling in light of DNA level in Southern blot hybridization with a maize respiratory CO2 (both photorespiration and ppc probe and total, enzyme-digested, cassava- mitochondrial dark respiration) was recognized genomic DNA (Figure 3-11; CIAT Report 1993; López earlier in different C3 and C4 species (Meidner 1962; et al. 1993; Tenjo et al. 1993). These studies were Moss 1962; Tregunna et al. 1964; El-Sharkawy repeated with about 60 more accessions, and and Hesketh 1965, 1986; Forrester et al. 1966; included me (malic enzyme; Figure 3-12) and mdh El-Sharkawy et al. 1967, 1968; Jackson and Volk, (malate dehydrogenase) maize probes. 1969; Volk and Jackson 1972) and in C3-C4 intermediates (Devi and Raghavendra 1993). No polymorphisms were found that would have related the elevated activity of cassava PEPC to a However, more studies are needed, using in situ higher copy number of the genes involved. Moreover, hybridization and immunofluorescent techniques, to the corresponding gene sequences in cassava elucidate the spatial distribution of the appeared similar to the maize probes used, as shown photosynthetic key enzymes within the cassava by good hybridization signals at high stringency mesophyll (CIAT Report 1993; López et al. 1993; (CIAT Report 1993). Tenjo et al. 1993). Cassava and wild relatives show low photorespiration (CO2 compensation So far, preliminary studies on the concentration was 20–30 ppm), relative to C3 species compartmentalization of PEPC in cassava have (Figure 3-14; El-Sharkawy and Cock 1987a; CIAT indicated the location of ppc transcripts between the Reports 1992, 1995; El-Sharkawy et al. 1992a; upper epidermis and the top end of the long-palisade El-Sharkawy 2004); high percentage (40%–60%) of layer (CIAT Report 1993). The location tends to leaf-fed 14C incorporated into C4 acids after 5–10 s support the hypothesis that, over a range of photon under light; and elevated PEPC activity (Cock et al. flux densities and temperatures, the palisade cells 1987; El-Sharkawy and Cock 1987a, 1990). However, are capable of refixing and/or recycling all respiratory they lack the typical C4 kranz leaf anatomy that is 49 Cassava in the Third Millennium: … L-HindIII CG 996-6 P. vulgaris CG 927-12 Z. mays M Arg 11 M. grahamii M Bra 12 CG 996-6 M Bra 110 CM 4864-1 HMC-1 M Col 1684 M Arg 2 CMC 40 M Bra 132 M Bra 124 M Bra 172 M Arg 6 M Arg 13 M Bra 242 M Bra 359 M Bra 299 M Bra 71 M Arg 7 M Bra 243 M Bra 85 M Bra 405 M Arg 9 M Bra 73 L-HindIII M Bra 217 M Bra 273 M Bra 404 M Bra 77 M Bra 125 M Bra 233 M Bra 258 M Arg 12 CG 927-12 M Bra 416 L-HindIII M Arg 15 M Bra 329 M Bra 356 M Bra 435 M Bra 191 M Bra 325 M Bra 383 M Bra 237 M Bol 1 M Bra 355 M Bra 309 M Bra 450 M Bra 453 M Bra 328 M Bra 400 L-HindIII L-HindIII Figure 3-11. Southern hybridization of BamHI-digested cassava Figure 3-12. Southern hybridization of BamHI-digested cassava DNA, hybridized with a maize ppc probe (CIAT DNA, hybridized with a maize me probe (CIAT Reports 1993, 1994; JE Mayer, MA El-Sharkawy, Reports 1993, 1994; JE Mayer, MA El-Sharkawy, RM de Estefano, and FA Tenjo 1993, unpublished). RM de Estefano, and FA Tenjo 1993, unpublished). Note the variable degrees of hybridization with the Note the variable degrees of hybridization with the maize ppc probe within cassava germplasm and maize me probe within cassava germplasm. wild Manihot grahamii. required to compartmentalize the key C3 rubisco and pathway and therefore demonstrate C3-C4 C4 PEPC enzymes (El-Sharkawy and Hesketh 1965, intermediate photosynthetic behavior (Cock et al. 1986; Laetsch 1974; Hatch 1977, 1987). We suggest 1987; El-Sharkawy and Cock 1987a, 1990; that cassava and Manihot species are probably El-Sharkawy 2004, 2005). evolving biochemically towards a C4 photosynthetic 50 Productivity, Photosynthesis, Ecophysiology, … (A) 1.5 cv. M Col 89 1.5 cv. M Bra 314 1.2 1.2 0.9 0.9 0.6 0.6 0.3 0.3 0 0 0 500 1000 1500 0 500 1000 1500 Photosynthetic photon flux density (µmol per m2/s) (B) 0 o 4.0 C 30 oC 35 oC 4 3.0 2.0 PIB 1.0 PIB 0 0 10 20 0 10 20 0 10 20 Minutes Minutes Minutes Figure 3-13. (A) Differential CO2 releases in CO2-free air from the upper ( ) and lower ( ) surfaces of amphistomatous cassava leaves (cvs. M Col 89 and M Bra 314) as a function of photon flux density at a constant leaf temperature of 27 oC. Note the consistent lack of CO2 release from the upper surface of leaves of both cultivars when the abaxial stomata were blocked versus release from the lower surface. This indicates the complete refixation/recycling of respiratory carbon dioxide (both photorespiration and dark mitochondrial) within the long-palisade layer, which occupies more than 60% of leaf thickness. (B) Recorder’s traces of CO2 releases in CO2-free air under light and dark from the upper surface of amphistomatous cassava leaves (cv. M Bra 314) at 30, 35, and 40 oC leaf temperatures. Photon flux density was 1200 µmol per m2/s ( refers to light off; refers to light on; PIB to post-illumination burst of CO2). Note the lack of carbon dioxide release under light, which was observed in several light–dark cycles over a longer period (>1 h); the decrease in PIB magnitude with rising leaf temperature and eventual disappearance at 40 oC; and the pronounced surge of carbon dioxide within 3 min of darkness. The lack of carbon dioxide release under light was attributed mostly to an efficient refixation/recycling system in the palisade cells (El-Sharkawy and Cock 1987a). (B) 70 (A) 60 20 50 15 40 30 10 20 5 y = -3.84 + 0.2177x 10 y = -8.01 + 0.28x - 0.0003x2 r2 = 0.94 r2 = 0.89 0 0 20 40 60 80 100 -10 100 200 300 400 500 600 -5 Intercellular CO2 ( m mol/mol) Intercellular CO2 ( m mol/mol) Figure 3-14. Relationship between leaf photosynthesis (Pn) and intercellular CO2 concentration in cassava cultivar M Col 1684 (A) (CIAT Report 1992; El-Sharkawy et al. 1992a) and in wild Manihot rubricaulis (B) (CIAT Report 1995; SM de Tafur and MA El-Sharkawy 1995, unpublished). Note the linear response and the low photorespiration where the CO2 compensation point was about 20 in (A) and 28–30 µmol/mol in (B); a saturated Pn in M. rubricaulis at 400 –500 µmol/mol intercellular CO2 is apparent. 51 CO2 release in CO2-free air Pn ( m mol CO2 per m 2/s) (µmol CO2 per m2/s) CO2 release in CO2-free air (µmol CO2 per m2/s) Pn ( m mol CO2 per m 2/s) Cassava in the Third Millennium: … Effects of Water Stress in leaves from cassava plants cultivated in growth chambers and developed under brief water deficits. Photosynthetic enzymes The palisade cells demonstrated a higher density of immunogold labeling of the P-protein subunit of the Three-month-old cassava plants were exposed to water photorespiratory enzyme glycine decarboxylase (or stress for 3 and 8 weeks in the field. After 3 weeks of GDC). These findings may add another dimension to water stress, activities of PEPC, rubisco, and the C4 the C3-C4 intermediate hypothesis in cassava and to decarboxylase NAD-ME were observed, overall, to have the essential role of PEPC in recycling respiratory CO2 declined, particularly rubisco, in leaf extracts within palisade cells (Figure 3-13; El-Sharkawy and (Table 3-8; CIAT Report 1993). The average PEPC-to- Cock 1987a, 1990). rubisco ratio, indicating the relative importance of these two enzymes, was also reduced by stress. Even so, Ueno and Agarie (1997) concluded that the chamber-grown cassava cultivars were C3 and not However, after 8 weeks of stress, PEPC activity, C3-C4 intermediates. This conclusion, however, is averaged across all clones, was 13% higher than in questionable on the basis of two important aspects: unstressed crops, with differences among accessions first, the patterns of distribution and confinement of (Table 3-9; CIAT Report 1993). However, rubisco GDC observed in some C3-C4 intermediate species with activity was 42% less in the stressed crops. This kranz-like leaf anatomy are not necessarily applicable differential effect of stress on the activities of these two to other C3-C4 intermediates lacking such anatomy. key photosynthetic enzymes resulted in a much higher Second, the observed GDC labeling patterns in PEPC-to-rubisco ratio in the stressed crops than in the chamber-grown plants are not, however, incompatible unstressed ones. These data indicate that, under with the role of PEPC in the refixing or recycling of prolonged water deficit, the relative importance of the respiratory CO2 in cassava leaves. Moreover, the degree C4 PEPC versus the C3 rubisco becomes more of expression and distribution of GDC within leaf pronounced, lending support to the hypothesis that the tissues are probably affected by the developmental C4 PEPC enzyme may play a significant role in stages of leaves and by the environmental conditions photosynthetic activity under drought with high air during growth (Rylott et al. 1998). temperatures (CIAT Report 1993; El-Sharkawy 2004), probably by reducing both photorespiratory and Our hypothesis of C3-C4 intermediate cassava does mitochondrial dark CO2 losses and by increasing net not exclude the presence of rubisco and the enzymes carbon uptake and hence productivity. associated with the photorespiratory cycle in the palisade cells. Nor does it restrict them to spongy or Moreover, recent evidence suggests that PEPC is bundle-sheath cells in the absence of a perfect C4 kranz possibly located in the upper end of the long-palisade leaf anatomy and lack of complete separation and parenchyma. This further supports the role of compartmentalization of the key C4 and C3 enzymes in PEPC involvement in refixing or recycling respiratory palisade, spongy, and bundle-sheath chlorenchyma CO2 when highly dense abaxial stomata are partly cells (El-Sharkawy and Cock 1987a; El-Sharkawy closed under conditions of drought, high solar 2004). irradiance, and high temperatures with dry air, particularly in hypostomatous leaves, which normally Possibly, a limited CO2-concentrating mechanism possess >400 stomata/mm2 (El-Sharkawy et al. (via cytosolic PEPC) in palisade cells may operate, as 1984b). Besides increasing carbon uptake, such a indicated by the disappearance at high temperatures of mechanism for CO2 recycling protects the leaves from the post-illumination burst (PIB) of CO2 in CO2-free air photoinhibition by dissipating excess absorbed photons and the pronounced CO2 surge within a short period in (Osmond et al. 1980; Osmond and Grace 1995). In the darkness via the upper leaf surface (Figure 3-13B; field, leaves of over 100 cassava cultivars remained El-Sharkawy and Cock 1987a). Under these conditions, photosynthetically active, although at much reduced the oxygenase reaction by rubisco (in palisade-cell rates, under prolonged drought with hot dry air and chloroplasts) might be suppressed. When adaxial intense solar radiation (El-Sharkawy et al. 1990, 1992b; (upper leaf surface) stomata were blocked, CO2 El-Sharkawy 1993; de Tafur et al. 1997a, 1997b). releases through lower leaf surfaces in light and CO2-free air were substantial over a wide range of Ueno and Agarie (1997) examined the photon flux density (Figure 3-13A; El-Sharkawy and mitochondria of palisade and spongy mesophyll cells Cock 1987a). 52 Productivity, Photosynthesis, Ecophysiology, … 53 Table 3-8. Activities of selected photosynthetic enzymes in leaf extracts from clones of field-grown cassava, comparing well-watered plants with those affected by 3 weeks of water stress, starting 92 days after planting at Santander de Quilichao, Colombia. Values are means ± SD; activities are expressed in µmol per mg Chl/min. Note the much higher reduction in C3 rubisco activity, compared with C4 PEPC activity in leaves that developed before stress was initiated. Clone Unstresseda Stresseda PEPC Rubisco NAD-ME PEPC/ PEPC Rubisco NAD-ME PEPC/ rubisco rubisco CM 4013-1 0.37 ± 0.60 0.31 ± 0.05 0.40 ± 0.06 1.19 0.31 ± 0.03 0.41 ± 0.09 0.19 ± 0.05 0.76 CM 4063-6 0.57 ± 0.06 3.72 ± 0.11 0.39 ± 0.06 0.15 0.41 ± 0.04 1.69 ± 0.10 0.17 ± 0.09 0.24 SG 536-1 0.67 ± 0.05 0.39 ± 0.20 0.55 ± 0.18 1.72 0.57 ± 0.12 0.81 ± 0.20 0.39 ± 0.50 0.70 M Col 1505 0.45 ± 0.01 1.18 ± 0.08 0.16 ± 0.02 0.38 0.49 ± 0.10 0.49 ± 0.12 0.29 ± 0.06 1.00 Average 0.51 1.4 0.38 0.86 0.45 0.85 0.26 0.68 % change due to stress -12 -39 -32 -21 a. PEPC refers to phosphoenolpyruvate carboxylase; rubisco to ribulose bisphosphate carboxylase; NAD-ME to the C4 photosynthetic pathway, subtype nicotinamide adenine dinucleotide malic enzyme. SOURCES: CIAT Report (1993); Y López and MA El-Sharkawy (1992, unpublished). Cassava in the Third Millennium: … 54 Table 3-9. Activities of selected photosynthetic enzymes in leaf extracts from clones of field-grown cassava, comparing well-watered plants with those affected by 8 weeks of water stress, starting at 92 days after planting at Santander de Quilichao, Colombia. Values are means ± SD; activities are expressed in µmol per mg Chl/min. Note the large reductions in C3 rubisco activity, compared with the C4 PEPC, in leaves that developed under stress, resulting in a higher PEPC/rubisco ratio. This photosynthesis-based biochemical assay is useful in selecting for tolerance of prolonged drought (Tables 3-10 and 3-11). Clone Unstresseda Stresseda PEPC Rubisco PEPC/ PEPC Rubisco PEPC/ rubisco rubisco CM 4013-1 0.86 ± 0.12 0.28 ± 0.10 3.10 1.18 ± 0.17 0.30 ± 0.01 3.9 CM 4063-6 0.89 ± 0.05 2.30 ± 0.03 0.39 1.42 ± 0.26 0.62 ± 0.02 2.3 SG 536-1 1.46 ± 0.42 0.44 ± 0.12 3.30 1.33 ± 0.22 0.25 ± 0.08 5.3 M Col 1505 1.09 ± 0.10 0.57 ± 0.13 1.90 0.96 ± 0.16 0.89 ± 0.14 1.1 Average 1.08 0.9 2.2 1.22 0.52 3.2 % change due to stress +13 -42 +45 a. PEPC refers to phosphoenolpyruvate carboxylase; rubisco to ribulose bisphosphate carboxylase. SOURCES: CIAT Report (1993); Y López and MA El-Sharkawy (1992, unpublished). Productivity, Photosynthesis, Ecophysiology, … In cultivars with amphistomatous leaves, exchange atmospheric CO2, higher O2, and stressful (measured at saturating photon flux density and environments, as believed so far? Reinfelder et al. normal air) of both CO2 gas and H2O vapor via either (2000, 2004) found functional C4 photosynthesis in the leaf surface was substantial. It was also proportionate unicellular marine diatom, thus possibly providing to stomatal densities and stomatal conductance on evidence to support the hypothesis. both sides (El-Sharkawy et al. 1984b). Only in some uncultivated C3-C4 intermediate species such as those Moreover, in some amphibious sedges such as found in the genera Flaveria, Panicum, and Diplotaxis, Eleocharis vivipara, different culms on the same plant did a kranz-like leaf anatomy with developed bundle can have C3, kranz-less, photosynthetic characteristics sheaths appear (Ku et al. 1983; Brown et al. 1985; when they develop under water but C4, kranz-type Brown and Hattersley 1989; Araus et al. 1990; Ueno et characteristics when formed in air (Ueno 2001). In this al. 2003). The GDC is probably confined to this case, C4 photosynthesis was apparently linked to anatomy (Hylton et al. 1988). kranz-type anatomy, but with the incomplete compartmentalization of rubisco, which was located in C4 photosynthesis in the absence of the typical both mesophyll and bundle-sheath cells (Ueno 1996). kranz leaf anatomy in some uncultivated plants, and implications for understanding the Hibberd and Quick (2002) also reported on the origin of the C4 syndrome biochemical characteristics of C4 photosynthesis, that is, high C4 enzyme activity and the respective Bienertia cycloptera, an uncultivated species of the controlling genes. These were found to already exist Chenopodiaceae family, grows in salty depressions in and be expressed in the stem and petiole Central Asia. Recent findings indicated that this plant photosynthetic cells that surround vascular tissues of has a functional C4 pathway but lacks the typical kranz C3 flowering plants. These features therefore indicate a anatomy where key C4 and C3 enzymes are possible first step in the induction and evolution of the presumably located and compartmentalized within the C4 syndrome. cytosol or chloroplasts of the same mesophyll cell (Voznesenskaya et al. 2001, 2002). The induction and evolution of the biochemical components of the C4 syndrome in the plant kingdom Likewise, the submersed monocot Hydrilla perhaps took place long before the more complex verticillata, which also lacks the kranz anatomy, was structural and anatomical components had evolved in found to possess a functional C4 pathway with PEPC terrestrial plants. Extensive research has recently been and rubisco being, respectively, present in the cytosol conducted on the molecular mechanisms underlying and chloroplasts of all cells. That is, the enzymes were the C4 syndrome; its multiple families of genes and not segregated into special and separate cell types, as isogenes encoding different isoforms of PEPC in C3, C4, is common in terrestrial C4 species (Salvucci and C3-C4 intermediate, and the crassulacean acid Bowes 1983; Magnin et al. 1997; Reiskind et al. 1997). metabolism (CAM) systems; and the expression Shifts from C3 to C4 photosynthesis can also occur patterns of the respective controlling genes in different under specific environmental conditions. In this plant species, organs, tissues, and subcellular submersed species, a CO2-concentrating mechanism organelles (Hermans and Westhoff 1990, 1992; apparently operates in the chloroplasts where rubisco Rajagopalan et al. 1994; Westhoff et al. 1997; Sheen and decarboxylation enzymes are located. The 1999; Westhoff and Gowik 2004). Such gene-level mechanism may represent an ancient form of C4 studies increase understanding of how C4 photosynthesis that evolved long before the kranz photosynthesis evolved and is controlled. They may anatomy-dependent C4 syndrome appeared in also pave the way for possible bioengineering of more terrestrial species (Magnin et al. 1997; Reiskind et al. efficient leaves in economically important crops. 1997). In light of these advances and discoveries, the If this is indeed an ancient mechanism, then an re-evaluation and revision of classification systems, important question arises on the first induction step of previously used in the past to identify C3, C4, or C3-C4 C4 photosynthesis on earth: was the CO2-concentrating intermediate plants, is therefore warranted. These mechanism first induced and then did it evolve in classifications were based on only a few given criteria unicellular aquatic organisms in response to limiting of leaf anatomy, subcellular structure and organization, supplies of CO2 in the water? Did this happen before C4 physiology, and biochemistry. Cassava is a case in plants evolved onto land in response to much reduced point, where its photosynthetic characteristics 55 Cassava in the Third Millennium: … comprise perhaps the only discovery so far of C3-C4 was lower) and -1.6 MPa (during dry or sunny periods intermediate photosynthesis in cultivated plants. The when VPD was much higher), with stressed crops often case therefore points to the need for more showing slight reductions. These values fall in the comprehensive classification systems. ranges previously reported for cassava under extended periods of soil water shortages in the field (Connor and In cassava and its wild relatives, wide genetic Palta 1981; Porto 1983; Cock et al. 1985; El-Sharkawy variations exist for C4 PEPC activity, correlating with et al. 1992b; Cayón et al. 1997; de Tafur et al. 1997a). leaf photosynthesis and yield under extended water They are higher than those normally observed in other stress in the field (Calatayud et al. 2002; El-Sharkawy field crops under stress. These findings indicate that 2004; El-Sharkawy et al. 2008). These attributes cassava conserves water and prevents extreme leaf should be exploited when selecting and breeding for dehydration through stomatal sensitivity to stress, that enhanced photosynthetic capacity, at least when is, the crop uses stress avoidance mechanisms. identifying parental materials (Tables 3-7 to 3-10; CIAT Reports 1990 to 1994; El-Sharkawy and Cock 1990; The phenomenon of osmotic adjustment (OA) in López et al. 1993; El-Sharkawy 2004). Also notable are mature leaves therefore appears to have developed the C4 decarboxylation enzymes NAD-ME and NADP- under water and edaphic stresses, as has been ME showing activity in cassava, with differences among observed in several other field crops (Hsiao 1973; cultivars (Table 3-10), and comparable with those Hsiao et al. 1976; Jones and Turner 1978; Turner et al. observed in C4 and C3-C4 species. 1978; Ackerson and Hebert 1981; Morgan 1984). It does not operate in field-grown cassava, because Wild species such as Manihot rubricaulis and pre-dawn and mid-day, bulk, leaf-water potential M. grahamii represent good genetic sources for always remains above -0.8 MPa and -2.0 MPa, elevated PEPC activity. They also show more efficient respectively, during prolonged water deficits. Hence, leaf anatomy, having developed a second palisade OA is of little importance as a possible mechanism layer, albeit short, on the lower side of their underlying cassava’s tolerance of drought. Recent amphistomatous leaves (Table 3-7; Calatayud et al. studies with potted cassava grown in the greenhouse 2002; El-Sharkawy 2004). The existence of two showed that, after few days of water deficit, the largest palisade layers and the distribution of stomata on both increases in solutes occurred in the youngest and not leaf sides may provide an adaptive advantage in terms yet fully expanded leaves (Alves 1998, 2002). The of carbon uptake (Parkhurst 1978; Solárová and smallest increases occurred in mature ones, Pospisilová 1979; Pospisilová and Solárová 1980; Tichá confirming the lack of importance of OA to mature 1982; El-Sharkawy et al. 1984b; Gutschick 1984; Mott leaves. Even so, further study on field-grown plants is and O’Leary 1984). For similar reasons, known genetic needed if results are to be extrapolated to field diversity in rubisco characteristics should also be conditions and to obviate acclimation problems recorded (Paul and Yeoh 1987, 1988). (El-Sharkawy 2005). Because biochemical assays are often expensive Osmoregulation requires the investment and and difficult to use in screening large breeding accumulation of solutes and assimilates for its populations, molecular biology techniques, genetic development under stress. McCree (1986) examined markers, and mapping tools would be useful for the relative carbon costs involved in OA in sorghum identifying desirable genetic traits (Beeching et al. grown under either water deficit or salinity. He 1993). concluded that the metabolic costs of storing photosynthates and using them for OA were less than Leaf water status, canopy light interception, those of converting photosynthates to new biomass, and leaf photosynthesis although costs did increase slightly under salinity. Under drought, changes occur in the biosynthesis, Trials showed that pre-dawn leaf-water potential contents, and distribution of plant growth regulators (Figure 3-15A; CIAT Report 1992) remain at about such as ABA within plant organs and tissues -0.5 MPa for all cultivars throughout most of a 3-month (particularly roots, leaves, and buds). Changes in stress period, with virtually no differences between regulators may be important for the plant’s sensing stressed and unstressed crops. Mid-day leaf water changes in both soil water and atmospheric humidity. potential (Figure 3-15B) in all cultivars in both stressed They may also enable the plant to control stomatal and unstressed crops fluctuated between -0.6 MPa movements, leaf formation and extension, root growth, (during wet periods when, presumably, leaf-to-air VPD bud dormancy, and other biological functions such as 56 Productivity, Photosynthesis, Ecophysiology, … 57 Table 3-10. Activities of selected photosynthetic enzymes in leaf extracts from cassava clones grown in the field at Santander de Quilichao, Colombia, 1992. Values are means ± SD. Note the wide range of genetic variation for enzyme activity that could be used to select and breed for enhanced photosynthesis and, hence, productivity. Also note that cultivar CMC 40 (also known as M Col 1468) had the highest rubisco and PEPC activities, and the highest root yield under prolonged terminal water stress (Table 3-11). Clone Activities (µmol per mg Chl/min)a PEPC Rubisco NAD-ME NADP-ME PEPC/rubisco CM 523-7 1.57 ± 0.10 3.62 ± 0.62 1.84 ± 0.1 0.41 ± 0.04 0.43 CM 507-37 1.91 ± 0.10 6.84 ± 0.66 1.37 ± 0.4 0.46 ± 0.18 0.28 M Col 1684 2.90 ± 0.19 6.96 ± 1.18 2.05 ± 0.6 0.36 ± 0.03 0.42 CMC 40 3.07 ± 0.27 8.16 ± 0.71 1.84 ± 0.6 0.24 ± 0.05 0.38 a. PEPC refers to phosphoenolpyruvate carboxylase; rubisco to ribulose bisphosphate carboxylase; NAD-ME to the C4 photosynthetic pathway, subtype nicotinamide adenine dinucleotide malic enzyme; NADP-ME to the C4 photosynthetic pathway, subtype nicotinamide adenine dinucleotide phosphate malic enzyme. SOURCES: CIAT Report (1992); López et al. (1993). Cassava in the Third Millennium: … (A) Pre-dawn measurements 0 -0.5 -1.0 CM 489-1 CM 1335-4 -1.5 0 -0.5 -1.0 CM 922-2 CM 2136-2 -1.5 (B) Mid-day measurements 0 -0.4 -0.8 -1.2 CM 489-1 CM 1335-4 -1.6 0 -0.4 -0.8 -1.2 CM 922-2 CM 2136-2 -1.6 95 125 155 185 95 125 155 185 Days after planting Figure 3-15. Leaf-water potential in water-stressed ( ) and well-watered ( ) cassava crops during stress, starting 90 days after planting. Values are means of 5 to 10 leaves from the upper canopy and taken at pre-dawn (A) and mid-day (B). Note the small differences between the two water regimes and the four crops’ pre-dawn and mid-day water potentials, and the increases in water potential during high ambient humidity. The pre-dawn and mid-day levels were more than -0.8 and -2.0 MPa, respectively, indicating the striking stomatal control in cassava, regardless of soil-water status (CIAT Report 1991; El-Sharkawy 1993). 58 Water potential (MPa) Water potential (MPa) Productivity, Photosynthesis, Ecophysiology, … PEPC activation and expression, and possibly the Another important mechanism for conserving switching or induction from C3 to CAM or C4 water under extended stress is to significantly reduce photosynthesis in some species (Jones and Mansfield light interception (Figure 3-16; CIAT Reports 1991 to 1972; Huber and Sankhla 1976; Ackerson 1980; Walton 1995). The leaf canopy is reduced, mostly through 1980; Radin et al. 1982; Zeiger 1983; Henson 1984; restricted new leaf formation, smaller leaf size, and leaf Radin 1984; Davies et al. 1986; Schulze 1986; Turner drop (Connor and Cock 1981; Porto 1983; Palta 1984; 1986; Jones et al. 1987; Zeevaart and Creelman 1988; El-Sharkawy and Cock 1987b; El-Sharkawy et al. Zhang and Davies 1989; Chu et al. 1990; Chapin, III, 1992b)—this factor is also essential for reducing water 1991; Taybi and Cushman 1999; Alves and Setter 2000; consumption. Although reduced leaf area would Ueno 2001). conserve water, it would also reduce total biomass and yield (Figure 3-9; Table 3-6; Connor and Cock 1981; The adaptive “stress avoidance mechanism in Connor et al. 1981; Porto 1983; El-Sharkawy and Cock cassava” that operates via stomatal sensitivity to both 1987b; CIAT Reports 1991 to 1995; El-Sharkawy et al. soil and atmospheric water deficits is of paramount 1992b, 1998b; El-Sharkawy and Cadavid 2002). importance for the crop’s tolerance of prolonged Nevertheless, once released from stress, cassava drought (>3 months) and hot dry air in seasonally dry recovers rapidly by forming new leaves, which increase and semi-arid zones (El-Sharkawy 1993; de Tafur light interception and canopy photosynthesis. Thus, 1997a, 1997b). Coupled with this mechanism is a deep previous losses in biomass, particularly root yield, are rooting system (reaching soil layers more than 2 m compensated (Figure 3-16; El-Sharkawy and Cock deep) that allows the crop to extract available stored 1987b; CIAT Reports 1991 to 1995; El-Sharkawy et al. water (Connor et al. 1981; CIAT Reports 1983 to 1994; 1992b, 1998b; El-Sharkawy 1993; El-Sharkawy and Porto 1983; El-Sharkawy and Cock 1987b; Cadavid 2002). El-Sharkawy et al. 1992b; de Tafur et al. 1997a; Cadavid et al. 1998). 100 80 60 40 20 CM 489-1 CM 1335-4 0 100 80 60 40 20 CM 922-2 CM 2136-2 0 95 145 195 245 95 145 195 245 Days after planting Figure 3-16. Light interception in water-stressed ( ) and well-watered ( ) cassava crops. Note the large reductions in light interception over time in the stressed crops because of a lack of leaf formation, the small size of new leaves, and the dropping of old leaves. Note also the increases after recovery ( ) from stress as new leaves formed (CIAT Report 1991; El-Sharkawy 1993). 59 Light interception (%) Cassava in the Third Millennium: … Cassava leaves also remain adequately active Colombia, and sub-Saharan Africa; El-Sharkawy 1993; during water shortages in the field (Figure 3-17). de Tafur et al. 1997b; El-Sharkawy 2004). In this Stressed leaves can maintain a photosynthetic rate that ecosystem, a second wet cycle is needed to allow is 40%–60% that of unstressed leaves over a 3-month recovery of growth and complete root bulking. stress period. Cultivars show differences, for example, hybrid CM 489-1 demonstrates smaller reductions than Evaluating Germplasm for Tolerance of others. Once recovered from stress, previously stressed Water Stress leaves can approach the rates of unstressed ones. Furthermore, newly formed leaves of previously Cassava germplasm can be evaluated for different traits stressed crops show even higher photosynthetic rates while grown under different levels of water stress. The than those of the unstressed crops (Figure 3-17). studies described in the next three sections were These higher photosynthetic rates in new leaves conducted under prolonged early water stress coincide with higher stomatal conductance to water (occurring 2–6 months after planting); mid-season vapor; higher mesophyll conductance to CO2 diffusion; stress (4–8 months after planting), and terminal and higher N, P, Ca, and Mg in leaves than unstressed (i.e., end-of-season) stress (6–12 months after crops (CIAT Report 1990; El-Sharkawy 1993; Cayón et planting). al. 1997). Productivity, nutrient-use efficiency, Moreover, Cayón et al. (1997) reported greater photosynthesis, and water uptake mobilization of potassium (an average of 0.79% K) in newly developed leaves of previously stressed crops, Three-year field trials were conducted at CIAT– whereas new leaves from unstressed crops averaged Quilichao experiment station to study the effects of 0.96% K. This finding suggests a higher demand for prolonged water stress imposed at different growth assimilates in storage roots, as K is normally stages on cassava productivity, nutrient uptake and use translocated, together with sugars, to sinks (Giaquinta efficiency, leaf photosynthesis, and patterns of water 1983). Thus, leaf photosynthesis is also controlled, in uptake (CIAT Reports 1992, 1993; Caicedo 1993; this case, by sink demand and strength (Burt 1964; El-Sharkawy et al. 1998b; El-Sharkawy and Cadavid Thorne and Evans 1964; Nösberger and Humphries 2002). Figure 3-18 illustrates the dynamics of dry 1965; Humphries 1967; Herold 1980; Ho 1988; matter accumulation in storage roots over the growth Wardlaw 1990; Pellet and El-Sharkawy 1994; cycle of four contrasting clones. Under early stress El-Sharkawy 2004). The dynamics of K in leaves of (initiated at 2 months after planting and terminated at field-grown cassava may therefore be used as an 6 months), root yield at 6 months was significantly indicator of root sink strength and source–sink smaller than the control for all clones in both growth relationships. cycles. These remarkable physiological responses to The same trends were observed in shoot biomass mid-season water stress point to cassava’s potential to but with greater reductions than those observed for tolerate prolonged drought, and its resilience and roots (CIAT Reports 1992, 1993; Caicedo 1993; ability to recover from stress when water becomes El-Sharkawy et al. 1998b; El-Sharkawy and Cadavid available, as in subhumid zones with intermittent dry 2002). Under mid-season stress (initiated 4 months spells or in seasonally dry zones with well-marked after planting and terminated at 8 months), yield at bimodal rainfall distribution. Under these conditions, 8 months was also significantly lower than for the longer leaf life, that is, increased leaf retention, coupled well-watered control in both cycles, except for CMC 40 with resistance to pests and diseases (Byrne et al. (also known as ‘M Col 1468’ in Colombia). Reductions 1982; El-Sharkawy 1993), is advantageous in saving in shoot biomass were less pronounced than those dry matter invested in leaves and in allowing under early stress (Caicedo 1993; El-Sharkawy et al. partitioning of excess photosynthates towards storage 1998b; El-Sharkawy and Cadavid 2002). roots. Under both early and mid-season stress, leaf area, The crop can also survive, but with higher losses of as determined from periodic harvests, was also leaf canopy and less dry matter in storage roots, in significantly smaller than for controls, resulting in a semi-arid zones with an annual rainfall of less than much reduced canopy light interception (Figure 3-19; 600 mm and with periods of water deficits of more CIAT Report 1992; El-Sharkawy and Cadavid 2002). than 4–5 months (e.g., Northeast Brazil, northeastern Once the cassava crops were allowed to recover, new 60 Productivity, Photosynthesis, Ecophysiology, … (A) Leaves under stress (B) New leaves after stress 30 20 10 CM 489-1 CM 489-1 0 30 20 10 CM 922-2 CM 922-2 0 30 20 10 CM 1335-4 CM 1335-4 0 30 20 10 CM 2136-2 CM 2136-2 0 95 117 139 161 183 205 200 210 220 230 240 250 260 Days after planting Days after planting Figure 3-17. Leaf photosynthesis (Pn) in the upper canopy when affected by mid-season water stress (CIAT Report 1991; El-Sharkawy 2006). (A) Leaves under water stress; refers to recovery. (B) New leaves after stress period. refers to leaves under stress; to control. 61 Pn ( m mol CO2 per m 2/s) Pn ( m mol CO2 per m 2/s) Pn ( m mol CO2 per m 2/s) Pn ( m mol CO2 per m 2/s) Cassava in the Third Millennium: … (A) First crop cycle (B) Second crop cycle 16 CM 523-7 CM 523-7 14 12 10 8 6 4 2 0 16 CMC 40 CMC 40 14 12 10 8 6 4 2 0 16 CM 507-37 CM 507-37 14 12 10 8 6 4 2 0 16 M Col 1684 M Col 1684 14 12 10 8 6 4 2 0 2 4 6 8 10 12 2 4 6 8 10 12 Months after planting Months after planting Figure 3-18. Storage root dry matter yield over time in response to prolonged water stress imposed at different growth stages (early, i.e., 2–6 months; mid-season, 4–8 months; terminal, 6–12 months after planting) and the control in four cassava cultivars. Vertical bars = ± SE (n = 4); (A) first crop cycle; (B) second crop cycle. refers to control; to early stress; to mid- season stress; to terminal stress. Note the reduction in yields during stress and recovery at final harvest from early and mid-season stress. Cultivars differed, with cv. CMC 40 (also known as M Col 1468) having the highest yield under stress. (El-Sharkawy and Cadavid 2002.) 62 Root yield (t/ha dry weight) Root yield (t/ha dry weight) Root yield (t/ha dry weight) Root yield (t/ha dry weight) Productivity, Photosynthesis, Ecophysiology, … leaf area formed rapidly, developing values similar to or 2002). The resulting higher nutrient-use efficiencies for higher than those of the controls, thus resulting in all elements in both root and total biomass were increased light interception (Figure 3-19). In the early caused mainly by increased reductions in shoot stressed crops, increases in shoot biomass were lower, biomass and stable root yields, and higher HI and remained lower, than under other water regimes. (Table 3-12). Across clones, increases in nutrient-use This indicated adverse effects of early stress on shoot efficiency due to early stress were >35% and >10% in biomass recovery (Caicedo 1993; El-Sharkawy et al. roots and total biomass, respectively. However, among 1998b; El-Sharkawy and Cadavid 2002). nutrient elements, the lowest percentage increases were for nitrogen-use efficiency and the highest for Under terminal stress (initiated 6 months after magnesium. planting until final harvest at 12 months), final root yield at 12 months was less than the control. The Similar trends were observed for mid-season largest reductions occurred in clone CM 523-7 (also stressed crops, but with lower values than for early known as ‘ICA Catumare’ in Colombia). An exception stress. Under terminal stress, which started after peak was CMC 40, whose yield was higher under stress. crop growth at 6 months and after the bulk of nutrient Genotype × water regime interaction was significant uptake took place between 2 and 5 months (Howeler (P < 0.01), indicating the soundness of the strategy of and Cadavid 1983; Howeler 2002), nutrient-use breeding and selecting for specific edaphoclimatic efficiency increased minimally in terms of root zones. Similar findings were recently reported in the production, except for magnesium, which showed a Sudanian savanna of Nigeria, using variations in the 25% increase. soil-water table as a variable for testing responses of cassava cultivars to water stress (Okogbenin et al. These findings clearly illustrate the beneficial effect 2003). of responses to water stress on conserving soil fertility, as well as on nutrient-use efficiency. Cassava is known Final yields of several clones across 2 years were for its high levels of tolerance of both water stress and not significantly different among water regimes poor soils (CIAT Reports 1990 to 1995; Howeler and (Table 3-11), indicating cassava’s capacity to tolerate Cadavid 1990; El-Sharkawy 1993; Pellet and El- extended water deficit in subhumid and seasonally dry Sharkawy 1993a, 1993b, 1997; Cadavid et al. 1998; warm climates with bimodal precipitation patterns. Howeler 2002; El-Sharkawy 2004). Its capacity to Compared with clone CM 523-7, CMC 40 had the accumulate more dry matter per unit of water and higher yield and shoot biomass under terminal stress, nutrient absorbed than most other food crops points to and the smaller leaf area, probably because of the high its inherent advantage in marginal edaphoclimatic leaf photosynthesis observed in the field under diverse conditions. environments (El-Sharkawy et al. 1990; El-Sharkawy et al. 1992a; Pellet and El-Sharkawy 1993a). Furthermore, these data have important implications for a breeding strategy for low-input, Moreover, the upper-canopy leaves of CMC 40 agricultural production systems (Hershey and Jennings showed greater activity for both C3 and C4 main 1992). Selection and breeding for plant types that enzymes than did the leaves of CM 523-7. In µmol per demand less water and fewer nutrient resources mg Chl/min, values were 8.2 for rubisco and 3.1 for (e.g., medium-statured to short cultivars) may help PEPC in CMC 40 versus 3.6 and 1.6 in CM 523-7 stabilize and sustain adequate productivity in (Table 3-10; CIAT Report 1992; López et al. 1993). resource-limited environments. In 2-year field trials These findings indicate the importance of selecting held at CIAT–Quilichao, a group of clones that were tall and breeding for high leaf photosynthesis, particularly (high top biomass), medium-statured (medium top under stress. Variations among clones for leaf biomass), and short (low top biomass) were evaluated photosynthesis, as measured in the field, were for productivity and nutrient-use efficiency (CIAT observed (Figure 3-20). Report 1996, 1997; El-Sharkawy et al. 1998a). Differences in root yields among this group of clones Nutrient uptake and use efficiency (planted at 10,000 plants/ha) were small because of higher HI in the medium-statured and short cassava Plant nutrient contents at final harvest were much than in tall cassava, with early root bulking tending to less in stressed crops, particularly at early stages occur in both medium-statured and short clones (El-Sharkawy et al. 1998b; El-Sharkawy and Cadavid (Table 3-13). 63 Cassava in the Third Millennium: … 64 CM 507-37 CM 523-7 M Col 1684 M Col 1468 (A) 100 80 60 40 20 0 (B) 100 80 60 40 20 0 (C) 100 80 60 40 20 0 80 160 240 300 80 160 240 300 80 160 240 300 80 160 240 300 Days after planting Days after planting Days after planting Days after planting Figure 3-19. Interception of light (× 102 %) by four cassava cultivars affected by early water stress (A); mid-season water stress (B); and terminal water stress (C). refers to stress; to control; to stress starting; to recovery. (CIAT Report 1992; El-Sharkawy 2006.) Light interception (%) Light interception (%) Light interception (%) Productivity, Photosynthesis, Ecophysiology, … 65 Table 3-11. Effect of prolonged water stress imposed on four cassava cultivars at different growth stages, Santander de Quilichao, Department of Cauca, Colombia, over the 1990/91, 1991/92, and 1992/93 seasons. Parameters evaluated were storage root yield and shoot biomass at 12 months after planting, and mean leaf area index (mean LAI) over the growth cycle. The data given below are from the 1991/92 and 1992/93 seasons. Note that cv. CMC 40 (also known as M Col 1468) had the highest root yield under prolonged terminal water stress and the highest activities for phosphopenolpyruvate carboxylase (PEPC) and rubisco activities (Table 3-10). Cultivar Stress treatment Stress treatment Stress treatment (root yield at t/ha, dry weight) (shoot biomass at t/ha, dry weight) (mean LAI) Control Early Mid-season Terminal Control Early Mid-season Terminal Control Early Mid-season Terminal CM 507-37 14.0 11.1 11.3 11.1 6.0 2.7 5.6 5.3 2.3 1.3 1.8 2.3 CM 523-7 13.8 12.8 12.1 9.7 5.3 4.2 5.2 4.5 2.3 1.4 1.3 2.0 CMC 40 10.0 10.4 12.1 14.6 7.8 3.9 5.7 6.7 1.7 1.1 1.1 1.7 M Col 1684 13.6 10.3 12.5 11.5 5.0 2.2 4.0 4.3 1.8 1.1 1.3 1.8 Average 12.9 11.2 12.9 11.7 6.0 3.3 5.1 5.2 2.0 1.2 1.4 2.0 LSD0.05 NS* 0.8 0.3 Treatment × cultivar 2.7 1.4 0.5 * NS = not significant at 5%. SOURCES: Caicedo (1993); El-Sharkawy et al. (1998b); El-Sharkawy and Cadavid (2002). Cassava in the Third Millennium: … 66 (A) 50 CM 507-37 CM 523-7 M Col 1684 CMC 40 40 30 20 10 0 60 120 180 240 300 60 120 180 240 300 60 120 180 240 300 60 120 180 240 300 (B) 50 40 30 20 10 0 120 165 210 255 300 120 165 210 255 300 120 165 210 255 300 120 165 210 255 300 (C) 50 40 30 20 10 0 180 210 240 270 300 180 210 240 270 300 180 210 240 270 300 180 210 240 270 300 Days after planting Days after planting Days after planting Days after planting Figure 3-20. Photosynthetic rate (Pn) of upper-canopy leaves of four cassava cultivars affected by early water stress (A); mid-season water stress (B); and terminal water stress (C). refers to stress; to control; to stress starting; to recovery. Values are averages of four leaves ± SD. (CIAT Report 1992; El-Sharkawy 2006.) Pn ( m mol CO2 per m2/s) Pn ( m mol CO2 per m2/s) Pn ( m mol CO2 per m2/s) Productivity, Photosynthesis, Ecophysiology, … 67 Table 3-12. Effect of prolonged water stress on cassava at different growth stages on dry root yield, total harvestable biomass (t/ha), and nutrient-use efficiency (kg dry matter/kg total nutrient uptake) at final harvest, using an average of four clones. Note the higher nutrient-use efficiency under prolonged early and mid-season water stresses, compared with well-watered crops. The higher nutrient-use efficiency was mainly due to larger reductions in top biomass (and hence less nutrient uptake), compared with the smaller reductions in storage roots (and hence higher harvest indices). Traita Stress treatmentb Control Early (2–6 MAP) Mid-season (4–8 MAP) Terminal (6–11 MAP) Roots Total Roots Total Roots Total Roots Total biomass biomass biomass biomass Root yield 11.5 — 11.9 — 13.1 — 11.0 — Total biomass — 15.8 — 15.5 — 18.2 — 14.5 N-UE 93 144 126 159 97 139 85 127 P-UE 615 947 971 1232 777 1109 645 966 K-UE 112 172 173 219 146 210 115 173 Ca-UE 270 414 408 519 300 433 274 413 Mg-UE 379 577 616 780 504 722 473 712 % change due to stress Root yield +3 +14 -4 Total biomass -2 +15 -8 N-UE +35 +10 +4 -3 -9 -12 P-UE +58 +30 +26 +17 +5 +2 K-UE +54 +27 +30 +22 +3 0 Ca-UE +51 +25 +11 +5 +1 0 Mg-UE +63 +35 +33 +25 +25 +23 a. N-UE, P-UE, K-UE, Ca-UE, and Mg-UE refer to use efficiency of nitrogen, phosphorus, potassium, calcium, and magnesium, respectively. b. MAP refers to months after planting. \SOURCES: CIAT Report (1993); El-Sharkawy et al. (1998b); El-Sharkawy and Cadavid (2002). Cassava in the Third Millennium: … Table 3-13. Dry root yield and top biomass (t/ha) for 15 cassava clones of differing biomass weights (higher, intermediate, and lower) grown at Santander de Quilichao, Colombia. Data are from the first cycle (1994/95). Note the early bulking (i.e., storage root-filling capacity) trends within the first 5 months in clones with medium or short stature, a trait advantageous for selecting and breeding improved materials for semi-arid ecosystems. Biomass weight Root yield Tops at 303 days at days after planting after planting 126 182 303 Higher (mean of 5 clones) 1.63 2.64 11.32 6.6 Intermediate (mean of 5 clones) 2.32 2.80 10.90 3.7 Lower (mean of 5 clones) 2.21 3.02 10.39 2.6 LSD0.05 0.55 NS NS 0.95 SOURCE: El-Sharkawy et al. (1998a). The higher shoot biomass of tall cultivars meant for mono- or intercropping. Current farming practices higher nutrient uptake and less nutrient-use efficiency use about 5000 and 10,000 plants/ha in intercropped in terms of root production. In contrast, the total plant and monocropped cassava, respectively. The more nutrient uptake in medium-statured and short cultivars rapidly the canopy closes during early growth, the less was 15% to 30% less (Table 3-14; El-Sharkawy et al. likely soils are prone to erosion. This breeding objective 1998a). Furthermore, short cultivars had 12% higher should be combined with greater leaf photosynthesis, leaf photosynthesis than tall ones (El-Sharkawy and de longer leaf life, and host-plant resistance or tolerance of Tafur 2010). These data support the strategy of pests and diseases (i.e., improved leaf retention; breeding and selecting for medium to short plant Figure 3-21; Lenis et al. 2006), particularly for architecture, which would be advantageous for higher developing improved germplasm targeted to seasonally efficiency in the use of both native soil nutrients and dry and semi-arid zones (Byrne et al. 1982; Cock and applied fertilizers, particularly if crop residues are not El-Sharkawy 1988a, 1988b; El-Sharkawy et al. 1990, recycled to the soil. 1992b; Hershey and Jennings 1992; El-Sharkawy 1993, 2004). Short cassava would be furthermore beneficial for both increasing productivity and reducing soil erosion The short cultivar M Col 2215 was selected in if it is planted at higher densities than normally used 1987–1989 for its high drought tolerance, high dry matter content in storage roots, and high PEPC activity in leaf extracts (El-Sharkawy et al. 1990, 2008). It was Table 3-14. Nutrient-use efficiency for root production at introduced to Ecuador and evaluated for several years 10 months after planting (kg dry root/kg total in the semi-arid western coast, where it yielded better nutrient uptake) for tall, medium-statured, or short than local varieties. Farmers participated in field trials cassava. Note the significantly higher nutrient-use and quickly accepted it, which led to its official release efficiency in both medium-statured and short clones, compared with the tall ones. The higher under the name ‘Portoviejo 650’ in 1992. values were mainly a result of both much smaller top biomass (and hence smaller nutrient uptake), as root Water uptake and use efficiency yields were comparable, regardless of plant heights (Table 3-13). The medium-statured and short clones with higher nutrient-use efficiency are advantageous Patterns of water uptake in various clones during for sustainable production in low-input production extended water stress imposed at different stages of systems and in low-fertility soils. Values are averages growth are shown in Figure 3-22. In all stress of 2 years (1994–1996). treatments, cassava withdrew more water from the Group of 5 cultivars Nutrient deep soil layer (at 2 m deep), after the upper layer was N P K Ca Mg almost depleted. Moreover, the water uptake from this Tall 110 715 132 347 589 deep layer increased as stress progressed, particularly in the terminal stress treatment, indicating deep Medium-statured 133 837 149 439 686 rooting behavior, as previously reported (Connor et al. Short 131 885 161 430 669 1981; El-Sharkawy and Cock 1987b; CIAT Reports 1991 LSD0.05 17 85 22 77 91 to 1994; El-Sharkawy et al. 1992b; de Tafur et al. SOURCE: El-Sharkawy et al. (1998a). 1997a; Cadavid et al. 1998). 68 Productivity, Photosynthesis, Ecophysiology, … (B) (A) 200 180 173 173 Total: 681 mm 160 Quixadá, Ceará, NE Brazil Altitude: 179 m; latitude: 4o 140 57’ S 120 100 98 98 80 60 52 40 40 20 18 17 3 1 1 7 0 Jan Feb Mar Apr May June July Aug Sep Oct Nov Dec Figure 3-21. Screening for drought tolerance for the semi-arid ecosystem at Quixadá, Ceará, Northeast Brazil. (A) Long-term (30 years) annual precipitation; 80% occurs over 4 months and the rest of the growing season is dry, with high air temperatures, high evapotranspiration, and high solar radiation. Soils are sandy, with low water-holding capacity, and very low in nutrients. (B) Cassava germplasm at 8 months, showing good leaf retention and sustainable canopy. Several clones were selected with high yield potential, tolerance of drought, low HCN, and tolerance of major pests and diseases. Yield was >12 t/ha fresh root at 12 months with a dry matter content of >25% that could be greatly enhanced with a second wet cycle. References: El-Sharkawy 1993; de Tafur et al. 1997b. Stress (days) 30 46 40 60 73 57 90 113 106 (A) (B) (C) 0 30 60 90 120 150 180 0.00 0.03 0.06 0.00 0.03 0.06 0.00 0.03 0.06 Water uptake (m3/m3) Water uptake (m3/m3) Water uptake (m3/m3) Figure 3-22. Patterns of water uptake by cassava (averages of four cultivars) during water deficits of differing lengths, Santander de Quilichao, Department of Cauca, Colombia. (A) Stress at 2 months after planting; (B) stress at 4 months after planting; and (C) stress at 6 months after planting. Note the greater water extraction from deeper soil layers that increased as water stress progressed over time, particularly in terminally stressed crops (C) (El- Sharkawy et al. 1992b; CIAT Report 1993; de Tafur et al. 1997a; El-Sharkawy 2006). By volume, the soil water available in the first 2 m capacity to conserve and deplete deep soil water slowly of soil ranges from 8% to 12% (Connor et al. 1981; over extended stress. For two cultivars (M Col 1684 and El-Sharkawy et al. 1992b). Hence, water uptake under its hybrid CM 507-37) subjected to a 3-month mid- any of these prolonged stress treatments would season water shortage, El-Sharkawy et al. (1992b) probably not exceed about 200 mm (i.e., the total reported that total water uptake, as estimated from available water at 2 m deep). This indicates cassava’s periodic sampling of soil cores at 2 m deep, was 69 Soil depth (cm) Precipitation (mm) Cassava in the Third Millennium: … around 100 and 160 mm during 35 and 96 days of much smaller than the values obtained in C3 species that stress, respectively. The latter value was equivalent to were grown in large weighable containers in a semi-arid 70%–75% of the plant-available water at a depth of 2 m climate almost a century ago by L.J. Briggs and in this soil, and much less than the rate of pan H.L. Shantz at Akron, Colorado, USA (Stanhill 1986). evaporation of about 4.4 mm/day at the trial site. The actual evapotranspiration ratio of cassava might In recent studies in Ghana, Oguntunde (2005) used have been even lower than the estimated values here, as the sap flow method to estimate daily cassava canopy dropped leaves may account for 2–6 t/ha (El-Sharkawy transpiration under prolonged natural stress, which he and Cock 1987b; El-Sharkawy et al. 1992b; Pellet and estimated as 0.8–1.2 mm. This is equivalent to 24% of El-Sharkawy 1997). In terms of economic yield, the potential evapotranspiration. El-Sharkawy et al. (1992b) estimated evapotranspiration ratio for cassava of about found that, over 43 days of peak canopy growth (117 to 500 in this trial is much less than the values for grain 160 days after planting), estimated crop water-use sorghum (868), proso millet (567), and maize (1405) efficiency values were 4.4–4.8 g/kg of water in stressed obtained in the Briggs and Shantz trials (Stanhill 1986). crops and 3.7–4.9 g/kg in unstressed crops (clone M Col If adjusted for moisture content in the grains of these 1684 and its hybrid CM 507-37, and using total oven- cereals, the values would be much greater than in dried biomass). cassava. These findings indicate cassava’s potentially high water-use efficiency and further strengthen its Because cassava has a long growth cycle and a low comparative advantage in water-limited zones. Under LAI during a significant portion of its growing season, non-limiting rainfall or with irrigation, however, cassava seasonal crop water-use efficiency is reduced. A cassava would be more efficient in terms of annual calories crop grown in a field lysimeter was estimated as having production per unit land area and water consumption a seasonal water-use efficiency of about 2.9 g total dry than most tropical C4 grain crops (El-Sharkawy 1993, biomass/kg water. This value compares favorably with 2004). the value found for grain sorghum (C4), which is about 3.1 g/kg, and is much higher than that found for field El-Sharkawy (2005) predicted that cassava bean (C3), which is about 1.7 g/kg (El-Sharkawy and productivity would probably be enhanced further by rises Cock 1986; El-Sharkawy 2004). Because cassava has a in atmospheric CO2 and temperature (i.e., as a result of higher HI (0.6–0.7), water-use efficiency in terms of global climate change), which should result in much economic yield would be even higher than for either higher water-use efficiency. This prediction was sorghum or field bean, which have lower HI values. corroborated by recent findings that leaf photosynthesis and root yield of field-grown cassava under elevated A large field trial on yield, involving 16 improved levels of CO2 in the tropics (i.e., 680 cm3/m3 in open-top cassava cultivars, was established in a seasonally dry chambers) had higher values than plants grown under zone (Patia Valley, Cauca, Colombia) that had less ambient CO2 (Fernández et al. 2002). These findings than 1000 mm of precipitation in 10 months. Average indicated an absence of photosynthetic down-regulation harvestable total dry biomass, excluding dropped leaves often observed in other plant species (Kramer 1981; and fine roots, was more than 30 t/ha (El-Sharkawy et Mooney et al. 1991; Pettersson and McDonald 1994; al. 1990). In this trial, the mean oven-dried root yield Webber et al. 1994; Woodrow 1994). ranged among cultivars from 15 to 27.4 t/ha, with an overall mean of 20 t/ha. About 60% of rainfall occurred The absence of photosynthetic down-regulation in in months 6 and 7 of the growth cycle, with perhaps cassava grown under elevated CO2 was apparently some water runoff and deep percolation into the clayey associated with the higher carboxylation efficiency of the soil occurring. C3 rubisco, despite reductions in soluble protein and N contents in leaves. Thus, higher nitrogen-use efficiency However, if we assume all rainfall to have been in terms of CO2 uptake is indicated. El-Sharkawy (2004) effectively used by the crops and lost only through reported significant positive correlations between dry evapotranspiration (i.e., through plant transpiration and root yield and photosynthetic N-use efficiency across a evaporation from exposed soils), then an wide range of field-grown cassava cultivars with no CO2 evapotranspiration ratio of 270–300 is obtained. This enrichment. (Photosynthetic N-use efficiency is defined ratio is water loss per unit of total dry matter produced. as CO2 uptake per unit of total leaf N, as measured in Such a ratio is comparable with values (excluding soil normal air and with high solar irradiance in upper- evaporation) observed in tropical C4 crop species such canopy leaves.) as maize, millet, sorghum, and sudangrass. It is also 70 Productivity, Photosynthesis, Ecophysiology, … Furthermore, soluble sugars and starch contents in Boyer (1996) reviewed and discussed advances in leaves of plants grown under elevated levels of CO2 drought tolerance in field crops and the possible were reduced. These findings suggest that higher mechanisms underlying enhanced crop water-use demands are made by strong sinks for assimilates, as efficiencies. Deep-rooting characteristics account for indicated by the concomitant increases in both shoot many differences in drought tolerance among species. biomass and storage root yield (Fernández et al. 2002). These inherent mechanisms may partly explain why Ziska et al. (1991) also reported 56% increases in leaf stressed cassava is still able to produce more photosynthesis of cassava plants grown for long adequately than cereals and grain-legume food crops. periods under elevated levels of CO2 under controlled They also further strengthen the relevance of the conditions (at 300 cm3/m3 more than ambient CO2), strategy to expand cassava cultivation into drought- indicating an absence of down-regulation. prone areas where severe food shortages may occur (Hershey and Jennings 1992; El-Sharkawy 1993, 2004; In contrast to the above findings, Gleadow et al. de Tafur et al. 1997a; Okogbenin et al. 2003). (2009) reported lower leaf photosynthetic rates in plants grown at higher than ambient CO2, particularly in Selecting for Tolerance of Low-Fertility those grown at the highest level. They also found Soils significant reductions in shoot and storage root biomass. However, we point out that the authors To alleviate pressures on natural resources, particularly studied potted cassava grown under greenhouse in marginal soils where most cassava is produced with conditions at different levels of CO2, that is, at 360, few or no inputs, selecting for tolerance of low-fertility 550, and 710 ppm CO2. Obviously, these findings soil is warranted (Hershey and Jennings 1992; indicated a feedback inhibition due to the rooting El-Sharkawy 1993, 2004). Potassium (K) and systems being confined by the growth media used. phosphorus (P) are the two most limiting nutrients, Cassava is a tropical shrub that requires large volumes mainly because harvested roots remove large quantities of soil. When grown under inappropriate conditions, it of K (>60%) and most acidic soils in the tropics have will not express either its leaf photosynthetic capacity low levels of P (Howeler 1985; CIAT Reports 1988 to or its potential productivity. Thus, as warned earlier in 1997; Howeler and Cadavid 1990; Pellet and the chapter, such findings are invalid and any resulting El-Sharkawy 1993a, 1993b, 1997; El-Sharkawy and conclusions must be questioned. In contrast, field Cadavid 2000; Howeler 2002). Large screening trials of research conducted in CIAT’s sunny, hot, humid, and cassava germplasm were conducted in low-fertility soils tropical environment, demonstrated cassava’s high at CIAT–Quilichao over 10 years to evaluate tolerance photosynthetic capacity and productivity. of low soil-P levels (CIAT Reports 1986 to 1996; Hershey and Jennings 1992; Pellet and El-Sharkawy These photosynthetic attributes, combined with a 1993a, 1993b; El-Sharkawy 2004) and, more recently, high optimal temperature for leaf photosynthesis for low K levels (CIAT Reports 1992 to 1996; El- (Figure 3-4) and elevated activity of the C4 PEPC in Sharkawy and Cadavid 2000). cassava leaves (Tables 3-7 to 3-10), may confer adaptive advantages for cassava growth and Table 3-15 presents data on yield and root dry productivity in a globally warming climate. matter content, with and without applied K fertilizer, for a group of the screened accessions. Low levels of K in In seasonally dry tropical ecosystems, excess rains these soils were indicated by the strong responses to K often recharge deeper soil layers. Cassava’s deep- applications of all clones tested. The average dry root rooting characteristics are of paramount importance, yield for accessions receiving K applications was particularly where the crop must endure several 10.3 t/ha. In contrast, yield for accessions not receiving months’ of prolonged drought. These characteristics, K fertilizer was 5.9 t/ha. Dry matter content was, combined with partial stomatal closure in response to respectively, 38.1% and 36.2%. However, genetic both soil and atmospheric water deficits; reduced leaf differences were wide for yield and for tolerance levels, canopy and light interception; and adequate leaf as estimated by the calculated low-K adaptation index photosynthesis make cassava a highly drought- (i.e., the product of yields at K levels relative to the resistant crop. overall mean in the trial). This pattern of conserved water use results in Two accessions (CM 2777-2 and CM 3372-4) had optimizing seasonal crop water-use efficiency high tolerance levels with an adaptation index that was (El-Sharkawy and Cock 1986; El-Sharkawy 2004). 50% higher than the overall mean index (1.0). They 71 Cassava in the Third Millennium: … Table 3-15. Dry root yield (t/ha), root dry matter (DM; %), and low-K adaptation index for 15 cassava clones grown at Santander de Quilichao, Colombia. Data are from the second cycle (1994/95). Clones with high adaptation indices are good genetic sources for selecting and breeding for tolerance of low soil-fertility (El-Sharkawy and Cadavid 2000). Clones Zero K 100 kg K/ha Low-K adaptation indexa Dry root Root DM Dry root Root DM CM 2777-2 7.9 31.8 13.3 35.8 1.73 HA CM 3372-4 7.8 38.9 12.8 40.8 1.64 CG 402-11 7.6 22.9 11.5 27.3 1.44 CG 1141-1 6.9 40.4 12.0 42.2 1.36 CG 165-7 6.2 35.2 12.1 37.8 1.23 IA CM 4777-2 5.6 40.5 13.4 42.1 1.23 CM 4729-4 7.5 39.9 9.8 38.8 1.21 CM 4574-7 5.7 35.9 9.8 36.9 0.92 LA CM 3311-3 6.0 38.6 9.2 37.5 0.91 SG 107-35 5.6 41.3 9.7 40.1 0.89 CM 5286-3 4.9 30.6 10.7 35.9 0.86 CM 2177-2 6.5 34.9 7.0 36.9 0.75 CM 3306-4 3.8 41.9 10.3 43.4 0.64 CM 2766-5 3.5 32.1 8.1 35.2 0.47 CM 3299-4 3.3 37.9 5.1 41.2 0.28 Mean of all clones 5.9 36.2 10.3 38.1 1.00 LSD0.05 1.8 3.7 2.5 2.6 a. (yield with zero K) (yield with 100 kg K/ha) Low-K adaptation index = (mean yield with zero K) (mean yield with 100 kg K/ha) Index of adaptation to low soil K: H = high; I = intermediate; L = low. SOURCE: CIAT Report (1995). therefore represent suitable genetic sources for Figure 3-23 presents data on yields, whether breeding improved germplasm. Pellet and El-Sharkawy with or without P application, of a group of (1997) identified clones that had high yields, whether 33 accessions. Some clones had high yields, with or with or without fertilizer, indicating that selecting these without P fertilizer, indicating high tolerance of low clones, instead of landraces or other varieties, for high soil-P, as shown by their enhanced low-P adaptation yield would not be detrimental to soil fertility. indices. Cassava relies on vesicular arbuscular El-Sharkawy and Cadavid (2000) also reported on the mycorrhizae (VAM) for P uptake (Howeler et al. existence of genetic variation in clones responding to K 1982; Howeler and Sieverding 1983). However, in a 5-year trial. These clones also showed high yield Pellet and El-Sharkawy (1993b) reported that potential, whether with or without K application, and cultivar differences in P uptake were related more to high K-use efficiency in terms of root production. differences in fine-root-length density than to VAM infection rates. Uptake efficiency (estimated as One clone (CM 507-37) had good levels of leaf uptake per unit root length) did not differ among retention and a deep fine-root system (El-Sharkawy cultivars. This finding again indicates the and Cock 1987b; El-Sharkawy et al. 1992b), indicating importance of the fine-root system in cassava the importance of these traits. Moreover, clone plant–soil relationships. CMC 40 (i.e., M Col 1468) showed the highest nutrient- use efficiency under extended water stress at different Furthermore, these authors concluded that growth stages. It had higher biomass and yield yield response to P was regulated by the balance (El-Sharkawy et al. 1998b; El-Sharkawy and Cadavid between the potential for shoot growth and for 2002), but low efficiency under wet conditions (Pellet storage roots. Adaptation to low-P could be and El-Sharkawy 1997; El-Sharkawy and Cadavid improved by selecting for high fine-root-length 2000), highlighting that the genotype × environment density, moderate shoot growth, and stable high HI. interaction is important in this case. This conclusion was further corroborated by 72 Productivity, Photosynthesis, Ecophysiology, … 45 2.0 40 1.8 35 1.6 1.4 30 1.2 25 1.0 20 0.8 15 0.6 10 0.4 5 0.2 0 0 = No P = 75 kg/ha P = Low-P adaptation index Figure 3-23. Screening cassava germplasm for tolerance of low-phosphorus soils. Note that some clones had good yield potential at low and high levels. More than 1600 accessions were screened, and clones selected for the breeding program. Low-P adaptation index was calculated as in Table 3-15. (CIAT Report 1992; El-Sharkawy 2006; Borrell 2010.) enhanced nutrient-use efficiency under stress through These findings indicate that selecting for and higher reductions in shoot biomass than in roots (i.e., assembling several desirable plant traits in one higher HI) and in terms of plant architecture genotype is possible. Complementary (medium-statured and short versus tall cultivars) multidisciplinary or, even better, multi-institutional (Table 3-12; El-Sharkawy et al. 1998a, 1998b; research is crucial in this case, as it would enhance El-Sharkawy and Cadavid 2002). research efficiency and the benefit-to-cost ratio (El-Sharkawy 2005). Moreover, in another group of accessions, low-P adaptation indices were correlated with standing Highlights and Conclusions shoot biomass at harvest (not including dropped leaves), number of harvested roots per plant, and The research reviewed here on cassava productivity, seasonal average, upper-canopy-leaf photosynthesis physiology and/or ecophysiology, and responses to (CIAT Report 1990; El-Sharkawy 2004). This finding environmental stresses was conducted in indicated the importance of both carbon assimilation collaboration with a multidisciplinary team at CIAT. source and capacity, and of root sink capacity in The Center also holds a diverse germplasm bank of selecting and breeding for tolerance of low-fertility the crop, which has been assembled over 40 years. soils. Notably, clone CM 489-1, with a high adaptation The research objectives revolved around the strategy index to low-P (Figure 3-23), had the following adopted for developing new technologies to enhance characteristics: high photosynthetic rate at different crop productivity in most of the edaphoclimatic zones levels of P; high efficiency in the use of nutrients and under which cassava is cultivated, particularly solar radiation (Pellet and El-Sharkawy 1993a, 1993b, stressful environments. 1997); high yields, with or without mid-season extended water deficits (Table 3-6; Figure 3-9; Under favorable environments in lowland and El-Sharkawy 1993); less reduction in leaf mid-altitude tropical zones with near-optimal climatic photosynthesis during water stress (Figure 3-17); and and edaphic conditions for the crop to realize its high PEPC activity in leaves under field conditions inherent potential, cassava is highly productive in that correlate with photosynthesis (El-Sharkawy terms of root yield and total biological biomass. For 2004). example, under trial conditions, improved germplasm 73 Fresh root yield (t/ha) CG 668-4 CMC 40 CM 5431-2 CG 1457-2 M Cub 32 M Col 1684 SM 328-1 CM 532-7 CG 913-4 CM 489-1 Avg of 33 clones P adaptation index Cassava in the Third Millennium: … can, after 10–12 months’ growth, attain >15 t/ha of Among these leaf traits is the elevated activity of the oven-dried roots, containing 85% starch. The C4 PEPC enzyme. Breeding programs could exploit physiological mechanisms underlying such high the genetic variations found within cassava potential productivity are: germplasm and wild Manihot for both leaf photosynthesis and enzyme activity. Leaf area 1. High leaf photosynthetic potential, duration under stress, together with host-plant comparable with those in efficient C4 crops resistance or tolerance of pests and diseases, is a (assuming the following conditions are critical trait because yield correlates with leaf common: high humidity, adequate soil retention capacity (Lenis et al. 2006). Deep rooting moisture, high leaf temperature, high solar capacity is another important trait for selecting and radiation, and a Pn rate that exceeds 40 µmol breeding improved germplasm for drier zones. CO2 per m2/s); In cooler zones such as higher altitudes in the 2. Long leaf life (>60 days), with the leaves tropics and lowland subtropics, cassava growth is remaining active for most of their life spans; slower and the crop stays in the ground for longer to achieve adequate yields. Under these conditions, leaf 3. Sustainable leaf canopy that optimizes light formation is slower, leaf photosynthesis is much interception during a significant portion of the reduced, but leaf life is longer (Irikura et al. 1979; growth cycle; and El-Sharkawy et al. 1992a, 1993). Wide genetic variations exist for photosynthesis that may be 4. High harvest index (>0.5), coupled with valuable for selecting and breeding for genotypes that strong root sink (i.e., larger number of storage better tolerate cool climates. Combining enhanced roots/plant). leaf photosynthesis with the normally longer leaf life in cool climates may improve productivity. Under stressful environments in seasonally dry and semi-arid tropics, productivity is reduced, with more Selecting for medium-statured and short cassava reduction in aboveground parts (shoots) than in instead of tall cassava is advantageous for saving on storage roots (i.e., higher HI). Under these conditions, nutrient uptake and ensuring higher nutrient-use the crop possesses some inherent adaptive efficiency for root production without sacrificing mechanisms for tolerance. The most important one is potential yield. Germplasm from the core collection the remarkable stomatal sensitivity to changes in was screened for tolerance of soils low in P and K, atmospheric humidity, as well as in soil water. By resulting in the identification of several accessions closing stomata under water stress, the leaf remains with good levels of tolerance. hydrated and photosynthetically active, although at reduced rates, over most of its life span. Results also point to the importance of field research versus greenhouse or growth-chamber Together with this “stress avoidance mechanism” is studies that do not calibrate for representative a capacity for deep rooting that enables the plant to environments to account for acclimation factors slowly extract water from as deep as 2 m. The crop (El-Sharkawy 2005). Calibration becomes even more therefore not only survives dry periods of up to critical when data from indoor-grown plants are used 3 months long, but also produces a reasonable yield to extrapolate to the field or to develop crop models. through its efficient use of water and nutrients. Moreover, leaf canopy is much reduced under Much remains to be done to further improve prolonged stress, contributing to lower crop water productivity while conserving dwindling natural consumption. When it recovers from stress, cassava resources such as water and land. Developing rapidly forms new leaves with higher photosynthetic countries, in particular, need more support to capacity, which compensates for yield reductions from continue with maintenance research, which aims to the previous prolonged stress. upgrade previous findings and technologies; contribute to sustainable agricultural, economic, and Productivity over a wide range of germplasm and in social developments; and enhance food supply to different environments correlates with upper canopy meet increasing demands. leaf photosynthesis, as measured in the field. The relationship stems mostly from non-stomatal factors, Basic research can be cost-effective, with high that is, from biochemical and anatomical leaf traits. returns, even if slower. 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Plant, Cell Environ 12:73–81. 88 Part B The Crop Chapter 4 Cassava Planting Materials Javier López1 Introduction Situation of Cassava “Seed” Cassava propagates vegetatively. this enables it to the timely availability of good quality planting materials form clones, where all plants of a variety are the constitutes a decisive factor for the dissemination and same, both externally and in root and foliage use of new cassava varieties. the lack of improved seed production. however, biotic (pests and diseases) and (i.e., planting stakes) is often a feature of crops of simple abiotic (climate and soil) environmental factors can asexual propagation, but is accentuated in cassava considerably modify individual plants, changing, for because of its biology, farmers’ socioeconomic status, example, their height, vigor, flowering, branching, and lack of organized seed-supply systems. root production, and starch and hydrocyanic acid (hCN)2 contents. One significant feature that the Biological aspects environment can affect is the quality of planting materials, degrading them, even to the point where a Cassava is one of the few crops whose planting materials, given variety may disappear. in themselves, have no economic value. In grain crops (e.g., maize and beans) and even in crops with vegetative Factors that can reduce yields of cassava plants propagation such as potato, yam, and sugarcane, include systemic diseases such as those caused by planting materials that are not used as seed still have viruses, bacteria, and phytoplasmas; low soil-fertility; value as food. even seeds, such as those of horticultural nutritional imbalances; and even moderate levels of crops, that have no other use, at least have the advantage soil salinity. these factors can also reduce the of occupying very little space, and the potential for being capacity of planting materials to express the conserved over prolonged periods under good storage genotypes’ respective yield potential. conditions. Cassava, in contrast, is planted for its roots, and stems that are not used as seed have no other the effect of such negative factors during several attribute of value. Cassava also has other characteristics vegetative propagation cycles of the cassava crop that hamper large or medium-scale seed production. can result in a cumulative reduction of quality in planting materials, leading to their gradual Low storage potential deterioration (Lozano et al. 1984). Introducing the use of good-quality planting stakes as part of the Cassava planting materials deteriorate during storage as package of “best” farming practices would permit stems dehydrate, reserves are lost through sprouting, the acquisition of healthy vigorous plantings, with and pests and other pathogens attack. the result is a yields that are close to the respective genotypes’ gradual reduction in the number of usable stakes, as the potential. storage period increases. to date, despite considerable research, no technology is available that solves these 1. Soil agronomist, formerly of Cassava program, CIat, Cali, problems. however, the potential for storage is known to Colombia. be a varietal characteristic. Some cultivars such as e-mail: ingjavierlopez@yahoo.es M Col 1468 (previously called CMC 40) can be stored for 2. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, Abbreviations, and Technical as long as 6 months, while others such as M Col 1684 Terminology, this volume. can deteriorate in as quickly as 2 or 3 weeks. 91 Cassava in the Third Millennium: … table 4-2. approximate weight and volume of seed of some Growth habit is related to such varietal differences. crops. For example, stems from non-branching or late- branching clones can be stored for longer periods than Crop Weight of Weight of Seed for 1 ha 100 stakes 100 seeds Weight Volume those from early branching clones. the nutritional (g) (g) (kg) (m3) status of the mother plants may also affect the stems’ Cassava 7000 700 2.00 storage potential. rice 2.4 150 0.26 Soybean 16 90 0.12 Low multiplication rate Bean 45 80 0.10 Maize 30 20 0.03 On the average, a mature cassava plant in good condition produces only 10 or so 20-cm-long commercial stakes. Cropping conditions can reduce Cultivation by small farmers this figure to 5 or even fewer stakes. this means that, from 1 ha, over 1 year, only enough stakes to plant Most cassava production is carried out by small 10 new hectares can be obtained. Such figures farmers, who use traditional production systems that represent a very low multiplication rate when compared result in low, but stable, yields. Cassava-growing areas with grain crops (table 4-1). Such a situation has the are characterized as having little infrastructure and following consequences: usually poor soils that are sometimes marginal for crop production. poor soil fertility leads to both reduced root 1. expanding the planted area rapidly is very production and poor quality planting materials, mainly difficult. because of insufficient nutritional reserves. Small farmers use intensive-labor agronomic practices, as 2. the costs incurred to produce 1 ha of crop for they possess few resources to exploit in their work. seed acquisition must be divided among a low number of stakes. Uncertain demand 3. the seed producer must dedicate a Cassava farmers habitually produce their own planting considerable amount of land to obtain planting materials as, cassava being a crop with vegetative materials (table 4-1). propagation, usually produces seed at the same time that the previous crop is harvested. Farmers who buy Weight and volume cassava seed either: the handling and transportation of cassava • are planting for the first time stakes are wasteful and expensive operations because • have stopped planting long enough so that no of the planting materials’ considerable weight and planting materials are conserved volume. a single cassava stake weighs the equivalent • Wish to change varieties of 230 maize seeds. planting materials for 1 ha • Wish to considerably increase the planting area (10,000 stakes) weigh about 0.7 t and occupy a volume of about 2 m3. hence, many farmers tend to use small the volume of sales of a cassava seed producer stakes. table 4-2 compares the weight and volume of depends on variations in the planted area, which, in its cassava seed with those of seed of four other species. turn, depends on how root prices are performing. table 4-1. Seed plot area needed to plant 100 ha and Stake Quality multiplication rates for cassava and four other crops. Crop area (ha) Multiplication ratec For seed to be a highly productive technological component, it must have quality. experience has Cassava 12.5a 10 demonstrated that good quality seed will give good Bean 6.7b 225 results in the field, whereas poor quality seed will lead Soybean 4.0b 600 to unsatisfactory results and failure. Quality is that set rice 2.5b 1600 of genetic, physiological, and health attributes that Maize 0.7b 22,500 enable stakes to give rise to productive plants. the a. Land occupied for 1 year. presence of high levels of these three essential b. Land occupied for 1 semester. components of quality indicates that seed is at its c. Number of stakes (or seeds) obtained from one stake (or seed over 1 year. maximum integrated quality. In contrast, weakness in 92 Cassava Planting Materials any component introduces a constraint. thus, perfect Physiological quality genotypes cannot express their true potential if their seed has physiologically deteriorated and shows poor the tangible result of physiological quality is the stake’s germination. ability to sprout and give rise to a vigorous plant. physiological quality involves seed nutrition, seed age, the qualitative attributes of a variety, generated and seed viability: by genetic improvement, will be transferred to the farmer only where its characteristics do not deteriorate Seed nutrition. the nutritional status of a stake is from one generation to the next through seed fundamental to the initiation of a new plant because, in multiplication. the 20 days following planting, the stake’s growth into a plant is exclusively at the expense of the reserves Genetic quality accumulated in the stem. three weeks after planting, with the appearance of the first leaves and roots, Genetic quality is produced through improvement. photosynthesis begins to contribute to plant growth, Crosses, selections, and regional trials are all used to which, however, continues to use the stake’s nutrient develop materials that contain a genetic program that reserves until day 40 (hunt et al. 1977). is appropriate for the conditions found in different agroecological areas. When the selected materials are Soil fertility markedly affects the growth of aerial crystallized into varieties acceptable to users, they are parts in cassava and, especially, the nutritional status then recommended for mass and commercial use. to of the stems used as planting materials. In low-fertility be useful to the agricultural community, mass soils, stem length and quality are diminished, but can quantities of stakes will be needed for each such be considerably improved through fertilizer variety. It is during multiplication that the need for applications. Such applications increase the level of maintaining genetic identity appears. nutrient reserves in the stems, thus improving their performance when used as planting materials. Genetic quality can be ensured by planting authentic seed, that is, when planting materials are Indeed, different levels of N, p, and K have been chosen from crops certified by entities such as the studied in plots planted with seed. results showed that Colombian Institute of agriculture (ICa, its Spanish both the concentration and contents of N, p, and K in acronym). Varietal mixes are avoided, and authenticity stems vary with levels of N, p, and K in the soil. thus, is maintained through preventive methodologies such cassava plants grown in a low-fertility soil produce as not planting immediately into land previously stems with low contents of N, p, and K. When that soil planted with different cassava varieties. Inspections are is given applications of high levels of fertilizers, the also carried out to rogue out atypical plants. resulting stems present high contents, not only of N, p, and K, but also of starch, reducing sugars, and total the genetic factors that most affect the seed sugars (table 4-3). When such stems are used as production of a cassava variety are general vigor and planting materials, the percentage of stakes branching habit. Vigor affects the total growth of a germinating is strongly influenced by K levels and the plant’s aerial parts and, as a result, the number of balance of K with N and p. branches from which stakes can be obtained. Branching habit influences the availability of primary table 4-3. Nutrient contents of stakes according to levels of and secondary stems, which are the parts most used fertilizer applied to the soil from which they were for planting materials. obtained (mg/stake). Nutrient Level of fertilizer application In general, vigorous varieties produce more stakes Low Intermediate high than non-vigorous ones. however, the greatest N 70 131 139 difference lies in the type of branching. Late-branching p 10 23 25 varieties have a larger proportion of primary and K 19 49 72 secondary stems than early branching genotypes. Starch 2620 3390 4290 hence, increased branching leads to more and heavier stakes. reducing sugars 330 460 500 total sugars 390 520 680 93 Cassava in the Third Millennium: … We point out that the stakes’ capacity for came from a stake with low nutrient contents (N0p0K0), germination is not affected by whether or not they are while that on the right came from a stake with high planted in a soil with fertilizer applications. What is nutrient contents (N2p2K2). Both stakes were planted in important are the stake’s levels of nutrient reserves. If an acid low-fertility soil with no fertilizer applications. stakes with high nutrient contents are used, then a thus, the difference between these two plants would be higher production of stems, suitable for use as planting exclusively in terms of the quantity of nutrient reserves materials, is possible. this is very important for seed the stakes had. production programs because of cassava’s low multiplication rate (table 4-4). hence, the photograph demonstrates that the use of stakes having good nutritional status will likely ensure In addition, an application of fertilizer to the seed that the variety’s true yield potential is reached. Such a plot, emphasizing K, will result in stakes that produce, low-cost technological component would enable farmers in their turn, denser foliage—a factor of special interest to increase cassava production, together with adequate for sustainable agriculture in hillside regions, where, by soil conservation. increasing soil cover, it reduces hydric erosion. What was described above is highly significant to Finally, the use of stakes with adequate nutrient seed production programs, particularly those directed contents will increase the total production of fresh towards regions with soils classified as acid and of low roots, mainly because roots will be larger and, to a fertility, namely Oxisols and Ultisols. Such soils are lesser extent, more numerous (table 4-4). found in the current or potential cassava-growing areas of Bolivia, Brazil, Colombia, and Venezuela. Figure 4-1 shows two plants of the same variety (M Col 1684) and age (12 months). the plant on the left Seed age. One cassava stake normally forms one to four shoots, which form the primary stems. the appearance of flowers produces branching in these table 4-4. effect of nutrient contents of stakes on the average primary stems, with the consequent formation of production of stems and roots, using cassava variety secondary, tertiary, and other stems, according to that M Col 1684. variety’s flowering and branching cycle. Consequently, Nutrient contents average production (fresh weight) the plant’s primary stems represent the oldest tissue, Stems roots while the secondary, tertiary, and more recent stems (kg/ha) (t/ha) represent the youngest tissues. Low 3252 16,260 Intermediate 3611 21,180 Increasing tissue age results in increased thickness high 4658 27,160 and lignification of the xylem, together with a proportional reduction of medullary tissue. When this process is sufficiently advanced, the stems are considered mature enough and suitable as seed, as the thickness and lignification provide them with sufficient nutrient reserves and resistance to dehydration. Indeed, any section of a stem from basal parts to the apical meristem can give rise to new plants. however, commercially, herbaceous parts are discarded because of their low dry matter content and high probability of becoming dehydrated in the field after planting. the rest of the stem, however, can be used as seed. Nevertheless, a direct relationship apparently exists between age of seed and the performance of the new plant. Most researchers believe that stakes taken from primary stems Figure 4-1. Differences between a plant developing from or basal parts give rise to plants with higher yields than well-nourished seed (at right) and that from poorly those developed from stakes taken from apical parts. nourished seed (at left), when both are grown in similar low-fertility soils that did not receive fertilizer applications, as indicated by the sign “SIN” (Spanish this difference in yields may be attributed to for “without”). differences in the stakes’ nutrient reserves, as their 94 Cassava Planting Materials chemical composition (N, p, K, Ca, and Mg) varies reflected in low yields. they also pose a risk when between different sections of the stem. Increases in introduced into areas free of such problems (Lozano yield, the older the stakes, may result from a higher et al. 1986). concentration of nutrients, mainly N and K, and a higher dry matter content (table 4-5) (enyi 1970). Diseases transmitted by stakes. Cassava can be hence, the highest total quantities of N, p, K, starch, attacked by several pathogens, either systemic or and fiber accumulates in the oldest parts of the stems. localized, that are transmitted through planting materials, reducing crop yields by: Seed viability. Stake viability is directly related to its moisture content. In a 10 to 12-month-old plant, • reducing sprouting in stakes stems have about 70% moisture. the stakes they • Killing stakes after sprouting produce will have a viability of almost 100%. Once the • reducing normal plant vigor stakes are cut, dehydration starts, and accelerates • reducing the number of bulked roots when they are stored in a place with high temperatures • permanently harboring potential inocula that and low relative humidity. the effect can be so severe attack future plantings that a reduction of 20% in moisture content can reduce sprouting of the seed by 50% (table 4-6). Systemic pathogens. these are capable of invading the entire plant. they usually do not produce a visual indicator for estimating moisture content symptoms in lignified and mature tissues, hindering and, thus, stake viability is the speed at which latex, a identification once the diseased material is cut. characteristic of euphorbias, flows from a recently cut Symptoms almost always develop in the leaf system, or stake. If it flows immediately, then the stake has unlignified young branches, or even in the root system sufficient moisture and, thus, good germination power. (Lozano and Jayasinghe [1983]). these plants as the stake becomes dehydrated, the latex appears constitute the source of primary inocula in new more slowly and its quantity is less. plantings. the systemic pathogens spread by planting materials include: Quality of plant health Fungi. the most important systemic fungal In seed production, health problems may arise, pathogen of cassava is Diplodia manihotis, which induced by pathogens (fungi, bacteria, phytoplasmas, produces brown necrotic streaks throughout the and viruses) and pests (insects and mites). these not affected vascular system. Other less important fungi only reduce the quantity of stakes that a plant can are Fusarium solani and F. oxysporum. Sphaceloma produce, but also reduce their quality, which is later manihoticola, causal agent of superelongation disease, although not properly systemic, produces a large quantity of spores in epidermal cankers on mature table 4-5. Dry weight of stakes, and root yield in cassava. stem tissues. the spores are so tiny that the pathogen Stake section Dry weight of stakes root yield is unidentifiable. their large numbers make them (g/stake) (kg/plant) appear systemic (Lozano and Jayasinghe [1983]). 1 (basal) 47.2 3.47 2 41.0 2.65 Bacteria. the most important bacterial disease 3 36.6 2.35 and one of the most serious for the crop is cassava 4 32.6 1.98 bacterial blight (CBB), caused by Xanthomonas 5 27.2 1.65 axonopodis pv. manihotis. the disease can cause 6 (apical) 24.2 1.80 economic losses of more than 50%. When cassava SOURCE: enyi (1970). stakes are infected with blight, germination losses may be more than 25%. this pathogen is restricted to the xylem tissues of the host’s immature stems, as the table 4-6. Influence of moisture loss on the viability of cassava bacterium cannot degrade the stem’s lignified tissues. stakes. It is therefore very difficult to detect this bacterium’s Moisture loss (%) reduction in shoots (%) presence in the lignified stems normally chosen for planting, particularly when they are already cut as seed. 10 10 20 50 however, the severity of the disease is considerably 60 100 reduced during dry periods. hence, during such 95 Cassava in the Third Millennium: … periods, visually selecting healthy planting materials pathogens. this apparent health must be confirmed from an infected crop is sometimes impossible. Its through crop inspections during climatic conditions capacity to disseminate through rain, insects, tools, that favor disease development. For example, from the and infested soil means that the pathogen can disperse middle until the end of the rainy season, symptoms of relatively quickly from a few diseased plants (Lozano superelongation disease, bacterial blight, and mosaics [1983]). caused by viruses are more noticeable than during dry periods. the most vigorous and healthiest plants in the phytoplasmas. Witches’ broom, caused by a crop should be identified before collection (Lozano and phytoplasma, has been found in Brazil, Mexico, the Jayasinghe [1983]). peruvian amazon, and Venezuela. although its incidence is not significant, the disease reduces yield in Pests transmitted through stakes. Damage infected plants by as much as 80% (Lozano [1983]). caused by insects attacking cassava planting materials includes reduced germination and plant establishment. Viruses. Leaf symptoms may occur in plants Dissemination of insect and mite eggs is more infected by viruses such as the african and american probable than that of larvae and adults, as the former common mosaics, leaf vein mosaic, and the Caribbean travel on the stem epidermis. Such a location makes mosaic. they can also cause symptoms in roots, such eggs relatively easy to detect. however, stemborers, as frogskin disease. Viroses also exist that, in some scale insects, and mite eggs are easily disseminated cultivars (carriers), do not show apparent visible through planting materials (Lozano [1983]). symptoms but gradually and slightly reduce the plants’ normal vigor and production. the risk of disseminating mites to other regions is higher when a severe outbreak occurs in one area and although healthy plants can be produced, testing seed is transported to another. the mite for their health is advisable, using laboratory Mononychellus tanajoa was possibly introduced into techniques such as serology, electronmicroscopy, and africa this way. Scale insects and mealybugs also hybridization of nucleic acids (Lozano and Jayasinghe spread this way. according to the degree of infestation, [1983]). these insects may reduce germination of stakes by 70%. the eggs and larvae of other insects, such as Localized pathogens. these pathogens’ invasive thrips, can also be found in buds on stems and capacity is not systemic, that is, they invade only branches, and are spread as infected stakes are limited areas or stem parts. their presence is transported (CIat 1987b). characterized by the formation of cankers, galls, and necrotic areas. Mites and insects that adhere to stems. this category of pathogens includes Erwinia Mites are probably the most serious pest of carotovora pv. carotovora (bacterial stem rot), which cassava. they frequently attack the crop during the dry causes degradation of the pith, which becomes season, and cause severe damage in most cassava- yellowish, reddish, or dark brown; Agrobacterium producing regions of the world. the principal species tumefaciens (bacterial stem gall), which produces galls are M. tanajoa (green mite), Tetranychus urticae (red in stem nodes; and Colletotrichum spp. (anthracnose) spider mite), and Oligonychus peruvianus. Mite and Phoma spp. (concentric-ring leaf spot), which infestations at the Centro Internacional de agricultura cause epidermal and cortical lesions (Lozano and tropical (CIat) include these three species and, Jayasinghe [1983]). Localized pathogens enter the experimentally, losses in yield have ranged from 20% to stem through wounds caused by mechanical means or 53%, depending on the duration of attack (Bellotti et al. insects, directly through stomata, or through petiole [1983]). invasion. attack from these pathogens usually decreases as the stem lignifies. Scale insects. Several species of scale insects have been identified as attacking cassava stems in almost all that part of the stem that is healthy can be used as cassava-producing regions of the world. the most planting material. Consequently, when selecting stakes, important are white scale Aonidomytilus albus, which care should be taken to discard those parts of the stem is spread worldwide, probably through planting affected by pathogens (CIat 1987b). as a guideline, materials; and Caribbean black scale Saissetia cassava planting materials should be collected from miranda. the most severe damage that these insects plantings that are apparently free of systemic cause appear to be loss of planting materials through 96 Cassava Planting Materials bud death. CIat studies of stakes heavily infected with Stake Production A. albus showed a 50% to 60% loss in germination (Bellotti and Schoonhoven 1978). A. Field phase thrips attack plants at their growing points, the principal objective of a multiplication plot is to reducing yield. For eight susceptible cassava varieties obtain the largest possible number of stakes per plant. in Colombia, average yield loss was 17.27% (Bellotti efforts must be made to avoid those factors or and Schoonhoven 1978). the production of planting circumstances that will reduce root yield of the plants materials can be reduced by as much as 57% (Lozano directly affected; or that will reduce the capacity of et al. 1986). the most important species is planting materials, derived from those plants, to Frankliniella williamsi. express the yield potential of the genotypes planted. Insects found within stems. the agronomic management of multiplication plots implies the use of all farming practices recommended Fruit fly. two species of fruit fly attack cassava in for obtaining high root yields, carrying them out at america: Anastrepha pickeli and A. manihoti. the minimal cost. hence, with sales of roots, sufficient larvae of this fly tunnels within the stems of cassava income would be acquired to cover production costs of plants, forming brown-colored galleries in the pith both roots and stakes. Usually, a profit margin remains area. a bacterial pathogen (Erwinia carotovora pv. that is significant for commercial seed producers and carotovora) is frequently found in association with fruit even for basic seed producers. to achieve these fly larvae, causing severe stem rot. this secondary rot objectives, the management of seed multiplication can reduce germination of stakes by as much as 16%, plots should incorporate the following causing reduced yields and loss of planting materials. recommendations: Yield of plants from damaged stakes are about 17% lower than that of plants from healthy materials Selection of land. the land for seed production (Bellotti and Schoonhoven 1978). should, ideally, be isolated from commercial cassava crops to prevent risk of contamination from insects Stemborers. planting materials can also suffer and, especially, pathogens. from stemborers, mainly larvae of Coleopteras such as Coleosternus spp. and Lagochirus spp., and of Land where cassava has been planted for lepidopterans such as Chilomima sp. that usually 3 consecutive years or more should not be used, as, cause sporadic or localized damage. Infestations may over the long run, with continuous planting, the land’s occur in growing plants, but also during storage of capacity to produce both planting materials and roots stems, requiring careful inspection of planting becomes notably reduced, regardless of soil fertility. materials before their use (Bellotti et al. [1983]). this is probably due to increased numbers of soil pathogens and to reduced numbers of beneficial termites. termites attack cassava, mainly in the microorganisms such as mycorrhizae. lowland tropics. they have been reported as a pest in various regions of the world, but mainly in africa. In For such land, the first recommended step is to Colombia, Coptotermes niger feeds on planting reduce the potential inocula load of pathogens present materials; roots; or growing plants with parts that have in the soil. Continuous cassava cropping can be dried up or become necrotic because of unfavorable interrupted by planting, for at least 2 years, crops such climatic conditions, pathogens, or poor quality seed. as sorghum and maize, whose pathogens are not usually pathogenic to cassava. Where forest crops are In studies conducted at CIat, termites destroyed felled, these gramineous crops should be planted for almost 50% of stored planting materials, and losses in 1 or 2 years before planting cassava. germination ranged between 25% and 30% (Bellotti and Schoonhoven 1978). On the Colombian Caribbean Soil salinity and stake quality. traditionally, a coast, termites attack stored stems, causing severe normal soil is considered as having an electrical loss of planting materials, and also reducing the conductivity of less than 4 dS/m and a sodium germination and establishment rates of stakes when saturation of less than 15%. however, cassava is these are planted with the insect inside. Stakes free of affected by much smaller levels. howeler (1981) points termites may also be attacked if a dry period comes out that the critical levels for this crop are a conductivity after planting. of 0.7 dS/m and a sodium saturation of 2.5%. 97 Cassava in the Third Millennium: … the performance of planting materials was studied seed with high contents planted in a soil with no in plots with moderate levels of salinity. Cultivar hCM-1 fertilizer applications could result in 53% more stems was planted in two types of soil: one with a conductivity suitable for use as planting materials. however, when of 0.5 dS/m and sodium saturation of 1.3%, and the such seed was planted on a soil that received fertilizer, other with a conductivity of 0.8 dS/m and saturation of the percentage was 100% (table 4-9). 3.0%. the plants in the plots with the higher level of sodium not only had smaller growth (thus reducing the Planting density. the cassava multiplication rate quantity of stakes produced—see table 4-7), but also, can be increased notably by increasing planting density when they were used as seed source for a new planting in seed plots. according to Villamayor Jr (1983), when in a normal soil, gave rise to plants with a smaller the number of plants per hectare is increased beyond production of both stakes and roots (table 4-7). the density normally used in commercial crops, each plant tends to maintain a stable number of primary Other desirable characteristics of land destined for stems. this permits a higher production of stakes, seed production are: even though they have a slightly smaller weight, as the 1. that they be owned: when land is rented and the completed contract is not extended, there is table 4-8. Influence of fertilizer applications (fertil.) on cassava a risk of having to dig up the cassava in advance stake production. and store the stems. hence, planting materials Cultivar No. of stakes/ average stake are lost in proportional to storage time. plant weight (g) No fertil. Fertil. No fertil. Fertil. 2. that they are distant from people and roads to M Mex 59 6.3 9.4 59 68 prevent theft of cassava by neighbors and M Ven 218 8.9 11.3 67 70 transients, with consequent loss of seed. M Col 63 4.9 6.7 46 54 M Col 22 5.2 6.2 58 60 3. that they are well fenced to prevent damage M Col 1684 4.2 8.4 53 63 from livestock, especially cattle and pigs. CM 91-3 4.9 4.4 46 63 SOURCE: Leihner (1986). Soil fertility. the seed plot should preferably be located in a soil of good natural fertility. Otherwise, a complete fertilizer application should be carried out, as table 4-9. Weight (kg/ha) of stems grown from seed with two soil fertility decisively influences both the amount and levels of nutrient contents, using cassava variety quality of the seed produced. In poor soils, the M Col 1684 grown in an acid low-fertility soil. production of planting materials is low, but increases in Nutrient contents Weight in soil with: both number and weight of stakes can be obtained by Fertilizer No fertilizer Difference applying fertilizers (table 4-8). high 6222 3095 3127 the study on seed nutrient contents mentioned Low 4487 2017 2470 above found that, compared with seed having low levels, Difference 1735 1078 table 4-7. Characteristics of stakes, and plants derived from those stakes, in two types of soil at the CIat–palmira experiment station, using cassava variety hCM-1 at 12 months old. Characteristic performance of: Stakes growing in soila plants derived from stakes growing in soila a B a B plant height (cm) 340.0 130.0 185.0 182.0 Weight of aerial parts (t/ha) 38.1 7.4 21.6 14.2 Seed produced (stakes/plant) 15.7 2.5 root production (t/ha) 35.9 29.1 Weight of seeds (t/ha) 8.7 1.3 Weight per stake (g) 55.5 51.0 a. Conductivity is 0.5 dS/m for soil a and 0.8 dS/m for soil B; sodium saturation is 1.3% for soil a and 3.0% for soil B. SOURCE: López (1990). 98 Cassava Planting Materials stems are slimmer. however, the yield of crops planted of a preemergent herbicide, complemented with one with these stakes is not affected. or two passes of manual weeding or applications of postemergent herbicides, should be sufficient to an increased planting density, however, reduces the maintain the crop free of weeds throughout its average root size. Under the conditions of Valle del growing period. the labor needed to apply Cauca, Colombia, the maximum production of preemergent herbicide, using a back fumigator, is commercial roots (i.e., of a size currently acceptable to reduced to 1 workday per hectare if planting density is the market) is achieved at 5000 plants per hectare in tall 1 × 1 m, a tK5 fan nozzle is used, a 2-m-wide path branching varieties, and at 10,000 plants per hectare in per pass is covered, and the herbicidal volume is erect varieties that are either short or tall (CIat 1975). 150 L/ha. Weed control. that weed competition reduces For manual weeding, the number of workdays yield is well known, not only for cassava but also for depends on the class of weeds, their height, and the other crops. It is also clear that ineffectual weed control tools used (machete, shovel, or hoe), but it can be will proportionally affect stake production. budgeted on an average of 15 workdays per hectare for each weeding. We point out that none of the a trial used different levels of weed control over the herbicides recommended for cassava, whether first 2 months of growth (CIat 1983). efficiency of preemergent or postemergent (including glyphosate), weed control, expressed in terms of different levels of damage the stakes, whether planted horizontally or competition between weeds and cassava, was reflected vertically, even when applied 8 days after planting. by the weight of aerial plant parts dropping as the percentage of control declined. the number of stakes Intercropping with maize. the practice of produced per plant was proportional to the weight of incorporating other species in a cassava crop usually aerial parts. reduces the production of both roots and aerial parts in direct proportion to competition from the other When weeds were not controlled, the growth of crops. It also reduces the average weight of stakes. aerial parts was reduced to such low levels that only one in three plants produced a stake of an acceptable at CIat, in 1989, an on-farm experiment was size and quality. In contrast, with no competition from carried out with five farmers located in different areas weeds, almost six stakes per plant were obtained over 2 years. to evaluate the influence of maize as an (table 4-10). hence, maintaining good weed control is intercrop on the quality of cassava planting materials, doubly of interest for optimizing stake and root stakes were taken from both a monoculture and an production. intercrop. these stakes were planted in the following season as a monoculture. Neither plant height nor Weed control is expensive, although costs vary branch or root production was affected by the origin considerably, with direct expenses ranging between 20% of the planting materials (table 4-11). and 50%. Costs depend on the class of weeds present, their size at planting, planting density, seed quality, and this finding demonstrated that the quality of rain distribution during the crop’s first months, among planting materials, whether obtained from cassava other factors. Under normal conditions, the application planted in monoculture or associated with maize, was not significantly different. although the intercrop led table 4-10. effect of competition with weeds on the production to a reduced number of stakes, this cropping system of cassava stakes. is currently used in many regions throughout the Control Weed control (%) Stakes/ Fresh weight system at 59 Dapa plant (t/ha) table 4-11. effect of intercropping with maize on cassava stake Branches roots quality.† Continuous 100 5.9 18.8 28.4 Origin of planting plant height Weight manual control material (m) (t/ha) preemergent 62 4.9 16.7 19.2 herbicideb Branches roots No weed control 0 0.3 2.6 3.5 Monoculture 1.79 a 8.20 a 17.32 a a. Dap = days after planting. Intercrop 1.73 a 8.00 a 16.56 a b. Diuron + alachlor at 1 kg and 2 L, respectively, per hectare. †. Values with the same letters in a column are not significantly SOURCE: CIat (1983). different. 99 Cassava in the Third Millennium: … 40 world and could also be used in the commercial production of cassava seed. thus, small artisanal 40 businesses could obtain seed from both cassava and maize. 40 40 Irrigation. Cassava has a reputation of being a hardy crop, resistant to drought. Indeed, when the dry 40 season begins, the plant reduces its production of new 40 leaves while continually dropping its old leaves. If the dry period becomes accentuated, more leaves fall, 40 decreasing leaf area to a minimum and growth 40 declines to an extent that the plant practically enters a period of latency. When the rains return, the plant uses 40 its carbohydrate reserves to produce leaves again and 0 30 60 90 120 150 180 210 240 270 300 thus resumes growth (Cock 1989). Dry period Days after planting Normally, cassava does not have critical periods in No dry period Dry period which the absence of rains may cause a total harvest loss. however, if drought is so prolonged that plants Figure 4-3. effect of a dry period on root production in cassava clone M Col 22 (adapted from Connor et al. 1981). die—as in the midyear dry periods of western Colombia—some varieties will drastically reduce the production of both roots and planting materials. For B. Harvest and postharvest phases example, a 10-week dry period, beginning 12 weeks after planting, when roots begin storing starch, caused Maturation and harvest. the quantity of seed that variety M Col 22 to reduce root production by almost can be produced at any given age is determined 30%, and branch and leaf production by almost 50% by genotype, climatic conditions (higher temperatures (Figures 4-2 and 4-3). lead to faster growth), soil fertility, weed control, and cropping system (competition from an intercrop as a result, although cassava has traditionally been delays the growth of aerial parts). however, regardless of cultivated exclusively with rainwater, its full yield circumstances, the number of usable stakes per plant is potential can only be reached if water management is very low, increasing only as tissues lignify. Under CIat included as a cultural practice. If irrigation is provided conditions (palmira), the number of stakes per plant in during dry periods, at a rate of 20 mm per week, root some varieties increases gradually, even after 12 months, yields will increase by almost 60% (Mohankumar et al. while in other varieties, after this age, the number begins 1984). to decline as excessive lignification covers buds, or the buds sprout (table 4-12). Storage. If a seed production plot completes 12 months of growth before harvest, the following could 16 be obtained: 14 12 10 • Fresh seed for the establishment of a new planting 8 • Maximum stake production 6 • Maximum root production 4 2 0 table 4-12. Seed production (stakes/plant) in cassava, according 0 30 60 90 120 150 180 210 240 270 300 to the age of the mother plant. planting density is 1 × 1 m. Dry period Cultivar Months after planting Days after planting 7 8 9 10 11 12 No dry period Dry period M Col 1468 4.6 6.5 10.8 11.1 11.5 11.0 Figure 4-2. effect of a dry period on the production of branches M Col 1505 5.9 6.1 6.5 7.1 8.6 10.5 and leaves in cassava clone M Col 22 (adapted from hMC-1 5.3 6.7 7.0 8.5 11.7 12.0 Connor et al. 1981). 100 Foliage production (t/ha) root production (t/ha) Cassava Planting Materials Given that maximizing income through sales of Storage of stems is facilitated when late- roots is recommended, then, to fix a reasonable price branching varieties are used. the long primary stems for stakes, the seed producer must decide on the best (about 1 m) are easy to manage (Figure 4-4), with time to harvest. early harvesting to take advantage of good yields when cut and facilitating the use of high root prices, whether varieties are early or late, motorized saws. they also store well. Figure 4-5 tends to result in low stake numbers per plant. that is, illustrates vertical storage in a semi-shaded place. the earlier the harvesting, the smaller the possible the stems are supported upright by a horizontal bar number of stakes—and the more immature the stems set at 60 cm from the ground. and the longer the storage needed. Before storage, soil should be scuffed and the problems that occur during storage are dampened so that each stem makes good contact dehydration, loss of reserves by sprouting, and attack with the soil. If, in the region, wood-eating insects by pests and pathogens. these problems gradually (e.g., termites) proliferate, an insecticide should be reduce the planting materials available, the longer the sprinkled over the soil. storage is. Currently, no technology is available that solves these problems. however, some principles help about 1 month after storage begins, apical buds reduce their negative effects: start to appear in all the stems, with foliage resuming growth. the stored stems shown in the center of • the branches to be stored should be cut to Figure 4-5 have just begun budding, whereas the lengths that are as long as possible. the longer stored branches at the right have been stored for a the storage period, the larger the portions that longer period and are presenting dense foliage. must be eliminated, because the extremes inevitably dry up, especially apical parts. the usable central parts thus become shorter. table 4-14. effect of chemical treatment on stored cassava hence, the more cuts a branch is stored as, the planting materials, using variety M Col 1684. smaller the central parts, representing the entire Days of storage Seed loss (%) branch, will be. No treatment With treatment • Storing branches vertically is preferable to horizontal storage, as fewer planting materials 30 34 23 will be lost and reductions in weight of usable 60 52 50 stakes will be smaller (table 4-13). 90 63 55 • Chemical treatment with an insecticide- SOURCE: Luna (1984). fungicide solution will, when storage conditions are unfavorable, help prevent deterioration of the seed (table 4-14). table 4-15. Influence of plant age on stored cassava branches • In some varieties, plant age at storage affects over 4 months. the proportion of usable planting materials Variety age at storage Seed loss (table 4-15). (months) (%) • Branches should be taken to the storage place M Col 22 8 31 as soon as the crop is harvested, as exposure to 18 8 the sun in the field reduces the seed’s capacity for storage (table 4-16). M Mex 11 8 4 18 2 table 4-13. Condition of cassava planting materials after 103 days of storage, North Coast region, Colombia, using variety M Col 2215. table 4-16. effect of direct solar exposure on cassava planting materials, using variety M Col 1505, and stored over Factor Before storage after storage 2 months. Vertical horizontal time of storage Seed loss Weight/branch (g) 340 307 240 (%) Stakes/branch (no.) 3.4 2.7 2.4 Immediately after harvest 10 Weight/stake (g) 76 63 54 8 days after harvest 23 101 Cassava in the Third Millennium: … Should a prolonged dry season occur, this foliage becomes dry and appears burned. this means that the stems must be irrigated every week. however, if the season becomes rainy, a warm microclimate of high relative humidity is created, favoring the development of diseases. hence, wide-spectrum fungicides should be applied. On terminating storage and cutting up the stems, apical extremes that have sprouted should be discarded. this is why stems should be stored vertically because, this way, only two or three apical buds sprout. In contrast, when stems are left in a slanting position, all the buds tend to sprout. thus, the entire branch is lost. an environment suitable for storing branches is one where the planting itself will be carried out, especially for late-branching varieties. In addition to the above-mentioned advantages, this type of branching enables workers to move within the crop without becoming entangled in the branches. hence, part of the crop is left without harvesting, and the branches to Figure 4-4. Late-branching variety, with long primary stems that be stored are taken into the crop’s interior and facilitate storage. arranged vertically, as previously described. In this case, the stored stems are supported by a cassava branch held horizontally by tying to plants that are still standing (Figures 4-6 and 4-7). Growing the crop on ridges will facilitate any eventual irrigation for the stored stems. Selecting planting materials. Because of its long growing cycle, cassava is continually subject to pressure from biotic (pests and diseases) and abiotic (climate and soil) factors. the quality of planting materials is thus reduced. traditional varieties have been under this type of pressure over considerable Figure 4-5. Storing cassava stems. Figure 4-6. Storing stems within the crop. 102 Cassava Planting Materials of stakes are also selected for their high root production, on the basis of the simple principle that plants with the highest yields should also be the healthiest (Lozano 1987). this type of selection has proven to be highly successful, and its advantage is more effective for clones that are susceptible to several production constraints (table 4-18) (CIat 1987a). Processing the seed. Cut. to cut the stakes, two aspects should be taken into account: length and age or stake’s location in the plant. Stake length is important in terms of the Figure 4-7. Detail of the way in which cassava stems should be number of nodes and the amount of nutrient reserves supported. and moisture they contain. Node number is closely related to variety, and age of both plant and stake. a mature plant has a larger number of nodes than a periods and its effect leads to a cumulative decrease in young plant. In addition, in mature plants, nodes in the quality of planting materials after many cycles of basal parts are shorter than in apical parts. vegetative propagation (Lozano et al. 1984). the effect of poor quality seed on production is unpredictable theoretically, obtaining a new plant would require but, sometimes, yields are reduced by much more than planting only a piece of stem that is barely large 50% (Lozano 1987). enough to contain a node. however, the possibility of such a short stake germinating and rooting under field hence, a positive selection of plants destined as conditions is remote because, to prevent dehydration, planting materials for seed plots is recommended. the soil must be continually kept moist for the first according to CIat (1987a), yields, especially of weeks after planting. In contrast, long stakes of 60 cm traditional varieties, may be increased only by using or more are highly likely to root and germinate. planting materials taken from vigorous and apparently however, their bulk presents difficulties for handling disease-free plants. this selection system is less and transport. Moreover, each mother plant would yield effective for new clones than for traditional ones a smaller number of stakes. (table 4-17). the influence that stake length has on yield has however, apparently healthy plants can be infected been a topic of research in several countries. results by latent viruses that do not show visible symptoms or show trends towards slightly increased yields with long by harmful endophytic fungi (Lozano and Laberry stakes, probably because they have a higher nutritional 1993). they may also have suffered disorders that are content, which permits a better starting growth in too recent to show symptoms. hence, in addition to plants and, thus, better bulking in roots. Most their external appearance, plants that serve as sources researchers believe that 20-cm stakes with at least five nodes would have sufficient nutrient reserves and an adequate number of buds to ensure good table 4-17. Yield (t/ha) of two traditional cassava clones and two establishment and crop yield. new hybrids, using visually selected stakes from the healthiest plants in a crop. Clone Visual selection No selection Selection table 4-18. Yield (t/ha) of three cassava varieties when seed was selected according to yield of mother plants. traditional Variety Yield of mother Increase M Col 22 18 24 plants (%) M Col 1438 9 13 Low high New CM 523-7 26 27 M Col 113 17.1 18.7 6 CM 342-170 21 23 M Col 22 33.9 38.9 17 M Col 1438 18.6 29.5 58 SOUrCe: CIat (1987a). 103 Cassava in the Third Millennium: … Stakes with fewer than five nodes have fewer • Eliminates mites and adhering insects. eggs bulked roots per plant and a smaller average weight and adults of mites and insects such as scales, than those from stakes with five or more nodes mealybugs (Phenacoccus sp.), and thrips can (table 4-19) (Gurnah 1974). be eliminated by immersing the stakes in a solution of an insecticide such as malathion Chemical treatment. the stakes, once planted, (CIat 1987b). may be attacked by insects and soil pathogens that usually affect buds first. they may also penetrate fine • Protects stakes from pathogens and insects roots, bases of shoots, extremes of the stakes, and in the planting site. table 4-20 illustrates wounds caused by handling. different treatments that can be given to stakes, including two that do not require chemical practices that help reduce risk of damage caused products. by disease pathogens and insects include selecting planting materials, avoiding those introduced from Differences in production attributed to selection regions where diseases or insects, transmissible by and stake treatment are more noticeable when stakes, are present; and applying chemical treatment. susceptible or infected clones are used than when the last acts in several ways: resistant clones are used. however, with the selection and treatment of stakes, beneficial effects sometimes • Eradicates pathogens that are present. cannot be seen, as in the following examples: Use of planting materials infected by Sphaceloma manihoticola (superelongation • When selecting and treating stems from disease) or Diplodia manihotis (dry rot) is vigorous plants growing in a region with no not recommended. however, where this is or only mild pathological or entomological absolutely necessary, those plants least affected problems. by superelongation should be chosen and treated with captafol or copper-based products. • When an incorrect product is used for For dry rot, stakes should be treated with treatment against a pathogen infecting the benomyl, which is a systemic fungicide. It is stake or infesting the soil where planting will also useful in the curative treatment of stakes take place. affected by Fusarium spp. and Scytalidium spp. (Lozano 1991). C. Production costs • Inactivates a present pathogen. When a production costs for a crop designed to produce planting material is not known to be free planting materials are much the same as those of bacterial blight, it should be treated with incurred to produce only roots. additional protection copper-based fungicides. the copper in these needs to be given to aerial parts to ensure that the fungicides exerts a bacteriostatic effect that seed is free of pests and pathogens. Disease control is inhibits the proliferation of the bacterium preventive, achieved almost exclusively through the use (Lozano 1991). of healthy seed and treatment with fungicides. In the field, additional costs include roguing contaminated plants and possibly applying insecticides to control table 4-19. effect of number of nodes in cassava stakes on insect vectors. yield and its components. Number Yield roots/ average root pest control, in contrast, requires habitual use of of nodes (t/ha) plant weight (kg) inputs, whether biological or chemical. the acquisition 2 5.10 3.45 0.12 of seed free of adults or eggs of insects and mites 3 6.10 3.80 0.14 implies the use of about an extra 10% more of inputs. 4 11.26 4.84 0.19 however, this category represents a very low (<5%) 5 13.71 5.49 0.20 proportion of production costs, so that to establish 6 13.73 5.29 0.21 adult cassava plants destined for seed production, 7 14.17 5.31 0.21 costs would be only slightly more than that of root 8 14.26 5.27 0.22 production. 104 Cassava Planting Materials table 4-20. treatment of cassava stakes before planting. problem product or method Dosage Soil pathogens Derosal + Orthocide® 6 cc + 6 g/L of watera root rots (Phytophthora spp.) ridomil® + Orthocide® 3 g/L + 3 g/Lb Bacterial blight (Xanthomonas campestris) Kocide® (a bacteriostatic copper fungicide) 3 g/La Dry rot (Diplodia manihotis) Benlate® + Orthocide® 3 g/L + 3 g/La Superelongation disease (Sphaceloma manihoticola) Difolatan® 6 g/Lc Insects and mites Malathion (or Sistemin®) 3 cc/L (3 cc/L)c Bacterial blight { thermotherapy: immersion of stakes root rots in water at 49 °C for 49 mind Insects and mites pathogens of the vascular system { Immersion in suspension of Trichoderma (Fusarium spp., Diplodia manihotis, (1 kg/bucket) for 10 mind and Phytophthora spp.) a. CIat (1987a). b. Álvarez et al. (1998). c. Lozano (1991). d. Álvarez (pers. comm.). If production costs of seed plants are defrayed by Cutting stems. Once having gathered the stems, selling the roots, seed production costs would be then these are cut into stakes 20 cm long. the number of represented in postharvest activities (table 4-21), with workdays varies with the method used, such as: the costs being smaller if the materials are cut and packed immediately after harvest, and higher if they • a worker, sustaining a stem in one hand and must be stored. In the latter case, the longer the cutting it with a machete in the other would storage, the higher the cost per stake, as increased obtain 3000 soft-stem stakes in 1 workday. stake deterioration leads to a higher proportion of waste. • a worker, using a machete, but supporting the stem on a log, would obtain up to although, in the field, the best plants can produce 8000 stakes per day. up to 12 stakes at 12 months (2.3 branches per plant and 5 to 6 stakes per branch), in practice, 1 hectare • an operator, using a circular saw activated by a planted at 1 × 1 m does not yield 120,000 stakes for 3-hp motor, can cut between 15,000 and the following reasons: 18,000 stakes per day, depending on the variety. those varieties that do not branch or 1. Most crops usually have some less developed branch late and have long stems yield more plants that have one or more branches that do stakes. not meet the conditions for use as seed. Packaging. Consistently packing the same 2. Waiting until plants are 12 months old before number of stakes in each sack is advisable, as this harvesting is neither practical nor profitable. measure helps control the number of cut stakes (total harvesting when plants are about 10 months and per workday), the number of stakes transported, old will give time to complete the harvest and and the number of stakes planted (total and per prepare the land for a new planting. workday). Commercially, 17,000 branches, that is, about 80,000 stakes, would be obtained from 1 ha the way stakes are packed depends on the (table 4-22). distance from the planting site. thus, seed traveling a short distance can be packed without taking too many Collecting stems. If workers do not have to travel precautions, but seed being transported to distant sites far, then, in 14 workdays, they can gather from 1 ha should be packed in an orderly way, as illustrated in about 16,000 stems as suitable seed. Figure 4-8. this method allows placing several bundles 105 Cassava in the Third Millennium: … table 4-21. estimate of direct production costs (in Colombian pesos) of cassava seed per hectare. Item Unit Quantity Unit cost total value Additional costs during cropping Insecticides Liter 1.5 24,000 36,000 application Workday 1.5 10,000 15,000 Subtotal $51,000 Postharvest costs 1. Collection of 16,000 branches Labor Workday 14 10,000 140,000 Subtotal $140,000 2. Treatment and storage Labor Workday 7 10,000 70,000 Benlate® Kilogram 0.5 86,000 43,000 Orthocide® Kilogram 0.5 14,000 7,000 Sistemin® Liter 0.5 24,000 12,000 Subtotal $132,000 3. Conditioning Cut 80,000 stakes Workday 16 10,000 160,000 treatment Workday 4 10,000 40,000 Benlate® Kilogram 1 86,000 86,000 Orthocide® Kilogram 1 14,000 14,000 Sistemin® Liter 1 24,000 24,000 Zinc sulfate Kilogram 6.5 2,000 13,000 polypropylene sacks Sack 160 500 80,000 Subtotal $417,000 Total 1: direct costs, including storage $740,000 Cost per stake 9.25 Total 2: direct costs, no storage $608,000 Cost per stake 7.60 table 4-22. production of cassava stakes in a commercial plot. Variety Branches Number of stakes per: per plant Branch hectare hMC-1 1.54 4.5 69,300 M Col 1468 1.47 4.5 66,100 M Col 1505 1.78 5.0 89,000 M Col 2215 1.60 4.5 72,000 CM 523-7 1.60 4.5 72,000 M Ven 77 1.61 5.5 88,500 of seed, one on top of the other, without causing physical damage to the stakes during loading, transport, and unloading. For 1 workday, about 20,000 stakes can be casually packed, and 10,000 in Figure 4-8. Cassava stakes should be packed in an orderly way, an orderly fashion. as seen in the sacks to the left. 106 Cassava Planting Materials Treating the stakes. the material with which the the organization and production technology of seed sacks are made influences the final cost of the stakes supply systems clearly must be adjusted to ensure because of the cost of the sack itself on the one hand, operation under the crop’s real conditions. In particular, and, on the other, the quantity of an aqueous cassava should not have imposed on it the formal solution of insecticides and fungicides (table 4-22) requirements that exist for other crops with long used to treat the stakes. although highly suitable for histories of seed development. packing stakes, sisal sacks are the least recommendable as they cost five times as much, and Cassava seed production clearly does not attract absorb almost 10 times more solution than large amounts of capital as does hybrid maize or rice. polypropylene sacks. thus, 10,000 cassava stakes, this means that thought must be given to creating placed in sisal sacks that are then soaked in solution, subsidized governmental programs to produce and require 35 L of solution for adequate treatment. Only distribute seed, or to developing sustainable systems 10 L of these actually treat the stakes, with the other for the circumstances of the cassava farmer. Special 25 L having soaked into the sacks themselves at a rate attention must be paid to the farmer’s socioeconomic of 1 L per sack. In contrast, 10,000 stakes in status, the biological nature of the crop and its seed, polypropylene sacks need less than 15 L for adequate and the limited availability of human, physical, and treatment. institutional resources in the targeted regions. Seed-Supply Systems Importance and characteristics Improved seeds are the biological input through which establishing a supply system of good quality stakes is new biogenetic technologies are incorporated into important because it will: production systems. Consequently, scarcity can seriously constrain the dissemination and use of new • Increase the crop’s productivity varieties. In contrast, availability where and when seed • reduce pest and disease dissemination is needed can decisively influence the adoption of • Increase the genotypes’ life cycle technologies and agricultural development. • permit more efficient use of agricultural inputs the development of organized seed-supply systems Furthermore, if farmers have good quality seed, where crops have unstable and atomized markets is an research projects in different fields (e.g., improvement, under-researched field and almost non-existent for entomology, and pathology) will have an improved crops such as cassava. at best, some research on chance of producing the desired technological and biological technologies is conducted on seed economic impact. production and conservation. however, little attention has been given to the development of those essential Overall, a seed program will determine the functions that (1) enable the implementation of an possibility of guaranteeing supply in a region by organized system and (2) accelerate the flow of genetic establishing technical procedures and an organization technologies from research to widespread use. that favors effective technology transfer with positive effects on cassava production. the following Compounding this situation are the facts that characteristics are desirable in a seed program: cassava is mostly grown by farmers of few resources, the crop has a year-long growing period, and its • ability to produce significant quantities of seed multiplication rate is very low at 5–10 stakes per planted that will permit rapid expansion of the cultivated stake. the supply system is predominantly traditional, area or of new varieties. that is, farmers save their seed, having no tradition of buying and selling seed. the seed’s bulkiness restricts • possession of an efficient quality control its movement between regions and communities. mechanism. the appearance of improved varieties and the • production of seed at a quality that is at least crop’s incorporation into new industrial markets equivalent to the best available source. constitute positive factors that will help generate interest for improved seed. however, given the • ability to sell seed at acceptable prices for characteristics of the crop and its production systems, users. 107 Cassava in the Third Millennium: … • production of seed through a self-sustaining but not for cassava stakes, which, because of organizational scheme. their great weight and volume, hamper handling and transportation. Furthermore, they • possession of efficient mechanisms to access cannot be stored over prolonged periods. new varieties, technical assistance, and training, among others. A proposed system Colombian case study Market conditions and the biological nature of this type of seed clearly suggest the need for an alternative to produce high quality cassava stakes that would production and distribution system. the proposed meet the category of certified, already established seed scheme is conceived as an organized system, in which companies should preferably be in charge. these are different participants carry out different but well organized to distribute, have quality control complementary functions and, together, pursue a systems, and can offer guarantees to produce high common objective: to ensure availability of good quality seed. In the absence of such companies, this quality seed at the right time and at a reasonable price. work could be commissioned to progressive farmers these functions, which should relate to each other as who have experience in seed production. links of a chain, are the generation of new varieties, production of basic seed, production and distribution hence, a document was prepared, which of commercial seed, and use of that seed by farmers. established the minimum requirements that cassava stakes of different categories (basic, certified, and Generating varieties. National and international selected) should have. production of this planting entities of research on plant breeding are responsible material was started. however, the scheme did not for generating varieties. research includes activities operate satisfactorily because: such as trials on adaptation to different agroecosystems, pest and disease resistance, yield, a. the price of cassava roots is not stable over and root quality. time. root prices depend on the area planted. Larger or smaller areas lead to higher or lower Producing basic seed. this task should be supply, thus changing the price. When the price carried out by national entities for research or seed is high and farmers see an increased production. Given the adaptation of varieties to specific profitability of the crop, the demand for stakes regions and the bulky and perishable nature of the increases and farmers are more willing to pay seed, such production should be regionalized. this for them. But when the price for roots is low, stage can be successfully carried out, using a revolving demand for seed is not so high, thus fund with sales of roots and stakes maintaining the discouraging farmers who may even opt to fund. the use of rapid propagation would be abandon the activity. recommendable only for this stage because of the high costs of producing this type of planting material. b. the farmer who purchases cassava stakes for the first time tries to continue to produce his or Producing commercial seed. Because a major her own seed where possible. Conventional aspect of seed production is continuity of offer, this seed producers prefer crops for which seed activity should be carried out by experienced cassava hybrids can be produced that farmers cannot farmers who grow cassava for the long term. Farmers multiply. thus, they maintain their clients who habitually produce crops other than cassava do “captive”. not guarantee continuity of seed supply, as, given the first difficulty such as reduced root price, they will c. the production of cassava planting materials change to another crop. is, for conventional seed producers, a totally foreign activity, as they cannot use their Long-term cassava farmers have, as their main current infrastructure of cleaning, economic purpose, root production. they would also conditioning, drying, storage, and other be able to produce seed, with technical assistance. activities. thus, in times of limited or no demand for seed, they would ensure their income through sales of roots until d. Seed companies centralize production to the seasons when demand for seed is high, which supply large areas. this is reasonable for grains would then constitute an important additional income. 108 Cassava Planting Materials to avoid the drawbacks of extensive crops in • the stakes are chemically treated by immersion terms of storing and transporting planting materials for 5 min in a solution of one or more fungicides and the harvesting and marketing of large quantities and including insecticides. of roots, production should not concentrate on a few producers to supply large areas. Instead, farmers • the stakes are planted in a horizontal position in should be strategically selected for their location in a substrate composed of sand and soil, placed the region to supply small neighboring areas. on a gravel base that provides good drainage. the substrate must be placed into beds that In areas with plant health problems and low- measure 2.3 × 1.2 × 0.2 m, surrounded by fertility soils, seed of traditional and improved varieties a narrow groove into which water is deposited can be multiplied, producing high-quality stakes in that, on evaporating, maintains high relative terms of health and nutritional contents. they will humidity. then perform better than the region’s usual seed. In those regions free of plant health problems and with • a roof of transparent plastic covers the container acceptable soil fertility, the greatest impact is and groove, being placed in such a way that achieved through new varieties, as the quality of it forms a propagation chamber. the high stakes from seed plots would be similar to that the temperature and high relative humidity stimulate farmers themselves produce. sprouting in the buds (Figure 4-9). Rapid propagation. Because cassava’s low • When they are 5–10 cm tall, the shoots are cut multiplication rate does not permit quick production at 1 cm above the neck, using a sharp blade that of an abundant quantity of stakes from new varieties has been disinfected with one of the products or from healthy stakes of traditional varieties, a mentioned above. each stake of two buds can methodology was implemented to help solve this provide about eight shoots, depending on the problem. although several variants have recently been variety and vigor of the stake. developed, rapid propagation of cassava stakes can be carried out through two basic systems: • From each shoot, leaves are cut off, leaving only those of the crown to prevent wilting. the little a. Shoot induction method. It consists of stem is cut exactly below a bud to stimulate inducing shoots and their later rooting from stakes rooting. Immediately afterwards, the shoots are carrying two nodes. adult plants are used, obtaining placed in a container of cold boiled water to stop about 100 stakes from late-branching varieties or latex from escaping (Figure 4-10). about 80 from early branching varieties. the two-noded stakes are planted in propagation • to encourage rooting, the shoots are passed chambers to produce shoots in quantities that to bottles containing water, which are then depend on the variety and type of stake used. thus, placed in a rooting chamber, comprising a table varieties with little vigor soon cease to produce carrying an aluminum or wooden structure that shoots, while others continue producing them even supports a plastic cover. after 1 year. On the average, a stake with two buds produces eight shoots a year, cutting every 20 days, in alternate form, a shoot from each bud. this means that, from one late-branching adult plant about 800 shoots can be obtained in 1 year. the procedure is as follows: • high-yielding, healthy, and mature plants of about 10 months old are selected from the field. • Stakes with two buds are cut, using a saw disinfected with sodium hypochlorite, formol, or alcohol. Figure 4-9. humid chamber. 109 Cassava in the Third Millennium: … Figure 4-10. Shoots in water for rooting. Figure 4-11. plants in plastic bags. • after 2 or 3 weeks, the shoots are ready for planting, either directly in the field or in plastic bags, where they acclimatize for their later transplanting (Figure 4-11). acclimatization should preferably be done in a screenhouse with a special mesh that prevents entry of insects such as whiteflies that carry viral diseases (Figure 4-12). One of two work modalities can be chosen. the first is continuous production of planting materials, where, every 3 weeks—the frequency of the cut— workers take to the field those shoots already acclimatized, in such a way that, by the 18th cut, Figure 4-12. Screenhouse with a special mesh to prevent the transmission of viruses by insect vectors. 1 year has been completed. the shoots of the first cut will have become adult plants. the final total would be 8000 stakes, 20 cm long, from each mother be done in January, in humid chambers, as, at this plant. time, the mother plants planted in the previous season will be 8 to 9 months old. planting in the chambers the second modality is the acquisition of shoots cannot be carried out any earlier because the mother over 9 weeks. If we take as an example planting in the plants will have little planting material. first semester (april–May), then the next planting must 110 Cassava Planting Materials On planting in January, the first cut is made in References February. If cuts are made every 20 days, then a total of four cuts of shoots would be ready for planting To save space, the acronym “CIAT” is used instead of before the rainy season ends. Under these conditions, “Centro Internaccional de Agricultura tropical”. about 300 shoots would be obtained and converted into plants and harvested all at the same time a year Álvarez e; Barragán MI; Madriñan r. 1998. pudrición later, producing about 3000 commercial stakes. radical y marchitez de la yuca. Information bulletin. CIat; Universidad Nacional de Colombia, Cali, b. Leaf-and-bud cuttings. although more Colombia. equipment is required than for the shoot acquisition system, its potential for propagation is much greater. Bellotti aC; Schoonhoven a van. 1978. plagas de la yuca that is, in 1½ years, about 60,000 stakes can be y su control. CIat, Cali, Colombia. 73 p. produced from a single mother plant. It consists of inducing the rooting of a bud that is removed, together Bellotti aC; reyes Q, Ja; arias V, B; Vargas h, O. with its corresponding leaf. the procedure is as follows: [1983]. Insectos y ácaros de la yuca y su control. In: Domínguez Ce, ed. Yuca: Investigación, producción • Well-developed leaves are cut from selected y utilización. CIat; United Nations Development 3 to 4-month-old plants, using a sharp programme (UNDp). Cali, Colombia. p 367–391. disinfected blade. the cut must include a small piece of stem. the folioles are also trimmed to CIat. 1975. Informe anual 1975. Cali, Colombia.54 p. less than half their length. CIat. 1983. Informe anual 1983. Cali, Colombia. • the cuttings are immediately placed in a container with cold boiled water to prevent latex CIat. 1987a. annual report 1986 [of the] Cassava from escaping. program. Cali, Colombia. • they are then taken to the rooting chamber, CIat. 1987b. Selección y preparación de estacas de yuca which consists of a metallic table provided with para siembra—Guía de estudio para ser usada como an aluminum structure that is itself covered complemento de la unidad audiotutorial sobre el with plastic. the chamber has two sides where mismo tema. Scientific contents: JC Lozano; the plastic can be opened like a curtain to place JC toro; a Castro; aC Bellotti. Cali, Colombia. 26 p. or remove materials and permit aeration. In the upper part of the structure, very fine sprinklers Cock Jh. 1989. La yuca, nuevo potencial para un cultivo are placed to continually mist the cuttings for tradicional. CIat, Cali, Colombia. 240 p. (Also 12 h per day. available in English as Cock JH. 1985. Cassava: new potential for a neglected crop. Westview Press, • the cuttings are planted in plastic or asbestos Boulder, CO, USA.) trays, containing a substrate of sterilized coarse sand. the trays are placed on the table. the Connor DJ; Cock Jh; parra G. 1981. response of cassava leaves are left at an angle, supported by wire to water shortage, 1: Growth and yield. Field Crops rows placed at 20 cm from the table’s surface. res 4(1):181–200. • Between 8 and 15 days, when the roots are enyi BaC. 1970. the effect of age on the establishment about 1 cm long and the petiole has detached, and yield of cassava sets (Manihot esculenta the shoots are ready for planting into plastic Crantz). Beitr trop Subtrop Landwirtsch bags for acclimatization over 3 weeks in a tropenveterinarmedizin 8(1):71–75. screenhouse. they are then taken to the field and in 5 months will become new mother Gurnah aM. 1974. effects of method of planting plants from which new leaf-and-bud cuttings and the length and types of cuttings on yield and may be obtained for propagation. some yield components of cassava grown in the forest zone of Ghana. Ghana J agric Sci 7(2):103–108. 111 Cassava in the Third Millennium: … howeler rh. 1981. Nutrición mineral y fertilización de la Lozano JC; Laberry r. 1993. hongos endófitos también yuca. CIat, Cali, Colombia. 55 p. en yuca. Bol Inf 17(2):5–6. hunt La; Wholey DW; Cock Jh. 1977. Growth physiology Lozano JC; pineda B; Jayasinghe V. 1984. effect of cassava. Field Crops abstr 30(2):77–91. of cutting quality on cassava performance. In: Symposium of the 4th International Society for Leihner De. 1986. physiological problems in the tropical root Crops. Centro Internacional de la papa production of the cassava planting material. In: Cock (CIp), Lima, peru. Jh, ed. Global workshop on root and tuber crops propagation—proc regional workshop held at CIat, Lozano JC; Bellotti aC; Vargas O. 1986. Sanitary Cali, Colombia, 1983. CIat, Cali, Colombia. p 57–72. problems in the production of cassava planting material. In: Cock Jh, ed. Global workshop on López J. 1990. producción comercial de semilla de yuca. root and tuber crops propagation—proc regional Seed Unit [of] CIat, Cali, Colombia. 33 p. workshop held at CIat, Cali, Colombia, 1983. CIat, Cali, Colombia. p 73–85. Lozano JC. [1983]. el peligro de introducir enfermedades y plagas de la yuca (Manihot esculenta Crantz) por Luna JM. 1984. Influencia de armazenamento de manivas medio de material vegetativo de propagación. In: de mandioca na produção de raizes e ramas. MSc Domínguez Ce, ed. Yuca: Investigación, producción thesis. escola Superior de agricultura de Lavras, y utilización. CIat; United Nations Development Lavras, MG, Brazil. 100 p. programme (UNDp), Cali, Colombia. p 475–484. Mohankumar B; Kabeerathumma S; Nair pG. 1984. Soil Lozano JC. 1987. alternativas para el control de fertility management of tuber crops. Indian Farming enfermedades en yuca—reunión de trabajo (spec issue) 33(12):35–37. sobre intercambio de germoplasma: cuarentena y mejoramiento de yuca y batata. CIat; Centro Villamayor Jr, FG. 1983. root and stake production of Internacional de la papa (CIp), Cali, Colombia. cassava at different populations and subsequent yield evaluation of stakes. philipp J Crop Sci 8(1):23–25. Lozano JC. 1991. Control integrado de enfermedades en yuca. Fitopatol Venez 4(2):30–36. Lozano JC; Jayasinghe U. [1983]. problemas fitopatológicos en la yuca diseminados por semilla sexual y asexual. In: Domínguez Ce, ed. Yuca: Investigación, producción y utilización. CIat; United Nations Development programme (UNDp), Cali, Colombia. p 485–490. 112 CHAPTER 5 Soils and Fertilizers for the Cassava Crop Luis Fernando Cadavid L.1 Introduction Water (25%) Soil is usually studied as an “entity” in which the plants grow and develop. Yet, it should be considered as a dynamic system from the viewpoint of fertility Mineral matter and productivity. When considering crop nutrition, (45%) specifically cassava (Manihot esculenta Crantz), the relationships between soil, plant, and water should be taken into account and not only each factor separately. That is, the three factors should be studied as a whole. Another important aspect of plant nutrition is the Air (25%) subject of fertilizer application as a management practice for recovering, sustaining, and maintaining soil Organic matter (5%) fertility and increasing crop productivity. Overall, considerable ignorance exists on the adequate Figure 5-1. A soil’s ideal volumetric condition for plant growth. interpretation of the chemical and physical analyses of soil that form the basic diagnosis tools for Logic supposes that this condition is not met and recommending chemical or organic fertilizers. that soils present a real condition, which determines their potential for production. To better understand this A principal objective of this chapter is to bring point, we use two examples: a sandy soil located in readers up to date on concepts relating to nutrition of Pivijay, Magdalena, Colombia, and another, clay, soil the cassava crop, basic aspects of soil, and how to located in Santander de Quilichao, Cauca, also in make correct recommendations for fertilizers as a soil Colombia (Figures 5-2 and 5-3). management practice. These soils were continuously planted to cassava for Soil and Its Productivity 8 and 2 years, respectively. As observed, the volumetric percentage in each case is different, requiring different Traditional definition management (Cadavid L 2000). Soil is a dynamic system that is usually composed of A sandy soil has a higher percentage of macropores, four phases: solid, liquid, gaseous, and biological. more aeration, less water retention, less organic matter Figure 5-1 shows the ideal volumetric conditions of a content and, thus, less N availability. In contrast, the clay soil for normal plant growth. soil has a higher number of micropores, less aeration, higher water retention, more organic matter content and, as a result, a higher cation exchange capacity (CEC)2. 1. Soil Agronomist, formerly of Cassava Production Systems, 2. For an explanation of this and other abbreviations and acronyms, see CLAYUCA, Cali, Colombia. Appendix 1: Acronyms, Abbreviations, and Technical Terminology, E-mail: luisfernandocadavidlopez@yahoo.es this volume. 113 Cassava in the Third Millennium: … Real condition Ideal condition Water (4.4%) Water (25%) Air (29.1%) Mineral matter (45%) Mineral matter (65.5%) Organic matter Air (1%) (25%) Organic matter (5%) Figure 5-2. Comparing the ideal soil condition with the reality of a sandy soil in Pivijay, Magdalena, Colombia, planted to cassava over 8 consecutive years. Real condition Ideal condition Water (25%) Water Mineral (39.0%) matter Mineral matter (45%) (42.9%) Air (25%) Air Organic Organic matter (12.5%) (5%) matter (5.7%) Figure 5-3. Comparing the ideal soil condition with the reality of a clay soil in Santander de Quilichao, Cauca, Colombia, planted to cassava over 2 consecutive years. Agricultural definition • Solid phase • Liquid phase (soil solution) For agricultural purposes, soil should be studied from • Exchange phase two viewpoints: fertility per se and productivity. To • Root phase understand soil productivity, the soil–plant–water • Aerial parts phase (foliage) relationship must be studied. In these terms, soil is a dynamic system formed by five well-defined phases Figure 5-4 shows the nutrient dynamics in the that interact with each other (Guerrero 1980, cited by soil–plant system. The topics treated below are Cadavid L 1995): considered basic to the mineral nutrition of the cassava crop. 114 Soils and Fertilizers for the Cassava Crop Aerial parts Translocation Redistribution N (solid phase) Solubilization Organic and N (liquid phase) Parental Mineralization Adsorption mineral, and H2O + salts N (root phase) material primary and (free ions) secondary compounds Fixation Recycling Immobilization Leaching Artificial resupply: N (exchange phase) Management Soil colloids: clay, humus (ion adsorption) Mineral fertilizer applications Green manures, harvest residues, Artificial resupply: rotations, manures, organic solids mulchs, etc. Eruptions Artificial resupply: Floods mineral solids Figure 5-4. Components of the soil–plant system and the dynamics of nutrients (adapted from Guerrero 1980). Soil solid phase. Its basic component comprises contributes to the soil nutrients (free ions) that can the parental materials made up of different rocks easily be taken up by plants. When this happens, the (igneous, sedimentary, and metamorphic). These, soil enters phase two (liquid phase) (Cadavid L 2000). through weathering, contribute organic and inorganic solid matter to form soils. This matter is, in itself, Soil liquid (soil solution) phase. This is made up insoluble. Plants cannot receive nutrients from it until it of elements (free ions + water) contributed by the soil undergoes physical, chemical, and biological solid phase, through solubilization and mineralization. transformation. This stage, which nourishes the plant, in its turn, becomes exhausted very rapidly. Many of these Solid matter undergoes solubilization (inorganic nutrients are easily lost through leaching (e.g., Ca, Mg, solids) and mineralization (organic solids). As a result, it K, and NO3). 115 Ionic exchange Cassava in the Third Millennium: … Other losses (irreversible) also occur through Ionic exchange is a phenomenon based on the fixation and immobilization. Fixation occurs when soil presence of negative charges in clays and other soil nutrients, especially N, P, and K, become part of colloids (Cassanova O 1996). Through these insoluble compounds and therefore difficult for plants charges, ions are released from minerals previously to assimilate. Radicals such as NH + 4 , H - 2PO + 4 , and K subjected to weathering, or from decaying organic remain lost from this phase through this process. compounds, rainwater, irrigation water, and When this happens with the participation of soil fertilizers. The ions can be adsorbed by soil microorganisms (e.g., fungi, bacteria, and particulates and, under these conditions, they are actinomycetes), organic matter becomes immobilized partially retained. However, such retention is and the contribution of nutrients such as N, P, and S is sometimes not sufficient to prevent ions from being reduced. either exchanged with other ions in the soil solution or adsorbed by the plant’s root system. According to As this phase becomes exhausted through the Thompson (1965), Garavito (1979), and Cassanova losses previously described, uptake of nutrients by O (1996), those ions weakly held on the surfaces of plants, and erosion, nutritional resupply occurs through particulates in direct contact with soil solution can ionic exchange in the soil exchange phase (Guerrero be rapidly replaced in exchange reactions. These 1980; Cadavid L 2000). ions are called exchangeable. Soil exchange phase. This phase is made up of Other ions can be adsorbed with such tenacity clays, organic matter, and Fe and Al oxides and or be located in barely accessible positions that their hydroxides (soil colloids), the constituents of which are release or release is either hindered or it is very slow. minerals and organic solids in the soil. These colloids These ions are called non-exchangeable. Potassium are responsible for chemical activity in soils. Hence, is an example of this situation, when it is held this phase is in continuous interaction with the liquid between laminas in the crystalline structure of illite phase through ionic exchange in the soil. It restores and micas. Figure 5-5 illustrates the attraction of nutrients exhausted in the liquid phase by the cations (+) for soil colloids (-). previously cited processes. Exchange phase Liquid phase H - 2PO4 H+ Clay NO C1- - Ca++ 3 Ca++ K+ CO2 Al+++ H+ Anions Ca++ SO = K+ Ionic exchange 4 Mg++ HCO - Mg++ Cations 3 H2BO - Al+++ 3 Na+ H PO - NH + 2 4 4 K+ NH + 4 K+ Humus Ca++ Root phase Adsorption Fixed ions Leached ions Translocation Figure 5-5. Exchange, liquid, and root phases of the soil, showing the dynamics of different ions. 116 Soils and Fertilizers for the Cassava Crop The strength with which cations can be retained in In practical terms, a plant can very capably adsorb exchange sites is as follows (Cassanova O 1996): those elements necessary for its metabolism, even from relatively low concentrations in the soil. What is Al+3 > Ca+2 = Mg+2 > K = NH + 4 > Na+ important is that this element is always present in the liquid phase that surrounds the roots (Calderón 1991). The CEC of a soil is defined as the quantity of Adsorption depends on several factors (Malavolta et al. cations retained in an exchangeable form within a 1989; Calderón 1991; INPOFOS 1993), including: given pH and is expressed in meq/100 g of soil (cmol/kg). Table 5-1 outlines data on the CEC of • Availability of the element different soil components (meq/100 g of matter), as • Soil moisture according to Cassanova O (1996). • Aeration • Organic matter content From these data a soil’s exchange matter can be • pH deduced through its CEC. For example, if a soil has a CEC of 10 meq/100 g of soil, then kaolinite probably Soil pH and availability. Soil pH has a major, direct forms the predominant part of that soil’s clay fraction, influence on the solubility and availability of elements that is, clay 1:1, with little activity. in the soil. When any symptom is observed in the field, the pH of the soil in which the plant is growing should Root phase. be measured. Often, this factor is closely related to the causes of the symptom. Cadavid L (1980) reported P Adsorption. Soil nutrients are continually removed deficiency and low crop yields for cassava grown in by the growing plant through adsorption. This is the Colombian Oxisols, Ultisols, and Inceptisols (soils with process by which the element N leaves the substratum pH < 4.5), where the content of usable P (method Bray (nourishing solution), reaches a part of any root cell, II) is < 3.0 ppm (for cassava, the critical level is and is then transported by xylem to other plant organs 10 ppm). This is a clear example of low availability of an (Malavolta et al. 1989). Nitrogen is an element that element being related to soil pH (Table 5-2). may be: Usually, adsorption is more intense in the 6.0 to • Essential, that is, the plant cannot complete its 6.5 band of pH. At higher acidity (very low pH values), normal life cycle in the nutrient’s absence the availability of N, P, K, Ca, Mg, S, B, and Mo (Garcidueñas 1993). diminishes, whereas that of Cu, Fe, Mn, and Al increases. At high pH values (alkalinity), the availability • Beneficial: It increases growth or production of P, B, Cu, Fe, Mn, Zn, and Al diminishes, whereas under given conditions. that of Mo, S, and K increases (Figure 5-6). • Toxic, by diminishing growth or production, or Chemical fertilizer applications (especially of even causing death of tissues, organs, or the nitrogenous fertilizers such as ammonium sulfate), entire plant. leaching of bases, carbonic acid excretion by plants, and high nutrient extraction (especially N, K, Ca, and Mg) contribute to soil acidification. An example of this situation was presented in a sandy soil of Pivijay, Table 5-1. Cation exchange capacity (CEC) of different soil Magdalena, Colombia, which had been planted to components. cassava for 8 consecutive years (Table 5-3). Exchange material CEC (meq/100 g) Average Range Other external factors that affect adsorption are Organic matter 200 100–300 aeration, soil temperature, speed of element adsorption, and presence of other ions. Vermiculite 150 100–150 Montmorillonite 80 60–100 Presence of other ions. As stated earlier, soil Chlorite 30 20–40 solution consists of a heterogeneous mixture of ions Illite 30 20–40 that includes essential, beneficial, or toxic elements. Kaolinite 8 2–16 The speed of absorption of an element (anions: Sesquioxides 0–3 0–3 NO - > Cl- > SO -2 4 > H2PO - 4 ; cations: NH4+ > K+ > SOURCE: Cassanova O (1996). 3 Na+ > Mg+2 > Ca+2) can be increased, reduced, or 117 Cassava in the Third Millennium: … Table 5-2. Effect of applications of phosphorus, according to sources of differing pH, on cassava yield (t/ha) at 12 months old, Carimagua, Colombian Eastern Plains, in soils with pH below 4.5 and P less than 3 ppm. Source Yielda (kg/ha) at the level of P2O5 of: 0 50 100 200 400 Xn (kg/ha) Check 6.5 — — — — 6.5 Triple superphosphate, applied in bands — 13.9 19.8 18.4 22.3 19.9 Simple superphosphate, applied in bands — 10.8 13.7 19.0 22.2 16.4 Mg phosphate, broadcast in bands — 8.2 13.1 11.2 13.7 11.6 Basic slag (Thomas), applied in bands — 10.9 10.9 11.9 13.8 11.9 Basic slag (Thomas), broadcast — 16.1 19.8 20.9 25.2 20.5 Phosphoric rock (PR) (Huila) at 20% acidulated, broadcast — 14.4 18.4 19.6 22.5 18.7 PR (Huila) + S, broadcast — 15.7 19.7 21.6 21.8 19.7 PR (Huila), broadcast — 13.0 17.4 18.9 19.6 17.2 Average of treatments 6.5 12.9 16.6 18.4 20.1 a. Average of two checks. SOURCE: Cadavid L (1980). K S Mo N Ca Mg Cu Zn MMnn P B Fe Al pH 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 Figure 5-6. Availability of different nutrients in the soil with respect to pH. 118 Soils and Fertilizers for the Cassava Crop Table 5-3. Monitoring of a sandy soil in Pivijay, Magdalena, 250 Colombia, planted continuously over 8 years to cassava and with no chemical or organic fertilizer applications. 200 Year pH P (ppm) K Ca Mg Fertility 150 (meq/100 g soil) 1 6.50 8.38 0.05 0.87 0.28 Low 100 2 5.60 7.10 0.03 0.65 0.20 50 3 5.30 4.70 0.04 0.55 0.13 4 5.30 5.70 0.03 0.48 0.12 0 5 5.30 6.35 0.04 0.43 0.11 0 1 2 3 4 5 6 Lime application (t/ha) 6 5.35 8.25 0.04 0.34 0.07 7 4.85 7.65 0.05 0.35 0.09 N–P–K + Zn N–P–K 8 4.15 5.18 0.03 0.32 0.09 Very low Figure 5-7. Effect of lime applications on Zn content in cassava SOURCE: Cadavid L (2000). leaves at 2 months, with or without applications of Zn to soil, Carimagua, Eastern Plains, Colombia (from Cadavid L et al. 1977). otherwise influenced by the presence of another. These influences are commonly called relationships of antagonism, inhibition, and synergism: Table 5-4. Effect of ions on each other in soil solution phase. Ion Second ion Effect of the second • Antagonism: The presence of an element presenta on the firstb reduces the adsorption of another, thus Cu2+ Ca2+ Antagonism preventing toxicity. For example, Ca+2 impedes Mg2+, Ca2+ K+ Competitive inhibition excess adsorption of Cu+2 or Al+3. H2PO – 4 Al3+ Non-competitive inhibition K+, Ca2+, Mg2+ Al3+ Competitive inhibition • Inhibition: Reduced adsorption of an element H2BO3 NO – 3 , NH + 4 Non-competitive inhibition induced by the presence of another ion, K+ Ca2+ (hc) Competitive inhibition usually causing deficiency. For example, K+ SO 2– 4 SeO 2– 4 Competitive inhibition versus Ca+2 or Mg+2; Al+3 versus H2PO - 4 ; Al+3 MoO 2– 4 Cl– Competitive inhibition versus Ca+2 or Mg+2; H2PO - 4 versus Zn+2; Ca+2 Zn2+ SO 2– 4 Competitive inhibition versus K+ (in high concentration); and Ca+2 Zn2+ Mg2+ Competitive inhibition versus Zn+2. Cadavid L et al. (1977) reported Zn2+ Ca2+ Competitive inhibition an example of this situation in the soils of the Fe2+ H2BO3 Non-competitive inhibition Eastern Plains of Colombia (Oxisols; Figure 5-7). Zn2+ Mn2+ Competitive inhibition K+ H – 2PO4 Non-competitive inhibition • Synergism: The presence of a given element MoO 2– Ca2+ 4 (lc) Synergism increases the adsorption of another. For MoO 2– H 2– 4 2PO4 Synergism example, Ca+2 in low concentrations increases Cu2+ MoO 2– 4 Non-competitive inhibition absorption of K+ or of H - 2PO ; Mg+2 4 versus a. hc = high concentration; lc = low concentration. H2PO - 4 ; and H2PO - 4 versus MoO -2 4 . This b. See text for explanation of terms. circumstance may have practical SOURCE: Malavolta et al. (1989). consequences in fertilizer application, as it represents a greater economy and better use of mineral fertilizers. certain soil fungi. The plant receives nutrients through the mycelia of the fungus and this, in turn, receives For cassava grown in acid-soil Oxisols, an carbohydrates from the plant (Cano 1999; Sánchez de application of 500 to 1000 kg/ha of dolomitic lime may P 1999). Plants that have been inoculated with increase P availability and its adsorption, because of the mycorrhizae, in this case, cassava, possess an presence of Mg+2 and Ca+2 ions. Table 5-4 shows increased adsorption surface, adsorbing, in particular, examples of the effect between ions. P ions from the soil when concentrations of this element are low. Tables 5-5 and 5-6 show the action of Presence of mycorrhizae. Mutualistic symbiotic vesicular-arbuscular mycorrhizae (VAM) in soils of Cuba associations exist among the roots of many plants and and Colombia (Sieverding 1984; INIVIT 1999). 119 Zn in leaves (ppm) Cassava in the Third Millennium: … Table 5-5. Combined effect of mycorrhizae and N–P–K fertilizer cycle, sufficient N, P, K, Cu, Fe, and B; whereas Ca, on the production of cassava clone ‘Señorita’ under Mg, S, Mn, and Zn accumulated mainly in the stems. field conditions, Cuba. The authors also found that the maximum increase in Treatment Fresh roots (t/ha)a nutrient accumulation during the growth cycle Check 42.3 c occurred between 2 and 4 months after planting. This Mycorrhizae 49.3 b period corresponded to the maximum accumulation of Myco. + 25% N–P–K 50.4 b dry matter for M Col 22 and other cultivars. After Myco. + 50% N–P–K 51.1 b 6 months, the adsorption rate for most nutrients Myco. + 75% N–P–K 51.4 b declined. Myco. + 100% N–P–K 61.6 a 100% N–P–K 52.0 b Nijholt, cited by both Howeler (1981) and Howeler CV% 3.87 and Cadavid L (1983), indicated that total accumulation SE (+ or –) 1.17 of dry matter continues throughout the growth cycle. However, it declines in leaf blades and petioles after a. Values with the same letters in the column are not significantly 6 months, whereas it increases until the end of the different at. cropping cycle in stems and roots. SOURCE: INIVIT (1999). Tables 5-7 and 5-8 show the accumulation of dry The mycorrhizae that affect the absorbent roots of matter and nutrients of different cassava cultivars in cassava and many other crops belong to the group the acid soils of Santander de Quilichao, Cauca, known as vesicular-arbuscular endomycorrhizae. Their Colombia (El-Sharkawy et al. 1998). hyphae grow between and within root cortex cells, producing ramifications within them. These are called Nutrient extraction. The cassava crop extracts arbuscules and vesicles. Hyphae also grow in soil, large amounts of nutrients from the soil, sufficient to where they can extend for several centimeters along be considered as an extra loss. Table 5-9 describes the roots (Howeler 1983). Other more common, but also average nutrient extraction (kg/ha) per ton of harvested efficient fungi found in the cassava crop include fresh roots. The high export of elements, particularly Glomus manihotis, Entrophospora colombiana, and N, K, and Ca, is notable (Howeler and Cadavid L 1983; Acaulospora mellea in Colombian soils. Cadavid L 1988a, 1995, 1997). Aerial parts phase. Nutritional disorders of the crop. The plant, in itself, determines its “state of health”. When stress Accumulation and distribution of dry matter in occurs through scarcity or excess of water, deficiency cassava. The concentration of nutrients in cassava or toxicity of a nutrient, or physical or mechanical varies considerably between plant parts and also during injury to organs, the plant manifests characteristic the growth cycle (Howeler 1983; Cadavid L 1988a). As symptoms that indicate that something is wrong. This the plant grows, N, P, and K contents decline in leaves condition of anomaly manifesting in one or more (leaf blade and petiole), but tend to increase in stems symptoms becomes another tool for diagnosis (see and roots. below under Deficiencies and toxic effects ...). In a study conducted by Howeler and Cadavid L In cassava, the frequent absence of clear (1983), the authors indicated that, with cv. M Col 22, symptoms of macronutrient deficiency means that the roots accumulated, at the end of the 12-month nutritional problems can be easily overlooked (Howeler Table 5-6. Effectiveness of different species of vesicular-arbuscular mycorrhizae (VAM) for the cassava crop, Colombia. Species Cassava Effectiveness for: Capacity to compete with growth other microorganisms P adsorption Root length Glomus manihotis High High Average High Entrophospora colombiana High High High Little Acaulospora mellea Average Average High Average SOURCE: Sieverding (1984). 120 Soils and Fertilizers for the Cassava Crop Table 5-7. Biomass of aerial parts and tuberous root yield (t/ha, dry weight) of cassava plants with high, medium, and low height. Means taken at 2, 4, 6, and 10 months after planting, Santander de Quilichao, Cauca, Colombia. Height of cultivar Yield (t/ha) of aerial biomass at months: 2 4 6 10 2 4 6 10 1994/95 1995/96 Tall CG 402-11 0.3 2.3 3.6 7.1 0.2 2.3 5.5 8.8 M Pan 51 0.3 1.8 4.9 4.7 0.3 2.5 3.4 5.0 Average CM 507-37 0.2 2.4 2.6 3.7 0.3 2.6 3.2 5.6 SG 107-35 0.3 1.3 1.7 3.2 0.3 2.3 2.3 4.9 Short CG 1141-1 0.2 1.2 1.8 2.6 0.2 1.4 1.8 2.1 M COL 22 0.2 1.4 1.2 3.0 0.2 1.5 1.3 2.0 Height of cultivar Tuberous root yield (t/ha) at months: 2 4 6 10 2 4 6 10 1994/95 1995/96 Tall CG 402-11 0.01 0.9 1.5 9.2 0.01 0.6 5.4 14.5 M Pan 51 0.01 1.6 2.4 8.7 0.01 1.2 5.0 8.6 Average CM 507-37 0.01 1.7 2.6 11.6 0.02 1.4 5.8 13.2 SG 107-35 0.02 2.3 2.9 11.0 0.02 1.9 6.5 11.7 Short CG 1141-1 0.01 2.6 4.0 15.0 0.01 1.6 6.2 10.3 M COL 22 0.01 2.2 2.7 9.7 0.01 1.9 5.4 7.3 SOURCE: El-Sharkawy et al. (1998). 1981). In such cases, the state of availability of soil • Mobile elements in lower and older leaf blades. nutrients must be known and confirmed by plant tissue These leaf blades yield their nutrients by analyses and the plant’s responses to fertilizer phloematic translocation to the youngest leaf applications. blades. Sometimes, symptoms of nutritional disorders can • Elements of intermediate mobility in young be confused with those of fungal diseases such as plant parts and expanded leaf blades (upper leaf necrosis caused by anthracnose, insect attack (e.g., Zn blades). deficiency with thrip attack), herbicidal damage (chlorosis and necrosis), and poor drainage and excess • Immobile elements in young meristematic leaf water (chlorosis or yellowing of leaf blades). blades and root meristems. The elements present in the old leaf blades are not Mobility of nutrients in the phloem. When translocated to the youngest leaf blades or new attempting to detect nutritional deficiency by tissues. observation of visual symptoms, the mobility of nutrients in the phloem should be taken into account Functions of Nutrients in the (Table 5-10). According to Howeler (1981), Kramer Cassava Plant (1989), Malavolta et al. (1989), and Calderón (1991), some ions are distributed more easily than others and Some nutrients have a structural function. Others help can show very different mobility within the phloem. establish enzymes (prosthetic group) or activate them According to this criterion, deficiency symptoms are and intervene in different processes within the plant. expected to first appear in cassava plants as follows: More information is found in Figure 5-8. 121 Cassava in the Third Millennium: … Table 5-8. Dry matter content (DM, g per plant) and nutrient content (mg per plant) in several parts of cassava plants (cultivar M Col 22) receiving fertilizer applications over a 12-month cycle, Santander de Quilichao, Cauca, Colombia. Contents in month: 1 2 3 4 5 6 8 10 12 DM Leaf blades 1.8 22.7 76.0 100.6 56.2 100.2 50.5 58.7 67.0 Petioles 0.2 4.9 21.5 38.2 19.0 27.4 8.6 12.1 11.5 Stems 14.1 29.1 58.9 125.2 182.1 269.1 302.7 428.6 459.9 Roots 0.1 7.1 80.5 229.6 360.0 571.9 782.6 942.4 1387.0 Total 16.2 63.8 236.9 493.7 617.3 968.6 1144.4 1441.8 1925.4 N Leaf blades 89 1231 4230 5300 2703 4877 2206 2702 3350 Petioles 6 134 368 485 202 378 144 182 207 Stems 117 422 1146 1919 3022 4191 4707 5984 6930 Roots — 125 1078 2250 4428 5605 7043 9424 9709 Total 212 1912 6824 9954 10,355 15,051 14,100 18,292 20,196 P Leaf blades 5 71 267 227 137 288 136 147 174 Petioles — 10 35 34 16 31 10 20 18 Stems 37 71 157 205 358 422 482 378 766 Roots — 11 153 344 576 629 861 1036 1387 Total 42 163 612 810 1087 1370 1489 1581 2345 K Leaf blades 24 337 1408 1716 507 1564 712 817 945 Petioles 9 161 598 744 347 561 159 201 207 Stems 58 213 872 1681 2581 2588 2817 3233 3676 Roots 5 123 1248 2870 4176 4463 5635 6879 10,402 Total 96 834 4126 7011 7611 9176 9323 11,130 15,230 Ca Leaf blades 15 157 583 924 525 857 424 452 435 Petioles 4 68 212 393 248 420 125 165 186 Stems 216 244 485 864 1061 1704 1986 2412 3083 Roots 1 20 113 321 432 915 939 1508 1248 Total 236 489 1393 2502 2266 3895 3474 4537 4952 Mg Leaf blades 9 67 248 411 166 276 146 146 174 Petioles 2 23 77 142 68 130 32 41 56 Stems 93 125 216 401 424 586 707 746 1147 Roots — 9 72 230 288 400 626 660 693 Total 104 224 613 1184 946 1392 1511 1593 2070 S Leaf blades 2 61 203 335 185 256 101 88 241 Petioles — 4 5 — 14 30 7 7 14 Stems 15 19 63 101 227 383 360 337 578 Roots — 5 8 — 216 171 391 283 555 Total 17 89 279 436 642 840 859 715 1388 SOURCE: Howeler and Cadavid L (1983). Table 5-9. Average extraction of nutrients per ton of fresh roots harvested from several cassava cultivars (total plant). Cultivar Extraction (kg/ha) of: Source N P K Ca Mg S Several 4.91 1.08 5.83 1.83 0.79 — Howeler (1981) M Col 22 4.66 0.54 3.52 1.14 0.48 0.32 Howeler and Cadavid L (1983) CM 523-7 6.90 0.88 3.71 1.47 0.74 0.51 Cadavid L (1988a) M Col 1468 3.97 0.62 3.56 1.53 1.28 — Caicedo (1993) M Col 1684 3.13 0.44 2.70 1.35 0.86 — Caicedo (1993) CM 507-37 3.89 0.60 2.76 1.09 0.78 — Caicedo (1993) CM 523-7 3.46 0.55 3.02 1.10 0.78 — Caicedo (1993) Mean of authors 4.42 0.67 3.58 1.36 0.82 0.42 SOURCE: Cadavid L (1995). 122 Soils and Fertilizers for the Cassava Crop Table 5-10. Mobility of nutrients through the phloem. Potassium (K). Stunted plant growth, small leaf Mobile Intermediate Immobile blades. Under very severe conditions, purple spots Nitrogen Sulfur Calcium appear, apexes and margins of lower or middle leaf Phosphorus Copper Boron blades suffer yellowing and become necrotic; necrosis Potassium Iron Strontium of petioles or stem tissues; fine cracks appearing in Magnesium Manganese stems and, runners. Sodium Zinc Chlorine Calcium (Ca). Reduced root growth, upper leaf Molybdenum blades are small and deformed. Rubidium Magnesium (Mg). Marked intervenal chlorosis in SOURCES: Howeler (1981); Kramer (1989); Malavolta et al. (1989); Calderón (1991). lower and middle leaf blades; plant height reduced to some degree. Deficiencies and toxic effects in the cassava Sulfur (S). Uniform yellowing of upper leaf blades; crop similar symptoms have sometimes been observed in the rest of the plant. A plant that presents any symptoms of any kind is a “diseased” plant. Disease is a detrimental physiological Boron (B). Reduced plant height; short internodes activity provoked by a primary causal agent. It and petioles; young leaf blades small and deformed; manifests as an abnormal activity and is expressed purple-gray spots in completely extended leaf blades; through characteristic pathological conditions known sticky exudation on stems and petioles; reduced lateral as symptoms (Sánchez 1968), which can be necrotic root development. (e.g., spots, blight, dieback, chlorosis, and cankers), hypoplastic (e.g., chlorosis, witches’ broom, etiolation, Iron (Fe). Uniform chlorosis of upper leaf blades and dwarfism), and hyperplastic (e.g., abscission, and petioles, which become white under severe anther apoptosis, and leaf roll). conditions; reduced plant growth; young leaf blades small but not deformed. According to Sánchez (1968), the soil’s chemical composition can directly cause physiogenic diseases Manganese (Mn). Intervenal chlorosis of upper or or indirectly favor the development of pathogenic middle leaves; uniform chlorosis under severe diseases (caused by other live organisms such as fungi, conditions; reduced plant growth; young leaf blades bacteria, and nematodes). An example is that of small but not deformed. cassava crops growing in soils deficient in K and where anthracnose, Phytophthora induced diseases, and Zinc (Zn). Yellow or white intervenal spots in young other fungal diseases causing, for example, necrosis, leaf blades that, under severe conditions, become dieback, and root rots, can develop, drastically narrow and develop chlorosis in the vegetative apex; reducing tuberous root production. necrotic spots on lower leaf blades; reduced plant growth; often confused with thrip attack. Deficiencies. Howeler (1981) outlined the principal symptoms of deficiencies in the cassava crop, as Toxic effects. Howeler (1981) also outlined the follows: principal symptoms of toxicity in the cassava crop. Nitrogen (N). Stunted plant growth; and, in some Aluminum (Al). Reduced plant height and root cultivars, uniform yellowing of leaf blades that begins growth; yellowing of old leaf blades under severe on the lower surfaces and rapidly extends to the entire conditions. plant. Boron. Necrotic spots appear in old leaf blades, Phosphorus (P). Reduced plant growth, smaller leaf especially on the margins. blades and lobes, and thin stems. Under severe conditions, lower leaf blades become yellow, flaccid, Manganese. Yellowing of old leaf blades, with and necrotic, and fall easily to the ground. Reddish purple-brown or blackish spots throughout the nervura; coloring is sometimes presented. leaf blades become flaccid and fall to the ground. 123 Cassava in the Third Millennium: … Structural Nitrogen Phosphorus Ionic absorption Calcium Photosynthesis Magnesium Sulfur Respiration E Boron Synthesis Chlorine Multiplication Iron Manganese Cellular differentiation and heredity Cobalt Constituent of enzymes Prosthetic group Potassium Osmotic properties Calcium Magnesium Opening and closing of stomata Sulfur Photosynthesis Boron Chlorine Respiration Copper Synthesis E Iron Transport of carbohydrates Manganese Molybdenum Membrane operation Zinc Storage and transfer of energy Nickel Symbiotic fixation of N Cobalt Enzyme activator Potassium Calcium Osmotic properties Magnesium Opening and closing of stomata Sulfur Photosynthesis Boron Chlorine Respiration E Copper Synthesis Iron Transport of carbohydrates Manganese Membrane operation Molybdenum Zinc Storage and transfer of energy Nickel Symbiotic fixation of N Cobalt Figure 5-8. Functions of nutritional elements in the plant (adapted from Malavolta et al. 1989). When the liquid and exchange phases of the soil Deficiency is presumed to occur when the following are exhausted for lack of nutrients because of constant conditions are fulfilled: loss, and deficiency symptoms begin to appear, an artificial resupply of these through chemical fertilizer When solubilization + mineralization < application becomes necessary. This is also true for N fixation + immobilization + extraction + in the solid organic phase of the soil, which can be leaching (losses) replenished only through organic fertilizer application. 124 Soils and Fertilizers for the Cassava Crop Soil Fertility and the Crop’s Nutritional is reduced, maintained, or increased (INPOFOS 1993). Status Table 5-3 shows an example of a sandy soil from the North Coast in Colombia, where soil fertility increased or When fertilizer application is considered necessary, a declined according to management, time, and crop. diagnosis of the soil must be made to determine possible deficiencies and correct them in a timely The success of analysis lies in obtaining a good soil fashion before a crop is established. If this crop is sample. Usually, the following are determined: organic cassava, possible limitations of the soil where the crop matter, P, K, Ca, Mg, S, Al, Na, Zn, B, soil acidity (pH), will be established must be known, including the and soil texture (Figure 5-9). Laboratory data are given in availability of soil nutrients and the crop’s nutritional local and international units, usually: percentage (%), requirements. parts per million (ppm), and milliequivalents per 100 g of dry soil (meq/100 g of dry soil) or g/kg, mg/kg, and A diagnosis of nutritional problems in the soil aims cmol/kg, respectively, according to the latest laboratory to discover the availability of nutrients in a given soil and regulations, not only in Colombia, but also in most of the how these levels would affect an established crop. The world. fundamental objective of chemical diagnosis is to evaluate the soil’s capacity to provide nutrients to the Critical levels of soil parameters plant, that is, to measure its fertility. Diagnosis of soil fertility and nutritional problems for crops is usually Howeler (1981), Cadavid L (1988b), and Howeler and carried out by: Cadavid L (1990) have established a series of parameters (critical levels) that serve as tools for correctly interpreting • Chemical and physical analyses of the soil* a soil analysis (Table 5-11). • Plant tissue analyses* • Critical levels of nutrients in the soil or plant To more clearly understand the definition of critical tissues of a specific crop (i.e., cassava in our level, the following example is given: case)* • Knowledge of nutritional disorders (deficiencies, If, for the cassava crop, the critical level for P is toxic effects) 10.0 ppm (Bray II) and the soil analysis gives a value of • Crop’s response to fertilizer applications* 1.0 ppm, then, P can be considered as a limiting element • Crop’s nutritional requirements (i.e., nutrient in this soil. The crop would most probably manifest extraction)* deficiency of this nutrient. Also, any P applications are • Knowledge of original materials of a specific soil highly likely to induce a positive and highly significant • Knowledge of the soil’s taxonomic classification response, as manifested in increased yields (i.e., • Knowledge of previous crop and its exploitation increased fresh-root production in t/ha). If the determined of that soil and its intensity. value is higher than the critical level, then the crop would probably not respond to applications of this nutrient. Chemical Soil Analyses With laboratory data and knowledge of critical levels Soil sampling and later analyses before planting of soil parameters already established for cassava, a good become very important tools in diagnosing and interpretation can be achieved but not necessarily a correcting nutritional problems, thereby preventing correct recommendation. For example, some Oxisol deficiencies from affecting plant growth and soils of the Colombian Eastern Plains, as in the case of development. In cassava, the absence of clear Carimagua (Altillanura plains) in the Department of Meta, symptoms of macronutrient deficiencies makes usually have chemical and physical characteristics as nutritional problems difficult to see easily. Thus, leaf presented in Table 5-12. and chemical analyses become key tools for determining a plant’s nutritional status (Howeler 1981). When these values are compared with the already established critical levels, the analysis indicates those Soil analyses help monitor the state of soil fertility nutrients in deficiency. In this specific case, the soil over the years, providing information on whether fertility obviously has average N content. It is also very low in P, K, Ca, and Mg. Its zinc content is average to low; and pH is extremely acid. Content of exchangeable Al is high and * The analyses marked with asterisks are of the greatest interest, as they form the basis on which to calculate a formula for applying Al saturation is 77.4%. Sulfur content may be low fertilizers to a given crop and its soil. (although this datum does not appear in this example). 125 Cassava in the Third Millennium: … 100 0 100 0 % Clay % Silt 90 10 0 100 80 20 100 0 % Sand Key 70 30 Clay 60 40 50 50 Silty clay 40 Sandy clay 60 Clay loam Silty clay-loam 30 70 Sandy clay-loam 20 Loam 80 Sandy loam Silt loam 10 Loam 90 y sand Silt Sand 0 100 100 90 80 70 60 50 40 30 20 10 0 Percentage of sand Sand: 0.05–2.0 mm Figure 5-9. USDA soil texture triangle as applied to Colombian soils (unmarked arrows). Table 5-11. Critical levels of soil parameters for the cassava crop. when a crop needs fertilizer application, which can be pH Al sat. P K Ca Mg Zn S determined through the use of the following formula (%) (ppm) (Guerrero, 1980): (meq/100 G (ppm) dry soil) WRC – SN 4.0 80 7.0* 0.15 0.25 0.12a 1.0 8.0 NF = 100 * E 8.0 10.0** 0.17 a. Bray I method. where, b. Assuming that the ideal Ca/Mg ratio for the cassava crop is 2:1 NF = need for fertilizer application (kg/ha) (LF Cadavid L, pers. comm.). c. Bray II method. WRC = weighted requirement of crop (kg/ha) SN = availability of the nutrient in the soil (kg/ha) E = efficiency of the fertilizer (%) Fertilizer recommendations or amendments. 100 = percentage constant Fertilizer application is a management mechanism and, as such, should be conceptualized in terms of Crop’s nutritional requirements. This value recovering, maintaining, and sustaining soil fertility and refers to the nutrients extracted by the plant that have increasing crop productivity. It is important to know been quantified at the end of the cropping cycle (i.e., at 126 Clay: P < e 0rc .0 e 0n 2ta m ge m of clay Sil t: 0 .00 2– 0.0 5 m m Pe rce nta ge of sil t Soils and Fertilizers for the Cassava Crop Table 5-12. Chemical and physical characteristics of the soil at Carimagua, Colombian Eastern Plains. Texture pH OMa P Al Ca Mg K Zn (%) (ppm) (meq/100 g dry soil) (ppm) Clay loamb 4.44 4.56 3.0 3.15 0.54 0.30 0.08 1.5 Interpretationc Acid M M–L M–H L L M–L M–L a. OM = organic matter. b. When data on texture are given as percentages of sand, silt, and clay; to determine textural class, see Figure 5-9. c. H = high; L = low; M = medium. harvest). Cassava is a plant that extracts large amounts N; usable P and S; and exchangeable K, Ca, and Mg. of nutrients from the soil, especially N, K, and Ca. If The availability of a given nutrient is quantified the entire plant is considered, then for 1 ton of fresh according to results of the analysis (%, ppm, and roots harvested, cassava extracts 4.42 of N, 0.67 of P, meq/100 g of dry soil), expressed in kg/ha. 3.58 of K, 1.36 of Ca, 0.82 of Mg, and 0.42 of S (kg/ha each) (Cadavid L 1995). Hence, the apparent density of the soil must be considered (which, in this type of soil, is 1.3 g/cm3), on If this soil (Oxisol from the Altillanura plains, which depends the weight of a hectare of soil. The Carimagua, Meta, Colombia) is taken as an example weight, in its turn, depends on plowing depth as a and, assuming that the average production (with function of the average depth of the crop’s root system intermediate-level technology) of the local variety (which, for cassava, is 20 cm). ICA-Catumare (CM 523-7) is 15 t/ha but farmers want to achieve a weighted production of 30 t/ha, then the Ws = weight of hectare of soil = Vs (cm3) * (g/cm3) cassava crop will need the levels of nutrients as Vs = L * L * D = volume of 1 ha of soil (cm3) described in Table 5-13. where, Nutritional requirements indicate the amount of L = length of plot side (cm) nutrients that a plant needs to fully develop. This D = working depth of plot (cm) quantity is provided by the soil alone or by the soil plus fertilizers. The amount of nutrients extracted or Thus, in our case: removed from the soil in the final harvest has given rise to a criterion for fertilizer application: the restitution or Vs = 10,000 cm * 10,000 cm * 20 cm = return to the soil of nutrients that were extracted from 2 × 109 cm3 it to maintain fertility at the original level. Thus, it is not Ws = 2 × 109 cm3 * 1.3 g/cm3 * kg/1000 g = an ascertained recommendation, as nutrient availability 2.6 × 106 kg is not included in the soil. However, meq/100 g of dry soil should be Nutrient availability in the soil. This factor expressed in kg/ha. Starting with the term equivalent- is determined in the laboratory through chemical gram (i.e., element’s atomic weight divided by its analysis. Nutrients occur in term of values for available valence), and if we take as an example, potassium (K), then: Table 5-13. Nutrients extracted from cassava according to yield. An equivalent-gram (Eq) of K = molecular weight in g/valence Nutrient Extraction (kg/ha) for fresh-root yield Eq K = 39/1 = 39 g Estimated Weighted (15 t/ha) (30 t/ha) 1 meq K = 39 g/1000 = 0.039 g N 66.3 132.6 Hence, P 10.1 20.1 K 53.7 107.4 0.039 g K is found in 100 g dry soil Ca 20.4 40.8 X kg K will therefore be present in Mg 12.3 24.6 2.6 × 106 kg/ha X = 1014 kg K/ha 127 Cassava in the Third Millennium: … In other words: colloidal materials). These soils, for example, fix large amounts of this element (around 500 ppm). In 1 meq K/100 g = 0.039 g K = 1014 kg K/ha fertilizers that include N and K, efficiency is between 50% and 70%. In fertilizers carrying Mg and Ca as lime, If the datum reported by the soil laboratory is efficiency is between 50% and 60%. For NF, we will use 0.08 meq/100 g of dry soil, then the availability of the the case of K: nutrient in the soil is: WRC = 107.4 kg/ha 1.0 meq K/100 g soil SN = 81.1 kg/ha 1014 kg K/ha, for one of 1.3 g/cm3 E = 70.0% 0.08 meq/100 g soil; X kg K/ha 107.4 kg – 81.1 kg * 100 X = 81.12 kg K/ha NF = 70 The same procedure is used with Ca and Mg. NFK = 37.6 kg/ha When data reported in soil analyses are given in ppm, they are converted to kg/ha, as follows: If we complete this formula for P, Ca, Mg, and N, the results would be: 1 ppm is equivalent to having: NFP = 61.2 kg/ha 1 kg in 1 × 106 kg NFCa = –400 kg/ha 1 kg P in 1 × 106 kg soil NFMg = –115 kg/ha X kg P in 2.6 × 106 kg/ha soil X = 2.6 kg P/ha Thus, to determine the need for fertilizer application for total nitrogen (TN), then: That is, 1 ppm P = 2.6 kg P/ha OM% , thus TN = 4.56 = 0.228 (high level) TN = If in our example, 3.0 ppm of P were reported, 20 20 then, the availability of P in the soil is: AN = 0.228 × 0.025 = 0.0057 1.0 ppm P is in 2.6 kg/ha “AN” is usable nitrogen and 2.5% is a percentage 3.0 ppm P will be in X kg/ha of average mineralization (this factor may be between X = 7.8 kg P/ha 1% and 5%). 0.0057 × 2,600,000 kg/ha Continuing with our formula for determining the AN = = 148.2 kg/ha need for fertilizer application, the term efficiency still 100 needs to be defined. It is merely the efficiency of NFN = –22.0 kg/ha fertilizer application on the basis of different losses of a soil nutrient after application. These losses may occur According to these data, the fertilizer applications through: required would be 60 kg P/ha and 40 kg K/ha. The formula is adjusted according to the data on response • Leaching (NO – 3 , K+, Ca+2, and Mg+2) to fertilizer application in terms of area. Hence, for this • Volatilization (NH – 2 , NH3, and N2O) type of soil, 50 kg N/ha + 60 kg P/ha + 50 kg K/ha + • Fixation (NH + 4 , H – 2PO + 4 , and K ) 500 kg/ha of dolomitic lime would be recommended. • Immobilization (N, P, and S) The recommendation would also be to apply • Erosion (N, P, K, Ca, and Mg) 280 kg/ha of diammonium phosphate (DAP), which • Adsorption by the plant would contribute 50 kg N/ha and 58 kg P/ha, and add 100 kg/ha of potassium chloride (KCl) or 119 kg/ha of With the data of weighted requirement of the crop potassium sulfate if sulfur is less than 8 ppm and (WRC), availability of the nutrient in the soil (SN), and 10 kg/ha of borax (equivalent, on breaking up, to efficiency of fertilizer application (E), an approximate 1 kg B/ha). The lime would contribute about 100 kg fertilizer application formula can be readily established. Ca/ha and 50 kg Mg/ha. The applications of DAP and We point out that the efficiency of fertilizers carrying P KCl + borax are carried out between day 30 and day is 10% to 30%, depending on the amount of fixed P 45 after planting, in simple band and covering to (this factor is closely linked to the soil class and its prevent losses. Lime is applied by broadcast 15 days 128 Soils and Fertilizers for the Cassava Crop before planting and incorporating with the last task of content of P (3 ppm, Bray II method), P applications soil preparation. of up to 400 kg/ha, regardless of source and form of application, showed a highly significant response Cassava response to chemical and organic in yields (Table 5-2). However, with an application of fertilizer applications 50 kg/ha of P, yield almost tripled. A viable alternative for recovering, maintaining, and Table 5-14 outlines the beneficial effect of high increasing the fertility and productivity of soils applications of P on the content of this element in dedicated to cassava cropping, and for increasing the soil. Differences are notable between sources: crop yield and quality, is fertilizer application, either highly water soluble, superphosphate type, and chemical or organic. slow-release sources such as phosphoric rock and calfos. Different studies conducted on the response to applications of chemical or organic fertilizers have The results of this type of trial underscore the been most useful, as observed in results: the importance of phosphoric fertilizer application in beneficial and highly significant effect on the soils deficient in P. They show that response to production and recovery of soil fertility. Tables 5-2 applications of this element occurs and that and 5-14 to 5-22, and Figures 5-10 to 5-12 confirm slow-release sources may constitute an excellent these results. alternative, as, when applied by broadcasting, they are more efficient, thus reducing the high fixation of In a clay loam soil (kaolinitic) of the Colombian P existing in this type of soils (Haplustox) (Cadavid L Eastern Plains (Carimagua, Meta), with relatively low 1980). Table 5-14. Phosphorus content (ppm) in a soil at Carimagua, Meta, Colombia, at 13 months after sources of P were applied. Treatmenta P content (ppm) of levels of P2O5 at: 0 50 100 200 400 X4 (kg/ha) Check 1.7 — — — — 1.7 Triple superphosphate, applied in bands — 1.6 2.6 3.0 3.6 2.7 Simple superphosphate, applied in bands — 1.7 4.6 3.7 3.0 3.3 Mg phosphate, broadcast in bands — 2.3 2.3 3.1 23.7 7.9 Basic slag (Thomas), applied in bands — 3.7 2.0 5.9 14.6 6.6 Basic slag (Thomas), broadcast — 2.5 6.3 12.3 31.1 13.1 Phosphoric rock (PR) (Huila) 20%, acidulated, broadcast — 4.2 4.9 7.7 40.6 14.4 PR (Huila) + S, broadcast — 3.7 4.2 9.6 28.3 11.5 PR (Huila), broadcast — 3.1 12.1 21.8 25.7 15.7 Mean of treatments 1.7 2.9 4.9 8.4 21.3 SOURCE: Cadavid L (1980). Table 5-15. Chemical characteristics of a soil at Santander de Quilichao, Cauca, Colombia, after one application of phosphorus. Year Pa OMb pH Al Ca Mg K Pc Al sat. (kg/ha) (%) (cmol/kg) (mg/kg) (%) 1979 0 6.28d 4.2 3.88 0.98 0.32 0.20 2.80 72.1 1995 0 4.95 4.0 3.21 0.88 0.33 0.26 2.85 68.8 1995 75 5.80 4.1 3.33 1.38 0.34 0.28 35.10 62.3 a. Annual application. b. OM = organic matter. c. Bray II method. d. 1985. 129 Cassava in the Third Millennium: … Table 5-16. Dry-root yield and index of adaptation to low P for 32 cassava clones in soils of Santander de In Ultisol clay soils in Santander de Quilichao, Quilichao, Cauca, Colombia, 1994/95. Cauca, Colombia, which have a very low P content Clone Dry-root yield Index of (2.80 ppm, Bray II), cassava was planted continuously (t/ha) adaptation to over 15 years to observe responses to applications of P low Pa (triple superphosphate as the source) and determine an Zero P 75 kg P/ha index of adaptation to low P (Tables 5-15 and 5-16). CG 333-4 7.4 10.4 1.89 SG 779-9 7.1 10.4 1.81 The data given in the previous tables show a SM 380-3 6.0 11.2 1.65 marked response to the constant application of 75 kg P/ha, as the soil, after 15 years, recorded a substantial CM 5830-4 6.6 10.1 1.63 HAb increase of this element (35.1 ppm, compared with CM 4365-3 6.3 10.1 1.56 2.85 ppm without application), thus increasing its CM 4774-2 6.1 10.1 1.51 fertility. CM 849-1 6.7 9.5 1.47 CM 3555-6 6.8 8.8 1.47 For yield, Table 5-16 shows a positive and highly SG 545-7 5.7 10.0 1.40 significant response to applications of P. Differences CG 1141-1 5.3 10.6 1.38 between genotypes were observed when the index of adaptation to low P was considered. Many clones have CG 1355-2 5.4 10.4 1.38 high yields with and without applications of P; and CM 3311-3 5.9 9.4 1.36 some (e.g., CG 333-4, SG 779-9, SM 380-3, and CG 95-1 6.1 8.4 1.26 CM 4774-2) had indices of adaptation to low P of more M Bra 589 5.5 9.2 1.24 IAb than 1.5, indicating a high level of tolerance of low P, as CG 5-79 5.4 9.0 1.19 well as high response to phosphoric fertilizer applications. SM 366-2 6.2 7.6 1.15 M Col 1468 5.4 8.5 1.13 Considering the continuous planting of cassava for CM 507-37 5.4 8.2 1.09 more than 15 years and the average to low levels of M Cub 32 5.2 8.4 1.07 productivity without applications of P, acid soils with CG 996-6 4.3 10.0 1.05 low available P, but high organic matter contents, can M Col 1505 4.6 8.9 1.00 probably support sustainable yields with moderate SG 495-19 4.9 7.4 0.89 applications of this nutrient (i.e., <50 kg P/ha). This is related to the presence of vesicular-arbuscular CM 523-7 4.4 7.8 0.84 mycorrhizae and degree of infection. M Bra 390 5.5 6.2 0.84 CM 4772-3 4.4 7.6 0.82 In soils of Santander of Quilichao, cassava roots of CG 522-10 3.6 8.8 0.78 all clones show a high percentage of infection, HMC-1 3.5 6.0 0.51 LAb indicating effective fungus-cassava association. M Col 1684 3.0 6.6 0.49 In soils where cassava is planted over long periods, CM 5586-1 3.1 5.8 0.44 K must be taken into account. Because of high M Bra 191 4.3 4.1 0.43 extraction, these soils lose their reserves easily, CG 915-1 3.3 2.1 0.17 presenting deficiencies of this nutrient. According to CM 2766-5 1.9 2.4 0.11 research conducted in different types of soil in the M Pan 51 2.8 1.2 0.08 country, K is an essential and limiting element in Average of all 5.1 8.0 cassava production (Cadavid L 1997; El-Sharkawy and clones Cadavid L 2000). LSD 5% 1.5 1.8 In an Ultisol of Santander de Quilichao, planted a. Index of adaptation to low P: yield at zero P; yield at 75 kg P/ha; and average of yield at zero P; average of yield at 75 kg P/ha. with cassava over 12 consecutive years, a highly b. HA = high adaptation; IA = intermediate adaptation; LA = low significant response to K is shown in tuberous root adaptation. production with applications of 50 kg/ha or more (Table 5-17). The soil showed a significant recovery in K content, increasing from 0.06 to 0.33 cmol/kg, which is considered high for this type of soil. 130 Soils and Fertilizers for the Cassava Crop Table 5-17. Effect of applications of N–P–K fertilizer on yield and fertility of a soil planted to cassava over 12 consecutive years, Santander de Quilichao, Cauca, Colombia.. Application Fresh roots of OM Bray II P K Critical levela (kg/ha) M Col 1684 (t/ha) (%) (mg/kg) (cmol/kg) N P K 1983/84 1994/95 1984 1995 1984 1995 1984b 1995 P K (mg/kg) (cmol/kg) 0 0 0 16.4 8.3 6.2 5.2 4.0 6.4 0.06 0.12 10.0 0.15 50 50 50 25.3 21.5 6.0 5.3 3.9 15.9 0.08 0.14 0 100 100 30.2 20.5 5.7 5.2 4.6 40.6 0.11 0.48 50 100 100 32.3 22.8 5.7 5.3 3.8 48.6 0.08 0.34 100 100 100 32.8 22.0 5.9 5.3 3.8 46.2 0.09 0.33 100 0 100 23.8 16.2 5.9 5.4 4.2 10.1 0.09 0.27 100 50 100 32.8 23.4 6.2 5.4 3.7 24.8 0.09 0.19 100 100 0 25.7 10.3 5.8 5.3 3.7 46.0 0.06 0.09 100 100 50 29.7 21.0 5.8 5.1 4.0 37.1 0.07 0.14 a. As according to Howeler (1981). b. In 1983, 0.07 cmol/kg, and 5 years earlier (continuous plantings of cassava), 0.30 cmol/kg. SOURCE: Cadavid L (1995). In an Inceptisol (clay soil) of Santander de When a complete or simple fertilizer is selected, Quilichao, which had a high content of organic carbon knowledge of the levels of elements that the product (4.8%), low P (2.0 mg/kg), and average content of K has is essential, that is, the way the contents of a (0.18 cmol/kg), 14 cassava clones were evaluated over fertilizer are expressed in the product, such as N, 5 continuous years (Table 5-18). Although the K level in P2O10, K2O, CaO, MgO, CaCO3, and MgCO3, and the the soil was average, dry-root yield indicated a positive percentage. For example, the chemical fertilizer and significant response to K applications of up to 13–13–21 is expressed as 13% of N, 13% of P2O5, and 50 kg/ha, on average, for all clones in the first cycle. In 21% of K2O. This means that 100 kg of commercial the fifth cycle, almost all clones showed a positive product contains 13 kg of N, 13 kg of P2O5, and 21 kg response up to 100 kg K/ha. Yield, however, declined of K2O. through the constant removal of this nutrient from the soil and other losses in the system. To recommend fertilizers, such expressed values cannot be used. Instead, values must be expressed in Table 5-18 also shows the effect of applications of terms of kg of N, P, K, Ca, and Mg. Hence, the K on the quality of tuberous roots in terms of total expression given by the manufacturer must be hydrocyanic acid content (ppm). The positive effect is converted to the real expression. For this purpose, notable, as HCN content drops as the rate of K conversion tables, taken from a literature review on application increases (El-Sharkawy and Cadavid L fertilizer application, are given in Table 5-23. 2000). The quantity of commercial product that will be Tables 5-17 and 5-19 and Figures 5-10 and applied in accordance with the recommended nutrient 5-11 show the beneficial effects of N, P, and K levels (element base) must be known. Thus, the applications on yield in soils of Santander de Quilichao, following formula is taken into account (Cadavid L and Mondomo, and Pescador in Cauca, Colombia. Calle C 1997): RN * 100 CP * ABeneficial effects on soil fertility and productivity, CP = and on cassava crop yield also occur when organic ha DNCP sources are used such as manures, incorporated green where, manures, or mulch. These not only help improve soil CP = commercial product (kg or t/ha) fertility and increase yield by releasing nutrients, but RN = recommended nutrient (kg/ha) they also help improve soil structure and aggregation, 100 CP = 100 kg of commercial product (kg) increase water retention, and increase microbial activity ha = 1 ha (10,000 m2) in soils (Cadavid L 1995). Tables 5-20, 5-21, and 5-22, DNCP = grade of nutrient element in the and Figure 5-12 illustrate the positive response to this commercial product (kg) class of fertilizers. A = area of application (ha or m2) 131 Cassava in the Third Millennium: … Table 5-18. Effect of potassium fertilizer applications on dry-root yield (t/ha) and on total HCN content (ppm) of 14 cassava cultivars in a soil in Cauca, Colombia, 1989–1994. Cultivar Dry roots (t/ha) In year 1 of potassium fertilizer application In year 5 of potassium fertilizer application (kg/ha) at: (kg/ha) at: 0 50 100 200 0 50 100 200 M Col 1505 12.6 17.0 14.4 14.9 4.5 8.5 9.0 9.1 CM 91-3 11.6 15.5 15.0 17.6 3.3 7.7 5.2 7.4 CM 489-1 12.5 17.2 15.3 16.1 5.7 8.0 10.4 11.3 CM 507-37 14.6 18.3 17.1 16.0 5.8 10.8 12.7 14.1 CM 523-7 12.4 15.7 16.9 13.0 6.4 9.7 12.2 11.9 CM 1585-13 14.5 15.4 14.6 14.4 5.9 7.2 11.4 11.1 HMC-1 16.2 19.2 18.5 19.5 8.3 9.0 10.8 9.1 HMC-2 15.0 14.5 15.4 13.2 4.2 5.4 7.2 5.8 CMC 40 10.1 13.4 12.5 11.6 3.2 4.9 4.2 3.8 M Col 1684 14.0 13.9 14.3 16.2 4.4 10.0 10.5 9.5 M Cub 74 13.1 14.1 14.2 14.9 4.8 7.9 8.8 10.5 M Pan 70 14.9 16.6 16.4 16.1 5.6 9.9 10.9 9.2 M Ven 25 14.3 15.3 15.7 14.2 8.5 10.7 12.2 12.4 SG 105-35 14.9 15.8 16.2 15.4 3.9 9.1 11.8 10.7 Average 13.6 15.9 15.5 15.2 5.3 8.5 9.8 9.7 LSD 5% for cultivars 2.6 2.8 3.9 2.8 2.2 2.2 2.3 2.7 LSD 5% for K levels 1.2 1.2 0.6 Cultivar Total HCN content (ppm) In year 2 of potassium fertilizer application In year 5 of potassium fertilizer application (kg/ha) at: (kg/ha) at: 0 50 100 200 0 50 100 200 M Col 1505 297 183 171 216 329 259 243 210 CM 91-3 217 173 157 140 264 263 225 179 CM 489-1 308 190 160 158 334 201 133 161 CM 507-37 671 401 406 401 1169 1049 674 780 CM 523-7 281 163 142 134 331 313 370 265 CM 1585-13 201 148 168 148 219 205 153 178 HMC-1 206 187 163 141 202 173 193 188 HMC-2 307 149 134 112 449 423 370 353 CMC 40 185 140 177 182 124 163 147 103 M Col 1684 765 570 523 647 986 1074 996 754 M Cub 74 297 177 124 127 282 221 246 273 M Pan 70 271 236 182 208 216 256 206 181 M Ven 25 1034 955 812 926 1969 1625 1462 1403 SG 105-35 417 203 241 214 281 209 190 647 Average 390 277 254 268 511 460 401 405 LSD 5% for cultivars 255 141 143 105 207 208 227 651 LSD 5% for K levels 75 48 SOURCE: El-Sharkawy and Cadavid L (2000). 132 Soils and Fertilizers for the Cassava Crop Table 5-19. Response of cassava to applications of several levels of N, P, and K in five sites of the region covering Mondomo and Pescador, Cauca, Colombia, 1983. Fertilizera Fresh-root yield (t/ha) Average Mondomito Agua Blanca Telecom Tres Quebradas Pescador N0P0K0 8.5 12.7 13.0 10.2 3.3 9.5 N0P2K2 11.0 25.5 25.9 16.5 12.6 18.3 N1P2K2 13.6 20.5 21.8 18.4 13.1 17.5 N2P2K2 11.0 24.8 27.1 23.2 16.2 20.5 N3P2K2 13.8 29.7 27.3 29.2 19.7 23.9 N2P0K2 8.0 13.2 16.0 9.3 6.0 10.5 N2P1K2 14.3 25.2 23.5 21.5 15.0 19.9 N2P3K2 12.0 24.6 26.4 24.7 19.6 21.5 N2P2K0 10.6 25.5 23.1 14.8 7.4 16.3 N2P2K1 14.3 24.9 25.9 17.8 16.5 19.8 N2P2K3 14.4 26.3 24.6 24.8 16.7 21.4 N3P3K3 18.5 28.0 27.3 29.9 12.3 23.2 a. Sources of fertilizer: N0 = 0 N1 = 50 N2 = 100 N3 = 200 kg N/ha as urea. P0 = 0 P1 = 50 P2 = 100 P3 = 200 kg P/ha as triple superphosphate. K0 = 0 K1 = 50 K2 = 100 K3 = 200 kg K/ha as potassium chloride. SOURCE: Cadavid L and Howeler (1984). 30 25 20 15 10 5 0 0 250 500 750 10–30–10 fertilizer (kg/ha) Figure 5-10. Effect of chemical fertilizer application on average yield of cassava cv. CMC 92 in the Mondomo Region, Cauca, Colombia (from Cadavid L 1997). 35 30 25 20 15 10 5 0 CMC 92 Regional Amarilla Batata Selección Average No fertilizer application With fertilizer application Figure 5-11. Effect of chemical fertilizer application on yield of four cassava cultivars in soils prepared by plowing with ox (one pass), Mondomo, Cauca, Colombia (from Cadavid L 1997). 133 Fresh-root yield (t/ha) Fresh roots (t/ha) Cassava in the Third Millennium: … 45 40 35 30 25 20 15 10 5 0 Check Terciopelo Zornia Centrosema Guandul Groundnut Cowpea Indigofera Kudzu Green manure Green manure + 10–30–10 Figure 5-12. Effect of (1) incorporating green manures and (2) these plus 10–30–10 fertilizer on yield of cassava cultivar M Col 1684 in an exhausted Ultisol of Santander de Quilichao, Cauca, Colombia, 1984 (from Cadavid L 1995; Cadavid L 1987). Table 5-20. Effect of source and application of P on cassava yield at two sites (San Julian and Mondomito), Cauca, Colombia. P (kg/ha) Fresh-root yield (t/ha) San Juliana 1981 Mondomitob 1983 P sourcec Application (t/ha) M Col 1684 M Col 1458 CMC 92 M Col 1468 0 46.9 29.4 25.8 12.7 25 57.2 31.1 25.5 18.1 4.2 50 50.5 33.5 28.1 19.3 Manure 8.4 25 57.8 41.9 25.3 13.0 1.9 50 52.7 33.5 26.7 23.7 Chicken manure 3.8 25 49.9 39.2 28.2 17.8 0.191 50 49.1 36.5 26.2 16.5 10–30–10 0.382 a. Santander de Quilichao, virgin plot. b. Mondomo. c. Sources of phosphorus (analysis): P source Content (%) of: N P K Ca Mg Manure 2.0 0.6 1.7 2.9 0.6 Chicken manure 2.7 1.3 2.0 7.7 0.7 10-30-10 10.0 13.1 8.3 SOURCE: Cadavid L (1995). 134 Fresh-root yield (t/ha) Soils and Fertilizers for the Cassava Crop Table 5-21. Effect of green manure on yield of cv. CM 507-37 in an exhausted soil of Santander de Quilichao, Cauca, Colombia, planted over 3 consecutive years (1990–1993), with no chemical fertilizer applications. Green manure incorporated Fresh-root yield (t/ha) in 1st cycle 2nd cyclea 3rd cyclea All 3 cycles No green manure 27.4 22.5 12.7 20.9 Zornia latifolia 34.1 26.6 19.7 26.8 Common weedb 32.3 21.0 16.3 23.2 Pueraria phaseoloides 47.1 27.3 16.1 30.2 Arachis pintoi 37.9 22.8 18.3 26.3 Macroptilium gracile 30.5 23.6 16.1 23.4 Centrosema acutifolium 45.5 25.3 20.9 30.6 Desmodium ovalifolium 43.4 24.1 21.5 29.7 a. Residual effect of green manure. b. Common grass (Paspalum sp.). SOURCE: Cadavid L (1995). Table 5-22. Effect of tilling, mulching, and chemical fertilizer applications on the chemical characteristics of a sandy soil, Pivijay, Magdalena, Colombia, over 6 years. Tilling method 15–15–15 fertilizer at 330 kg/ha No chemical fertilizer application Period OM Bray II P Ca Mg K OM Bray II P Ca Mg K (%) (1:1 pH) (ppm) ( meq/100 g soil) (%) (1:1 pH) (ppm) (meq/100 g soil) Soil before tillinga — — — — — — 0.18 6.10 3.38 0.87 0.28 0.05 Conventional 1.20 5.40 18.88 0.34 0.08 0.05 1.10 5.35 8.25 0.34 0.07 0.04 1988/89 Conventional with to mulcha 1.33 6.25 23.43 0.79 0.38 0.13 1.45 6.50 13.65 0.86 0.49 0.17 Zero tilling 1.05 5.53 17.30 0.36 0.08 0.05 1.08 5.30 9.43 0.36 0.07 0.04 1993/94 Zero tilling with mulcha 1.48 6.28 27.03 0.77 0.45 0.16 1.45 6.43 14.50 0.80 0.46 0.16 a. Previous crops: cassava, maize, and sesame. SOURCE: Cadavid L et al. (1995). Table 5-23. Factors for converting expressions in oxide bases to expressions in element bases and vice versa.a To better understand this formula, let us observe the following example: P2O5 × 0.44 or (0.4364)a = P P × 2.29 or (2.2914) = P2O5 RN = 70.0 kg K/ha K2O × 0.83 or (0.8302) = K A = 89 ha K × 1.20 or (1.2046) = K2O PC = potassium chloride (KCl from 60% K2O) CaO × 0.71 or (0.7147) = Ca Ca × 1.40 or (1.3992) = CaO In the first place, we must convert K2O to K: MgO × 0.60 or (0.6030) = Mg Mg × 1.66 or (1.6582) = MgO 60% K2O × 0.8302 = 49.81 K or, SO4 × 0.33 or (0.3333) = S more exactly: S × 3.00 or (3.0000) = SO4 60% K2O/1.2 = 50 K a. Values in parentheses should be used for calculations demanding high accuracy. This means that 100 kg of commercial product SOURCE: Monómeros Colombo-Venezolanos (1989). (KCl) has 50 kg of K (DNCP), giving rise to the formula: 70 kg K 100 kg KCl CP = × × 89 ha 1 ha 50 kg K CP = 140 kg KCl × 89 = 12,460 kg = 12.46 t KCl 135 Cassava in the Third Millennium: … References Cadavid L, LF; Calvo FA; Howeler RH. 1977. La interacción de cal con fósforo y elementos menores en la To save space, the acronym “CIAT” is used instead of producción de yuca (Manihot esculenta) en Oxisoles “Centro Internacional de Agricultura Tropical”. de los Llanos Orientales de Colombia. CIAT, Cali, Colombia. 25 p. Cadavid L, LF. 1980. El uso de rocas fosfóricas en el cultivo de la yuca (Manihot esculenta Crantz). CIAT, Cadavid L, LF; Acosta A; El-Sharkawy M. 1995. Efecto de Cali, Colombia. 38 p. preparación, mulch y abonamiento en el cultivo de la yuca (Manihot esculenta Crantz) en suelos arenosos Cadavid L, LF. 1987. Abonos verdes en suelos agotados de Colombia. Suelos Ecuat 25:7–8. dedicados a la siembra de yuca (Manihot esculenta Crantz). Suelos Ecuat 17(2):178–183. Calderón SF. 1991. Concepción moderna de la nutrición vegetal. In: Fundamentos para la interpretación de Cadavid L, LF. 1988a. Efecto de fertilización y humedad análisis de suelos, plantas y aguas para riego. relativa sobre la absorción y distribución de nutrientes Sociedad Colombiana de la Ciencia del Suelo (SCCS), en yuca (Manihot esculenta Crantz). Master’s thesis. Bogotá, DC, Colombia. Facultad de Ciencias Agropecuarias, Universidad Nacional de Colombia–Palmira, Colombia. 290 p. Cano CA. 1999. Las micorrizas arbusculares, su importancia y usos en la agricultura. La Mina S.A., Cadavid L, LF. 1988b. Respuesta de la yuca (Manihot Guatemala. 12 p. (Multicopied.) esculenta Crantz) a la aplicación de NPK en suelos con características diferentes. Facultad de Ciencias Cassanova O, EF. 1996. Introducción a la ciencia del suelo. Agropecuarias, Universidad Nacional de Colombia– 2nd ed. Universidad Central de Venezuela, Caracas, Palmira, Colombia. 199 p. Venezuela. 379 p. Cadavid L, LF. 1995. Utilización de abonos verdes en El-Sharkawy MA; Cadavid L, LF. 2000. Genetic variation suelos dedicados a la siembra de yuca (Manihot within cassava germplasm in response to potassium. esculenta Crantz). 17 p. (Multicopied.) Exp Agric (UK) 36(3):323–334. Cadavid L, LF. 1997. Manejo productivo de suelos de El-Sharkawy MA; Cadavid L, LF; Mejía de Tafur S; Caicedo ladera cultivados con yuca (Manihot esculenta JA. 1998. Genotypic differences in productivity and Crantz). In: Seminar on “Fertilidad del suelo y su nutrient uptake and use efficiency of cassava as potencial productivo, fundamentos para la influenced by prolonged water stress. Acta Agron interpretación de análisis de suelos, plantas y aguas 48(1–2):9–22. para riego: Seminario fertilidad del suelo y su potencial productivo”, held in Palmira, Valle del Garavito NF. 1979. Propiedades químicas de los suelos. Cauca, 1995. Sociedad Colombiana de la Ciencia del 2nd ed. Instituto Geográfico “Agustín Codazzi” (IGAC), Suelo (SCCS), Bogotá, DC, Colombia. p 134–143. Subdirección Agrológica, Bogotá, DC, Colombia. 321 p. Cadavid L, LF. 2000. Nutrición del cultivo de la yuca (Manihot esculenta Crantz). In: Training course on Garcidueñas RM. 1993. Fisiología vegetal aplicada. 4th ed. “Sistemas de producción de yuca, Santo Domingo de MacGraw-Hill/Interamericana, Mexico City, DF, Mexico. los Colorados, Ecuador, febrero 2000”. Consorcio 275 p. Latinoamericano y del Caribe de Apoyo a la Investigación y al Desarrollo de la Yuca (CLAYUCA), Guerrero RR. 1980. Hacia la formulación de un modelo Palmira, Colombia. suelo-planta. In: Silva MF, ed. Fertilidad de suelos: Diagnóstico y control. 12th ed. Sociedad Colombiana Cadavid L, LF; Calle CF. 1997. La fertilización de la yuca de la Ciencia del Suelo (SCCS), Bogotá, DC, (Manihot esculenta Cranz). 13 p. (Multicopied.) Colombia. p 1–10. Cadavid L, LF; Howeler RH. 1984. La fertilización de la Howeler RH. 1981. Nutrición mineral y fertilización de la yuca (Manihot esculenta Crantz) en la región de yuca (Manihot esculenta Crantz). CIAT, Cali, Mondomo y Pescador, Cauca. Suelos Ecuat Colombia. 55 p. 17(2):178–183. 136 Soils and Fertilizers for the Cassava Crop Howeler RH. 1983. La función de las micorrizas vesículo- Monómeros Colombo-Venezolanos. 1989. Los fertilizantes arbusculares en la nutrición fosfórica de yuca. Suelos químicos, propiedades y comportamiento Ecuat 13(2):51–61. agronómico. Serie Punto Verde, No. 6. Bogotá, Monómeros Colombo Venezolanos, S.A. 54 p. Howeler RH; Cadavid L, LF. 1983. Accumulation and distribution of dry matter and nutrients during a Sánchez PA. 1968. Conferencias de fitopatología y control 12-month cycle of cassava. Field Crops Res de enfermedades. Facultad de Ciencias 7:123–139. Agropecuarias, Universidad Nacional de Colombia– Palmira, Colombia. 146 p. Howeler RH; Cadavid L LF. 1990. Short- and long-term fertility trials in Colombia to determine the nutrient Sánchez de P, M. 1999. Endomicorrizas en requirements of cassava. Fertil Res 26(1–3):61–80. agroecosistemas colombianos. Departamento de Ciencias Básicas, Universidad Nacional de Colombia– INIVIT (Instituto Nacional de Investigaciones de Viandas Palmira, Colombia. 227 p. Tropicales). 1999. Hoja divulgativa. Cuba. 2 p. Sieverding E. 1984. Aspectos básicos de la investigación INPOFOS (Instituto de la Potasa y el Fósforo). 1993. de la micorriza vesículo arbuscular. In: Sieverding E; Diagnóstico del estado nutricional de los cultivos. Sánchez de P, M; Bravo O, N, eds. Investigaciones Quito, Ecuador. 55 p. sobre micorrizas en Colombia: Proc. Primer Curso Nacional sobre Micorrizas en Colombia, Palmira, Kramer PJ. 1989. Relaciones hídricas de suelos y plantas, febrero 1984. Facultad de Ciencias Agropecuarias, una síntesis moderna. Editorial Harla, Mexico. Universidad Nacional de Colombia–Palmira, 538 p. Colombia. p 1–14. Malavolta E; Vitti GC; Oliveira SA de. 1989. Avaliação do Thompson LM. 1965. El suelo y su fertilidad: Propiedades estado nutricional das plantas: Princípios e físicas, biológicas y químicas del suelo en relación aplicações. Associação Brasileira para Pesquisa de con su formación, clasificación y tratamientos desde Potassa e do Fosfato (POTAFOS), Piracicaba, Brazil. el punto de vista de la fertilidad. 3rd ed. Editorial 201 p. Reverté S.A., Barcelona, Spain. 410 p. 137 Cassava in the Third Millennium: … CHAPTER 6 Conservation of Soil under Cassava Cultivation Luis Fernando Cadavid L.1 General Considerations cultivation, thus changing their potential use. According to Cadavid L (1987, 1988, 1990, 1997) and Cassava is a hardy crop, able to endure long dry periods Howeler and Cadavid L (1984), results have been and adapt to a wide range of soils and climates. It is disheartening in that deforestation has increased and, planted in soils with textures that range from sandy therefore, so have soil loss to erosion (whether hydric through loamy to clayey. It is grown at altitudes between or anthropic erosion), and soil nutrient loss to both sea level and 1700 m, but prefers temperatures that runoff and high extraction by the crop (chemical average 24 °C and a relative humidity of about 72%. erosion). Table 6-1 outlines the principal chemical and In recent decades, soil erosion has increased physical characteristics of the soils where cassava is alarmingly, because of misuse of this resource. Such planted in Colombia. As can be observed, a high degradation of soils (both physical and chemical, percentage of these soils, which occupy a large area of especially in hillsides) produced by humans has caused our national territory (Figure 6-1), presents low contents widespread poverty among rural inhabitants and, of N, P, K, Ca, Mg, S, B, and Zn, thus constituting consequently, given rise to mass migration towards limitations for the crop’s development and growth. large cities, which, in turn, has created more belts of Chapter 5 of this volume describes the critical levels of extreme poverty (Cadavid L 1990). soil parameters established for cassava. Colombia has 114,179,000 hectares, of which Normally, this crop is planted in flat areas or in 49.5% present some form of erosion, whether severe, regions where slopes are less than 15%. However, moderate, or light. In 9,705,150 of these hectares because of population pressure on land to produce (8.52%), the soil situation is serious, perhaps difficult to food, hillsides are being brought under cassava recover, according to data outlined in Table 6-2 (IGAC 1987, cited by Cobo 1998). Howeler (1986) indicates that, according to a United Nations study, Colombia is losing every year 426 million tons of soil, which corresponds to 3.7 t/ha of national territory. One example is in the upper Cauca where, according to Suárez (1984, cited by Cadavid L 1987, 1988, 1990), of the 2,200,000 ha under CVC jurisdiction, 800,000 present problems of erosion and, of these, 100,000 suffer severe to very severe erosion (Table 6-3). We point out that, in this country, a high percentage of cassava is planted in hillside areas, on slopes of more than 15%, in soils of low fertility, and 1. Soil Agronomist, formerly of Cassava Production Systems, CLAYUCA, Cali, Colombia. under poor management. Such cases include the E-mail: luisfernandocadavidlopez@yahoo.es region of Mondomo, Pescador, and San Antonio in 138 Conservation of Soil under Cassava Cultivation 139 Table 6-1. Chemical and physical characteristics of the soils where cassava is planted in Colombia. Site Department pH OM Al Na Ca Mg K Al Na P S Zn B Mn EC Bouyoucos BD 1:1 (%) sat. sat. (mmhos/ textureb (g/cm3) (meq/100 g) (%) (%) (ppm) cm)a Nus Antioquia 5.1 4.0 0.70 — 1.60 0.70 0.10 22.6 — 7.0 — 2.00 0.10 — — SCL 1.40 Luruaco Atlántico 7.5 2.7 — 0.39 22.10 10.10 0.45 — 1.18 42.5 — — — — — C 1.50 Malambo Atlántico 6.2 0.6 — 0.17 1.67 1.00 0.06 — 5.86 4.2 — — — — — S — Caloto Cauca 5.7 10.4 — — 21.40 12.00 0.20 — — 3.0 — — — — — C — S. de Quilichao Cauca 4.3 8.1 2.73 — 1.95 0.82 0.22 47.7 — 10.5 — 2.40 0.46 — — C 1.00 Paz de Ariporo Casanare 4.7 0.9 1.40 0.10 0.18 0.06 0.10 76.1 5.43 3.5 — 0.26 — 0.86 0.07 SL 1.50 Paz de Ariporo Casanare 4.5 2.2 2.00 0.11 0.10 0.06 0.16 82.3 4.53 2.0 — 0.27 — 3.09 0.10 SL 1.50 Yopal Casanare 4.5 1.9 3.70 0.10 1.40 0.90 0.20 58.7 1.58 97.0 1.5 4.90 0.10 — — L — Ayapel Córdoba 4.8 2.8 2.20 — 0.30 0.20 0.05 80.0 — 3.0 — 1.00 0.20 — — SC 1.30 Ricaurte Cundinamarca 7.5 2.2 — 0.16 26.55 3.00 0.48 — 0.53 215.0 — — — — — SiCL 1.50 Armenia Quindío 5.8 1.6 0.15 0.22 4.63 0.86 0.49 2.4 3.46 21.0 7.0 5.80 0.04 0.18 — SL 1.40 Barragán Quindío 5.6 2.9 0.18 0.10 4.50 1.40 0.45 2.7 1.50 36.0 9.0 16.00 0.01 — — SiL 1.20 Montenegro Quindío 5.5 2.1 0.08 0.28 3.17 0.86 0.83 1.5 5.36 30.0 8.0 7.00 0.10 0.25 — SL 1.43 Villavicencio Meta 4.7 4.6 2.86 — 0.49 0.17 0.13 78.4 — 11.8 — 0.30 — — — C 1.30 La Tebaida Quindío 6.0 1.1 — 0.09 5.10 2.36 0.59 — 1.11 9.0 0 7.70 0.01 0.41 — SL 1.40 Montenegro Quindío 5.5 0.7 0.12 0.09 4.45 1.11 0.74 1.8 1.38 26.0 3.0 0.30 0.01 0.50 — SL 1.40 Candelaria Valle 6.9 1.4 — 0.46 11.30 4.62 0.39 — 2.74 83.0 — — — — — SCL 1.35 El Zulia Norte de Santander 6.3 2.9 — — 0.77 1.70 0.60 — — 108.0 — 2.60 — — — SC — El Zulia Norte de Santander 6.9 2.7 — — 4.20 1.40 0.32 — — 15.0 — 4.50 — — — SCL 1.50 San Cayetano Norte de Santander 5.2 1.9 0.20 — 1.30 0.60 0.14 8.9 — 2.0 — 14.80 — — — SC — LQ1 CIAT Valle 6.8 2.8 — 0.17 14.90 7.32 0.36 — 0.74 41.5 15.0 3.70 0.56 — — SiC 1.49 LN3 CIAT Valle 6.9 6.1 — 0.17 9.21 7.60 0.85 — 0.95 79.0 35.5 — 0.62 — — CL 1.60 Jamundí Valle 4.7 6.0 1.59 — 3.24 0.71 0.39 26.8 — 6.3 127.4 3.20 0.49 — — C 1.10 B/bermeja Santander 4.8 2.4 1.47 — 1.25 0.37 0.06 16.7 — 2.8 — 0.40 0.20 2.60 — SCL 1.34 El Zulia Norte de Santander 6.1 1.0 — 0.08 2.50 0.42 0.13 — 2.56 5.0 5.0 2.10 0.32 27.30 — CL 1.35 LP3 CIAT Valle 7.2 2.2 — 0.26 12.62 8.36 0.77 — 1.18 53.5 0.33 4.83 0.78 0.69 — SiC 1.60 Jamundí Valle 5.0 6.0 0.26 — 5.86 1.47 0.72 3.1 — 5.3 95.5 3.28 0.54 — — C 1.10 Buga Valle 6.3 1.4 — 0.22 8.33 5.56 0.11 — 1.55 40.2 42.0 4.08 0.35 — — CL 1.58 Caicedonia Valle 5.5 2.6 0.21 — 5.42 0.74 0.38 3.1 — 49.8 46.2 9.47 0.39 — — SCL 1.35 Ortega Tolima 7.4 1.4 — 0.23 19.90 4.10 0.56 — 0.93 44.9 — 0.70 — 52.6 — SL 1.50 Purificación Tolima 6.8 0.5 — 0.17 11.30 3.90 0.42 — 1.08 40.9 — 2.30 — 37.3 — SL 1.50 Agua Azul Casanare 5.5 0.8 0.09 1.09 3.76 1.21 0.46 1.4 16.5 47.0 15.0 6.60 0.03 41.0 0.42 SL — Sardinata Norte de Santander 5.1 1.8 0.40 — 0.90 0.40 0.08 22.5 — 18.0 — 0.10 — 36.2 — CL 1.35 Espinal Tolima 6.0 0.3 — 0.33 4.50 1.10 0.17 — 5.40 23.3 — — — — — SL 1.40 Mondomo Cauca 4.5 7.2 5.70 — 0.79 0.30 0.23 73.0 — 1.76 — — — — — C 0.87 Pescador Cauca 4.6 8.5 3.10 — 0.47 0.15 0.11 81.0 — 1.20 — — — — — C — Santo Tomás Atlántico 5.8 1.5 — — 1.43 0.41 0.11 — — 3.10 — — — — — S 1.48 Media Luna Magdalena 6.1 0.2 — — 0.87 0.28 0.05 — — 8.3 — — — — — S 1.50 a. EC = electrical conductivity. b. C = clay, CL = clay loam, L = loam, S = sandy, SC = sandy clay, SCL = sandy clay loam, SiCL = silty clay loam, SiC = silty clay, SiL = silt loam, SL = sandy loam. Cassava in the Third Millennium: … S (<8 ppm) Ca and Mg (<0.25 and <0.12 meq/100 g) OM as % (<2%) acid pH P (<10 ppm) K (<0.15 meq/100 g) Na saturation as % (>3%) Zn (<1 ppm) B (<0.15 ppm) Figure 6-1. Nutritional problems of the cassava crop in Colombia, by region. Table 6-2. Erosion records, Colombia. Table 6-3. Degrees of erosion according to the universal soil loss equation (USLE). Intensity Current intensity of erosion in Colombia Loss (t/ha per year) Degree Affected area Proportion of country’s 10 1 very light (ha) surface area (%) 10 to 20 2 light Very severe 829,575 0.73 20 to 100 3 moderate Severe 8,875,575 7.79 100 to 300 4 severe Moderate 14,706,795 12.90 300 5 very severe Light 26,337,546 23.11 0 irreversible damage Very light 5,675,950 4.96 SOURCE: Curiel (1986, cited by Cadavid L 1987). No erosion 55,508,310 48.53 Other areasa 2,259,049 1.98 Total 114,174,800 a. They correspond to marshes, swamps, rivers, and urban areas. SOURCE: Cobo (1998). 140 Conservation of Soil under Cassava Cultivation northern Cauca; hillside areas of northern Valle del Planting system Dry soil loss (t/ha) Cauca; and many areas of Quindío, Risaralda, Tolima, and Norte de Santander. Cassava is planted Double furrows of cassava with four of cowpea 105 under the current production system of monoculture, with two or more continuous plantings and no agronomic management practices. Except for the soils of Quindío, Risaralda, and 60 240 60 Norte de Santander, many of these regions present soils with very low contents of P, K, Ca, Mg, and Zn (Table 6-1), particularly presenting deficiencies of P Cassava intercropped with cowpea 50 and K. Hence, yields are less than 10 t/ha (Figure 6-2; Cadavid L 1997). These demonstrate how the state of soil erosion determine yield and that applying only P cannot re-establish soil productivity lost through this cause (Howeler 1984). 80 Because of inadequate practices of both soil and cassava crop management in a soil classified as Conventional preparation, using oxen 43 Inceptisol (Typic Dystrandept; an Andosol in the recent classification) in Mondomo, Cauca, Colombia, about 100 t/ha of dry soil were lost from a planting of cassava that alternated with cowpea (Vigna sinensis) 80 after 10 months (Figure 6-3; Howeler 1984; Cadavid L 1990). Also in the same soil, when cassava was planted in monoculture and without Cassava on ridges 40 agronomic management practices, about 40 t/ha of dry soil were lost in a cycle of 10 months (Figure 6-3). Table 6-4 indicates soil loss, according to 80 management, in a field at Agua Blanca, Mondomo, Double furrows of cassava intercropped with a grass 17 35 30 25 20 60 140 60 140 60 15 10 Cassava with maize mulch 11 5 0 P at 0 kg/ha P at 50 kg/ha Eroded soil Non-eroded soil 80 cm Figure 6-2. Effect of applying P on the production of cassava cv. CMC 92 in eroded and non-eroded soils, Figure 6-3. Effect of several cassava planting systems on soil Mondomito, Cauca, Colombia. loss through erosion over 10 months, Mondomito, SOURCE: Howeler and Cadavid L (1984, cited by Cauca, Colombia. Cadavid L 1997). SOURCE: Howeler and Cadavid L (1982). 141 Fresh-root yield (t/ha) Cassava in the Third Millennium: … Table 6-4. Cassava yield and total quantity of eroded soil after receiving various soil conservation practices, Agua Blanca, Cauca, Colombia. Treatment Cassava yield Dry soil erosion (t/ha)a (t/ha)b 1. Preparation with oxen; applications of lime, no fertilizer, planting at 80 × 80 cm 6.9 35.9 2. Preparation with oxen; applications of lime and fertilizer, planting at 80 × 80 cm 13.6 22.9 3. Preparation with oxen; applications of lime, fertilizer, and maize mulch; planting at 80 × 80 cm 15.9 15.1 4. Preparation with hoe, strips 1 m wide with double furrows; 1 m no preparation 15.6 14.1 5. Preparation with oxen; double furrows; cassava alternating with 1 m of imperial grass 15.8 19.8 6. Preparation with oxen; double furrows; cassava alternating with 1 m of Brachiaria grass 13.3 9.8 7. No preparation; planting with a barretón (long-handled digging stick) at 80 × 80 cm; applications of lime and fertilizer 17.6 9.8 a. Average of three varieties: CMC 92, Batata, and Regional Amarilla. b. Loss over 14 months between planting and harvesting the cassava crop. SOURCE: Howeler (1984). Cauca, Colombia, planted with cassava (cvs CMC 92, paradoxically, within a period of no more than Batata, and Regional Amarilla) in a 14-month cycle. As 10 years, land with steep slopes and no conservation observed, soil losses are high as soil preparation tasks practices to protect it from erosion, will lose a layer of intensify and increase even more when fertilizers are up to 1 cm thick (Torres 1981). not applied. Productive Management of Soils under Because of these and other inadequate practices Cassava Cultivation of soil use and management, the Mondomo Region and other similar areas of the national territory show Despite the constraints mentioned above, viable symptoms of hydric erosion, chemical degradation alternatives exist for recovering, conserving, and (high extraction by crop and runoff), and severe increasing the fertility and productivity of soils under biological degradation (Figure 6-4). cassava cultivation. Increases can be made in terms of yield of tuberous roots, their improved quality, and Research on these alarming results has planting materials of excellent vigor. demonstrated that the formation of 1 cm of soil from sandy material requires 200 to 400 years, or 3000 to Managing hillside soils 12,000 years are needed to develop a deep soil, suitable for cultivation (Ortiz 1986). However, With the current management of hillside soils under cassava cultivation, farmers obtain very low yields and cause irreversible damage to the soil through high erosion rates. The recommendation is to intensify the crop, making it more profitable through increasing yield per hectare. This, in its turn, makes reducing the planting area and preparation systems feasible, thus leaving the steepest soils in fallow or under forest (Howeler 1984). The idea is to change the predominant scheme of migratory (slash-and-burn) or subsistence agriculture in many areas of the American tropics and arrive at a sustainable, more profitable, and competitive agriculture. Table 6-5 lists viable management alternatives for achieving this objective, as according to several research projects. Figure 6-4. Severe erosion in the Mondomo Region, Cauca, Colombia. Preparing the soil. It is usually believed that, for a SOURCE: Cadavid L (1987). cassava crop to successfully germinate, grow, and 142 Conservation of Soil under Cassava Cultivation Table 6-5. Practices for improving the management of hillside soils and increasing cassava yields. 1. Improve planting materials through selection and treatment of cassava stakes. 2. Reduce planting area by using improved farming techniques and reducing planting on steep slopes. 3. Reduce land preparation (zero and minimum tilling). 4. Prepare the soil and plant seed according to contour lines. 5. Use suitable fertilizer applications. 6. Plant strips of live barriers. 7. Cover soil with mulches of sugarcane, maize, or weeds themselves. 8. Plant green manures and incorporate them. develop, indiscriminate use of agricultural machinery In soils with slopes of more than 10%, a team of (plows, rakes, and rotovator) are needed to break up oxen is normally used, together with a plow. However, the ground, leaving it as loose as possible for planting. by planting cassava and being ignorant of adequate However, this results in negative consequences, not management techniques, farmers place pressure on only for soil structure by increasing aggregation and these lands, causing severe damage to soil structure compaction, but it also leads to later soil loss through and loss of organic matter and nutrients through hydric erosion (Cadavid L 1987). erosion (Tables 6-6, 6-7, and 6-8). Table 6-6. Total loss of dry soil (t/ha) through erosion after removing eight species from that land during 1989–1993, Sri Racha, Thailand. The soil is a sandy loam and has a 7% slope. Cropping cycles First period Second period Total (no.) (28 months) (22 months) (50 months) Cassava for root production 4 168.5 a 142.8 a 311.3 Cassava for leaf production 2 138.5 ab 68.8 b 207.3 Maize 5 35.5 cd 28.5 d 64.0 Sorghum 5 46.1 cd 42.9 c 89.0 Groundnut 5 36.2 cd 37.6 cd 73.8 Mung bean 6 55.3 cd 70.9 b 126.2 Pineapplea 2 21.3 d 31.4 cd 52.7 Sugarcaneb 2 94.0 bc — — F test ** ** CV (%) 42.7 11.4 a. The second cycle is the ratoon crop. b. Only for a second period of 28 months. SOURCE: Putthacharoen et al. (1998, cited by Howeler 2001). Table 6-7. Nutrients found in sediments eroded from cassava plots that had received various treatments, Thailand and Colombia. Site and treatment Dry soil loss Missing nutrients (kg/ha per year) (t/ha per year) Na Pb Kb Mgb Cassava, 7% slope, Sri Racha, Thailandc 71.4 37.1 2.18 5.15 5.35 Cassava, 5% slope, Pluak, Daeng, Thailandd 53.2 22.3 1.25 3.27 — Planted cassava, 7% to 13% slope, Quilichao, Colombiae 5.1 11.5 0.16 0.45 0.45 Cassava with legume cover, Quilichao, Colombiae 10.6 24.0 0.24 0.97 0.81 Cassava with grass barriers, Quilichao, Colombiae 2.7 5.8 0.06 0.22 0.24 Cassava planted on a 12%–20% slope, Mondomo, Colombiae 5.2 13.3 1.09 0.45 0.36 Cassava with a legume cover, Mondomo, Colombiae 2.7 6.5 0.04 0.24 0.20 Cassava with grass barriers, Mondomo, Colombiae 1.5 3.5 0.02 0.13 0.10 a. N total. b. Available P and interchangeable K and Mg. SOURCE: As cited by Howeler (2001): (c) Putthacharoen et al. (1998); (d) Tongglum et al. (2000); (e) Ruppenthal et al. (1997). 143 Cassava in the Third Millennium: … Table 6-8. Effect of two contrasting management treatments (T1 and T2) a of soil and crop on both runoff and soil loss through erosion such as nutrients lost in runoff and on the sediments eroded over 2 years of cropping cassava on a 7%–13% slope in Santander de Quilichao and on a 13%–20% slope in Mondomo, both sites in Colombia, cropping years 1987/88 and 1988/89. Variable or element Santander de Quilichao Mondomo 1987/88 1988/89 1987/88 1988/89 T1 T2 T1 T2 T1 T2 T1 T2 Runoff (m3/ha) 950 1750 1400 2420 340 1470 540 1000 Nutrients lost through runoff (kg/ha) Total P 0.16 0.33 0.22 0.47 0.08 0.39 0.13 0.26 Total K 1.49 2.79 1.58 3.08 0.61 3.26 1.47 3.96 Total Ca 2.67 3.50 2.96 5.45 1.29 5.11 2.88 7.56 Total Mg 0.43 0.58 0.30 0.75 0.14 1.22 0.20 1.01 Nutrients lost through 3.00 30.40 5.10 68.00 1.50 33.80 2.60 12.60 Dry soil loss (t/ha) eroded sediments (kg/ha) Interchangeable P 0.08 0.41 0.07 1.12 0.01 0.44 0.03 0.18 Interchangeable K 0.34 2.73 0.42 5.05 0.17 3.04 0.27 1.11 Interchangeable Ca 4.08 32.83 6.94 73.44 2.58 31.10 4.47 11.59 Interchangeable Mg 0.25 2.92 0.33 7.08 0.10 3.00 0.19 0.61 a. T1 = cassava planted according to contour lines; T2 = cassava planted in rows following the slope. SOURCE: Adapted from Reining (1992, cited by Howeler 2001). If the intensity of tilling is reduced, soil loss Zero and minimal tilling are systems in which soil through erosion can be diminished without losses through erosion are minimized, diminishing from significantly affecting cassava production. Moreover, by 50–100 t/ha of dry soil to less than 10 t/ha (Figure 6-3). following contour intervals, unprepared strips can be Costs are less and implementation is directly related to left and only the planting site is prepared or left without the soil structure; degree and class of plant cover tilling (Tables 6-9 and 6-10; Figure 6-5; Howeler and (organic matter content is an important factor); prior soil Cadavid 1982; Howeler 1984; Cadavid L 1987, 1990, management (e.g., quantity of chemical fertilizers and 1995). dung applied in previous plantings); degree of erosion, Table 6-9. Cassava yield and total quantity of eroded soil after applying various soil conservation practices, San Emigdio, Valle, Colombia. Treatment Cassava yield Dry soil erosion (t/ha)a (t/ha)b 1. Preparation of the entire land with a pick; fertilizer application; planting cassava at 80 × 80 cm 24.1 3.2 2. Preparation of 5-m-wide strips with a pick; planting cassava at 80 × 80 cm; alternating with 20.1 2.0 unprepared strips with 1-m width 3. Preparation with a pick; fertilizer application; planting of two furrows of cassava, alternating with 9.7 2.6 1 furrow of Brachiaria humidicola 4. Preparation with a pick; applications of fertilizer and maize mulch; planting at 80 × 80 cm 18.7 0.3 5. Preparation with a pick; 1-m-wide strips with double furrows of cassava, alternating with 30.5 2.2 unprepared strips with 1-m width 6. No preparation; fertilizer application; planting with a barretón (digging stick) at 80 × 80 cm 21.6 1.9 7. Preparation; little fertilizer application; planting with two furrows of cassava, alternating with 18.9 1.7 1 furrow of imperial grass 8. No preparation; no fertilizer application; planting with a barretón at 80 × 80 cm 6.5 2.4 a. Average of two varieties. b. Loss over 13 months between planting and harvesting the cassava crop. SOURCE: García (1984, cited by Howeler 1986). 144 Conservation of Soil under Cassava Cultivation Table 6-10. Effect of soil management on cassava yield and on soil loss through erosion on a plot with a 30% slope, Mondomito Region, Cauca, Colombia, 1985/86. Management systems Dry soil loss Yield of cultivar (t/ha)b (t/ha)a _ 1 2 3 X Oxen (one pass), no fertilizer 6.0 17.0 12.4 21.2 16.9 Oxen (one pass), with fertilizer 3.4 9.3 27.8 27.3 21.5 Strips, alternating with unprepared strips, with fertilizer 1.2 7.1 4.8 17.2 9.7 No preparation, with fertilizer 2.1 27.5 20.5 29.4 25.8 Oxen, with fertilizer, imperial grass barrier 3.5 20.4 14.4 24.1 19.6 Strip of cassava, with fertilizer, alternating with beans 2.3 18.6 19.0 11.3 16.3 a. 13 months after planting. b. 1 = Regional Amarilla; 2 = Selección 40; 3 = CMC 92 (Algodona). SOURCE: Cadavid L (1987). 32 36 This method aims to reduce the prepared area by 50%. One example is the case of cassava strips planted 28 two furrows to one of native grass without soil preparation. The whole area can be prepared and 24 28 intercropped with strips of grasses or legumes, 1 or 2 m wide, and alternating with strips of cassava planted on double furrow according to contour lines and across 20 the slope. 16 20 Figures 6-6, 6-7, 6-8, 6-9, and 6-10 outline research results on the effect of live barriers on cassava 12 production of the crop and on soil loss through erosion in the Mondomo Region, Cauca, Colombia (soils 8 12 36 10 4 32 9 28 8 0 4 24 7 1 2 3 4 Soil management 20 6 5 Regional Amarilla Batata 16 4 12 1. Ox, no fertilizer 3. Ox, fertilizer, maize mulch 3 8 2. Ox, fertilizer 4. No preparation, fertilizer 2 = Eroded soil 4 1 0 0 Figure 6-5. Effect of tilling method and fertilizer application 1 2 3 4 5 6 on the yield of two cassava cultivars and soil loss Soil management in an Inceptisol with a 45% slope, Agua Blanca, Mondomo, Cauca, Colombia, 1982/83. Regional Amarilla CMC 92 SOURCE: Adapted from Cadavid L (1990). 1. Ox, no fertilizer, hoe 5. Planting-hole method, 2. Ox, fertilizer, hoe fertilizer soil group or class, and the soil’s natural and potential 3. Ox, fertilizer, machete + 6. No preparation, fertilizer fertility; type and amount of weeds; and the variety to herbicide = Eroded soil 4. Planting-hole method, be planted (Howeler 1984; Cadavid L 1987, 1990). no fertilizer Live barriers. The live barriers are strips or rows Figure 6-6. Effect of preparation method with weeding and fertilizer application on the yield of two cassava of permanent plants, of dense growth, and planted cultivars and on soil loss through erosion with a 40% across the slope. The objective of these is to reduce slope. Tres Quebradas, Mondomo, Cauca, Colombia, the velocity of runoff, thus preventing soil drag and 1985/86. consequent loss of nutrients. SOURCE: Cadavid L (1990). 145 Fresh-root yield (t/ha) Dry soil erosion (t/ha) over 14 months Fresh-root yield (t/ha) Dry soil erosion (t/ha) over 13 months Cassava in the Third Millennium: … 32 6 8 28 32 5 24 4 6 20 24 16 3 12 2 4 8 16 1 4 0 0 1 2 3 4 5 6 8 2 Soil management Selección 40 CMC 92 0 0 1. Ox (1 pass), no fertilizer 5. Ox (1 pass), fertilizer, 1 2 3 4 2. Ox (1 pass), fertilizer imperial grass barrier 3. Ox (1-m strips), fertilizer 6. Ox (1 pass), fertilizer, Soil management 4. No preparation, fertilizer cassava + beans Regional Amarilla CMC 92 = Eroded soil 1. 1-m strips of native grass Figure 6-7. Effects of different agronomic practices on the yield 2. Ox, barrier of imperial grass of two cassava cultivars and dry soil loss with a 30% 3. Ox, barrier of king grass slope, Mondomito, Mondomo, Cauca, Colombia, 4. Ox, strips of cassava and beans 1985/86. = Eroded soil SOURCE: Cadavid L (1987, cited by Cadavid L 1990). Figure 6-9. Effect of live barriers and associated crops on the yield of two cassava cultivars and on soil loss through erosion with a 40% slope, Tres Quebradas, Mondomo, Cauca, Colombia, 1985/86. SOURCE: Cadavid L (1990). 28 36 24 20 28 16 20 12 8 12 4 0 4 1 2 3 Soil management Regional Amarilla Batata 1. Strip, hoe + native grass 2. Ox, strip of imperial grass 3. Ox, strip of Brachiaria humidicola Figure 6-10. Cassava alternating with strips of Brachiaria = Eroded soil humidicola, Mondomo Region, Cauca, Colombia. Figure 6-8. Effect of live barriers on the yield of two cassava SOURCE: Cadavid L (1987). cultivars and soil loss from an Inceptisol with a 45% slope, Agua Blanca, Mondomo, Cauca, Colombia, 1982/83. SOURCE: Adapted from Cadavid L (1990). 146 Fresh-root yield (t/ha) Fresh-root yield (t/ha) Dry soil erosion (t/ha) over 14 months Dry soil erosion (t/ha) over 13 months Fresh-root yield (t/ha) Dry soil erosion (t/ha) over 13 months Conservation of Soil under Cassava Cultivation classified as Inceptisols). As can be observed, this drops and risk of erosion is reduced (Table 5-19; management alternative is adequate and does not Figure 5-11). This theme was amply dealt with in prejudice crop yield. What is most important is the Chapter 5, this volume. management of the companion row or strip. Mulch effect. Howeler (1984, 1986) and Cadavid L Imperial (Axonopus scoparius) and brachiaria (1987, 1990, 1997) report that the protection of soil (B. decumbens and B. humidicola) are grasses that, against the impact of rain is also obtained by applying although they compete for light, are acceptable mulch, that is, plant residues such as maize stubble, barriers—the yield of intercropped cassava is grass, beans, rice straw, and banana leaves. acceptable—compared with king grass (Saccharum sinense), which causes drastic decline in production. Over time, mulch benefits both soil and crop, providing nutrients, increasing soil moisture, decreasing Cassava strips alternating with strips of native soil temperature, increasing macrofaunal activity (e.g., grasses (Pennisetum sp., P. purpureum, and Paspalum earthworms), and improving the water infiltration rate notatum) provide an intermediate alternative, although (Tables 6-9 and 6-12; Figure 6-5). the grasses’ aggressiveness and competitiveness need controlling. Other recommendable live barriers plants Table 6-12. Effect of mulches of several grasses and legumes are vetiver (Vetiveria zizanioides), lemon grass on the yields of maize, soybean, cowpea, and (Cymbopogon citratus), and citronella grass cassava in an Alfisol, Nigeria. (C. winterianus) (Ruppenthal 1995) (Table 6-11). Mulch Yield (t/ha) Maize Soybean Cowpea Cassava Fertilization effect. Without a doubt, this Check, no mulch 2.1 0.51 0.43 8.0 agronomic management practice has the most impact Panicum maximum 1.7 0.50 0.62 3.5 on a soil’s fertility and productivity and on cassava yields. Howeler (1986, 2001) and Cadavid L (1987, Brachiaria ruziziensis 3.8 1.14 1.04 17.4 1997) indicate that applying fertilizers to this crop not Melinis minutiflora 3.4 0.77 0.87 1.8 only increases yield, but it also produces more Centrosema pubescens 3.7 0.75 0.76 15.0 vigorous plants that also possess greater leaf area. Pueraria phaseoloides 3.4 0.80 0.79 19.5 Hence, soil is protected against the impact of rain Stylosanthes guianensis 3.1 0.91 0.67 19.8 SOURCE: Lal et al. (1981, cited by Howeler 1986). Table 6-11. Fresh-root yield of some cassava cropping systems in Santander de Quilichao and Mondomo for the first 4 to 5 years of the experiment1. Cropping system Yield (t/ha) in: Quilichao2 in period: Mondomo2 in period: 1987/893 1989/904 1990/91 1991/92 1988/895 1990/91 1991/92 Monoculture Following contour lines 30.7 a 28.4 35.6 a 23.3 a 15.3 a 15.4 abc 13.4 a In furrows on slope 28.3 a — — — 15.4 a — — On flat land 31.9 a 28.5 35.7 a 22.7 ab 19.7 a 18.4 13.5 a Minimum tillage 7.7 c — — — 15.7 a — — With mulches — 30.9 — — — — — With grass barriers Cassava + V. zizanioides — — 28.6 a6 23.5 a — 12.4 bc 12.2 a Cassava + P. purpureum 30.2 a7 24.4 23.6 a 16.2 ab 18.2 a 12.8 abc 11.0 a 1. Values with the same letters in a column are not significantly different. 2. In cropping periods 1990/91 and 1991/92, cassava was harvested at 11 months in Quilichao and at 8 and 9 months in Mondomo. 3. Average of two cropping periods, planting cassava variety CM 523-07; data from Reining (1992, cited by Ruppenthal 1995). 4. Data from LF Cadavid L, CIAT researcher, Santander de Quilichao, Colombia, The cassava variety was CM 507-37. 5. Cassava variety M Col 1522 (Algodona); data from Reining (1992, cited by Ruppenthal 1995). 6. 10-month-old cassava. 7. Only in the first 2 years; Paspalum notatum was planted as a grass barrier, following contour lines. SOURCE: Ruppenthal (1995). 147 Cassava in the Third Millennium: … According to Cadavid L (1990; 1997), mulch is a al. 1995) studied the effect of tilling and cover on soil system that can have mixed results. It may lead to properties and cassava yield over 5 consecutive years. excellent cassava yields and reduce risks of erosion They found that the interchangeable levels of K, Ca, (from 60% to 70%). However, it can have two serious and Mg were higher with cover; and that yield drawbacks: (1) if mulch is not handled properly, yields increased with applications of mulch, but not with are low; and (2) if it is not available on the farm (e.g., as tilling. residues of maize, beans, or the weeds themselves such as brachiaria or guinea grass), it is costly to As cited by Cadavid L et al. (1993), Hulugalle et al. transport. (1985) and Wade and Sánchez (1982) suggested that, in tropical Ultisols and without chemical fertilizer Managing soils in flat lands applications, crop yields may increase when tilling is combined with mulch applications, permitting Soil preparation and mulches. Hulugalle et al. increased absorption of nutrients, especially K. They 1987 (cited by Cadavid L et al. 1993) indicate that may also minimize soil crusting, reduce soil literature on the optimal tilling system for the cassava temperature, and improve water infiltration, thereby crop is scarce, as few studies have been conducted on protecting the soil more. this topic. According to the Food and Agriculture According to Cadavid L et al. (1993), a high Organization of the United Nations (FAO)2, in a sandy percentage of tropical soils present low fertility and are soil classified as a Cambic Arenosol, and planted for characterized by being very acid with low contents of N, 8 consecutive years with cassava in Media Luna, P, K, Ca, and Mg. Furthermore, soils may have Magdalena, Colombia, the use of mulch, together with undesirable physical conditions such as poor drainage, the preparation method, had a beneficial effect, being low capacity for water retention, high soil temperatures, highly significant for soil fertility and productivity and and fast infiltration rate. To these adverse factors are cassava yield (Cadavid L et al. 1993, 1995, 1998, added nutrient loss through runoff and leaching by Tables 5–23; Figures 6-11 and 6-12; Tables 6-13 to hydric and wind erosion, and high compaction caused 6-15). by poor soil management, as already commented above. Green manures effect. Green manures are crops, usually legumes, that are planted and, before flowering, Little research has been conducted on the optimal incorporated into the soil to improve it chemically and tilling system for cassava. However, some experiences with different soil classes in Africa and other tropical 70 5 regions have been reported in the last 13 years and may serve as an example of the different soils in which 60 4 cassava is planted in Colombia. 50 In a study carried out on a clayey and highly 40 3 weathered soil (Typic Paleudult) in southeastern Nigeria, the cassava crop was affected by tilling and 30 2 time (Gnahoua and Kabrah 1988). In the first planting 20 year, conventional tilling (subsoiling–raking–plowing) 1 increased yield by 10 t/ha, that is, 28.6 t/ha versus 10 18.6 t/ha for zero tilling. 0 0 N P K Ca Mg S DM We point out that, in the same study, the authors Nutrients and DM indicated that after 4 consecutive years, the positive Figure 6-11. Nutrient recycling (fallen leaves and petioles) in effects of conventional tilling disappeared and, as a cassava plants (cv. CM 523-7) at 10 months after result, yield declined from 28.6 to 16.8 t/ha, while planting and treatment with fertilizer applications, under zero tilling, yield remained constant at about Santander de Quilichao, Cauca, Colombia. 18 t/ha. SOURCE: Cadavid L (1988). 2. For an explanation of this and other acronyms and abbreviations, In an acid and low fertility Ultisol (Typic Paleudult) see Appendix 1: Acronyms, Abbreviations, and Technical of Nigeria, Hulugalle et al. (1990, cited by Cadavid L et Terminology, this volume. 148 Nutrient contents (kg/ha) Recycled DM (kg/ha) Conservation of Soil under Cassava Cultivation 149 Table 6-13. Effect of tilling, mulching, and chemical fertilizer application on the chemical characteristics of a sandy soil over 6 years, Pivijay, Magdalena, Colombia. Management With 330 kg/ha at 15–15–15 No chemical fertilizers Time OM pH P (ppm) Ca Mg K OM pH P (ppm) Ca Mg K (%) (1:1) Bray II (meq/100 g soil) (%) (1:1) Bray II (meq/100 g soil) Soil before managementa — — — — — — 0.18 6.10 8.38 0.87 0.28 0.05 1988/89 Conventional management 1.20 5.40 18.88 0.34 0.08 0.05 1.10 5.35 8.25 0.34 0.07 0.04 1993/94 Conventional management + mulch 1.33 6.25 23.43 0.79 0.38 0.13 1.45 6.50 13.65 0.86 0.49 0.17 Zero tilling management 1.05 5.53 17.30 0.36 0.08 0.05 1.08 5.30 9.43 0.36 0.07 0.04 Zero tilling management + mulch 1.48 6.28 27.03 0.77 0.45 0.16 1.45 6.43 14.50 0.80 0.46 0.16 a. Previous crops: cassava, maize, and sesame. SOURCE: Cadavid L et al. (1995). Table 6-14. Response, on average, of the aerial biomass, yield, and dry matter content of cassava (over 8 years of trials) and of total HCN content of roots (over 5 years of trials) to the following cultivation practices: mulching with plant residues, fertilizer applications, and tilling in sandy soils of northern Colombia. On-farm trials were initiated in 1988/89 in Media Luna, Magdalena, Colombia. Main treatment With fertilizer applicationa No fertilizer application Root Aerial Roots HCN in foliage Root Aerial Roots HCN in foliage yield biomass (DM, %)b and roots yield biomass (DM, %)b and roots (dw, t/ha)b (dw, t/ha) (dw, mg/kg) (dw, t/ha)b (dw, t/ha) (dw, mg/kg) Conventional tilling 5.51 3.18 30.2 158 2.19 1.43 30.1 227 Conventional tilling + mulch 5.92 3.98 30.9 146 4.66 2.93 30.6 149 No tilling 4.42 2.77 29.5 150 1.93 1.43 29.2 224 No tilling + mulch 6.11 3.85 31.0 140 4.66 2.95 30.4 158 Average 5.49 3.45 30.4 148 3.36 2.19 30.1 189 LSD 5%, Duncan’sd 0.26 0.31 NSc 12 LSD 5%, Duncan’se 0.77 0.68 0.88 18 0.35 0.49 0.77 0.32 a. Equal doses were applied per treatment of N, P, and K (50, 21, and 41 kg/ha, respectively) at 30 and 60 days after planting cassava. b. dw = dry weight; DM = dry matter. c. NS = not significant at a probability of 5%. d. Comparison of treatments of fertilizer applications. e. Comparison of means of treatments of fertilizer application. SOURCE: Cadavid L et al. (1998). Cassava in the Third Millennium: … 150 Table 6-15. Average response over 4 years (1993 to 1996) of nutrient contents of soil to cropping practices—mulching with plant residues, fertilizer application, and tilling—in sandy soils of northern Colombia. On-farm trials were initiated in 1988/89, in Media Luna, Magdalena, Colombia. Principal treatment With fertilizer applicationa No fertilizer application C P K Ca Mg Soil C P K Ca Mg Soil (mol/kg pH (mol/kg pH of DS)b (mmol/kg of DS)b of DS)b (mmol/kg of DS)b Conventional tilling 0. 54 0.56 0.49 1.85 0.46 4.99 0.50 0.22 0.37 1.78 0.43 4.91 Conventional tilling + mulch 0.62 0.68 1.14 3.64 1.70 5.76 0.69 0.37 1.36 3.85 2.04 5.93 No tilling 0.52 0.50 0.41 1.79 0.42 5.01 0.56 0.26 0.38 1.71 0.37 4.87 No tilling + mulch 0.67 0.65 1.25 3.62 1.85 5.73 0.66 0.40 1.41 3.57 1.97 5.89 Average 0.59 0.60 0.83 2.73 1.11 5.37 0.60 0.31 0.88 2.73 1.20 5.40 LSD 5% Tukey’sd NSc 0.04 NS NS NS NS LSD 5% Tukey’se 0.14 NS 0.14 0.89 0.25 0.31 0.06 0.08 0.30 1.01 0.39 0.36 a. Equal doses were applied per treatment of N, P, and K (50, 21, and 41 kg/ha, respectively) at 30 and 60 days after planting cassava. b. DS = dry soil. c. NS = not significant at a probability of 5%. d. Comparing treatments of fertilizer application. e. Comparing means of treatments of fertilizer application. SOURCE: Cadavid L et al. (1998). Conservation of Soil under Cassava Cultivation 45 (A) According to Cadavid L (1995) and Howeler et al. 40 (2000), several trials were established in Santander de M- 35 Quilichao (Cauca) and Media Luna (Magdalena), Colombia, over several years. The highly significant 30 M+ results are indicated in Tables 6-16 to 6-21, which verify 25 the beneficial effects of green manures on the cassava 20 crop. 40 (B) The use of green materials incorporated into soil is an excellent alternative for improving the physico- 35 chemical conditions of soils under cassava. For this purpose, the following materials should be selected: 30 zornia, kudzu, centrosema, desmodium, guandul, 25 groundnut, and indigofera (Table 6-16). Sesbania rostrata and Crotalaria juncea should also be selected, 20 although dry weight increases with each of them. 40 (C) The possibility of establishing green manure banks should also be sought by planting small areas with 35 materials that can resist several cuttings for this purpose. 30 25 A trial was established in a soil of Santander de Quilichao, Cauca, Colombia, to prove the effect of 20 cutting in several legumes and a forage grass, and observe their persistence through time and thus 40 (D) evaluate their qualities as green manures for the cassava crop (Table 6-21). The conclusions made from 35 the trial are summarized as follows: 30 1. Most of these materials adapt to soil acid 25 conditions and were proven in several trials (already described) as green manures. 20 4 8 12 16 20 2. The groundnut and cowpea do not permit Reading time several cuts, but one only, although, because (A) At 5 cm, conventional tilling of its high nutrient content, the groundnut is (B) At 20 cm, conventional tilling (C) At 5 cm, no tilling recommended as green manure. (D) At 20 cm, no tilling = with mulch (M+) 3. Most of these materials had medium to high = no mulch (M-); measurement during the dry season concentrations of nutrients and their (3 Feb 1991). contribution of dry weight to the soil is good, Figure 6-12. Soil temperature of a cassava crop (M Col 1505) as is their persistence, as they can resist in which the sandy soil was covered with mulch, several cuttings. Those that stood out include North Coast Region, Colombia. indigofera, kudzu, zornia, brachiaria, and the SOURCE: Cadavid L et al. (1998). genera Stylosanthes, Codariocalyx, Desmodium, and Styzolobium. physically (Prager and Angel, 1989). Some legumes The results of this study and the benefits reported perform better as green manures than others when for the cassava crop make this management practice incorporated, as they increase the amount of organic recommendable. This technology should be validated matter and assimilable nitrogen in the soil (Burbano to make better use of soil as a resource (Cadavid L 1989). 1995; Howeler et al. 2000). 151 Soil temperature (°C) Soil temperature (°C) Soil temperature (°C) Soil temperature (°C) Cassava in the Third Millennium: … Table 6-16. Nutrient contents of eight legumes incorporated into an exhausted soil, Santander de Quilichao, Cauca, Colombia (corrected and adapted from Cadavid L 1987). Legume Concentration (%) Quantity (kg/ha) contributed to the soil of:d N P K dw TN FN AN P K (t/ha) Styzolobium spp.a 2.16 0.24 1.10 2.0 43.2 28.0 15.2 4.8 22.0 Zornia latifolia 728 1.65 0.22 0.78 0.6 9.9 8.4 1.5 1.3 4.7 Centrosema pubescens 438 3.50 0.21 1.25 0.9 31.5 12.6 18.9 1.9 11.3 Cajanus cajanb 1.48 0.20 0.55 2.0 29.5 28.0 1.6 4.0 11.0 Groundnut cv. ICA Tatui 1.74 0.15 0.87 1.8 31.3 25.2 6.1 2.7 15.7 Cowpea cv. TVX 1193-059 D 1.29 0.18 0.98 0.5 6.5 7.0 -0.5 0.9 4.9 Indigofera hirsute 700 1.93 0.20 0.70 1.9 36.7 26.6 10.1 3.8 13.3 Pueraria phaseoloidesc 2.27 0.37 1.60 1.0 22.7 14.0 8.7 3.7 16.0 a. Black velvetbean. b. Guandul. c. Kudzu. d. dw = dry weight; TN = total nitrogen; FN = nitrogen fixed in humus (Torres 1981); AN = available nitrogen [TN minus FN, according to Torres (1981)]. SOURCE: Cadavid L (1995). Table 6-17. Effect of green manure on fresh-root yield (t/ha) of Nutrient Recycling two cassava cultivars in an exhausted soil of Santander de Quilichao , Cauca, Colombia, during 2 consecutive years (1983/84 and 1984/85). The cassava plant extracts large amounts of N, K, and Ca from the soil, which indicates that, within the plant, Treatment Weight of roots (t/ha) large amounts of these nutrients are recycled M Col 1684 CM 91-3 throughout its growth cycle. According to CIAT, in a 1st cycle 2nd cycle 1st cycle 2nd cycle cropping cycle as long as cassava’s, the possibility No green manure 16.9 13.6 16.5 10.3 exists that not only are nutrients recycled within the Velvetbean 19.9 19.0 18.4 17.0 plant, but large amounts return to the soil and is then Zornia 24.1 22.3 23.7 14.2 taken up again by the crop. The return is possible, Centrosema 25.2 15.2 20.5 12.2 partly through the fall of leaves and petioles during the Guandul 28.6 18.8 25.4 12.0 growth cycle. On average, cassava begins to lose its leaves from the third month after planting and Groundnut 29.4 24.6 29.6 15.6 progressively does so until the development cycle ends, Cowpea 19.0 19.5 15.0 11.4 by which time the plant has lost more than 80% of its Indigofera 25.7 12.7 27.6 9.5 leaf area. Figure 6-11 indicates how chemical fertilizer Kudzu 26.9 13.8 30.5 11.5 application can exert a highly beneficial effect on the SOURCE: Cadavid L (1995). production of fallen leaves and petioles. Table 6-18. Dry weight (dw) and nutrient contents (kg/ha) of green manuresincorporated into an exhausted soil of Santander de Quilichao, Cauca, Colombiaa. Green manure dw Quantity (kg/ha) of nutrient contributed to the soil incorporated (t/ha) TN FN AN P K Ca Mg S Zornia latifolia 2.83 63.4 39.5 23.9 4.2 23.2 16.4 8.8 5.7 Pueraria phaseoloides 2.68 84.4 37.5 46.9 5.6 36.7 18.5 8.3 5.6 Arachis pintoi 1.30 30.4 18.2 12.2 2.2 11.3 21.8 8.5 3.1 Macroptilium gracile 1.28 40.8 17.9 22.9 2.8 16.1 10.1 4.7 2.7 Centrosema acutifolium 2.70 75.6 37.8 37.8 4.6 28.1 19.7 6.8 6.2 Desmodium ovalifolium 3.00 50.4 42.0 8.4 4.2 22.5 18.9 8.4 5.4 Paspalum sp. 3.50b 39.2 49.0 -9.8 4.9 21.7 16.1 3.9 3.2 a. Green manures planted on the same exhausted plot and left in the soil for 2 consecutive years before being incorporated. Cassava cv. CM 507-37 was then planted at 6 months. TN = total nitrogen; FN = nitrogen fixed in humus (Torres 1981); AN = nitrogen available to the plant. b. Various cuts at the site. SOURCE: Cadavid L (1995). 152 Conservation of Soil under Cassava Cultivation 153 Table 6-19. Dry matter (DM) production of various green manures (GM) and the effect of their incorporation on the soil and cassava yield (cv. M Col 1684). Cassava was cultivated with chemical fertilizer1 applications or without them, at the CIAT–Quilichao station, cropping years 1983/84 and 1984/85. Green manure treatment GM DM Fertility of soil in 19832 Fertility of soil in 19843 Fresh-root yield4 (t/ha) (t/ha) pH OM P K P K 1983/84 1984/85 (%) (ppm) (meq/100 g) (ppm) (meq/100 g) No fert. With fertil. No fert. With fertil. 1. No GM — 4.1 5.5 3.8 0.10 3.6 0.08 16.9 c6 31.9 abcd 13.6 b 31.4 bcd 2. Cowpea 0.455 4.0 5.5 5.2 0.12 5.5 0.08 18.9 bc 26.5 cd 19.5 ab 32.2 abcd 3. Groundnut 1.755 4.1 5.9 5.1 0.14 6.2 0.09 29.3 a 39.0 a 24.6 a 30.0 cd 4. Guandul 1.95 4.1 6.0 4.6 0.13 6.6 0.07 28.6 33.8 abc 18.8 ab 38.9 a 5. Velvetbean 1.95 4.1 5.6 5.5 0.12 5.8 0.08 19.9 bc 23.6 d 18.9 ab 31.9 abcd 6. Zornia latifolia 0.55 4.1 5.6 5.2 0.12 5.1 0.07 24.1 abc 41.1 a 22.3 ab 28.6 d 7. Centrosema pubescens 0.90 4.1 5.9 4.6 0.11 5.9 0.08 25.1 abc 36.7 ab 15.2 ab 40.0 a 8. Indigofera hirsuta 1.90 4.1 5.8 5.5 0.13 6.7 0.08 25.7 ab 29.7 bcd 12.6 b 34.8 abcd 9. Pueraria phaseoloides 1.00 4.1 5.6 7.7 0.15 5.4 0.08 26.9 ab 40.4 a 13.7 b 37.3 abc Average 23.9 b 33.6 a 17.7 b 33.9 a F test: Effect of fertil. ** Effect of fertil. * Effect of GM ** Effect of GM NS Fertil. × GM NS Fertil. × GM ** 1. Application: 500 kg/ha of fertilizer 10–30–10 (N–P2O5–K2O) in two cassava crops; DM = dry matter; OM = organic matter. 2. Before planting the first cassava crop in 1983; average of treatments with fertilizer application and without it. 3. Before planting a second cassava crop in 1984; average of treatments with fertilizer application and without it. 4. Values in a row followed by the same letter are not significantly different according to Duncan’s Multiple Range Test at 5%; fertil. = fertilizer application. 5. Residual effect of green manures planted in 1983 on cassava yield obtained in 1984/85. 6. Additional yield: 520 kg/ha of groundnut and 420 kg/ha of guandul (measured as dry grain without pods). SOURCE: Howeler et al. (2000). Cassava in the Third Millennium: … 154 Table 6-20. Dry matter (DM) production of some native green manures and their effect as mulch (EM) on soil fertility, and on yield of cassava cv. M Ven 25 cultivated with fertilizer applicationa and without it in a sandy soil, Media Luna, North Coast Region, Colombia, 1984/85. Green manure DM of GM EM (at time of planting cassava) on: EM (2 months after planting cassava) on: Fresh-root yield (t/ha) treatment (t/ha) pH OM P Cations Macronutrients Cations No With (%) (ppm) (meq/100 g S) (ppm) (meq/100 g S) fertil. fertil. C a M g K NH 4-N NO 3-N P C a M g K 1. No green manure — 5.2 0.70 6.4 0.43 0.11 0.04 3.5 1.5 5.7 0.40 0.10 0.03 19.5 34.3 2. Native weeds 4.73 5.5 0.82 4.6 0.54 0.18 0.06 4.9 2.4 4.7 0.64 0.22 0.05 34.4 30.7 3. Cowpea 2.93 5.3 0.77 5.9 0.52 0.16 0.07 3.1 1.7 5.6 0.48 0.15 0.04 27.6 32.5 4. Groundnut 6.56 5.3 0.97 6.1 0.45 0.13 0.07 3.3 2.1 5.7 0.50 0.17 0.05 32.0 24.8 5. Guandul 3.93 5.1 1.15 8.4 0.54 0.17 0.07 3.3 1.9 6.8 0.47 0.15 0.04 30.2 29.7 6. Velvetbean 2.50 5.5 0.80 5.1 0.47 0.13 0.05 3.3 2.1 6.3 0.45 0.13 0.03 31.9 34.8 7. Juncea crotalaria 1.71 5.3 0.85 5.7 0.46 0.13 0.06 3.4 1.7 4.8 0.50 0.15 0.04 24.6 32.6 8. Canavalia ensiformis 3.29 5.0 0.85 8.0 0.56 0.17 0.09 4.6 2.6 7.3 0.71 0.20 0.06 34.0 32.9 9. Indigofera hirsuta 6.00 5.2 0.82 6.1 0.49 0.14 0.06 3.3 2.5 5.4 0.46 0.14 0.04 30.9 34.8 Average 29.4 32.3 a. Fertilizer application with 500 kg/ha of 15–15–15. SOURCE: Howeler et al. (2000). Conservation of Soil under Cassava Cultivation Table 6-21. Use of green manures for cassava in soils of Santander de Quilichao, Cauca, Colombia. Green manure Leaf analysis (%) dw (t/ha) per cut:a Cumulative dw (t/ha) N P K 1 2 3 4 Styzolobium spp. 2.16 0.24 1.10 4.9 3.1 1.3 NP 9.3 Cajanus cajan 1.48 0.20 0.55 2.9 1.2 0.6 — 4.7 Indigofera hirsuta 1.93 0.20 0.70 6.0 4.2 2.4 0.6 13.2 Pueraria phaseoloides 2.27 0.37 1.60 4.0 2.8 1.8 2.1 10.7 Zornia latifolia 1.65 0.22 0.78 4.0 4.4 2.5 0.4 11.3 Stylosanthes guianensis 1.54 0.22 1.38 2.6 2.8 1.9 2.3 9.6 Macroptilium glacile 1.62 0.27 0.83 0.9 2.7 1.1 0.4 5.1 Codariocalyx gyroides 1.32 0.15 0.88 3.1 5.5 2.7 2.7 14.0 Groundnut cv. ICA Tatui 1.74 0.15 0.87 1.0 2.4 2.7 NS 6.1 Desmodium ovalifolium 1.32 0.17 0.60 3.7 6.4 3.6 5.9 19.6 Cowpea cv. TVX 1193 059 1.29 0.18 0.98 0.3 2.3 2.6 NP 5.2 Canavalia sp. 2.60 0.25 1.71 6.8 1.1 1.2 — 9.1 Brachiaria humidicola 1.12 0.13 0.32 9.6 14.4 3.7 8.1 35.8 a. Cuts: 1 = 6 months after planting (MAP); 2 = 11 MAP; 3 = 14 MAP; 4 = 19 MAP; in cuts 1 and 2, planting was repeated three times; NP = green manure not planted. SOURCE: Cadavid L (1995). Biomass production can be recycled this way, are returned to the soil through leaves fallen during the corresponding to about 8% and 9% of final yield (the cassava’s growing cycle. entire plant) of the plants, with or without chemical fertilizer application, respectively. Figure 6-11 shows The use of mulch and the nutrients contributed are the allocation of the average nutrient contents in fallen directly related to microbial activity, rapid leaves and petioles of cv. CM 523-7 in a soil at decomposition over time, mineralization rate, nutrient Quilichao, Cauca, during 10 months of growth. losses to water activity, and other inherent soil factors. The nutrients that most contribute to these plant References organs are Ca and N. Magnesium and K contribute intermediate contents, whereas the poorest Burbano H. 1989. Las enmiendas orgánicas en el suelo: contributions came from S and P (Figure 6-11). In una visión sobre sus componentes orgánicos. itself, only the accumulation of nutrients in these two Universidad de Nariño, Pasto, Colombia. p 386–422. organs represents the recovery of a very high nutrient loss from the soil. It would be difficult to recover if no Cadavid L LF. 1987. El problema de la erosión en los adequate maintenance fertilizer applications were to be suelos de Mondomo, Cauca, Colombia, dedicados al made. cultivo de la yuca y sus posibles soluciones. Faculty of Agricultural Sciences of the Universidad Nacional de It is clear, however, that, in the final harvest, no Colombia–Palmira. 129 p. account is ever taken of the contribution of all the accumulated nutrients in fallen leaves and petioles Cadavid L LF. 1988. Efecto de la fertilización y humedad during the development cycle, or in leaves and petioles relativa sobre la absorción y distribución de contributed by the plant during harvest, which, on nutrimentos en yuca (Manihot esculenta Crantz). being returned to the soil, contribute nutrients to the MSc thesis. Faculty of Agricultural Sciences of the soil and plant through recycling. Universidad Nacional de Colombia–Palmira. 200 p. Howeler and Cadavid L (1983) suggest that a good Cadavid L LF. 1990. Investigaciones realizadas para la part of the N removed of the soil can be returned to conservación de los suelos de ladera. Suelos Ecuat the same soil by incorporating leaves and stems. CIAT 20(1):136–144. (1981) states that considerable amounts of this nutrient 155 Cassava in the Third Millennium: … Cadavid L LF. 1995. Utilización de abonos verdes en suelos Howeler RH. 1986. El control de la erosión con prácticas dedicados a la siembra de yuca (Manihot esculenta agronómicas sencillas. Suelos Ecuat 16(1):70–84. Crantz). Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia. 17 p. Howeler RH. 2001. Nutrient input and losses in cassava- based cropping system: examples from Vietnam Cadavid L LF. 1997. Manejo productivo de suelos de ladera and Thailand. Paper presented at the Workshop on cultivados con yuca (Manihot esculenta Crantz). “Nutrient Balances for Sustainable Production and In: Fertilidad del suelo y su potencial productivo: Natural Resource Management in Southeast Asia”, fundamentos para la interpretación de análisis de held in Bangkok, Thailand, February 2001. Centro suelos, plantas y aguas para riego. Proc Seminar on Internacional de Agricultura Tropical (CIAT); Regional Fertilidad del suelo y su potencial productivo, held at Cassava Office of the Department of Agriculture, Palmira, Colombia, 1995. Sociedad Colombiana de la Chatuchak, Bangkok. 30 p. Ciencia del Suelo (SCCS), Bogotá, DC, Colombia. p 134–143. Howeler RH; Cadavid L LF. 1982. El cultivo de la yuca con conservación del suelo en la región de Mondomo. 7 p. Cadavid L LF; Acosta A; El-Sharkawy M. 1993. Manejo de (Multicopy.) un suelo arenoso en Pivijay, Magdalena, dedicado a la producción de yuca (Manihot esculenta Crantz). Howeler RH; Cadavid L LF. 1983. Accumulation and Suelos Ecuat 23(1/2):155–161. distribution of dry matter and nutrients during a 12-month cycle of cassava. Field Crops Res Cadavid L LF; Acosta A; El-Sharkawy MA. 1995. Efecto de 7:123–139. preparación, mulch y abonamiento en el cultivo de la yuca (Manihot esculenta Crantz) en suelos arenosos Howeler RH; Cadavid L LF. 1984. Prácticas de de Colombia. Suelos Ecuat 25:7–10. conservación de suelos para producción de yuca en ladera. Suelos Ecuat 14(1):303–310. Cadavid L LF; El-Sharkawy MA; Acosta A; Sánchez T. 1998. Long-term effects of mulch, fertilization and tillage on Howeler RH; El-Sharkawy MA; Cadavid L LF. 2000. The cassava grown in sandy soils in northern Colombia. use of grain and forage legumes for soil fertility Field Crops Res 57:45–56. maintenance and erosion control in cassava in Colombia. 30 p. CIAT (Centro Internacional de Agricultura Tropical). 1981. Utilización de la yuca. In: Programa de Yuca, Informe Ortiz M AP. 1986. Colombia, sus gentes y regiones: La Anual 1981. Cali, Colombia. p 231–250. erosión. Instituto Geográfico Agustín Codazzi, (IGAC). Bogotá, Colombia. p 16-39. Cobo QL. 1998. Diseño, construcción y evaluación de un minisimulador portátil de lluvia para estudios de Prager M; Angel S DI. 1989. Contribución de los abonos susceptibilidad a erosión de laderas. Thesis. Faculty verdes al mejoramiento de la calidad de los suelos. of Agricultural Engineering of the Universidad del Valle Centro Latinoamericano de Tecnología y Educación and the Universidad Nacional de Colombia–Palmira. Rural, Cali, Colombia. 45 p. 64 p. Ruppenthal M. 1995. Soil conservation in Andean Gnahoua G; Kabrah Y. 1988. Cassava yield trend and the cropping systems: soil erosion and crop productivity in dynamics of soil chemical parameters in Southeastern traditional and forage-legume based cassava cropping Côte d’Ivoire. In: VIII Symposium of the International systems in the South Colombian Andes. Margraf Society for Tropical Root Crops, held in Bangkok, Verlag, Weikersheim, Germany. 110 p. Thailand. p 237–242. Torres E. 1981. Manual de conservación de suelos Howeler RH. 1984. Prácticas de conservación de suelos agrícolas. Editorial Diana, Mexico. p 123–135. para cultivos anuales. In: Howeler RH, ed. Manejo y conservación de suelos de ladera. Proc Seminar on Manejo y conservación de suelos, held in Cali, Colombia. Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia. p 77–93. 156 CHAPTER 7 Weed Control in Cassava Fernando Calle and Hernán Ceballos1 Weed control in cassava has been studied relatively Cultural control little. Given its hardiness, this crop was believed to tolerate competition from weeds without undue harm. This method groups specific practices that enable the However, in Colombia, the presence of weeds during crop to be more competitive with weeds. Among the the first 60 days of the crop’s cycle was observed to most significant agronomic practices of this control reduce yields by about 50%, compared with cassava system are correct selection of cultivars, use of good that was free of weeds throughout the cropping cycle. quality “seed” or stakes, optimal planting density, and crop protection. Weeds pose a significant problem to most cash crops and, particularly to cassava. Weeds tend to Manual control determine a plant’s development and its later yields. The importance of weeds to food production and their As a consequence of the cassava plant’s slow initial control is clearly documented and supported by the growth, several passes of weeding must be carried out, literature. To achieve economically viable production, using manual implements, until the crop’s canopy losses caused by weeds must be adequately controlled. closes completely and limits weed development by This is very important for both the productivity of reducing the availability of light. This method is used in high-yielding genetic materials and the development of small plantings where labor is available and technology packages. For cassava, this problem is of inexpensive. such a magnitude that it sometimes represents 30% or more of production costs. Mechanized control Control Methods This method is usually employed in combination with manual or chemical control. It consists of using tools, In cassava, as in other crops, control must be such as cultivators, rotaries, or agricultural hooks, systematic and integrated. Different options exist for pulled by tractors or animals that pass between the controlling competing plants, whether cultural, manual, rows and furrows. It starts 15 to 30 days after the crop mechanized, chemical, or combinations among these is planted and continues for as long as crop cover approaches. No single control method exists that allows it. adapts to all the problems (CIAT 1973, 1976, 1979; Doll and Piedrahita 1973, 1976; López and Leinher 1980; Chemical control Rodríguez 1989; Carvalho 1990; Marcano et al. 1995; Quiñones and Moreno 1995; Baéz et al. 1998; Girón This control involves the use of preemergent and Alfonzo 2000; Rosenstein 2001). herbicides, which prevent weeds growing for 45 to 50 days, while the cassava canopy is still open. Because chemical control is usually insufficient for the period of cassava development, the farmer must conduct later weeding activities. Critical shortages of labor and its high cost mean that, currently, chemical 1. Agronomist and Breeder, respectively, Cassava Program, CIAT, Cali, Colombia. control, because of its advantages, becomes a practical E-mails: f.calle@cgiar.org and h.ceballos@cgiar.org 157 Cassava in the Third Millennium: … and economical option, particularly for large cassava Integrating Control Methods, Direct plantations. Seeding, and Herbicide Tolerance Available herbicides. For the chemical control Cassava is one crop for which the integration of weed of weeds in cassava crops, several products, with control methods is highly necessary, given that its slow preemergent or postemergent action, can be easily initial growth allows weeds to develop vigorously. obtained on the local market. Their selectivity, with Preemergent herbicides usually control weeds for only respect to the crop, ranges from medium to high 45 to 50 days, at the end of which the cassava canopy (Table 7-1). is still not closed. Hence, additional weed control becomes necessary, whether by applying postemergent Selecting the herbicide. The diversity of weed herbicides or weeding manually. populations that become established in the fields is the result of agricultural history. To correctly select the Direct planting of crops into mulches without preemergent herbicides, the predominant weeds must inversion plowing provides many advantages that are be identified before the soil is prepared. Knowing particularly relevant for cassava and the consequences which herbicides control what weeds is also necessary. of climate change. Perhaps the most immediate Weeds that escape the action of preemergent advantage is reduced production costs. Moreover, herbicides can be controlled by applying postemergent direct planting can also reduce the detrimental effects herbicides. Farmers who do not apply control of cassava cultivation can have on the environment. treatments to their crops frequently confront dense For example, the soil surface is not exposed to the weed infestations. environment while a sufficient mulch of dead and/or Table 7-1. Herbicides, and their combinations, for controlling weeds in cassava crops. Product Characteristics Commercial Technical Selectivitya Time of Dose of commercial Type of weeds name name applicationb product/ha controlled Karmex Diuron M Pre 2.0–3.0 kg Broadleaves Lazo Alachlor H Pre 3.0–4.0 L Grasses Cotoran Fluometuron M Pre 4.0–5.0 L Broadleaves Goal Oxyfluorfen M Pre 2.0–4.0 L Broadleaves, grasses Sencor Metribuzin M Pre 1.0–1.5 L Grasses Afalon Linuron M Pre 2.0–3.0 kg Broadleaves, grasses Treflan Trifluralin H IBP 2.5–3.5 L Broadleaves, grasses Dual Metolachlor H Pre 3.0–4.0 L Grasses Roundup Glyphosate Non-selective Post 2.0–3.0 L Broadleaves, grasses Basta Glufosinate Non-selective Post 1.0–3.0 L Broadleaves, grasses Fusilade Fluazifop H Post 1.0–3.0 L Grasses Gramoxone Paraquat Non-selective Post 2.0–3.0 L Broadleaves, grasses Karmex + Lazo M Pre 1.0–1.5 + 1.5–2.0 Broadleaves, grasses Cotoran + Lazo M Pre 1.0–2.5 + 1.5–2.0 Broadleaves, grasses Goal + Lazo M Pre 1.0–2.0 + 1.5–2.0 Broadleaves, grasses Afalon + Lazo M Pre 1.0–1.5 + 1.5–2.0 Broadleaves, grasses Karmex + Dual M Pre 1.0–1.5 + 1.5–2.0 Broadleaves, grasses Cotoran + Dual M Pre 1.0–2.5 + 1.5–2.0 Broadleaves, grasses Goal + Dual M Pre 1.0–2.0 + 1.5–2.0 Broadleaves, grasses Afalon + Dual M Pre 1.0–1.5 + 1.5–2.0 Broadleaves, grasses a. Smaller doses in lighter soils; M = medium; H = high selectivity. b. Pre, Post = preemergent and postemergent, respectively; see also text; IBP = incorporated before planting. 158 Weed Control in Cassava live vegetation protects it. This key approach to this volume). The first evidence of somatic embryos reducing soil erosion may increase as rainfall and transgenic cassava was reported between 1993 becomes more intense in the world’s cassava- and 1995 (Sarria et al. 1995, 2000) for tolerance of the growing regions. herbicide glufosinate-ammonium (Figure 7-1). Since then, several projects on transgenic cassava have been Mulches may also increase water-use efficiency, developed (Taylor et al. 2004), including reduced as run-offs are fewer and more water infiltrates into cyanogenic potential (Siritunga et al. 2004; Jørgensen the soil, where it remains for longer periods because et al. 2005); starch quantity and quality (Raemakers et of reduced evaporation from the soil surface. al. 2005; Ihemere et al. 2006); increased carotenoid Nutrients may also be more efficiently used and content in roots (Chavarriaga et al. 2009); and leaf retained. Soil structure can progressively improve retention (Zhang and Gruissem 2004). The silencing of under such minimal tillage systems. specific genes through RNA interference has also been demonstrated (Jørgensen et al. 2005). However, a major drawback of direct planting is the frequently unmanageable weed problem. As Other alternatives exploit natural or induced desirable as direct planting is, in practice, it has variation for herbicide tolerance in different crops developed quickly only where herbicide-tolerant (Sherman et al. 1996; Tan et al. 2005, 2006; Tan and crops are available. In 2008, herbicide-tolerant crops Bowe 2008). In most cases, tolerance of imidazolinones of soybean, maize, canola, cotton, and alfalfa arises from changes in the gene codifying for occupied 79 million hectares or about two-thirds of acetohydroxy acid synthase (AHAS). Resistance against the global biotech crop area of 125 million hectares, cyclohexanedione, found in maize, is regulated by the total area on which biotech crops are grown acetyl-CoA carboxylase, and that against triazine (ISAAA 2008). These data refer to plants that are originates in the psbA gene, which is related to genetically transformed to tolerate herbicides, photosynthesis (Tan et al. 2005, 2006). These particularly glyphosate. discoveries have led to the development of herbicide tolerance in different crops such as maize, rice, wheat, Genetic transformation is also feasible for canola, sunflower, lentils, sugar beet, cotton, soybean, cassava (see Chapter 21, Biotechnology for Cassava, lettuce, tomato, and tobacco. Figure 7-1. Genetically transformed cassava resistant to the herbicide Basta® (glufosinate-ammonium). This work was carried out for purely research purposes, as commercial exploitation of this product was not permitted. 159 Cassava in the Third Millennium: … Tolerance of herbicides can be achieved mostly The evaluation of partially inbred cassava materials through one of three mechanisms: (a) resistance at the started in 2009. A total of 700 cloned S1 genotypes herbicide’s site of action; (b) metabolic detoxification of were evaluated in the field. Each genotype was the herbicide; and (c) preventing the herbicide access represented by 12 plants, which had been planted in six from having to its site of action (Sherman et al. 1996). different blocks in the field (two plants per genotype in These considerations are relevant because, in some each block). Each block was treated with commercial cases, tolerance of herbicides can assume a dominant doses of the following herbicides: 2,4-D (Anikilamina®); or semi-dominant gene action, in addition to the more glyphosate (Roundup®); imidazolinone (Plateau®); common recessive behavior. Maternal effects have also sulfonylurea (Ally®); glufosinate-ammonium (Basta®; been reported (Tan and Bowe 2008). The most Finale®); and atrazine. Although results are still relevant examples of herbicide-tolerant crops are for preliminary, at least one genotype appears to have imidazolinone (i.e., CLEARFIELD®), glyphosate (i.e., obvious tolerance of glufosinate-ammonium. Roundup Ready®), and glufosinate (i.e., LibertyLink®) Figure 7-2 illustrates clear differences in vigor of these products. Tolerance of Roundup Ready® is based, so two plants, compared with related S1 genotypes. far, solely on genetic transformation. References CIAT has initiated two aggressive approaches to identifying herbicide tolerance in cassava. The first Baéz J; Antequera R; Ramos J; Gutiérrez W; Medrano C. approach, which induces self-pollinating cassava 1998. Densidad de siembra y control de malezas en germplasm to produce S1 genotypes, can expose el cultivo de la yuca (Manihot esculenta Crantz) en recessive sources of tolerance to herbicides. The siembra directa bajo las condiciones de la planicie genotypes thus produced can then be subjected to de Maracaibo. Rev Fac Agron Univ Zulia (Venez) different herbicides to detect phenotypes expressing 15(5):429–438. tolerance. The second approach is through the use of molecular markers for the application of TILLING or Carvalho JEB de. 1990. Controle de plantas daninhas em EcoTILLING (Till et al. 2003; Guang-Xi et al. 2007). mandioca. Centro Nacional de Pesquisa de Mandioca This approach is greatly facilitated by clearly e Fruticultura (CNPMF), Cruz das Almas, BA, Brazil. understanding the genes that must be mutated, and 38 p. the recent availability of the sequenced cassava genome. December 1 January 18 Figure 7-2. Examples of an S1 genotype (represented by two plants and highlighted by white arrows) with tolerance of glufosinate- ammonium. This genotype is surrounded by other, related, S1 genotypes. The difference in vigor and absence of typical damage in the growing tip on applying the herbicide strongly suggests that this genotype tolerates the herbicide. The photographs were taken at two different ages of the plant. 160 Weed Control in Cassava Chavarriaga P; Beltrán J; Ladino J; Vacca O; López D; Jørgensen K; Bak S; Busk PK; Sørensen C; Olsen CE; García M; Prías M; Oarra S; Al-Babili S; Beyer P; Puonti-Kaerlas J; Møller BL. 2005. Cassava plants Tohme J. 2009. Combining biotechnology, molecular with a depleted cyanogenic glucoside content genetics and breeding to improve the content of in leaves and tubers: distribution of cyanogenic carotenes in cassava roots. In: Proc 15th Triennial glucosides, their site of synthesis and transport, and Symposium of the International Society of Tropical blockage of the biosynthesis by RNA interference Root Crops, held in Lima, Peru, 2–6 November. technology. Plant Physiol 139:363–374. Centro Internacional de la Papa (CIP), Lima, Peru. p 63–64. López J; Leinher DE. 1980. Control químico de malezas en policultivos con yuca (Manihot esculenta Crantz). CIAT (Centro Internacional de Agricultura Tropical). 1973. Rev Comalfi 7(1/2):19–28. Informe anual 1972. Cali, Colombia. p 75–80. Marcano JJ; Paredes F; Segovia P. 1995. Control de CIAT (Centro Internacional de Agricultura Tropical). 1976. malezas en yuca. FONAIAP Divulg (Venez) 49:39–40. Informe anual 1975. Cali, Colombia. 63 p. Quiñones V; Moreno N. 1995. Control de malezas en CIAT (Centro Internacional de Agricultura Tropical). yuca en Barinas, Venezuela. Agron Trop (Maracay) 1979. Manejo y control de las malezas en el cultivo 45(1):85–94. de la yuca—Guía de estudio para ser usada como complemento de la unidad audiotutorial sobre el Raemakers K; Schreuder M; Suurs L; Furrer-Verhorst H; mismo tema. Cali, Colombia. 36 p. Vincken JP: de Vetten N; Jacobsen E; Visser RGF. 2005. Improved cassava starch by antisense inhibition Doll J; Piedrahita W. 1973. Effect of time of weeding of granule-bound starch synthase, I. Mol Breed and plant population on the growth and yield of 16:163–172. cassava. Paper presented at the Third International Symposium of Tropical Root Crops, Ibadan, Nigeria. Rodríguez R. 1989. Lucha contra las malezas en el cultivo 13 p. (Multicopied.) de la yuca (Manihot esculenta Crantz). Ciencia Téc Agric Ser Prot Plantas (Cuba) 12(1):91–109. Doll J; Piedrahita W. 1976. Métodos de control de malezas en yuca. Centro Internacional de Agricultura Tropical Rosenstein E. 2001. Diccionario de especialidades (CIAT), Cali, Colombia. 12 p. agroquímicas: Sección semillas, 11 ed. Editorial PLM, Bogotá, DC, Colombia. p 2–10. Girón C; Alfonzo E. 2000. Manejo integrado de malezas en yuca. Agron Trop (Maracay) 50(1):31–40. Sarria R; Torres E; Balcázar M; Destefano-Beltrán L; Roca WM. 1995. Progress in Agrobacterium-mediated Guang-Xi W; Tan M-K; Rakshit S; Saitoh H; Terauchi R; transformation of cassava (Manihot esculenta Crantz). Imaizumi T; Ohsako T; Tominaga T. 2007. Discovery In: Proc Second International Scientific Meeting of of single-nucleotide mutations in acetolactate the Cassava Biotechnology Network, held in Bogor, synthase genes by Eco-TILLING. Pestic Biochem Indonesia, 22–26 August 1994. Working Document Physiol 88:143–148. No. 150. Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia. p 241–244. Ihemere U; Arias-Garzón D; Lawrence S; Sayre R. 2006. Genetic modification of cassava for enhanced starch Sarria R; Torres E; Angel F; Chavarriaga P; Roca WM. production. Plant Biotechnol J 4:453–465. 2000. Transgenic plants of cassava (Manihot esculenta) with resistance to Basta obtained by ISAAA (International Service for the Acquisition of Agrobacterium-mediated transformation. Plant Cell Agri-biotech Applications). 2008. Global Status of Rep 19:339–344. Commercialized Biotech/GM Crops: 2008. Sherman TD; Vaughn KC; Duke SO. 1996. Mechanisms of action and resistance to herbicides. In: Duke SO, ed. Herbicide resistant crops. CRC Press, Boca Ratón, FL, USA. p 13–35. 161 Cassava in the Third Millennium: … Siritunga D; Arias-Garzón D; White W; Sayre R. 2004. Taylor N; Chavarriaga P; Raemarkers K; Siritunga D; Over-expression of hydroxynitrile lyase in transgenic Zhang P. 2004. Development and application of cassava roots accelerates cyanogenesis and food transgenic technologies in cassava. Plant Mol Biol detoxification. Plant Biotechnol J 2:37–44. 56:671–688. Tan SY; Bowe S. 2008. Developing herbicide-tolerant Till BJ; Reynolds SH; Greene EA; Codomo CA; Enns LC; crops from mutations. In: Proceedings FAO/IAEA Johnson JE; Burtner C; Odden AR; Young K; Taylor International Symposium on Induced Mutations in NE; Henikoff JG; Comai L; Henikoff S. 2003. Large- Plants, held in Vienna, Austria, 12–15 August. p 134. scale discovery of induced point mutations with high- throughput TILLING. Genome Res 13:524–530. Tan S; Evans RR; Dahmer ML; Singh BK; Shaner DL. 2005. Imidazolinone-tolerant crops: history, current Zhang P; Gruissem W. 2004. Extension of cassava leaf status and future. Pest Manage Sci 61:246–257. life by autoregulatory inhibition of senescence. Paper presented at the Sixth International Scientific Meeting Tan S; Evans R; Singh B. 2006. Herbicidal inhibitors of of the Cassava Biotechnology Network, held in Cali, amino acid biosynthesis and herbicide-tolerant crops. Colombia, 8–14 March 2004. Amino Acids 30:195–204. 162 Part C Pest and Disease Management CHAPTER 8 Cassava Diseases Elizabeth Álvarez1, Germán Alberto Llano2, and Juan Fernando Mejía3 World production of cassava roots was estimated at Cassava mosaic disease (CMD; begomovirus 233 million tons in 2008. Africa was the largest complex) producer with 118 million tons on almost Cassava brown streak disease (CBSD; an 12 million hectares, followed by Asia with ipomovirus) 78.7 million tons on 3.97 million ha. Cassava (Manihot Brown leaf spot (Cercosporidium henningsii) esculenta Crantz) is a significant staple, providing a Diffuse leaf spot (Cercospora vicosae) basic daily source of dietary energy for almost one White leaf spot (Phaeoramularia manihotis) billion people in 105 countries. It also has numerous Anthracnose (Colletotrichum spp.) agroindustrial uses. Cassava grows on marginal lands, tolerates drought, and can grow in low-fertility soils. Diseases Caused by Fungi Cassava is also the most inexpensive source of starch that exists, being used in more than 300 industrial Superelongation disease (Elsinoe brasiliensis) products (FAOSTAT, 2010). Importance. Superelongation disease (SED) attacks Cassava is still widely cultivated under traditional susceptible cultivars, especially during the rainy seasons. management. This suggests that large numbers of Damage caused by SED is highly variable, depending on farmers may be ignorant of the crop’s diseases and the level of cultivar resistance, climatic conditions, their integrated management. Hence, several diseases concentration of the initial inoculum, and the degree of threaten the sustainability of cassava production and contamination of planting materials (Álvarez and Llano its profitability. The principal diseases attacking the 2002). crop are: Losses can exceed 80% of total production in young Cassava bacterial blight (CBB4; Xanthomonas crops, whereas significant losses do not occur in crops axonopodis pv. manihotis or Xam) that are more than 6 months old. In Colombia, SED is Phytophthora root rots (PRR; Phytophthora spp.) found in the Eastern Plains, Atlantic Coast, and inter- Superelongation disease (SED; Sphaceloma Andean valleys. The disease is acute in agroecological manihoticola) areas with annual mean temperatures of 28 ºC and Cassava frogskin disease (CFSD; Candidatus annual precipitation of more than 1500 mm. In the phytoplasma, Cfdp of the 16SrIII-L and rpIII-H greenhouse, 8 h of misting at temperatures of 25 to subgroups) 30 ºC was sufficient to cause an outbreak, indicating how easily the pathogen develops in the field (Mejía 2001). 1. Plant Pathologist, Cassava Program, CIAT, Cali, Colombia. E-mail: e.alvarez@cgiar.org Distribution. Superelongation disease was first 2. Agronomist Consultant, Cali, Colombia. observed by Bitancour and Jenkins in 1950, on Manihot E-mail: germanlln@yahoo.com 3. Research Associate, Plant Pathology, Cassava Program, CIAT. glaziovii Muell.-Arg. in Brazil and Nicaragua and on M. Currently Doctoral Candidate, Plant Pathology, Università di esculenta in the Dominican Republic and Guatemala. Bologna, Bologna, Italy. E-mail: juan_fmejia@yahoo.es; The disease has since been reported (in order of juanfernando.mejiad2@studio.unibo.it 4. For an explanation of this and other acronyms and abbreviations, reporting year) in Costa Rica (Larios and Moreno 1976), see Appendix 1: Acronyms, Abbreviations, and Technical Colombia (Lozano and Booth 1979), Mexico (Rodríguez Terminology, this volume. 1979), Cuba (Pino 1980), Venezuela (Rondón and 165 Cassava in the Third Millennium: … Aponte 1981), the Dominican Republic (Sosa 1992), on the epidermis of the host and, after penetration, Barbados, Panama (Chávez 1992; Zeigler 2000), Brazil grows in the intercellular spaces in tissues of the (where it is restricted to the western regions of the epidermis and cortex. The fungus produces country) (Álvarez et al. 2003d), and Trinidad and gibberellins, which promote the exaggerated growth in Tobago (Reeder et al. 2008). At the end of 2008, the the plant’s internodes. Gibberellins, as suggested by disease was detected in Thailand (E Álvarez 2008, previous studies for other pathogens (Muromtsev and pers. comm.). The disease appears to be unknown in Globus 1975), play an essential role in the fungus’s Africa. nutrition. The fungus, which has a low production of hydrolytic enzymes, uses this hormone to obtain Symptoms and epidemiology. The characteristic sugars from the plant, promoting, at the molecular symptom of this disease is the exaggerated level, hydrolysis of carbohydrates with greater mass lengthening of stem internodes (Zeigler et al. 1980), (Mejía 2001). creating thin and weak stems. Diseased plants are much taller and/or weaker and spindlier than healthy According to Álvarez and Molina (2000), the ones. In green sections of stems, and in petioles and pathogen’s genetic diversity in Colombia is broad, leaves, deformations develop in associations with presenting differences among isolates within a single cankers. The lens-shaped cankers often have dark location and between locations. Isolates from the margins and are variable in size. In leaves, cankers are Atlantic Coast, Eastern Plains, and inter-Andean valleys found on the underside, along the primary or of Colombia and from central and southern Brazil secondary nervures. In stems, they may be more comprise two evolutionary units, with each unit relating diffuse. Frequently, young leaves curl, and do not to its respective country (Álvarez et al, 2001). develop fully nor do the leaf blades expand completely. Leaves also develop irregular white spots (Figure 8-1). For gene 18S rRNA, obtained from two isolates of Sometimes partial or total death of leaves occurs, E. brasiliensis, the sequencing of a region involving resulting in considerable defoliation. Dieback of the ITS1 and ITS2 was reported to GenBank (accessions plant may also occur. AY739018 and AY739019; CIAT 2004). The disease spreads from one place to another Host range. Elsinoe brasiliensis and Sphaceloma through the use of infected stakes. The principal species (the asexual state), which both attack cassava, focuses of infection frequently constitute the shoots have a wide range of Euphorbiaceae hosts, including originating from residues of old plants left in the field Euphorbia brasiliensis L., E. hypericifolia L., Jatropha after harvest. The disease spreads rapidly during the aconitifolia Muell. var. papaya Arbelaez, J. curcas L., rainy season. This rapid dissemination is believed to Manihot carthaginensis Muell., M. esculenta, and occur through the formation of spores in the cankers. M. glaziovii. These hosts are cosmopolitan weeds and These spores can survive for more than 6 months in widely cultivated ornamentals. infected plants and are carried by rain and wind. Many regions in Africa and Asia have climatic Etiology. Superelongation disease is caused by conditions that closely resemble to those of the Eastern the fungus Elsinoe brasiliensis, which initially grows Plains, Atlantic Coast, and inter-Andean valleys of A B C Figure 8-1. Symptoms of superelongation disease in cassava: (A) cankers on leaves, (B) cankers on petioles and stem, and (C) elongated stem. 166 Cassava Diseases Colombia, where the pathogen causes considerable Biological control. Spraying with suspensions of losses. These African and Asian regions therefore face Pseudomonas putida considerably reduced the severity the danger that the pathogen will be introduced of damage caused by SED, thereby significantly through planting materials of ornamentals such as increasing cassava yields (CIAT 1985). Jatropha spp. L., which are not necessarily restricted by the same sanitary regulations as cassava. Brown leaf spot (Cercospora henningsii) Because the host range is broad, completely Importance. Brown leaf spot has a broad eradicating the pathogen is impossible and a certain geographical distribution, being found in Asia, North amount of sufficient inoculum will be present America, Africa, and Latin America. It attacks naturally throughout the year. In Brazil, the weed Euphorbia M. esculenta, M. glaziovii, and M. piauhynsis Ule heterophylla L. was shown to be host to strains of (Ferdinando et al. 1968; Golato and Meossi 1966; Elsinoe brasiliensis that were highly pathogenic to Powell 1972). In India, Cercospora henningsii is an cassava (Álvarez et al. 2003d). Furthermore, the important pathogen, causing severe defoliation (Edison genetically very variable hosts are also able to maintain 2002). a variable population of the pathogen (Zeigler 2000). Symptoms and epidemiology. Symptoms in Integrated disease management. The use of cassava leaves are characterized by leaf spots visible on healthy seed, obtained from disease-free plants or from both sides. On the leaves’ upper surface, uniform brown plants derived from meristem culture, comprises a tool spots appear, with defined and dark margins. On the that may be sufficient to maintain disease-free crops. leaves’ undersurface, the lesions have less-defined However, one preventive method for eradicating the margins and, towards the center, the brown spots have pathogen is to immerse infected stakes for 10 min in a gray-olive background because of the presence of the captafol at 4.8 g/L of active ingredient (a.i.). When fungus’s conidiophores and conidia. As these circular symptoms are observed in the field, foliar spraying lesions grow, from 3 to 12 mm in diameter, they take up should be carried out with difenoconazole at an irregular angular form, their expansion being limited 0.07 cc/ha, followed by crop rotation with grasses. by the leaves’ major veins (Figure 8-2). In areas where the pathogen is endemic, planting should be carried out during periods with the least precipitation (CIAT 2003b). Infected plants (cassava or other Euphorbiaceae hosts) should be destroyed as soon as they are identified. The best way to eliminate this material is to pull up infected plants and burn them in situ (Zeigler 2000). Varietal resistance. The selection of resistant varieties is perhaps the best alternative for controlling SED. Between 1995 and 2007, CIAT evaluated about 6400 genotypes at Villavicencio (Colombia) and found 257 with resistance to SED. On-farm evaluations at Sincelejo (Sucre, Colombia) showed the following as resistant: M Ven 25 and CM 4843-1, followed by ICA Catumare, ICA Cebucán, ICA Negrita, Vergara (CM 6438-14), and CM 4574-7 (CIAT 2001, 2002b, 2003a). Pathogenic races of E. brasiliensis exist and are of high genetic variability. While they should be taken into account when improving resistance to SED (Álvarez and Molina 2000; Álvarez et al. 2003d), they are not thought to pose serious constraints to varietal improvement (Zeigler 2000). Figure 8-2. Leaf spots caused by Cercospora henningsii. 167 Cassava in the Third Millennium: … The veins found within the necrotic area are black. applied at 12 L/ha also provide good chemical control Sometimes, depending on how susceptible the variety (Golato and Meossi 1966). The best control over the is, an undefined yellow halo or discolored area can be disease can be achieved by using resistant varieties. observed around the lesions. As the disease progresses, Significant differences in varietal resistance have been infected leaves become yellow and dry before falling off, found in Africa (Chevaugeon 1956; Umanah 1970), possibly because of toxic substances secreted by the Brazil (Viégas 1941), and the extensive collection of pathogen. Susceptible varieties may undergo severe, or cassava varieties held at CIAT, Colombia (CIAT 1972). even total, defoliation during the hot rainy season. Diffuse leaf spot (Cercospora vicosae) When wind or rain carry conidia that have dropped from wounds of infected tissues towards leaves of a new Importance. This disease is found where brown planting, primary infections occur. If environmental leaf spot predominates, that is, in the hot cassava- humidity is sufficiently high, the conidia will germinate, growing areas of Brazil and Colombia (CIAT 1972; producing branched germinal tubes that frequently Viégas 1941). The pathogen causes severe defoliation anastomose (Chevaugeon 1956; Viégas 1941). in susceptible cultivars but, in Colombia, does not cause heavy crop losses. When lesions mature, stromata appear from which conidiophores emerge. Secondary cycles of the disease Symptoms and epidemiology. This disease is are repeated throughout the rainy season, when wind or characterized by the presence of large leaf spots, with rain carries conidia to new susceptible tissues of the undefined margins. Each spot may cover one fifth, or plant. The fungus survives the dry season in old lesions, more, of the leaf lobe. On the leaves’ upper surfaces, frequently those of fallen leaves. It renews activity with the spots are uniformly brown, whereas, on the lower the advent of the rainy season and growth of new leaves surfaces, spots also have grayish centers caused by the in the host. presence of the fungus’s conidia and conidiophores. The spots’ general appearance is similar to that of the Chevaugeon (1956) observed that, in a cassava spots induced by Phoma sp., although lesions induced plant, the lower leaves are more susceptible than the by the latter have concentric rings on the leaves’ upper youngest leaves. However, certain susceptible species surfaces (Figure 8-3). (e.g., M. carthaginensis Muell.) and M. esculenta cultivars can be severely attacked. Severe symptoms Defoliation may occur in susceptible cultivars, have been observed in young leaves, petioles, and even being more severe at the end of the rainy season and/or fruits of M. carthaginensis. Although plants “hardened” vegetative cycle. As the disease progresses, leaves by unfavorable conditions appear more resistant, no become yellow and dry before falling off. significant differences in susceptibility were found between plants growing in fertile soils and those Symptoms of this disease can be confused with growing in poor soils (Chevaugeon 1956). those of cassava bacterial blight (CBB; see below), except that the blight lesions are noticeably aqueous. Etiology. Cercospora henningsii, causal agent of the disease, grows in the intercellular spaces of leaf tissues, producing stromata from which conidiophores are produced in dense fascicles. The conidiophores are pale olive brown, semi-transparent, with uniform width and color, and non-branching. Sometimes, black perithecia appear, disseminated in the necrotic tissue of leaf spots and on the leaves’ upper surface (Powell 1972). The perfect state of C. henningsii is Mycosphaerella manihotis (Ghesquière 1932; Chevaugeon 1956). Management and control. To reduce the severity of infection, recommended cultural practices include reducing excess humidity during planting (Golato and Meossi 1966). Fungicides based on copper oxide and Figure 8-3. Leaf spots caused by Cercospora vicosae in a copper oxychloride, suspended in mineral oil, and cassava leaf. 168 Cassava Diseases Etiology. The fungus does not form stromata but sporulates abundantly. The conidiophores are reddish dark brown (Chupp 1953). The fungus has been recorded as a pathogen occurring only on Manihot spp. Mill. As its incidence on a single plant or in a given planting is very low and apparently confined to the plant’s lower leaves, its importance is relatively less. Management and control. • Planting with healthy and resistant cultivars • Using cultural practices that reduce humidity during planting White leaf spot (Phaeoramularia manihotis) Importance. This fungus is commonly found in the cold humid cassava-growing regions of Asia, America, North America, tropical Africa, and Latin America (Castaño 1969; Chevaugeon 1956; CIAT 1972). In these areas, the pathogen may cause considerable defoliation in susceptible varieties of M. esculenta, the only known host species (Chevaugeon 1956; Viégas 1941). Symptoms and epidemiology. Leaf spots caused by P. manihotis are smaller, with a different color, to those induced by C. henningsii. They vary from circular to angular, with diameters of usually 1 to 7 mm. They are normally white, but sometimes yellowish brown. Lesions are sunken on both sides, to half of the thickness of a healthy leaf blade. On the lower leaf surface, the white spots can be distinguished but they Figure 8-4. Leaf spots caused by Phaeoramularia manihotis. frequently have diffusely colored margins, which sometimes appear as brown-violet irregular lines, surrounded by brown or yellowish halos. The spots’ centers have a velvety grayish aspect during the White leaf spot is very similar to brown leaf spot. pathogen’s fruiting (Figure 8-4). However, brown spot usually occurs in warm but not humid areas, whereas white spot appears in cold humid The fungus penetrates the host through stomatal areas. These differences in their geographical cavities and then invades the host’s tissues through the distribution are also observed in Africa and Latin intercellular spaces. When leaf spots reach 5 to America, and are probably the result of different 7 mm in diameter, a stroma is formed, which produces responses of the respective causal agents to conidiophores. The disease’s secondary cycles are temperatures and humidity. The optimal temperature repeated throughout the rainy season as conidia are for germinating C. henningsii conidia is 39 ºC, with a dispersed by wind or rain splash. The fungus survives maximum temperature of 43 ºC. For P. manihotis, the dry season in old infected tissues and renews these temperatures are, respectively, 33 and 43 ºC activity at the beginning of the rainy season and with (Chevaugeon 1956). the host’s new growth. Management and control. The control measures Etiology. Phaeoramularia manihotis, the causal recommended for this disease are similar to those for agent, forms thin stromata in lesions on leaves. The brown leaf spot. Specifically resistant varieties are stromata produce conidiophores in loose fascicles that unknown, but field studies suggest they exist emerge through the stromata and are usually olive (JC Lozano 1979, unpublished data). brown (Powell 1972). 169 Cassava in the Third Millennium: … Concentric ring leaf spot (Phoma spp.) dieback during epiphytotes and even total plant death. Necrotic stems become dark brown and frequently Importance. This fungal disease, caused by appear covered with pycnidia. Phoma spp., usually appears in the cold cassava- growing areas of Colombia (CIAT 1972), Brazil (Viégas Field studies suggest that the more mature lower 1943a), Philippines, tropical Africa, and India leaves may be more resistant than the young upper (Ferdinando et al. 1968). According to Edison (2002), leaves. However, total defoliation, accompanied by this disease is an emerging problem in certain areas partial or total dieback, has been observed in where cassava cultivation is intensive. During the rainy susceptible cultivars. season and when the temperature is below 22 ºC, the disease may cause severe defoliation in susceptible Favorable conditions for the germination of fungal varieties and almost always produces stem dieback. spores occur at temperatures between 20 and 25 ºC. With artificial inoculation, infection is only achieved Symptoms and epidemiology. The disease is when inoculated plants are kept for 48 h at less than characterized by the presence of large dark brown leaf 24 ºC and with 100% relative humidity (JC Lozano spots, with usually undefined margins. These lesions 1979, unpublished data). Under field conditions, are commonly found at leaf points, margins of leaf disease always occurs during the rainy season and in lobes, or along the central vein or other secondary areas where the temperature is less than 22 ºC. veins. Initially, lesions appear as concentric rings of brown pycnidia on the leaf’s upper surface (Figure 8-5). The fungus’s survival mechanism during dry hot These rings are not found on old injuries because the periods is unknown. Viégas (1943b) suggested that the rain drags away mature pycnidia. In these cases, the fungus may produce its sexual state on infected stems spots are uniformly brown, and are very similar to those and leaf residues. However, this has not yet been caused by Cercospora vicosae. On the lower leaf observed or recorded. surfaces, very few pycnidia occur. Hence, lesions are uniformly brown. Etiology. The causal agent produces numerous, spherical, dark brown pycnidia, either individually or in Under conditions of high relative humidity, lesions small clusters, on surfaces of leaves or stems. Pycnidia may be covered by braid-like chains of grayish-brown measure 100–170 μm in diameter, their walls are hyphae. On the lower leaf surfaces, the nervures within formed by polyhedral cells; and their ostiole measures the lesions become necrotic, forming black bands that 15–20 μm. Conidiophores are short and hyaline, emerge from the spots. These spots grow, causing leaf producing small conidia (15–20 μm) that are unicellular blight. The fungus invades the infected leaf and then and ovoid or elongated (Ferdinando et al. 1968; Viégas the petiole, which becomes dark brown as it necroses. 1943a). On Lima-bean agar, the fungus forms pycnidia Leaves wilt and then fall, resulting in severe defoliation in profuse quantities, appearing in concentric rings. in susceptible cultivars. These cultivars may present Management and control. To date, no measures of control exist for the disease, even though it causes heavy losses in areas where environmental conditions are propitious for its development. Although no reports exist on varietal resistance, in the field in Colombia, resistance has been observed in naturally infected plantings. Chemical treatments such as carbendazim (3 g/L a.i.) and benomyl (0.6 g/L a.i.) during the rainy season may be equally effective in those areas where the disease is endemic. Cassava ash (Oidium manihotis) Importance. This disease was first recorded in Africa in 1913 (Saccardo 1913) and has since appeared in Latin America (CIAT 1972; Viégas 1943a) and Asia (Park 1934). The disease is characterized by the Figure 8-5. Leaf spots caused by Phoma sp. in cassava. presence of yellowish undefined spots on M. esculenta 170 Cassava Diseases leaves. Although it is widely disseminated and frequently observations suggest that resistant varieties exist (CIAT occurs during the dry season, the disease is considered 1972). Ferdinando et al. (1968) suggest that spraying to be of minor importance as it usually attacks only the with sulfur-based compounds can control the disease. lower leaves, in which it induces some necrosis. Cassava anthracnose (Glomerella manihotis) Symptoms and epidemiology. The first symptoms of disease are characterized by the Although cassava anthracnose has been known for a appearance of a white mycelium that grows on the leaf long time, it has been considered of minor importance. surface (Figure 8-6). The fungus penetrates the host It is characterized by the presence of sunken leaf spots, cells, using haustoria. The infected cells become 10 mm in diameter, that are similar to those caused by chlorotic and form undefined yellowish lesions. Within C. henningsii. The latter, however, appear towards the these yellowish areas, pale brown necrotic areas base of leaves, thus causing their total death. frequently appear. These are angular in shape and of different sizes. In some cassava varieties, the disease The pathogen also causes young stems to wilt and stops in the state of yellowish undefined lesions, which induces cankers on mature stems (Irvine 1969) then may become confused with those induced by (Figure 8-7). New leaves, produced at the beginning of insects and mites. the rainy season, are the most susceptible. The disease tends to disappear when the dry season begins (Irvine Fully developed mature leaves seem to be most 1969). This finding agrees with results obtained from susceptible to pathogenic attack, although the young artificial inoculations with an aqueous suspension of leaves of some varieties may also present symptoms. spores from the pathogen. Inoculation is successful if The disease commonly appears during the dry season incubation is at 100% relative humidity for 60 h. The and in warm areas. fungus will stop invading plant tissue when relative humidity drops to 70% (CIAT 1972). The insect Etiology. The sexual state of the causal agent, Pseudotheraptus devastans Distant is associated with Oidium manihotis, is Erysiphe manihotis (Ferdinando the disease (Fokunang et al. 2000), contributing to the et al. 1968). The fungus’s mycelium is white, producing pathogen’s dissemination and increasing the severity of numerous haustoria on the host’s epidermis. symptoms. Conidiophores rest in an erect position. They are simple, with the upper parts both longer and wider, as they form The organism causing this disease has been the conidia. Conidia are oval or cylindrical, unicellular, variously called Glomerella manihotis, Colletotrichum hyaline, and measure 12–20 × 20–40 μm. They are manihotis (Vanderweyen 1962), Gloeosporium produced in basipetal chains (Ferdinando et al. 1968; manihotis (Bouriquet 1946), and Glomerella cingulata Saccardo 1913; Viégas 1943b). (Irvine 1969). All these names possibly refer to one species, but this hypothesis is yet to be confirmed. Management and control. Although specific control of the disease is considered unnecessary, Stem anthracnose caused by a Colletotrichum sp. was recorded in Nigeria (IITA 1972). Green portions of Figure 8-7. Leaves and stem show cankers caused by Figure 8-6. Cassava ash symptoms, caused by Oidium sp. Glomerella manihotis. 171 Cassava in the Third Millennium: … the stems presented shallow oval depressions that were Cassava rust (Uromyces spp.) pale brown, but with a point of normal green tissue in the center. In the ligneous portions of the stems, lesions Importance. Although recorded in Brazil and were round, swollen, and in bands, forming deep Colombia, this disease is considered to be of minor cankers on the epidermis and cortex, and sometimes importance. It appears at the end of dry periods, deforming the stem. Its importance is unknown but its sometimes causing a type of shoot proliferation in stem prevalence, occurrence, and dissemination are apices (Normanha 1970). considerable. In Asia stem anthracnose was recorded in Thailand (E Álvarez 2009, pers. comm.) (Figure 8-8). Symptoms and epidemiology. Infection is characterized by pustule formation on leaf veins, petioles, or green branches (Figure 8-9). Pustules are light to dark brown, depending on their age or class of fungal fructification. Mature pustules are readily parasitized by the fungus Darluca filum. They are sometimes surrounded by chlorotic halos and, usually, induce deformation of affected parts. Wind is the principal dissemination agent. Etiology. In cassava, several species of rust pathogens have been recorded in different parts of the world. However, its incidence and severity are low. Some species of rust appear to occur only where temperatures are moderate and rainfall is high. Other species predominate during hot dry seasons. Stem rots In many cassava-growing areas, continuous cassava planting is not possible and stakes must be stored for later propagation. Stored stakes are attacked by three diseases that induce necrosis (CIAT 1972). These diseases considerably reduce stake viability, directly and indirectly, by increasing dehydration and causing necrosis. Although the three different causal agents have Figure 8-8. Disease symptoms observed on cassava stems. been recognized, the diseases these induce are not A B C Figure 8-9. Symptoms of cassava rust characterized by pustule formation on (A) leaf, and (B) and (C) stems. 172 Cassava Diseases clearly differentiated in most cases. Macroscopically, the appearance of two types of symptoms may be due the diseases look similar, particularly during their first to two different states of the same agent rather than of developmental stages. Furthermore, more than one two agents. causal agent may be present, creating a syndrome. Dry rot of stem and root (Diplodia sp.) The three diseases causing stem rots are stem necrosis caused by Glomerella cingulata, dry stem and Importance. This disease attacks stored cassava root rot caused by Diplodia sp., and necrosis caused by planting materials and residue stems left in the field. Its an unidentified Basidiomycete (Lozano and Booth occurrence is not as common as necrosis caused by 1979). Glomerella spp. Stem necrosis (Glomerella cingulata) Symptoms and epidemiology. The disease has two phases. The first is when root rot starts when soils Importance. This disease is the most common of are infested or when stakes from diseased plants are the three that induce rots or necrosis in stored cassava used. Symptoms, similar to those induced by root stakes. It also attacks residues of old stems left in pathogens, consist in sudden plant death caused by cassava plantings. root deterioration. Symptoms. Necrosis of stored stakes appears first The second phase includes stem rot caused by at the ends and then progresses slowly towards the systemic invasion of the fungus from the roots or by middle, before disseminating to all stakes (Figure 8-10). penetration through wounds. The disease is The disease occurs as a black discoloration of vascular characterized by black discoloration and necrosis of the bundles. It then develops surface blisters that later vascular bundles, which extend from the infection sites, break, exposing groups of black perithecia in well- that is, wounds in the stem. In the epidermis, they developed stromata. appear as blisters under which the stem’s internal tissues are discolored black or dark brown. The blisters Etiology. The causal organism appears to be break, showing confluent masses of black pycnidia Glomerella cingulata (Commonwealth Mycological (Figure 8-11). Gum may be excreted, and partial or total Institute 1979, pers. comm.). Ascospores are hyaline, wilting occurs. Dieback may also occur. unicellular, and slightly curved. Infection probably occurs through wounds and is favored by high The pathogen disseminates across great distances environmental relative humidity. through stakes from infected plantings. Within the same crop, dissemination is by wind and rain during The relationship between this fungus and fungal fructifications, use of infested tools and Colletotrichum sp., which causes anthracnose in irrigation water, and land preparation for later plantings. cassava, has not still been determined. For example, Etiology. The causal agent of dry rot of stem and root is Diplodia manihotis. In both the host and laboratory cultures, this organism produces pycnidia Figure 8-10. Necrosis caused by Glomerella cingulata in cassava stakes. Figure 8-11. Stem rot in a stake infected by Diplodia sp. 173 Cassava in the Third Millennium: … that erupt through the stem or root surface, pathogens that attack ligneous plants such as becoming confluent, stromal, and ostiolate. The cassava. These pathogens may be fungi or bacteria conidiophores are short and simple, producing dark that cause root deterioration, either as the crop grows two-cell conidia that are slightly elongated on or after harvest when roots are stored. reaching maturity. Infection is believed to occur through wounds, and is favored by high Control measures for these diseases are similar, environmental relative humidity. the best comprising cultural practices such as good drainage, selection of loose-textured soils, crop Management and control. To control the rotation, early harvest, and avoiding soils prone to disease, the cassava crop should be rotated with flooding. Treatments with fungicides may help nonsusceptible crops such as maize or sorghum, establish the crop, preventing root rots from attacking particularly when incidence is more than 3%. Planting during the crop’s first months. Ridomil® (2.5 kg/ha), stakes from healthy crops should be used and tools applied to the soil, and foliar applications of Alliette® disinfected. Planting materials should be selected and (0.4 kg/ha) have shown good results. Fungicides handled carefully both before and after storage. Only based on plant extracts, oils, and cytokinins help viable cuttings or buds should be planted. One control soil fungi, while offering a nonpolluting recommendation is to immerse cuttings in a solution organic alternative. Resistant varieties have also been of captan (3 g/L) and benomyl (3 g/L) for 5 min. reported (Castaño 1953; CIAT 1998; Drummond and Captan may be replaced by copper oxychloride. Gonçalves 1957; Fassi 1957; Müller and De Carneiro 1970; Sánchez 1998). Root rots Root rot or “black rot” (Rosellinia spp.) Root rots in cassava are important where soils are poorly drained or where excessively rainy seasons Importance. This disease has been reported in occur. In early growth, many microorganisms are many cassava-growing regions with heavy, poorly capable of inducing not only root rots in young drained soils that have a high content of organic cassava plants, but also in the storage roots of matter. It is also found in cassava crops planted after mature plants. Although several root diseases have forest crops or ligneous perennial species (Castaño been reported, little information exists about them. 1953; Viégas 1955). The disease has also been called Not even the symptoms are well described. “black rot” because of the characteristic black color of infected tissues and root cankers. Usually, infection kills young plants at germination or shortly afterwards. Infection in plants In Colombia, dry rots are found in the Coffee Belt older than 4 months may result in partial or total wilt, and in crops planted where coffee, cacao, or guamo depending on whether the root rot is soft or dry. (a shade tree used in coffee plantations) had Once invaded by one or more primary pathogens, previously been grown. infected roots may be invaded by a wide spectrum of other microorganisms. These are usually the Symptoms and epidemiology. Initially, the root otherwise weak saprophytic parasites, which become epidermis is covered with white rhizomorphs that later capable of degrading root tissues and masking the become black (Figure 8-12). Internally, infected identity of the primary causal agent. The resulting tissues of bulked roots are slightly discolored and root rots therefore appear to have the same exude liquid on pressure. The black mycelial bundles syndrome of symptoms. penetrate the tissues, where they grow, forming small cavities that contain mycelium of an off-white color. Pathogens causing root rots include The infected roots have a characteristic odor of Phytophthora spp., Fusarium sp., Scytalidium decaying wood. lignicola, Rosellinia spp., Sclerotium sp., and Fomes lignosus (Ferdinando et al. 1968; Jennings 1970; Etiology. Rosellinia necatrix, the perithecial Pereira 1998; Viégas 1955). state of Dematophora necatrix, is the causal agent of this disease (Castaño 1953; Viégas 1955). This fungus Some of these diseases often develop when induces root rot in other ligneous and herbaceous cassava is planted immediately after woody crops plants (Castaño 1953; Viégas 1955). However, very such as coffee. Soils of such crops are infested with little information is available on the epidemiology of 174 Cassava Diseases which is found in infected roots or towards the base of stems, is also disseminated through the soil. This mycelium can, sometimes, penetrate roots through wounds, causing subsequent rot. Although it is rarely lethal to young plants, this fungus may cause a high incidence of root necrosis in a plant. The disease is caused by Sclerotium rolfsii, a common soil organism but a weak pathogen. It has a white mycelium of cottony appearance. It also produces numerous round sclerotia, which characteristically form in the host or laboratory cultures. Figure 8-12. Rot caused by Rosellinia necatrix in cassava roots. Cottony cassava rot (Fomes lignosus) Although this disease is known in Latin America, it is the fungus in cassava. Its sexual state is generally currently of minor importance. The disease is identified believed to occur only very rarely (Castaño 1953). Other by the presence of a mass of white mycelium under the Rosellinia species also attack cassava. cortex of bulked roots and by the presence of white mycelial threads that look like cotton fibers covering Management and control. Although the disease part or all the epidermis of infected roots to the base of has not been reported in young plants, the stems. Internally, the infected tissues look dehydrated recommendation is still to avoid selecting planting and have a characteristic odor of decaying wood. materials from infected crops. Young plants may become infected and sometimes suffer sudden wilting, defoliation, and root necrosis. • Rotate with grasses whenever the incidence of plant death or root rot reaches 3%. The organism causing the disease is Fomes lignosus (IITA 1972; Jennings 1970). • Eliminate infected cassava residues and/or litter from perennial trees (e.g., trunks and Diseases Caused by Pseudo-fungi decaying branches). Root rots (Phytophthora spp.) • Plant in loose-textured soils. Importance. Root rots are a very common • Improve soil drainage. problem in cassava production, causing yield losses that may be as high as 80% of total production. • Treat by solarization, exposing the soil to the sun for 3 months. Distribution. Root rot caused by Phytophthora spp. affect cassava in different agroecological areas in • Chemical control with Topsin (thiophanate- Africa (Fassi 1957), tropical America (Müller and De methyl) at 2 g/L of commercial product and Carneiro 1970), and India (Johnson and Palaniswami applied to the soil before planting. 1999). In Nigeria, Cameroon, and Benin, the pathogens causing root diseases of economic importance include • Applications of Sincocin (plant extract) to the Sclerotium rolfsii, Botryodiplodia theobromae, Fomes soil at 1 L/ha are recommended. Stakes may lignosus, Rosellinia necatrix, Rhizoctonia solani, also be immersed in a solution of the product Phytophthora spp., and Fusarium spp. (Hillocks and at 1%. Wydra 2002). Root rot (Sclerotium rolfsii) Recent reports mention that cassava rots may cause losses between 5% and sometimes 100% in Latin This disease commonly occurs in young stakes and America, Asia, and Africa, specifically, Colombia, Brazil mature roots, covering affected parts with a cottony (W Fukuda and C Fukuda 1996, EMBRAPA, Brazil; mat. It has been reported only in Latin America (CIAT F Takatsu 1996, University of Brasília, Brazil, pers. 1972; Ferdinando et al. 1968). The white mycelium, comm.), Cuba (M Folgueras 2002, INIVIT, pers. 175 Cassava in the Third Millennium: … comm.), Mexico (LF Cadavid 2005, CLAYUCA, pers. comm.), India (J George 2004, CTCRI, pers. comm.), Uganda (W Serubombwe 2003, NARO, pers. comm.), Nigeria, Kenya, Indonesia, Ghana, Ecuador and probably in many other countries. In Asia, root rots have recently been described in the Nondindang District, Buriram Province, Khonburi District, Nakhon Ratchasima Province (Figure 8-13)— areas characterized by loam sandy soil. The genotypes showing symptoms are Rayong 5, Kasetsart 50, and Huay Bong 60 (E Álvarez 2009, pers. comm.). The disease was also observed at the Rayong Field Crop Research Center, affecting genotype Huay Bong 80 (Figure 8-14). Cassava root rots have also been observed in Vietnam. In India, Phytophthora palmivora is emerging as a serious threat to cassava in several industrial areas of Tamil Nadu, where it is endemic. Crop losses are as high as 50%. Differential reaction of cassava varieties to infection by Phytophthora was observed (Edison 2002). Figure 8-14. Cassava root rot symptoms observed in Rayong and at the Thai Tapioca Development Institute Symptoms and epidemiology. Phytophthora (TTDI) in Huay Bong, Nakhon Ratchasima drechsleri macerates the root parenchyma, causing a Province. A B Figure 8-13. Cassava plants showing symptoms of root rot and wilting in (A) Buriram Province and (B) Nakhon Ratchasima Province, Thailand. 176 Cassava Diseases penetrating odor and changing root color to cream conducted in different edaphoclimatic areas of Colombia (Figure 8-15A). P. tropicalis has been isolated from showed that different Phytophthora spp. are the major crops in Colombia (Figure 8-15B). In the State of cause of cassava root rots (Sánchez 1998). Other Sergipe (Brazil), in 1976–1979, P. drechsleri was found pathogens also causing root rots include: to cause rot in the neck and roots, irreversible wilting of aerial parts, and defoliation (Souza Filho and Fomes lignosus Tupinamba 1979) (Figure 8-15C). In contrast, Sclerotium rolfsii P. nicotianae var. nicotianae shows little pepstatin Armillariella mellea activity. The odor is mild, with brown discoloration Fusarium spp. (Soto et al. 1988). Root attack by P. drechsleri leads to Rhizoctonia sp. leaves falling and branch tips drying up before the plant Rhizopus sp. dies (Figuereido and Albuquerque 1970). Phytophthora Rosellinia necatrix (Lozano and Booth 1979) nicotianae also causes a similar leaf blight in cassava Pythium chamaehyphon (GenBank accession (Erwin and Ribeiro 1996; Lima et al. 1993). AY745748; CIAT 2004) Etiology. Farmers widely believe that root rots are Eleven species of Phytophthora have been reported caused by excess water in the soil. However, a study as causing root rot. These are: P. arecae (Coleman) Pethybridge (Álvarez et al. 1997c) P. capsici Leonian (Lima et al. 1993) P. citricola (CIAT 1999, 2000) P. cryptogea Pethybr. & Lafferty P. drechsleri Tucker (Figueiredo and Albuquerque 1970; Muller and De Carneiro 1970) P. erythroseptica Pethybridge (Fassi 1957) P. meadii (Barragán and Álvarez 1998) A P. melonis (GenBank accession AY 739021; CIAT 2000, 2004) P. nicotianae Breda de Haan var. nicotinae (Dastur) (Soto et al. 1988) P. palmivora (Johnson and Palaniswami 1999; (Álvarez and Llano 2002) P. tropicalis (GenBank accession AY 739022; CIAT 2000, 2004). The genetic diversity of these pathogens is broad and was determined through studies in Colombia with 80 isolates obtained from roots, young stems, and soils B from 19 municipalities. These studies included the pathogen’s pathogenicity, virulence, morphology, and molecular analysis of the internal transcribed spacer (ITS) region of the pathogen’s ribosomal DNA. Eleven genetic groups were identified through PCR-RFLP (Álvarez et al. 1997a, 1997c, 2000; Sánchez 1998). Phytophthora tropicalis was identified through sequencing of the ITS region of ribosomal DNA and isoenzymes, showing it to be genetically similar to P. capsici (CIAT 2000). The isolate was obtained from cassava roots in Barcelona, Quindío; P. palmivora was isolated from cassava roots at CIAT, Valle del Cauca. C Integrated disease management. The integrated Figure 8-15. Root rots (A and B) and plant wilt (C) caused by management of root rots includes the use of varietal Phytophthora spp. resistance and/or cultural practices. 177 Cassava in the Third Millennium: … Varietal resistance. A principal tool for managing Inoculated bulked roots demonstrated variation in root rots caused by various Phytophthora species is the the severity of symptoms, depending on whether they use of varietal resistance. Various examples exist of the came from resistant or susceptible clones. The successful adoption of cassava clones resistant to inoculation method was easier to carry out, less Phytophthora spp. In 1990, the Brazilian Agricultural expensive, and with faster results than the seedling Research Corporation (Embrapa) and the Agricultural method. No correlation was found between the two Research Center for the Humid Tropics (CPATU) inoculation methods (López and Lozano 1992). released two cassava clones resistant to root rots: cvs. Mae Joana (IM-175) and Zolhudinha (IM-158). Both Cassava seedlings planted in soil were also clones came from the State of Amazonas and are evaluated. The soil had previously been inoculated with planted in the várzea ecosystem (a type of floodplains) a suspension of each of zoospores, oospores, or of northern Brazil. The adoption of these clones, chlamydospores applied separately (Lima et al. 1993). together with the application of appropriate cultural Each inoculum type caused wilt and seedling death. practices, increased root yields by more than 80% in this region (Lozano 1991b). In 1995, Lima and Takatsu (1995) published the reactions of 13 cassava clones that had been stem- High yields and resistance to root rot caused by inoculated with three isolates of P. drechsleri in the P. drechsleri were obtained in clones MD-33 and Pao greenhouse. The isolate with the most virulence was (Mendonça et al. 2003). Pereira (1998) reported inoculated into roots in the field. To inoculate roots resistance to P. drechsleri in seven cultivars from a without harvesting them, inoculum was deposited in a group of 31 evaluated. Barragán and Álvarez (1998) small wound. The correlation between inoculated reported 15 resistant genotypes from a group of plants in the screenhouse and roots inoculated in the 60 elite genotypes evaluated. In 2003, Llano et al. field was +0.24. reported six individuals from a family of 126 individuals, with high resistance to P. tropicalis, P. palmivora, and In other studies (Loke 2004), several biochemical P. melonis. Although harvesting roots 14 months after and morphological markers, and leaf resistance were planting resulted in increased yield, it also identified for preselecting clones for resistance to demonstrated a higher incidence of root rots, thus P. tropicalis in cassava populations, based on showing that root rot incidence varies according to (1) reduced area of the parenchyma with the presence clones and harvest time. of scopoletin in roots after harvest; (2) a high relationship between iron and manganese; and In a participatory research study, indigenous (3) resistance in leaves 72 h after inoculation. communities of the Colombian Amazon adopted Scopoletin is a coumarin that is found in very low cassava clones resistant to Phytophthora spp. (Llano concentrations in fresh roots but which increases and Álvarez 2008; Llano et al. 2001). These clones were considerably after harvest. This substance is easy to selected in the laboratory (harvested roots) and quantify in roots, using ultraviolet light, and is related greenhouse (stems) from 700 genotypes provided by to the cassava root’s susceptibility to postharvest Embrapa and CIAT. physiological deterioration. To obtain reliable information on the genetics of Loke (2004) also demonstrated the benefits of such a complex disease, Takatsu and Fukuda (1990) using an index of resistance to P. tropicalis that concluded that standardized methods were needed for includes molecular markers. The objective of this index inoculating and evaluating resistance to each cassava is to select genotypes with durable resistance, based root rot pathogen. CIAT and the National University of on a large diversity of resistance or defense Colombia–Palmira identified cassava clones resistant to mechanisms. P. nicotianae var. nicotianae by first inoculating bulked roots of plants that were 10 to 12 months old. They Several studies to identify the genetic base of then added a suspension of the fungus to a nutritive resistance to Phytophthora have been conducted. For solution in which 45-day-old seedlings were growing. 25 cassava clones, a correlation of +0.31 was observed The roots of seedlings were colonized by the pathogen. between resistance during penetration (in the peel, The inoculated roots were evaluated in terms of the both epidermis and subepidermis) and after penetration percentage of the pathogen’s colonization of cortical (in the parenchyma). This finding indicated that these and parenchymatous tissues. forms of resistance are moderately associated (Corredor 2005; Loke 2004). Alvarez et al. (2003c), 178 Cassava Diseases Llano et al. (2004), and Loke (2004) evaluated the Cultural practices. The best cultural practices for cassava K family (150 F1 individuals from the cross the integrated management of root rots are TMS 30572 × CM 2177-2), inoculating root fragments. summarized below: Nineteen QTLs were identified as associated with resistance to different species of Phytophthora and • Selecting an appropriate, well-drained, and Pythium, three of which explained between 8.3% and moderately deep soil. If the land is flat and 11% of phenotypic variance. soils are clayey, planting should be done on ridges. Those QTLs that were expressed were also found to vary from one cropping cycle to another, depending • To catalyze resistance, fertilizers should be on prevailing environmental conditions. Minor genes applied in drench form, using potassium were demonstrated as controlling resistance to sources, and/or as foliar sprays, using P. tropicalis, P. melonis, and P. palmivora, with a high potassium phosphites. genotype × environment interaction existing. Although the population showed differences within its • If rot incidence reaches 3%, the cassava crop genetic base for resistance to Phytophthora, levels of should be rotated with grasses, at least once a resistance were not sufficiently high for use in year. improvement programs. Hence, identifying contrasting parents for the disease would be useful, as • Eradicating diseased plants by removing well as developing new populations for determining infected roots from the field and burning them. QTLs (Llano et al. 2004; Loke et al. 2004). • Selecting healthy plants to obtain clean seed. To identify genomic sequences in cassava that are Where the farming area is infested, then stakes homologous with genes of resistance to diseases of should be treated with metalaxyl at 0.3 g/L a.i. different plant species, two cassava families were evaluated for their resistance to P. tropicalis (GenBank • Treating stakes in hot water at 49 ºC for accession AY 739022), P. melonis (GenBank accession 49 min is an alternative to chemical treatment AY 739021), and P. palmivora, all causal agents of root (Álvarez et al. 2003b). rot. Two strategies were used to search for genes for resistance: (1) hybridization with probes for maize and Immersing stakes in a suspension of Trichoderma rice, using RFLP; and (2) amplifying conserved harzianum and T. viride at 2.5 × 108 spores/L, and regions of DNA, using the degenerate primers NBS later applying the same suspension in drench form and Pto kinase. Three cassava clones resistant to P. (CIAT 2006, 2007). Biological control of rots with tropicalis and P. palmivora were used, obtaining isolates of T. harzianum and T. viride is promising clones that were sequenced and homologized with (Bedoya et al. 2000; CIAT 2006, 2007; Edison 2002). known genes of resistance. Field trials in different agroecological zones of Colombia have shown that soil inoculated with strains With hybridization, cassava demonstrated very low of these types of Trichoderma will increase cassava homology with the monocotyledon genes tested. yield (CIAT 2001, 2006, 2007). Isolates of Trichoderma Twenty-eight NBS and 2 Pto kinase clones were spp. were selected on the basis of in vitro antagonism, obtained, of which 14 showed homologous sequence production of secondary metabolites that inhibit with resistance gene analogs (RGAs) and NBS-LRR Phytophthora spp., and bioassays in screenhouses. (GenBank accessions: AY730038, AY730040, AY730041, AY737490, AY745762, AY745763, AY745764, To identify practices of disease management that AY745765, AY745766, AY745767, AY745768, AY745769, are feasible for indigenous communities in the AY745770, and AY745771). Four of these showed an northwestern region of the Amazon (Colombia), open reading framework (ORF) with conserved motifs in participatory research trials were established, with the the nucleotide-binding site (NBS) region, which means women farmers making the evaluations. Soil they were considered to be RGAs. Altogether, three amendments were incorporated. These were ash, classes of RGAs were identified, none of which showed organic matter (dry leaves), and a 1:1 mixture of both association with resistance to Phytophthora (Llano et al. materials. Dosage was 200 g/plant. Cassava was also 2004). associated with cowpea (Vigna unguiculata), and stakes selected from the middle part of healthy plants. 179 Cassava in the Third Millennium: … In these trials, cassava yield increased by 446% Cassava heart rot with applications of the ash and organic matter mixture. Where only ash was used, yield increased by This physiological disorder damages bulked roots 272%. Stake selection increased yield by 366%. (Averre 1967). It occurs in moist and poorly drained Compared with traditional management, these soils in which roots present a dry internal necrosis that practices reduced root rots by 100% (incorporation of extends irregularly from the center to cortical tissues. the ash and organic matter mixture), 99% (association This disorder is observed in only 10%–20% of the roots with cowpea), 94.2% (ash only), and 89.7% (stake of an infected plant. The larger and thicker roots are selection) (Llano and Álvarez 2008). believed to be the most susceptible. Other Causal Agents of Cassava Rots Postharvest physiological deterioration (PPD) Other fungal root rots The cause of cassava roots’ rapid deterioration after harvest is unknown, whether it results from Other fungal species can induce root rots in cassava physiological or pathological effects, or a combination plants at different growth stages, but little information of the two. Numerous microorganisms have is available on these diseases and their importance. nevertheless been isolated from deteriorated roots, with These root rots are caused by: several being known to cause discoloration and rot. Armillariella mellea, which attacks both the stem Bacterial Diseases base and roots of mature plants (Arraudeau 1967; CIAT 1972) Cassava bacterial blight (Xanthomonas Phaeolus manihotis (Heim 1931) axonopodis pv. manihotis) Lasiodiplodia theobromae (Vanderweyen 1962) Pythium sp. (CIAT 1972) Importance. Cassava bacterial blight (CBB) is Fusarium sp. (CIAT 1972) regarded as one of the most limiting diseases of Clitocybe tabescens (Arraudeau 1967) cassava production, as it can cause total crop loss in Sphaceloma manihoticola (Bitancourt and affected areas. Jenkins 1950) Rhizopus spp. (Majunder et al. 1956) During the 1960s and 1970s, this disease caused Rhizoctonia sp. (Gonçalves and Franco 1941) major damage to the cassava crop. However, the Aspergillus spp. (Clerck and Caurie 1968) application of integrated management programs, Nattrassia mangiferae (Scytalidium sp.); introduction of quarantine measures in some countries, Verticillium sp.; and Rigidoporus sp. and identification and planting of resistant varieties have led to its satisfactory control (Hillocks and Wydra 2002; Bacterial root rots Lozano 1986). Some bacterial species belonging to the Bacillus, Distribution. Cassava bacterial blight has been Erwinia, and Corynebacterium genera are also known in Latin America since 1912, when it was believed to cause soft rots and/or fermentation in reported in Brazil (Kemp 2000). It spread to the bulked cassava roots (Akinrele 1964; Averre 1967). cassava-growing regions of Africa and Asia in the 1970s Symptoms of these soft rots are similar and are (Boher and Verdier 1994; Bradbury 1986). In Latin frequently accompanied by fermentation. These agents America, the disease has been reported from most of probably penetrate roots through wounds produced by the cassava-growing regions of Bolivia, Brazil, farmers during cultivation or by animals, insects, or Colombia, Cuba, the Dominican Republic, Mexico, fungi. They are frequently accompanied by other Panama, Trinidad and Tobago, and Venezuela (Cajar saprophytic microorganisms that help advance 1981; Fukuda 1992; Languidey 1981; Lozano and deterioration. Sequeira 1974; Rajnauth and Pegus 1988; Rodríguez 1979; Rodríguez 1992; Sosa 1992; Trujillo et al. 1982). The causal agent of cassava bacterial blight (see below) can also induce necrosis, discoloration, and dry In Asia, CBB has been observed during the rainy rot in the vascular tissues of infected roots (Lozano season in Thailand (Figure 8-16) as well as in many 1973; Lozano and Sequeira 1974). other countries but it is seldom very severe (E Álvarez 180 Cassava Diseases 1979, cited by Hillocks and Wydra 2002), the Democratic Republic of the Congo (Daniel et al. 1980), Côte d’Ivoire (Notteghem et al. 1980), Republic of South Africa (Manicom et al. 1981), Rwanda (Onyango and Mukunya 1982), Sudan (Kwaje 1984), Togo (Boher and Agboli 1992), Cameroon, Central African Republic, Tanzania, Kenya, and Burundi (Hillocks and Wydra 2002). Symptoms and epidemiology. Symptoms characteristic of CBB are small, angular, aqueous- looking leaf spots found on the lower surface of the leaf blade. Or symptoms may be leaf blight or brown leaf burn, wilt, dieback, and a gummy exudation in infected young stems, petioles, and leaf spots (Figure 8-17). The vascular bundles of infected petioles and stems are also necrotic, appearing as bands of brown or black color. Symptoms occur 11 to 13 days after infection (Lozano and Booth 1979). Some susceptible varieties present dry and putrid spots around necrotic vascular bundles (Verdier 2002). Figure 8-16. Cassava bacterial blight (CBB) symptoms observed The bacterium disseminates widely through stakes on cassava leaves of cv. Rayong 5 in Thailand. from infected plants, from one cropping cycle to another, and from one area to another. Within the crop, 2009, pers. comm.). The disease was first observed in the principal means of dispersal are water splash from Taiwan before 1945 (Leu 1976), and has since been rain and contaminated tools. The movement of people reported from Malaysia, Indonesia, Thailand (Booth and animals within the crop, especially during or after and Lozano 1978; E Álvarez and AC Bellotti 2009, pers. rain, may also help disperse the pathogen (Lozano comm.), Vietnam (E Álvarez and AC Bellotti 2009, pers. 1973). comm.) and India (Cherian and Mathew 1981). In Africa, the disease causes severe epidemics (Hillocks and Although the pathogen survives poorly in soil, this Wydra 2002), and appears in the following countries (in can be source of inoculum if it is contaminated, as well order of reporting year): Nigeria (Williams et al. 1973), as irrigation water, although in reduced proportions. Zaire (Maraite and Meyer 1975), Ghana (Doku and The bacterium can survive epiphytically on many Lamptey 1977), Benin (Korang-Amoakoh and Oduro weeds, which serve as sources of inoculum if control is A B C Figure 8-17. Symptoms of cassava bacterial blight, induced by the bacterium Xanthomonas axonopodis pv. manihotis: (A) angular leaf spots and leaf blight, (B) exudate on stem, and (C) plant wilt. 181 Cassava in the Third Millennium: … inadequate. Insects spread the disease over short (2) a cluster at 0.7 and comprising 81% of the distances. Venezuelan isolates included in this study, and 4 Brazilian isolates; and (3) a cluster at 0.4 and formed The severity of CBB becomes greater when by most of the Brazilian isolates, 3 isolates from temperatures fluctuate widely between day and night. Venezuela, 1 from Cuba, and 3 from Colombia. In this Hence, the disease is not important in areas of stable last group, clustering below the 0.4 similarity level also temperatures such as the Amazon Region, where the occurred, indicating great genetic variability within the cloud cover does not permit marked fluctuations in Brazilian sites, possibly related to the also high level of temperatures. genetic diversity observed for the host plant (Sánchez et al. 1999). When new pathogen strains are introduced Etiology. The causal organism, Xanthomonas into a given area, the genetic diversity already found axonopodis pv. manihotis (Xam), is a Gram-negative within the pathogen population is increased, thereby bacterium that is shaped like a slim cane. It is mobile favoring the development of new pathotypes (Restrepo by means of a polar flagellum. Its cells are not 1999). encapsulated, and the bacterium does not form spores. Integrated disease management. To control the The organism penetrates the host through stomas disease, integrated management should be carried out, and wounds in the plant’s epidermis. Infection is involving varietal resistance, cultural practices, and systemic, moving through the stems and petioles in biological control. xylem vessels and possibly also the phloem. Varietal resistance. The genetic control of CBB is Xam can be detected, using the polymerase chain the most efficient and economic method for the farmer, reaction (PCR), which amplifies a DNA fragment of but the cassava cropping cycle is long, with a very low 898 bp. This methodology permits detection to as low production of planting materials. Hence, the time as 300 cfu/mL in leaves and stems infected by CBB involved in producing resistant varieties is very long. At (Verdier et al. 1998). When Verdier and Mosquera CIAT, resistant varieties are identified through (1999) used the specific probe P898, they detected the evaluations in the Eastern Plains and the Atlantic bacterium in raw extracts of infected leaves and stems, Coast, where the disease is acute and endemic. They and in cassava fruits and sexual seed. According to are also evaluated in the greenhouse, under controlled Verdier et al. (1993), pathogen diversity is narrow in conditions, with temperatures at 30 °C and relative Africa but broad in South America, cassava’s center of humidity at 95%. origin. In several greenhouse studies, plants of different Restrepo et al. (1996) reported that the diversity of cassava varieties were inoculated with 39 isolates from the Colombian strains is very broad, at both pathogenic different regions of Colombia, Venezuela, and Brazil. and genetic levels. Diversity is also high in Brazil Fifteen genotypes were identified as having high to (Restrepo et al. 1999) and Venezuela (Verdier et al. intermediate resistance to CBB, scoring between 1998). 1.0 and 2.5 on a scale of severity from 1.0 to 5.0. These varieties included M Esc Fla 039, M Esc Fla 021, M Bra Previous studies also revealed geographical 383, M Col 2066, CM 3311-4, CM 7772-13, and SM differentiation among pathogen populations, according 1779-8 (CIAT 1999, 2000, 2001, 2002b, 2003a). to ecozone. Evidence also exists of pathotypes moving within and between regions, probably because of Between 1995 and 2007, about 6400 cassava movements of infected planting materials. In Colombia, genotypes were evaluated in Villavicencio (Colombia) analysis of pathogenic characteristics of Xam strains for their field resistance to CBB. Of these, 117 were collected in three ecozones led to the definition of identified as having partial resistance (CIAT 2001, different pathotypes specific to each ecozone (Restrepo 2002b, 2003a, 2006, 2007). 1999). In a 10 × 10 diallelic study, carried out in An analysis, using the AFLP technique, of the Villavicencio, with 45 families and 30 plants per family, genetic variability of 85 Xam isolates from Brazil, the cassava genotype CM 4574-7 was identified as Colombia, Cuba, and Venezuela distinguished three having high general combination ability. Its progenies groups: (1) a cluster at a similarity level of 0.6 and showed increased resistance to CBB and SED (Calle et formed of isolates from different localities in Colombia; al. 2005). 182 Cassava Diseases Tolerant varieties also exist such as M Bra 685, conditions. Nine quantitative trait loci (QTLs), located M Bra 886, ICA Catumare, ICA Cebucán, ICA on linkage groups B, D, L, N, and X, explained the Negrita, Vergara (CM 6438-14), CM 4574-7, and phenotypic variance of the crop’s response to Xam in Chiroza. However, the disease has increased in the greenhouse. severity in ICA Catumare, for which adequate selection of clean seed was not performed (Álvarez Jorge et al. (2001) reported eight QTLs and Llano 2002). Several genotypes have also been associated with resistance to CBB, and found identified as having resistance to several pathotypes changes in the expression of QTLs from one of the bacterium (Álvarez et al. 1999). cropping cycle to another in the field, which could be related to changes in the pathogen’s population Zinsou et al. (2004) recommended the cassava structure. A QTL, located in linkage group D, was genotype TMS 30572 for farmers in Benin, because conserved over two cropping cycles and in resistance of its high yield and relatively stable resistance to evaluations in the greenhouse. In a previous study, CBB across different environments. Kpémoua (1995) Jorge et al. (2000) showed that 12 different QTLs showed that resistance to Xam is associated with the control resistance to five Xam strains. production of phenolic compounds and the reinforcement of cell walls in the vascular system Hurtado et al. (2005) detected the molecular during early infection. marker, microsatellite SSRY 65, that could select resistant genotypes in a cassava family To determine the genetic control of resistance, corresponding to the cross CM 9208-13 × M Nga 19. 150 F1 individuals of the cross TMS 30572 × Furthermore, the authors identified two RGAs of the CM 2177-2 were inoculated with the pathogen and NBS class through amplification with PCR, using two evaluated for resistance under controlled conditions primers designed by Llano (2003). These RGAs in the greenhouse. Five different Xam strains from could identify plant individuals that were resistant to the world’s major cassava-growing areas were used the bacterium. in the study. Genetic analysis identified six genomic regions that control resistance to all Xam strains. One approach to assessing cassava genetic One region controlled >60% of resistance to each of diversity involves the structural analysis of genotypes the strains CIO-1 and CIO-136. Two regions resistant to CBB. Multiple correspondence analysis of accounted for >70% of resistance to strain CIO-84. AFLP data, using two primer combinations for Another 80% of resistance to strains CIO-136 and cassava genotypes resistant and susceptible to two ORST X-27 could be explained by 3 loci for each strains of Xam, elucidated the genetic structure of strain (Jorge et al. 2000). cassava germplasm resistant to CBB (Sánchez et al. 1999). Results revealed a random distribution of In three instances, the same genomic regions resistance or susceptibility, suggesting that controlled resistance to two strains. A marker was resistance to CBB has arisen independently many obtained by Southern hybridization of a PCR times in cassava germplasm. amplification product from cassava, using heterologous primers designed from conserved Phenolic compounds have been implicated in the regions of the Xanthomonas resistance gene in rice resistance of cassava (Manihot esculenta) to (Xa21). The region it marked accounted for 60% of xanthomonads. Cassava cultivars M Col 22 and phenotypic variance for resistance to strain CIO-136. CM 523-7 were inoculated with Xam and X. A backcross population, derived from crossing cassavae. CM 523-7 was susceptible to both members of the mapping population, has been pathogens, whereas M Col 22 was susceptible to developed and will provide more recombinations for Xam and resistant to X. cassavae. In the resistant fine mapping towards cloning resistance genes, and interaction, no disease symptoms were observed in for studying intra-locus and inter-loci genetic leaves. Bacterial growth was greatly reduced, and cell interactions (Jorge et al. 2000). wall-bound peroxidase activity increased twofold, probably related to lignin deposition (Pereira et al. A molecular genetic map of cassava was recently 2000). constructed from an F1 cross of noninbred parents. RFLP, AFLP, EST, SSR markers were used to map Preformed putative defenses include copious resistance to CBB. The F1 cross was evaluated with latex production, which contains protease, ß-1,3 Xam strains under both field and greenhouse glucanase, and lysozyme activities. ESTs from a latex 183 Cassava in the Third Millennium: … cDNA library revealed a constitutive expression of • Immersion in extract of citrus fruit seeds many defense-related genes including chitinase, (Lonlife®) glucanase, and PAL. A cDNA-AFLP analysis of cassava leaves suffering a hypersensitive response to • Heat treatment of stakes (Álvarez et al. 2008; Pseudomonas syringae pv. tomato revealed that 78 CIAT 2007), using hot water at 49 °C for genes, new to cassava, had expressed differentially. 49 min. Incidence of CBB in untreated stakes Homologs of a metalloprotease, glucanase, was 37%, but dropped to 7% when treated peroxidase, and ACC oxidase were all found to be with hot water. It dropped further to 0% when upregulated. Pathogenicity determinants of Xam are stakes were pretreated at 49 °C for 10 min 24 being studied in the disruption of the gum h before being treated with hot water for 5 h. biosynthesis gene (its EPS is produced copiously in Treatment with hot water did not, in practical plants) and the pel gene (pectate lyase appears as a terms, affect stake germination, reducing it single isoform) (Kemp et al. 2001). by only 18% in the most prolonged treatment (Ramírez et al. 2000). The induction of RGAs were amplified as a means of elucidating enzymes that activate under stress conditions the putative genes involved in cassava’s defense is probably responsible for conserving high response. For the cDNA-AFLP technique, of about stake germination, even after prolonged 3600 cDNA fragments screened, 353 fragments were treatment in hot water. specific to a resistant variety. Sequence analyses showed significant homology with resistance genes, Lozano (1986) also mentions the following NPK-1 related proteins, senescence-related proteins, practices for managing the disease: and other known proteins involved in disease resistance reactions. • Planting at the end of rainy periods • Crop rotation with grasses Using degenerate primers, 12 classes of RGAs • Planting barriers of maize to prevent were identified in cassava. Screening a cassava cDNA dissemination by wind library (root and leaf) with class-specific RGA probes • Improving soil drainage also led to the identification of 16 expressed gene • Weed control clones. Sequence analysis of clone L16 confirmed the • Fertilizers adapted mainly with sources of constitutive expression of a protein that shares potassium characteristics with previously reported resistance • Eradicating diseased plants genes (Restrepo et al. 2001). • Preventing the movement of people, machines, and animals from infected lots to López et al. (2004a) identified 6046 unigenes and healthy lots characterized a group of genes putatively involved in • Eliminating infected materials after harvest cassava’s defense response to Xam infection. López et by burning branches and stems al. (2004b) identified the RXam1 gene, homolog of • Incorporating harvest residues into the soil Xa21 from rice, in a 3600-bp DNA fragment. The gene is induced in the resistant variety (M Bra 685), In field studies conducted in Benin and Togo by 72 h after infection by Xam. Wydra et al. (2001), locally and regionally well- adapted control measures for CBB were identified Cultural practices. The following practices are such as: recommended: • Using locally preferred resistant varieties • Use of healthy planting materials obtained • Intercropping with locally used crops from disease-free crops, plants derived from • Amending soils with local materials meristem culture, and by rooting buds and/or • Fertilizer applications and recommendations shoots on phytosanitary measures carried out to reduce disease • Treating stakes by immersing them for 10 min in a solution of cupric fungicides such as Complementary studies elucidated some copper oxychloride or Orthocide® (captan) at mechanisms of resistance at the biochemical and 3 to 6 g/L genetic levels and molecular host-pathogen interactions. 184 Cassava Diseases New methods for detecting Xanthomonas Management and control. campestris pv. manihotis (Xcm), using • Using healthy seed immunological and genetic techniques, were • Planting with varieties resistant to the insect developed. Research results were partly verified vector under African conditions such as testing the cassava • Burning infected stems genome mapping population for reaction towards African strains to identify genetic markers and/or Bacterial stem gall (Agrobacterium resistance related genes. tumefaciens) Biological control. Spraying with suspensions of Symptoms and epidemiology. This disease Pseudomonas putida reduced the severity of generally appears on the lower parts of stems in damage caused by CBB, while cassava yields plants older than 6 months. Characteristic symptoms, increased significantly (CIAT 1985). However, this found on stem nodes, are galls that often become practice has not been adapted for farming very large, presenting a proliferation of buds on the conditions. epidermis (Figure 8-19). Infected plants may become weak and spindly, and in the early days of infection, Bacterial stem rot (Erwinia carotovora pv. suffer dieback to as far as major galls. A single plant carotovora) could have several galls on a stem and even along lower branches (Lozano et al 1981). Importance. This disease is important for the damage it does to the quality and germinability of The disease is usually initiated by infested soil planting stakes. being rain-splashed onto wounds caused by natural defoliation in stems of the plant’s lower parts. Symptoms. The disease is characterized by an aqueous and smelly stem rot or by medullary Management and control. Control is achieved necrosis of the plant’s ligneous parts (Figure 8-18). through rotation with another crop when more than Infected plants show bud wilt. The stem’s surfaces 3% of the planting is infected; disinfecting machetes typically show perforations made by insects of the with 2% sodium hypochlorite; always using planting genus Anastrepha Schiner, which act as vectors for stakes from healthy crops; and burning diseased the bacterium. These orifices are easy to distinguish materials within the crop (Lozano et al 1981). by the presence of dry latex, discharged as the stem is perforated. Diseased stakes used for planting will Another bacterial disease is caused by Erwinia not germinate or they produce weak spindly plants, herbicola. with a limited number of bulked roots (CIAT 1972). A B Figure 8-18. Symptoms caused by Erwinia carotovora: Figure 8-19. Galls on stem caused by Agrobacterium (A) wilt, and (B) damage to the medulla. tumefaciens. 185 Cassava in the Third Millennium: … Diseases caused by ‘Candidatus Costa Rica, Panama, Peru, and Venezuela (Calvert and Phytoplasmas’ Cuervo 2002), as well as in Nicaragua and Honduras. In (previously known as mycoplasma-like Venezuela, it was reported for the first time in the organisms or MLOs) States of Barinas and Aragua, with incidences between 11.4% and 14.3%, in cassava stakes grafted with Cassava frogskin disease (Ca. phytoplasma, ‘Secundina’, a variety used to diagnose the disease subgroup 16SrIII-L and rpIII-H) (Chaparro and Trujillo 2001). Importance. Cassava frogskin disease (CFSD) is Symptoms and epidemiology. Frogskin mostly an economically important disease affecting cassava attacks cassava roots, reducing their diameter, but roots. It was reported for the first time in 1971, in the some varieties may also show symptoms in leaves such Department of Cauca, southern Colombia. Its origin as mosaic, chlorosis, curling, and/or curvature in leaf appears to be the Amazon region of Brazil or Colombia margins (Figure 8-20A). However, these symptoms are (Pineda et al. 1983). difficult to distinguish under field conditions, and may be confused with damage from mites, thrips, viruses, Frogskin disease directly affects root production, and micronutrient deficiencies, or they can be masked causing losses of 90% or more. Symptoms consist of when temperatures are >30 °C. small, longitudinal fissures distributed throughout the root. As roots increase in diameter, the fissures tend to Characteristic CFSD symptoms in the roots include heal, giving the injuries a lip form. The root cortex or a woody aspect and the thick, cork-like peel, which is epidermis appears cork-like and peels off easily. also fragile and opaque. The peel also presents lip-like Depending on the severity of symptoms, the depth and slits that may join to create a net-like or honeycomb number of lesions increase until the root becomes pattern (Figures 8-20B and 8-20C). When roots do not deformed (Álvarez et al. 2003a; Pineda et al. 1983). bulk adequately (Figure 20D), the stems tend to be thicker than normal. In contrast, the roots of healthy Distribution. In the 1980s, the disease occurred in plants are well developed, with thin, brilliant, and most cassava-growing regions of Colombia and has flexible peel. continually spread. It has now been reported in Brazil, A B C D Figure 8-20. Symptoms of cassava frogskin disease in (A) leaves, (B) and (C) presence of lips in root, and (D) reduced root bulking. 186 Cassava Diseases Molecular tests, carried out on plants of cassava insect vectors. Numerous homopteran species and pink vinca (Catharanthus roseus (L.) G. Don) after (e.g., planthoppers, tree hoppers, and froghoppers) transmission trials with dodder (Cuscuta sp. L.), were collected from cassava fields in 9 departments detected the presence of phytoplasmas associated with and 17 sites in Colombia. Three genera—Scaphytopius the 16SrIII group. Graft transmission could transfer fuliginosus Osborn, Empoasca sp. Walsh, and phytoplasmas from infected to healthy plants (CIAT Stirellus bicolor Van Duzee (Hemiptera: Cicadellidae)— 2005). were the most frequently collected. These three species are known vectors of viruses and phytoplasmas for Insects were collected to identify the vector or other crops. Based on the evidence of high homology vectors of the phytoplasma causing the disease. A (80%) between insect and phytoplasma detected in homology of 90% was found among sequenced cassava, Sc. fuliginosus appears to be a potential fragments from tissue of the insect Scaphytopius candidate as the vector for CFSD (CIAT 2003b). marginelineatus Stål (Hemiptera: Auchenorrhyncha: However, tests for transmission have not yet effectively Cicadellidae) and from tissues of two cassava varieties. confirmed this hypothesis. The whitefly (Bemisia tuberculata) is still associated with the disease Etiology. The CFSD-associated phytoplasmas transmission. were identified as group 16SrIII strains by restriction fragment length polymorphism (RFLP) and sequence Integrated disease management. To date, the analyses of amplified rDNA products, and results were disease is managed principally by using stakes from corroborated by PCRs employing group 16SrIII-specific healthy plants. Heat treatment, followed by meristem rRNA gene or ribosomal protein (rp) gene primers. culture, has been used to obtain plants free of CFSD. Collectively, RFLP analyses indicated that CFSD strains Grafting with the susceptible variety Secundina is differed from all phytoplasmas described previously in useful for monitoring the effectiveness of the heat group 16SrIII and, on this basis, the strains were treatment (Flor et al. 2001). Treating stakes at tentatively assigned to new ribosomal and ribosomal temperatures of more than 55 °C appears promising protein subgroups 16SrIII-L and rpIII-H, respectively. but needs adjusting to reduce losses by the consequent This is the first molecular identification of a low germination of stakes. phytoplasma associated with CFSD in cassava in Colombia (Álvarez et al. 2009). Plantings with more than 10% of incidence (foliage, stakes, and roots) should be burned. Plant health The phytoplasma was not detected in healthy surveillance and quarantine systems need to be plants from the same varieties harvested in disease-free strengthened to prevent the entry or mobilization of fields. These results point towards the possible role planting materials from areas with the disease. played by phytoplasmas in this disease (Álvarez et al. 2003a; CIAT 2002a). The importance of the CFSD in Field and greenhouse studies carried out at CIAT cassava production systems has motivated other have reported 30 genotypes with different levels of scientific groups at CIAT, such as the Virology group, to resistance. These findings were confirmed through the undertake efforts to understand the characteristics of expression of leaf symptoms in grafts with variety the disease, its symptoms and its management Secundina (CIAT 2003b; Cuervo 2006). The use of practices. tolerant varieties will be a useful tool in controlling this disease. Cuttings from CFSD-infected plants in the greenhouse were taken, and rooted in deionized water Witches’ broom with different doses of chlortetracycline. Inhibition of leaf symptoms caused by CFSD was successful in two Importance. This disease, known as experiments when 50 ppm chlortetracycline were used, superbrotamiento in Spanish, has been reported in thus indicating that CFSD is not caused by a virus. Brazil, Venezuela, Mexico, and Peru (Figure 8-21). Nested PCR also showed that phytoplasmas were Although its incidence is not significant, the percentage present in leaves of infected plants when treated with of witches’ broom in affected plantings is much higher 0 ppm tetracycline (CIAT 2003b). than that of other diseases caused by American phytoplasmas. Crop losses can reach 80% (Lozano et Although the disease spreads mostly through al. 1981). In Asia a new cassava disease was observed infected stakes, the disease is believed to have at Quang Ngai, Vietnam (Figure 8-22). Typical 187 Cassava in the Third Millennium: … Figure 8-21. Symptoms of “superbrotamiento” in cassava. (Photo: B Pineda.) symptoms similar to witches’ broom are widespread in southern Vietnam, in Plangyao, Chacheoengsao, Thailand, and also in the Philippines (Figure 8-23). The disease may seriously affect yields and the availability of clean planting material. Figure 8-23. Disease symptoms observed on cassava plants in the Philippines. Symptoms. Several symptomatologies exist: 3. Stakes produce only a few dwarf and weak 1. Plants exhibit dwarfism and an exaggerated spindly sprouts that never reach normal size. proliferation of buds. Sprouts have short 4. When the affected cassava is uprooted, the internodes and small leaves, but do not show roots are thinner and smaller, with rough- deformation or chlorosis. textured skins, and drastically reduced starch 2. Proliferation of weak spindly sprouts on the content. stakes. A B C Figure 8-22. Cassava plants in Vietnam with exaggerated bud proliferation; (A) (B) shoot proliferation and/or usually (C) rachitic branches growing from a single stake; and shoots with short internodes and small leaves that show no deformation or chlorosis. (Photos: JF Mejía.) 188 Cassava Diseases The disease is transmitted mechanically and by the indicated that differences exist between the use of stakes from diseased plants (Lozano et al. 1981). phytoplasmas detected in eastern Thailand and southern Vietnam (E Álvarez, JF Mejía, and Etiology. The transmission of cassava A Bertaccini 2009, pers. comm.). phytoplasmas by Cuscuta sp. into pink vinca was 100% positive. Symptoms appeared 3 weeks after implanting Management. The use of healthy planting the host parasite into pink vinca in growth chambers at materials and the elimination of diseased plants in the 18–20 °C. No transmission was achieved with the field are recommended to prevent the disease insect Scaphytopius fuliginosus, even 3 months after (Lozano et al. 1981). The disease is reduced by exposure to feeding, whether cassava to cassava, selecting stakes from healthy plants and by restricting cassava to vinca, or vinca to vinca (Valencia et al. the movement of cassava planting stakes, especially 1993). from infected areas, and that of related species such as Jatropha. Varietal resistance also exists. In Vietnam, disease recognition was carried out in the country’s central and southern regions (Quang Antholysis Ngai and Dong Nai provinces). Samples for diagnosing phytoplasmas were collected in southern Vietnam at Importance. Antholysis in cassava was observed Hung Loc Agricultural Research Center and from a in crops in southwestern Colombia in 1981 by farmer’s plot in Dong Nai province, both sites about Jayasinghe et al. (1983), severely in some 60 km from Ho Chi Minh City. Phytoplasmas were experimental clones. However, this disease does not detected in the samples collected in Thailand and have economic importance and is only sometimes Vietnam. Diagnosis results confirm the association of observed. symptoms (high bud proliferation shoots with short internodes, and small leaves) with phytoplasmas. Symptoms. The disease appears in the inflorescence, with a characteristic virescence in the Phytoplasmas were detected in roots, small leaves, petals, which, instead of being their normal pink, and leaf veins showing symptoms. No phytoplasmas of become green. Hypertrophy of the petals is later the 16SrIII group (reported in America) were found in observed and they become structures similar to leaves the samples from Thailand and Vietnam. However, only (phyllody). The floral racemes lose their normal samples from eastern Thailand and southern Vietnam appearance and resemble sprouts, giving this have been evaluated. These results need to be syndrome its name “antholysis” (antho – flower; confirmed. Molecular tests based on the 16Sr gene lysis – dissolve, loosen) (Figure 8-24). A B C Figure 8-24. Symptoms of antholysis in cassava: (A) healthy flower, (B) virescence, and (C) phyllody. (Photos: B Pineda.) 189 Cassava in the Third Millennium: … Infected flowers commonly exhibit a very swollen Álvarez E; Loke JB; Sánchez J; Bellotti A. 1997b. Progress gynophore and develop internodes in the floral in the characterization of Phytophthora isolates, receptacle, a phenomenon known as apostasis. the causal agent of root rots of cassava. American Furthermore, elongation of the receptacle occurs Phytopathological Society - Annual Meeting, above the insertion of the pistil, with development of 9–13 August, Rochester, NY, USA. Phytopathology sprouts. Flower fertility is lost, resulting in 87(6):S4. nonfunctional flowers that abort prematurely. Affected plants do not present symptoms in other organs and, Álvarez E; Sánchez J; Chacón MI; Loke JB. 1997. Avances moreover, germination did not differ between infected en la caracterización de aislamientos de Phytophthora and healthy stakes (Jayasinghe et al. 1983). spp. el agente causal de pudriciones de raíces en yuca. ASCOLFI Congress at the International Center Etiology. By using an electron microscope, for Tropical Agriculture (CIAT), Cali, Colombia. Jayasinghe et al. (1983) observed oval or spherical August 1. pleomorphic structures only in phloem tissues. Transmission is 100% by stakes. Under greenhouse Álvarez E; Cadena SF; Llano GA. 1999. Evaluación de conditions, symptoms of antholysis appear within resistencia de yuca a doce cepas de Xanthomonas 1 month of planting, contrasting with healthy plants, axonopodis pv. manihotis. ASCOLFI Informa which take 5 months to flower. (Colombia) 25(4–6):57–59. Treatment with penicillin (500 to 1000 ppm) did Álvarez E; Chacón MI; Sánchez NJ. 2000. DNA not reduce symptoms, whereas tetracycline reduced polymorphism and virulence variation of a antholysis by 90%. This sensitivity and detection by Phytophthora population isolated from cassava Dienes’ stain confirmed that the causal agent is a Manihot esculenta Crantz. In: Carvalho LJCB; phytoplasma (Jayasinghe et al. 1983). Thro AM; Duarte Vilarinhos A, eds. Proc IV International Scientific Meeting of the Cassava Management. The disease is reduced by selecting Biotechnology Network (CBN), held in Brasília, stakes from healthy plants. Varietal resistance also Brazil, 3–7 Nov 1998. National Research Center for exists. Genetic Resources and Biotechnology (CENARGEN) of the Brazilian Agricultural Research Corporation References (EMBRAPA); CBN, Brasília, Brazil. p 279–287. To save space, the acronym “CIAT” is used instead of Álvarez E; Mejía JF; Lozada T. 2001. 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Adaptation and implementation of integrated control measures of cassava bacterial blight through collaborative research between European partners, IITA and NARS in Africa. Poster presented at the Fifth CBN meeting, held in St. Louis, Missouri, USA, 4–9 Nov 2001. 199 Cassava in the Third Millennium: … CHAPTER 9 Cassava Bacterial Blight, Caused by Xanthomonas axonopodis pv. manihotis Valérie Verdier1, Camilo López2, and Adriana Bernal3 Introduction Symptoms A limiting factor in cassava production is cassava Xam is a systemic pathogen and an epiphyte. It bacterial blight (CBB)4. This disease is distributed characteristically induces a combination of a wide extensively in Asia, Africa, and South America. range of symptoms, including angular spots in leaves, blight, wilt, exudates and lesions in stems, and death Losses caused by CBB vary greatly. If (Figure 9-1). environmental conditions are favorable for disease development and if no agronomic practices are Infection begins with an epiphytic phase of the adopted to control it, losses may reach 100% in only pathogen on leaves, which helps build inoculum. This, two or three cropping cycles. The disease spreads from one area to another and from one growth cycle to the next mainly through the planting of infected stakes. A B Dissemination also occurs over small areas through tools, insects, and rain splash. Disease severity depends very much on the cultivar, soil fertility, climate, and quantity of inoculum present in the area. Repeated cropping of highly susceptible varieties, without rotation, reduces soil C D E fertility, which increases the crop’s predisposition to the disease. The causal agent of the disease is the bacterium Xanthomonas axonopodis pv. manihotis or Xam. This pathogen induces a wide range of symptoms. In Colombia, the disease was very destructive in 1971. Since then, its presence has been reported in the country’s principal cassava-producing areas (Lozano F 1986; Restrepo and Verdier 1997). 1. IRD, 911 Avenue Agropolis BP 64501, 34394 Montpellier Cedex 5, France. E-mail: valerie.verdier@ird.fr 2. Department of Biology, UN, Ciudad Universitaria, Bogotá, Colombia. E-mail: celopezc@unal.edu.co 3. Faculty of Sciences, Universidad de los Andes, Bogotá, Colombia. Figure 9-1. Symptoms caused by the bacterium Xanthomonas E mail: abernal@uniandes.edu.co axonopodis pv. manihotis in cassava. (A) Angular 4. For an explanation of this and other abbreviations and acronyms, spots; (B) blight; (C) wilt; (D) exudates on a stem; see Appendix 1: Acronyms, Abbreviations, and Technical (E) deep lesions on a stem; (F) defoliation and plant Terminology, this volume. death. (Photos by Bernard Boher.) 200 Cassava Bacterial Blight, Caused by Xam in its turn, significantly increases the probability of The bacterium grows in a medium containing future infection through stomata and wounds. Leaf sucrose, producing colonies without pigmentation. It is spots appear as moist, angular areas that are clearly a Gram-negative rod, measuring 0.5 × 1.0 mm, and distinguishable on the lower surface of leaves. The leaf has a single polar flagellum. Except for the lack of blight is attributed to a toxin (3-methylthiopropionic pigmentation, most of its physiological and acid) produced by Xam. The bacterium colonizes biochemical characteristics are typical of the intercellular spaces in leaf mesophyll and xanthomonads. multiplies rapidly, producing large quantities of exopolysaccharide matrix. The leaf spots exude a More than 90% of Xam strains evaluated hydrolyze yellowish and sticky substance that concentrates into Tween 60, Tween 80, and starch. They grow in the drops, mainly on the lower side of leaves. These presence of 0.001% (w/v) of Hg(NO3), but not of 0.05% bacterial exudates are scattered to other plants by rain (w/v) of triphenyltetrazolium chloride or of 0.001% (w/v) drops, which fall and splash, during the rainy season of malachite green. They show βglucosidase activity, and, to a lesser extent, through insects. The pathogen and form acid from melibiose but not from D-ribose or multiplies and the consequent increased production of lactose. They grow in DL-glyceric acid, but not in bacterial exudates blocks vascular tissues, leading to mucic or saccharic acid, or ethane. They use the leaves wilting. L-threonine as their only source of nitrogen and are sensitive to 10 g of gentamicin and fusidic acid. Highly susceptible clones may be entirely defoliated. The bacterium enters the xylem vessels According to Restrepo and Verdier (1997), through lysis of cell walls in the tissue and multiplies considerable variation was observed among Xam rapidly in the vascular system, extending to all parts of strains in terms of biochemical, physiological, the plant and producing death. Symptoms can also serological, and genomic characters when analyzed, appear on fruits as wet areas and on the leaf sheath or using either the restriction fragment length in embryos. Seeds from infected fruits may be polymorphism (RFLP) or amplified fragment length deformed and the germination rate is low. Roots of polymorphism (AFLP) technique (Restrepo et al. 1999). infected plants usually do not present symptoms, except in some susceptible varieties, which may then For characterization, different types of probes for display dry and putrescent spots around necrosed Xam are being used by RFLP, whether genomic or vascular lines. This characteristic putrefaction is plasmid. Universal probes such as ribotyping have also exclusive to vascular tissues, with other root tissues been used. The African Xam strains belong to one of remaining normal. five ribotypes identified in South America and, when using RFLP analyses with a plasmid probe, 14 different Losses are usually correlated with the number of haplotypes can be distinguished. A high level of DNA infected stakes used in planting. When plants are polymorphism was detected in strains from South infected, their aerial parts may be completely America (Restrepo and Verdier 1997). destroyed. New shoots may develop from the stem, either above or below the soil surface. These young In Colombia, Xam strains collected from three shoots are susceptible under extreme and rainy edaphoclimatic zones (ECZs) were geographically conditions, rapidly becoming infected. If the planting differentiated (Restrepo and Verdier 1997). The material is infected, any shoots it produces will wilt and genetic diversity of Xam was shown to have a quickly die. microgeographical distribution (Restrepo et al. 2000b). Etiology Differences in virulence between Xam strains were described for the first time by Robbs et al. (1972). Such The causal agent of bacterial blight was renamed variation in virulence was also observed among strains several times between 1912 and 1915. It was first called from either Brazil or Africa. The speed at which Bacillus manihotis Arthaud-Berthet and Bondar; and differences in symptoms develop suggests variation in then called Phytomonas manihotis (Arthaud-Berthet aggressiveness. In 1998, a total of 10 pathotypes were and Bondar) Viegas. It was then renamed determined among Xam strains in Venezuela, using five Xanthomonas manihotis (Arthaud-Berthet) Starr, and cassava varieties as differentials (Verdier et al. 1998b). further X. campestris pv. manihotis Berthet and In 2000, a group of differential cassava varieties was Bondar. In 1995 Vauterin et al. proposed the name proposed to differentiate the virulence of Xam in X. axonopodis pv. manihotis (or Xam). Colombia (Restrepo et al. 2000a). Different pathotypes 201 Cassava in the Third Millennium: … were identified within a group of strains representing people and animals through cassava fields, especially the genetic diversity of Xam in Colombia. during or after rains, can help spread the pathogen. Disease Cycle and Epidemiology Other potential sources of inoculum are soils or contaminated irrigation waters, although their role in Infection begins with the multiplication of the pathogen infection is smaller, as the pathogen does not survive as epiphyte, occurring usually near the stomata. Leaves well in soil. In contrast, it survives as an epiphyte on are penetrated through stomatic openings or wounds. many weed hosts that then serve as inoculum sources. Twelve hours of high relative humidity suffice for Insects may also disseminate the bacterium, bacterial establishment. The most appropriate comprising as much as 10% of its dispersion over short temperature for infection is about 23 °C. distances. Apparently, the length of the photoperiod does not During drought, disease development is reduced affect the bacterium’s establishment. Xam is a vascular but the bacterium remains viable in plant tissues and pathogen that establishes itself inside vessels after a exudates, providing sources of inoculum when the rainy preliminary phase of intercellular development in the season arrives. mesophyll. If the bacterium invades lignified stems, it remains within the vascular tissues, where it can survive Incidence of Disease for up to 30 months. Host-pathogen interactions have been studied under controlled conditions, using The amount of damage caused by CBB varies in histological and cytochemical methods. different places of the world, but can be considerable. Crop losses can reach 30% when stakes are taken Studies on the epiphytic phase of the disease are from infected materials to disease-free plots. If well documented, both in the field and in vitro. A environmental conditions are favorable and control cytochemical study of the development of an measures are not adopted, losses can reach 100% aggressive strain in a susceptible host showed that within three harvesting cycles. Xam degrades the middle lamella and cell wall (Boher et al. 1995). This suggests that the bacterium’s lytic When weak pathogens such as Colletotrichum spp. activity favors its intercellular progress and penetration and Choanephora cucurbitarum invade tissues of vascular bundles. The bacterial extracellular matrix infected with CBB, the synergistic effect of these (xanthan), produced in all phases of pathogenesis, is pathogens increases disease severity. Such associated with the degradation of the host’s parietal combinations can produce losses of up to 90% of the structures. first harvest. Seed can be infected by rain, mechanical At the beginning of the 1970s, CBB epidemics in inoculation, or translocation of the pathogen through the Democratic Republic of the Congo caused losses of xylem vessels. A high percentage of planting materials the cassava crop (75%), with the total damage being collected from crops infected with CBB carry the compounded by the destruction of the leaves, which pathogen. However, they do not show symptoms, as are rich in protein and therefore used in the diet. the bacterium is latent in the embryo. Dormancy Famine developed, during which crop losses in central breaks shortly after germination. Although stakes Africa were 80%. In 1974, an epidemic was reported in germinate normally, symptoms can appear during stem Minas Gerais, Brazil, causing losses of 50% in a and leaves development. planting of over 10,000 hectares. The use of infected stakes is the principal reason Losses in other regions of America ranged between for the pathogen persisting from one growth cycle to 5% and 40% in 1975. In Asia, losses have not been the next. Another reason is the way it is dispersed over estimated, as the pathogen was introduced only the land. The pathogen can disperse over short recently, possibly in the mid-1960s. The disease is distances mainly through rain splash and contaminated endemic in certain regions of America and Africa, tools. Tools used to harvest cassava are simultaneously where it causes significant losses. The blight is used to cut stakes for the next plantings. Hence, the moderately important in Thailand and China, although, pathogen disseminates easily to healthy stakes taken especially in China, its incidence has been increasing from asymptomatic stems, which harbor the pathogen. over the last 2 years. Because wounds facilitate infection, the transit of 202 Cassava Bacterial Blight, Caused by Xam Disease severity increases when day-to-night However, the lack of available stakes encourages small temperatures fluctuate widely from 15 to 30 °C. This farmers to exchange planting materials, which may be explains the moderate to low severity of CBB in areas contaminated. Hence, variants of Xam are with relatively stable temperatures. This effect of disseminated or introduced into regions where the CBB temperature on the disease has helped researchers had not been previously detected. predict the relative importance of the disease in each region and to develop practical recommendations for In ECZ5 (high-altitude Andes), the disease is its control. widespread. Geographically isolated from the other zones by mountains, CBB is conditioned for altitude, Geographical Distribution in Colombia which permits the introduction of only a few cassava varieties. The genetic context of the host is therefore The principal edaphoclimatic zones (ECZs) where limited and, in certain plots (perhaps most), only the cassava is cultivated in Colombia were visited between genotype ‘Algodona’—a variety discovered by the 1995 and 2000. An ECZ is defined according to region’s small farmers—is found. Because of the climatic conditions; soil type; importance of the uniform population, the pathogen does not exert predominant ecosystem; and the crop’s principal pressure for change. limitations, both biotic and abiotic: In ECZ7 (semiarid region of Guajira), the disease • ECZ1 = subhumid tropical areas was not detected in the field, nor was the bacterium • ECZ2 = acid-soil plains of the Colombian found in collected samples. Recently, the disease was Eastern Plains detected as relatively severe in the Departments of • ECZ5 = high-altitude Andes Quindío and southern Valle del Cauca. Usually, plots in • ECZ7 = semiarid area of the Guajira region forest ecosystems are disease-free. In each ECZ, different sites were visited and Resistance to Xanthomonas different plots were evaluated for the presence of axonopodis pv. manihotis bacterial blight. For each plot, at least 15 plants were randomly chosen and qualified according to a scale of Resistance to Xam by Manihot esculenta is 1 to 5, where 1 refers to an asymptomatic plant and characterized mainly by hypersensitivity at the vascular 5 to a plant that died from CBB. Evaluations were scale, and is not observed in leaves. In this case, made in optimal periods (rainy seasons) for observing response is more defensive than constituting real symptoms. In each field, leaf or stem tissue was hypersensitivity. collected from plants infected by Xam to confirm the pathogen’s presence. Resistance to CBB is expressed as a gradual development of the disease in leaves and stems. In ECZ1 (North Coast), the disease incidence was Kpémoua et al. (1996) demonstrated that, in resistant severe on all farms or plots visited. The varieties most varieties and on a cellular scale, osmophilic used were M Col 2215 (‘Venezolana’) and M Col 1505, compounds accumulate in vacuoles, and cell walls in which were found to be highly susceptible to CBB in contact with the pathogen lignify rapidly. In addition, greenhouse evaluations. In this ECZ, the climate is tylosis, which closes off vascular bundles, occurs favorable for disease development and is a factor rapidly. Phenols and reinforcements of structural towards explaining the blight’s incidence. Indeed, barriers (lignin, callose, and suberin deposits) are also optimal conditions for CBB include alternate dry and produced. Thus, a resistant variety impedes the rainy seasons, very high relative humidity, and bacterium’s progress and no exudates are formed significant differences between the maximum and (Boher and Verdier 1994; Boher et al. 1995). minimum daily temperatures (Lozano and Sequiera 1974). Overall, the same reactions are presented in the tissues of both susceptible and resistant varieties. The In ECZ2 (Eastern Plains), disease is severe. In ECZs difference is that, in resistant varieties, reactions occur 1 and 2, the widespread distribution of the pathogen earlier and with greater intensity, so that the defensive can also be explained by the intensity with which response diminishes the extent of the disease cassava is cultivated in these areas and the length of (Kpémoua et al. 1996). time the pathogen has been present in the zones. 203 Cassava in the Third Millennium: … A very important characteristic is the increase in Observations are made at days 8, 15, and 30 after cells that produce phenols, found first in the phloem inoculation. Optimal conditions for disease and then in the xylem of resistant varieties that have development are 30 °C and a saturated relative been infected. Phenol compounds are known to play a humidity. Symptoms are scored on a scale of 1 to key role in plants’ resistance to pathogens. Other 5 (Figure 9-3), where: compounds, including new lignins, are synthesized only after being induced by the bacterium. Applications of 1 = necrotic area around inoculation point potassium fertilizer also increase resistance to Xam, 2 = exudate at the inoculation point probably because it improves lignification mechanisms 3 = wilting, regardless of quantity of exudate (one in vascular tissues. or two leaves) 4 = wilting of more than two leaves Evaluating resistance 5 = entire plant wilts Evaluation of resistance to CBB can be conducted at A categorical (i.e., quantifiable) appraisal can various levels, whether in the field or greenhouse, with therefore be made of the observations. seedlings and seeds, or in in vitro cultures. For field evaluations, the following scale of 1 to 5 is used A simple method of inoculating in vitro seedlings (Figure 9-2), where: has been described (Verdier et al. 1990). It is carried out under sterilized conditions on 6-week-old seedlings. 1 = absence of symptoms The inoculum is calibrated at 108 cfu/mL and is 2 = angular spots only, no wilt deposited, using a paintbrush, on the lower and upper 3 = extensive angular spots and leaf wilt, gum surfaces of the first two leaves (i.e., the oldest). The exudates in stems and petioles plants are left in a climate chamber at 28 °C with a 4 = extensive angular spots, wilt, leaf defoliation, day-to-night ratio of 16/8 h. and drying of apical parts 5 = drying of apical parts and plant death Identifying genes for resistance Plants are evaluated over three or four cycles and, Resistance to CBB is believed to be polygenic and in each cycle, four observations are made. additively inherited, with a variation that ranges between 25% and 65% (Hahn et al. 1979). Differences This type of evaluation is very useful in areas where between resistant and susceptible varieties are disease pressure is high, which facilitates observation expressed as a variation in the rate of colonization by of disease development and progress. Furthermore, Xam and penetration of vascular tissues. Hence, this type of evaluation does not require investment in resistance is considered to be quantitative (Kpémoua et inoculation materials or maintenance of plants under al. 1996). Because of the quantitative nature of special conditions. In Colombia, such evaluation is resistance, a strategy based on detecting quantitative practiced in the different ECZs where cassava is trait loci (QTLs) was developed to use the available cultivated, such as the Eastern Plains, Atlantic Coast, cassava genetic map to identify those genomic regions and Andean Region. When inoculum presence is low, involved in resistance. These regions are also known as spraying can be carried out with local strains of the quantitative resistance loci or QRLs. bacterium, together with sand or other abrasive material that wounds foliage and thus facilitates The cassava genetic map was developed through penetration by the pathogen. an intraspecific cross between TMS 30572 (an improved variety developed at IITA) and CM 2177-2 (an Stems are inoculated 1 month after planting elite line from CIAT). To detect QRLs, five bacterial mature stakes. Bacterial isolates are made to grow on strains (CIO84, CIO1, CIO136, CIO295, and ORSTX27) LPG agar medium 12 h before inoculation. To were selected. They corresponded to different inoculate, a colony is taken from the bacterial culture, haplotypes from different geographical regions of the using the end of a needle or toothpick, directly out of country, as according to Restrepo et al. (2004). the petri dish. With that same needle, the colony is Resistance was evaluated in an F1 population under introduced into the stem near the plant’s apical parts, controlled conditions in the greenhouse. In all, 12 at about 108 cfu per puncture. According to the QRLs were detected, located in linkage groups B, C, D, availability of material, 10 replications are made for G, L, N, and X, which explained 9%–27% of resistance each pair of bacterial isolate and cassava variety. (Jorge et al. 2000). Some QRLs were specific for 204 Cassava Bacterial Blight, Caused by Xam 1 2 3 4 5 Figure 9-2. A scale of 1 to 5 is used in the field to evaluate symptoms of cassava bacterial blight (see text). (Photo 1 by Válerie Verdier; photos 2–5 by Bernard Boher.) 205 Cassava in the Third Millennium: … (A) (B) 1 2 3 4 5 Figure 9-3. (A) Inoculating a stem; (B) a scale of 1 to 5 is used to evaluate symptoms in the greenhouse (see text). This technique is used to evaluate the resistance or susceptibility of a cassava variety to the pathogen. (Photos by Válerie Verdier.) certain Xam strains, while others, mainly in linkage changes correlated with the dynamics of Xam group D, were common to different Xam strains (Jorge populations (Jorge et al. 2001). In particular, QRLs et al. 2000). detected in linkage group D were observed as remaining constant over two production cycles. In the greenhouse, Similarly, resistance to bacterial blight was some QRLs were identified in this same linkage group. evaluated in the field under high disease pressure for Certain analyses suggest that this region may have three consecutive production cycles (Jorge et al. 2001). come from Manihot glaziovii (Jorge et al. 2001). Several QRLs were detected but a change was Similarly and more recently, QRLs have also been observed in the QRLs during the 2-year study. These identified for strains from Africa (Wydra et al. 2004). 206 Cassava Bacterial Blight, Caused by Xam Proteins for resistance to pathogens in different not survive long in the soil. Or they may be removed plant species possess conserved domains such as and burned. An interval of 6 months between two NBS, TIR, and LRR, which have been used to design cassava crops is sufficient to prevent transmission of degenerated primers and thus isolate resistance gene the pathogen in the soil. Weeds must be carefully analogs (RGAs) (Meyers et al. 1999). This strategy was controlled, as the pathogen can survive as epiphytes used to identify RGAs in cassava (López et al. 2003), for long periods. Rotating the cassava crop with maize including two of type TIR and 10 of type NBS. Analysis or sorghum effectively reduces primary infection by of a bacterial artificial chromosome (BAC) library CBB caused by rain splash. Four consecutive rotation enabled identification of low- or single-copy RGAs, as cycles will reduce the incidence and severity of the well as RGAs that are part of multigenic families (López disease to economically insignificant levels. et al. 2003). Mapping analyses located two BACs with NBS in linkage group E and four in linkage group J. In Losses can be reduced by changing planting times, the latter group, the presence of a region with at least especially in subtropical areas. Cassava is usually 15 NBS-type sequences could be established. planted at the beginning of the rainy season, when conditions are also optimal for infection by and Unfortunately, to date, no QTLs associated with dispersal of the pathogen. But the crop can be planted resistance have been identified in this region (López et towards the end of the rainy season, when al. 2003). More recently, additional data on QTLs environmental conditions are drier, thus reducing associated with two Xam strains permitted incidence of CBB. Disease-free planting materials are identification of a new QTL associated with resistance essential for maintaining the blight at low levels. to strain CIO151 in linkage group U (López et al. 2007). The marker responsible for this QTL corresponds to a A method for producing stakes free of bacteria is to BAC that contains an NBS-type RGA (B39P22). This root infected or uninfected stakes in sterilized water QTL explains 62% of resistance, suggesting the and then collect the apical parts of shoots. This presence of a major gene in this BAC clone. The gene method is useful for cleaning infected clones or stakes. is denominated as RXam2 for “resistance to Xam 2”. The pruning of aerial parts of infected plants sometimes helps reduce dispersal of the disease and Using primers generated from the resistance gene secondary infection. The success of this method Xa21 from rice, which confers resistance to X. oryzae depends on the susceptibility of the variety and on the pv. oryzae, led to the identification of a fragment of the interval between initial infection and pruning. It is more cassava genome that presents a high degree of successful with resistant and moderately resistant similarity with this gene. This fragment is related to a cassava varieties that are mildly infected. QTL that explains 13% of resistance to Xam strain CIO136 (Jorge et al. 2000). From a BAC clone, the Improving crop nutrition complete gene has been sequenced and is called RXam1 for “resistance to Xam” (López, 2004.). All Soil organic content can be improved by burying crop these data suggest that the protein codified by the residues in small containers (which also restricts RXam1 gene is implicated in resistance to strain pathogen survival), applying dung, or alternating CIO136. cassava with legumes. Potassium increases resistance to Xam, but small farmers find this fertilizer difficult to Control obtain. Losses caused by CBB can be reduced if a combination Improving the quality of planting materials of agronomic practices and detection methods is used, together with varietal resistance. The measures Improved quality can be achieved by carefully selecting described below have successfully reduced the healthy stems from which stakes are obtained. incidence of CBB and has even eradicated the However, farmers are not accustomed to selecting pathogen in some areas. stakes according to this criterion. Nevertheless, they can be trained to recognize bacterial blight symptoms Cultural practices and thus choose clean stems or those with little contamination for new plantings. This practice is also Crop rotation controls the blight only if the stakes used recommended for the control of other cassava to plant cassava are disease-free. All residues from diseases. Healthy planting materials can also be infected plants should be buried, as the pathogen does produced in controlled multiplication sites, an 207 Cassava in the Third Millennium: … especially important measure in areas with low or Dot-blotting uses a DNA fragment that acts as a medium disease pressure. specific probe for a pathovar. This simple and specific method can detect Xam colonies recovered from plant The production and distribution of high-quality tissues and also evaluate colonies of presumed Xam stakes is essential, and has proven invaluable, for isolates (Verdier and Mosquera 1999). The pathogen’s enhancing cassava production. This practice has been presence can be identified directly in cassava plant neglected in Colombia and should receive more tissues (leaves, stakes, fruits, seeds, and embryos). attention. Dot-blotting is a highly sensitive and fast technique that permits large-scale evaluation of stakes at relatively low The operation and management of these cost and with little equipment. Viable bacteria can also multiplication fields, which could be used to supply be detected through plating in semiselective medium small farmers, is not still organized. Such sites would for Xam (Fessehaie et al. 1999). facilitate better control over crop health, improve distribution of new varieties, and better control the Biological control introduction of new pathogens and pests. Cassava seed beds for planting stakes should preferably be placed in Pseudomonas putida strains, applied to leaves, can forest areas, where CBB can be avoided. significantly reduce the number of angular spots per leaf and the number of leaves blighted per plant in Applying detection methods susceptible cassava clones. In one study, cassava plants were impregnated by spraying with a solution of Cassava pathogens and pests disseminate largely 1 × 109 cells per milliliter of beneficial bacteria in water through the exchange of cassava stakes. Bacterial wilt four times per month during the rainy season, was introduced this way into Africa and Asia. Many of beginning one month after planting. Root production the cassava pathogens, including CBB, can be also increased, on average, by 2.7 times. Although the use dispersed through botanical seed. of these biocontrol agents looks promising for commercial plantings, more research is needed to Planting materials and seeds should be collected determine if this practice is indeed recommendable. only from healthy plants in crops that are presumably free of bacterial blight. These crops should be Resistant varieties inspected more than once before collection, especially towards the middle and end of the rainy season when The most appropriate and realistic method for the blight tends to be more severe, to determine overall controlling CBB is through host resistance. A certain plant health. Any abnormal seed or stake should be number of adopted varieties possess considerable discarded. To prevent dissemination of the bacterium resistance to CBB and have remained so over many and other pathogens through seed, seeds should be years. The genetic base of such resistance is currently visually reviewed with considerable care and selected limited, but should be expanded by using other for density. They are then dried in heat. Manihot species and natural hybrids of M. esculenta and M. glaziovii, and should be introduced, on a Different methods exist for detecting Xam in widespread basis, into locally adapted varieties. accordance with international plant health quarantine. The PCR procedure is simple and takes 2 h (Verdier et Functional Genomics in Cassava al. 1998a). This method detects Xam at 300 cfu/mL in plant tissues. Because of its specificity and sensitivity, To identify genes that are expressed in response to the method has considerable potential as a reliable Xam infection and other genes expressed in cassava procedure for detecting and identifying the CBB plants, a strategy of generating expressed sequence pathogen in infected plant tissue. tags (ESTs) was developed. These tags are short sequences that are generated from cDNA libraries, Nested PCR is also available for detecting Xam in meaning that they correspond to genes that express cassava seed (Ojeda and Verdier 2000). Nested PCR under given conditions, which thus indicate their increases sensitivity of detection and enables function. To obtain a wide range of genes, several types successful identification of the pathogen in seeds or of cDNA libraries were constructed from different plant embryos. A material can be evaluated in just one day. parts of different varieties that were either inoculated or 208 Cassava Bacterial Blight, Caused by Xam not inoculated with Xam. We generated 13,043 ESTs bacterium were obtained (Arrieta et al. 2011). These and assembled them into a unigene set of 5700 unique DNA fragments denote a genomic structure typical of a sequences, comprising 1875 contigs (overlapping bacterium belonging to the Xanthomonas genus. sequences, involving 9218 ESTs) and 3825 unique sequences. These may represent about 10% to 20% of The bacterium has a genome of about 5 Mbp, with the genes present in cassava (López et al. 2004). two operons of ribosomal RNA and more than 50 codifying regions for tRNAs (Arrieta et al. 2011). A With this information, the first microarray of phylogenomic study was developed, which used cassava was developed and used to study the kinetics hundreds of genes that were shared between this and of expression of these 5700 genes in response to other Xanthomonas species that had also been infection by Xam (López et al. 2005). Genes were sequenced. This study confirmed the phylogenetic identified, whose expression varied significantly proximity of Xam with closely studied bacteria such as between plants inoculated with the pathogen and Xanthomonas axonopodis pv. citri and Xanthomonas healthy plants (126 showed induction and 73 were euvesicatoria (Rodríguez et al. 2011). Xam’s repressed). The proportion of differentially expressed evolutionary proximity with other extensively studied genes was low and constant for the first 48 h after bacteria enabled comparisons that facilitated the inoculation but increased considerably by day 7 before search for pathogenicity genes in Xam. dropping at day 15 after inoculation. Among the important strategies used by Of the genes expressed differentially, most showed phytopathogenic bacteria are the production of similarity with proteins known to be important in plant proteins for adhering to the host, synthesis of toxins, protection against pathogens, for example, proteins production of exopolysaccharides, and the secretion implicated in the strengthening of cell walls or and translocation of proteins to the cytoplasm of the associated with oxidative stresses such as peroxidases, plant cell. In the genome of Xam, the following have so cationic peroxidases, and glutathione-S-transferase; or far been found (Arrieta et al. 2011): with protein degradation (proteases and ubiquitin), which are transcription factors responding to ethylene. • Eleven genes potentially associated with The repressed genes found were basically genes that adhesion to surfaces code for proteins involved in photosynthesis (López et • Three clusters of genes potentially associated al. 2005). with the biosynthesis of toxins • Two clusters that codify for type II secretion A group of 10 differentially expressed genes were system, which secretes enzymes that degrade studied, using real-time PCR. The pattern of expression host components (induction or repression) was conserved for all the • One cluster implicated in the biosynthesis of genes, using both methods. The induced genes exopolysaccharide xanthan represented a group with high potential for being used • One cluster of genes for cellular signaling for in genetic improvement programs, once their quorum sensing functional validation was confirmed (López et al. 2005). • One cluster that codes for type III secretion system Comparative and functional genomics of Xanthomonas axonopodis pv. manihotis The last system, type III secretion system or TTSS, is perhaps the most important for pathogenicity in Understanding the bacterium’s pathogenicity strategies Gram-negative bacteria (Alfano and Collmer 2004). and the plant’s natural defense strategies can help This system is highly conserved for the injection of generate innovative control methods that target critical effector proteins in the host’s cytoplasm. Once inside, points in disease development. Recently, strategies of these effectors suppress the host’s defenses and comparative and functional genomics have been used generally modify the host’s physiology to benefit the to accelerate the discovery of important genes for pathogen. However, in a resistant host, these effectors pathogenicity in this bacterium (Verdier et al. 2004). As are recognized by the plant’s surveillance system. Thus, a result, the genome of Xam strain CIO151 has been the set of effectors that a bacterium has determines sequenced, using state-of-the-art technology (the 454 whether it will cause disease in a plant with a given set and Illumina sequencing systems, reviewed in Metzker of resistance genes. When these genes are absent, the 2005). Thousands of sequence fragments were pathogen can freely invade the host, as its effectors will assembled until tens of genomic fragments of the then be fully virulent. 209 Cassava in the Third Millennium: … Each phytopathogenic bacterium is estimated to Although the defense mechanisms used by the have 35 to 50 genes that codify for effector proteins cassava plant against the pathogen are well known, the (Alfano and Collmer 2004). In the Xam genome, more genes for resistance need to be identified. The cassava than 20 effectors have been found after comparison genetic map has been established and serves as a basis with other phytopathogenic bacteria of the for searching for markers linked to resistance to CBB. Xanthomonas and Pseudomonas genera (Arrieta et al. The availability of techniques, together with genetic 2011). Two of these genes were found to be associated transformation, would enable rapid acquisition of new with pathogenicity. One is hpaF, which is shared with genetic materials with resistance to CBB. Recently, the many Xanthomonas bacteria and has previously been sequence of the cassava genome was released at associated with virulence in X. axonopodis pv. glycines www.phytozome.net/cassava.php. It covers 416 of the (Kim et al. 2003). The other is pthB (Castiblanco et al. 770 Mbp of its DNA, which is estimated to represent unpublished data), which has been used extensively in 95% of codifying DNA. Likewise, 47,164 loci that code population studies and which presents high sequence for proteins have been predicted. homology with genes of the TAL family (for “transcription activator-like” gene family) in With this large resource, strategies can be Xanthomonas. developed for identifying the repertoire of genes implicated in this plant’s immunity, and for more easily The TAL gene family contains a type of effector associating those markers with the appropriate that is translocated by the TTSS to the cellular phenotypic characteristics to accelerate the cytoplasm (Bonas et al. 1989), where it is directed to development of improved varieties. The big challenge the nucleus. There, it modulates the expression of will be to develop functional genomics tools to validate certain genes, according to a code that was recently the function of these genes and determine those that deciphered (Boch et al. 2009; Moscou and Bogdanove are important for resistance to CBB. The development 2009). Because pthB is crucial for pathogenicity, it is a of oligoarrays, mass sequencing of transcripts promising target in the generation of resistant plants. (RNAseq), and mapping by association with genes, markers, and candidates will help better represent Conclusions cassava’s molecular responses to CBB and identify genes and markers for genetic improvement. Cassava bacterial blight is an important disease. Because it is widespread in Colombia, the control With the complete sequencing of the genomes of methods previously described must urgently be both cassava and Xam, we have passed from an almost applied. The production and distribution of high-quality “orphan” state of research in this pathosystem to being stakes that are free of the pathogen is an essential step possibly part of a pathosystem model that allows us to in controlling the disease. understand the complex interactions and evolutionary relationships that have been molded over centuries of Current studies on the genetics of both the molecular dialogue between plants and bacteria. pathogen and cassava should lead to practical applications in the field. Where methods of biological Acknowledgement control (use of antagonists) or chemical control (applications of cupric compounds) do not result in The authors dedicate this chapter to the memory of expected reductions of disease incidence, then Bernard Boher, a pioneer on the study of this important modifications to farming practices and, especially, the disease, who opened a lot of other studies on cassava introduction of resistant varieties continue to be bacterial blight (CBB). effective alternatives for controlling CBB. References The results of characterizing the structure of Xam populations can be applied in the selection and Alfano JR; Collmer A. 2004. Type III secretion system introduction of resistant materials. The breeder can effector proteins: double agents in bacterial disease now evaluate genotypes, using a reduced number of and plant defense. 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A simple cipher 185:3155–3166. governs DNA recognition by TAL effectors. Science 326:1501. 211 Cassava in the Third Millennium: … Ojeda S; Verdier V. 2000. Detecting Xanthomonas Vauterin LHB; Kersters K; Swings J. 1995. Reclassification axonopodis pv. manihotis in cassava true seeds by of Xanthomonas. Int J System Bacteriol 45:472–489. nested polymerase chain reaction assay. Can J Plant Pathol 22(3):241–247. Verdier V; Mosquera G. 1999. Specific detection of Xanthomonas axonopodis pv. manihotis with a DNA Restrepo S; Verdier V. 1997. Geographical differentiation hybridization probe. J Phytopathol 147(7–8):417–423. of the population of Xanthomonas axonopodis pv. manihotis in Colombia. Appl Environ Microbiol Verdier V; Schmit J; Lemaitre M. 1990. Étude en 63:4427–4434. microscopie électronique à balayage de l’installation de deux souches de Xanthomonas campestris pv. Restrepo S; Duque MC; Tohme J; Verdier V. 1999. 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Rev Soc Brasil Fitopatol 5:67–75. 212 CHAPTER 10 Insects and Mites that Attack Cassava, and their Control* Anthony C. Bellotti1, Bernardo Arias V.2, Octavio Vargas H.3, Jesús A. Reyes Q.4, and José María Guerrero5 Introduction in the Americas (Table 10-1). The host plant does, indeed, display broad genetic variation, which correlates Cassava (Manihot esculenta Crantz) is a major energy with the numerous types of organisms that feed on the source for millions of people who live in the tropics and plant or are in symbiosis with it. Of the 17 general groups subtropics. In the last 26 years, considerable efforts of pests described in Table 10-1, 35 species are found in have been made to study the crop and its associated America, 11 in Africa, and 6 in Asia. In all, about pest complex. Research entities include several 200 arthropod species feed on cassava (Bellotti and international organizations such as the Centro Schoonhoven 1978a, 1978b). Many are specific to Internacional de Agricultura Tropical (CIAT)6 in cassava, having adapted, in diverse ways, to this species’ Colombia, the International Institute of Tropical natural biochemical defenses, which include laticifers and Agriculture (IITA) in Nigeria, and the Centro Agronómico cyanogenic components (Bellotti and Riis 1994; Bellotti Tropical de Investigación y Enseñanza (CATIE), in Costa 2000a). Rica; and many national programs in Latin America (e.g., Colombia, Brazil, and Cuba), Africa (e.g., Many of these species are minor pests and cause few Cameroon, Nigeria, and Uganda), and Asia (e.g., India, or no losses in yield. Others are classified as major pests Indonesia, China, and Thailand) (Bellotti et al. 1999; because, apparently, they have co-evolved with the crop, Bellotti 2000b). which has then become their principal or only host. These pests can cause severe damage to the crop, as Cassava, as plant and crop, originates in the manifested in yield losses. Such major pests include Neotropics. However, the exact place of origin is mites, whiteflies, thrips, mealybugs, lace bugs, debatable, but was probably within a wide region of the stemborers, hornworm, and subterranean burrower bug. Amazon Basin, encompassing various habitats Other pests such as insect scales, leafhoppers, white (Renvoize 1973; Allem 1994). Bellotti et al. (1994) grubs, cutworms, leafcutting ants, fruit flies, shoot flies, suggest that this may be one reason why such a and termites can cause sporadic or local damage to the diversity of arthropods is recorded as attacking the crop crop. These are considered as minor or generalist pests, and may attack the crop opportunistically, especially during drought when the only source of available food is cassava (Bellotti 2000b). * This document contains information published in the Proceedings of the XXVII Congress of the Sociedad Colombiana de Entomología (SOCOLEN), 2000. Insects harm cassava by reducing the 1. Emeritus Scientist/Consultant, Entomologist/Agrobiodiversity, photosynthetically active area of the plant (leaves), thus IPM, Cassava Program, CIAT, Cali, Colombia. diminishing yields; attacking stems, which debilitates the E-mail: a.bellotti@cgiar.org 2. Research Associate, Plant Production, IPM, Cassava Program, plant’s support and inhibits transport of nutrients; and CIAT. E-mail: bernaarias1@gmail.com attacking planting materials (“seed”) and thus reducing 3. Entomologist, FEDEARROZ, Bogotá, DC, Colombia. shoot production in stake germination. They can also 4. Entomologist, Asociación Colombiana de Ciencias Biológicas, Palmira, Colombia. E-mail: jesus_antonior@hotmail.com attack roots and cause secondary rots. Some pests are 5. Research Assistant, Taxonomy of Phytophagous Mites, IPM Unit, vectors and spread diseases. CIAT. E-mail: jmguerrerob@yahoo.com 6. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, Abbreviations, and Technical Observations indicate that pests attacking the plant Terminology, this volume. over a prolonged period—such as mites, whiteflies, 213 Cassava in the Third Millennium: … Table 10-1. Global distribution of arthropod pests important to the cassava crop. Pest Principal species Americas Africa Asia Mites Mononychellus tanajoa X X Tetranychus urticae X X Oligonychus peruvianus X Mealybugs Phenacoccus manihoti X X P. herreni X Root mealybugs Pseudococcus mandioca X Stictococcus vayssierei X Whiteflies Aleurotrachelus socialis X Aleurothrixus aepim X Bemisia tabaci X X X B. tuberculata X Hornworms Erinnyis ello X E. alope X Lace bugs Vatiga illudens X V. manihotae X Amblystira machalana X Burrower bug Cyrtomenus bergi X Thrips Frankliniella williamsi X X Scirtothrips manihoti X Corynothrips stenopterus X Scale insect Aonidomytilus albus X X X Fruit flies Anastrepha pickeli X A. manihoti X Shoot flies Neosilba perezi X Silba pendula X Gall fly Jatrophobia (Eudiplosis) brasiliensis X White grubs Leucopholis rorida X X X Phyllophaga spp. X Others X Termites Coptotermes spp. X X X Heterotermes tenuis X Stemborers Chilomima spp. X Coelosternus spp. X Lagocheirus spp. X X X Leafcutting ants Atta spp. X Acromyrmex spp. X Grasshoppers Zonocerus elegans X Z. variegatus X Total 35 11 6 SOURCE: Bellotti 2000b; Arias and Bellotti 2001. 214 Insects and Mites that Attack Cassava, ... thrips, mealybugs, stemborers, ins ect scales, and lace is not geographically uniform. For example, the bugs—will reduce yield more extensively than those that mealybug Phenacoccus herreni, which causes cause defoliation and damage to plant parts over short considerable damage in Northeast Brazil, was probably periods. Some pests, such as the hornworm, leafcutting introduced from northern South America (Venezuela or ants, fruit flies, and shoot flies, allow the cassava plant Colombia), where this insect’s populations are to recover from short-term damage, particularly if this is controlled by natural enemies not found in Brazil not repeated. (Bellotti et al. 1994; Smith and Bellotti 1996). Phenacoccus manihoti, a serious pest in Africa, is Because cassava is a crop that is mostly grown in found only in Paraguay and certain areas of the State marginal areas, it usually faces prolonged dry seasons of Mato Grosso in Brazil and of the Department of and deficient soils (abiotic factors) and many pests and Santa Cruz in Bolivia (Lohr and Varela 1990; Bellotti diseases (biotic factors). Farmers in such areas are often 2000a, 2000b). Studies on the CGM have in a difficult socioeconomic situation. When a cassava demonstrated a high degree of polymorphism and a planting is planned, selecting varieties that are resistant large complex of Mononychellus species in northern or tolerant of most these biotic factors is therefore South America, unlike what is found in Brazil (Bellotti important. This way, farmers do not need to resort to et al. 1994). This diversity is associated with the great the application of pesticides in the crop’s first months. wealth of phytoseiids that control Mononychellus spp. Nor do they need to accept losses of root yield because in cassava crops (Bellotti et al. 1987, 1999; Bellotti of pests and diseases. Varietal resistance, or host-plant 2000a). resistance (HPR), thus becomes a significant pest control measure. Other control measures such as Insects that Attack Planting Materials appropriate farming practices, pesticide applications, and biological control are also used, and are discussed The planting of stakes free of insect pests and other in more detail below. damage is important for obtaining good shoot development (i.e., germination) and the satisfactory Cassava Arthropod Pest Complex establishment of young plants. Cassava is a no vegetation production cycle develops Insect scales over 1 to 2 years—a long cycle for a commercial crop. It propagates vegetatively and has considerable drought Various species of insect scales have been identified as tolerance. It is usually planted with other species, either attacking cassava stems in many cassava-producing as an intercrop or in staggered rotation, the system regions of the world. The quality of planting materials most commonly used by farmers. Such agronomic can be noticeably reduced if stakes are infested with characteristics contribute, without doubt, to the scales. diversity of the arthropod pests feeding on this crop. • White scale, Aonidomytilus albus (Cockerell), The arthropod pest complex extends over a broad can reduce shoot development by 50% to 60%, region of the crop’s production area, highlighting the according to the severity of infestation. need for care in placing quarantine measures to prevent Immersing infested stakes in insecticide pathogens being introduced into pest-free areas (Frison solutions reduces infestations but heavily and Feliu 1991). The accidental introductions of the infested stakes will germinate poorly even after cassava green mite (Mononychellus tanajoa Bondar or treatment. Accordingly, stakes infested with CGM) and mealybug (Phenacoccus manihoti Mat. Ferr.) scales are not recommended for use as from the Americas into Africa have caused considerable planting materials. Aonidomytilus albus has losses throughout the African cassava belt and have been found in most cassava-producing regions required a massive effort in biological control (Herren of the world. and Neuenschwander 1991; Neuenschwander 1994a). In Asia, none of the principal cassava pests has yet been • Individuals of black scale or Saissetia miranda established and the arthropod pests so far observed (Cockerell & Parrott), gray scale or have not caused serious losses in yield (Maddison Hemiberlesia diffinis (Newstead), and 1979). Ceroplastes sp., as well as those of A. albus, are not noticeable when populations are low or Recent explorations in the Neotropical cassava- are found in young crops. Instead, they are growing areas indicate that the arthropod pest complex highly visible in older crops, where isolated 215 Cassava in the Third Millennium: … plants or sections of the crop become heavily roots, that is, they are rhizophagous, and tend to infested and from which epizootics can start in a damage newly planted stakes, either before or after following cropping cycle if stakes are not shooting (or germination) (FIDAR 1998). selected and treated. Burning of harvest residues is advisable for preventing these pests A worldwide pest. White grubs are a cassava pest from resurging. throughout the world and constitute a serious problem in Indonesia, where the most important species Fruit fly appears to be Leucopholis rorida. Another significant pest comprises the Phyllophaga spp. in Colombia. The Two species of fruit fly have been identified as attacking literature also mentions the following: Lepidiota cassava in the Americas: Anastrepha manihoti da stigma, Euchlora viridis, E. nigra, E. pulchripes, Costa Lima and A. pickeli da Costa Lima. The larvae of Anomala obsoleta, Heteronychus plebejus, Opatrum this fly tunnels up or down the plant’s stems, forming micans, Carpophilus marginallus, Dactylosternum brown galleries in the pith, thereby promoting stem rot. sp., Inesida leprosa, Petrognatha gigas, and Sternotomis virescens (Leefmans 1915; Dulong 1971; In mature plants, affected stems have light to dark CIAT 1976). brown pith, with an aqueous appearance due to the association existing between this pest and a bacterium, The white grubs most frequently found in Erwinia carotovora. Germination of stakes obtained Colombia belong to the family Melolonthidae, which from such plants may be reduced by as much as 16%, has four subfamilies: Cetoniinae, Melolonthinae, taking several weeks. This pest is described below in Dynastinae, and Rutelinae. Victoria and Pardo (1999) more detail under the section “Stem-perforating found that the principal genera of rhizophagous white insects”, page 235. grubs that attack cassava in the Department of Cauca are Phyllophaga sp. (Melolonthinae), Cyclocephala sp. Stemborers (Dynastinae), and Anomala sp. (Rutelinae). However, the study of subterranean pests in Colombia verified Stemborers, mostly belonging to the orders Lepidoptera that white grubs form a complex by virtue of and Coleoptera, have been found in stakes used for abundance of species, lack of crop specificity, and their planting. Infestation usually occurs when plants are temporary and local action. growing and also during storage of planting materials. Stored stakes should be carefully inspected before use. Victoria and Pardo (1999) used black light traps in Normally, these insects are detected by the presence of several sites in the Municipalities of Caldono, Buenos galleries and perforations in the stem, accompanied by Aires, and Santander de Quilichao (Department of such signs as milky exudates, fine or coarse sawdust, Cauca) and collected 21,739 examples belonging to residues of protective tissues, stem parts, and cankers. 44 species of the subfamilies Dynastinae, Rutelinae, and Melolonthidae. Most had been already recorded for Insects that Attack Stakes and Seedlings their economic importance to the region and other parts of the country. Captured specimens belonged to White grub the genera Aspidolea, Cyclocephala, Stenocrates, Ancognatha, Dyscinetus, Coelosis, Strategus, Together with the Spanish names mojojoy and mojorro, Podischnus, Golofa, Ligyrus, Phileurus, Plectris, this name describes beetle larvae (Coleoptera) that Phyllophaga, Astaena, Chariodemia, Macrodactylus, attack cassava. They are white, measuring about Isonychus, Barybus, Pelidnota, Anomala, and 5 cm. Their dark coffee-colored heads carry large jaws. Leucotureus. Three pairs of legs are found in the thoracic area, and the abdomen is prominent and dark. The damage that these grubs cause consists of destroying the cortex of planted stakes, so that their They are easy to find, as they live in the top 15 to tissues rot and die. When 1 to 3-month-old plants are 30 cm of the soil or on its surface in decomposing attacked, leaves wilt and the plants suddenly die organic matter (e.g., trunks and leaves), adopting a because the larvae feed on the cortex at the base of the crescent or “C” position. However, when temperatures stem. They usually feed under the soil, forming tunnels are high and humidity drops, they tend to burrow deep within the stake, preventing nutrients from moving into the soil, seeking cooler and damper places. This towards the plant’s aerial parts. Furthermore, they makes their control more difficult. They feed on plant consume newly forming roots. 216 Insects and Mites that Attack Cassava, ... Biology. The biology of Leucopholis rorida in B. bassiana, and Bac. popilliae) and Beauveria Indonesia is described as follows, with respect to the brongniartii, which, under controlled conditions, cause cassava crop. Adults are active at the beginning of the 50% mortality. rains, but the most severe damage occurs 4 to 6 months later. Nine days after mating, females Londoño (1999) had good results when he used oviposit deeply in the soil, at 50 to 60 cm. They lay up insectariums to evaluate 36 isolates of organisms for to 37 pearly white individual eggs that hatch within their control of white grubs. Among the control agents 3 weeks. The larval stage lasts for almost 10 months, were nematodes Steinernema carpocapsae, which with the 4 to 6-month-old larvae being the most caused 90% mortality, and Heterorhabditis sp., which destructive. The larvae live at depths of 20 to 30 cm, achieved 70%. According to Londoño and De Los Ríos where they feed on roots of cassava and other hosts, (1997), these organisms could cause mortality as high including maize, rice, grasses, and sweet potato. Pupae as 100%. are found more deeply, at about 50 cm. The prepupal stage lasts for 14 days and the pupal, about 22 days. Victoria and Pardo (1999) searched for natural enemies in several sites in the Department of Cauca The grubs undergo complete metamorphosis: egg, and found the following entomopathogens associated larva (grub), prepupa, and pupa. The larval or grub with white grubs: M. anisopliae in seven sites, stage undergoes three instars, with their capacity to eat B. bassiana in one site, Bac. popilliae in two sites, and increasing as they develop, doing the most damage several nematodes in seven sites. during the third instar. Parasitoids and predatory insects are not well The larval stage lasts from 3 or 4 months to studied, but the following have been found: dipterans 9 months, according to species. Genera of shorter of the families Tachinidae (10 sites) and Asilidae (one larval stages that attack cassava include Anomala and site), and an elaterid coleopteran (Elateridae pos. Cyclocephala. These have short biological cycles, Conoderus) in four sites. Hymenopterans were found in having two generations a year that appear in the two two of 21 sites. rainy periods, that is, March–April and October– November. This type of grub is known as bivoltine. Chemical control. White grubs are effectively Other genera have longer biological cycles, appearing controlled by lorsban (30 to 40 kg of paste concentrate once a year, that is, they are univoltine. This second or p.c. per hectare) or carbofuran (3 to 4 g of p.c. per group includes the Phyllophaga spp., the economically plant), applied under the stakes in the soil. Treatment most important genus of cassava pests in Colombia. by immersing stakes in insecticide solutions is not as effective as applications to moist soil. Another Attacks occur most frequently when cassava grows treatment also used when plants are small is liquid in a soil previously occupied by grasses or weeds. At carbofuran 4F applied to the soil at the plants’ base. soil preparation, high populations of larvae are usually seen. Cutworms Biological control. Several parasitoids, predators, Several species of cutworms attack cassava, damaging and entomopathogens have been identified as the plants in three ways according to their location in attacking white grubs. The most studied of these are the soil: the entomopathogens, including the fungi Metarhizium anisopliae and Beauveria bassiana, and • Ground cutworms, for example, Agrotis the bacterium Bacillus popilliae, which causes milky ipsilon, damage seedlings near the soil surface disease of white grubs. Experiments carried out at (either on or under it), leaving the cut piece CIAT (1974) indicated that the fungi can effectively lying on the soil. These larvae are dark gray control the grubs. with a greasy aspect or brown with streaks of light colors. Londoño (1999) indicated that some natural enemies of white grubs are found in eastern Antioquia. • Climbing cutworms, for example, Spodoptera Not only are they useful for their natural incidence but eridania and S. sunia, climb up the stems of also because they cause significant mortality when seedlings and consume buds and leaves before inoculated into the soil. These enemies include the finally making annular cuts in the stems, which three organisms mentioned above (M. anisopliae, cause plant wilt and death. The well-developed 217 Cassava in the Third Millennium: … larva is dark gray or almost black, with yellow or In Colombia, Heterotermes tenuis and orange lateral bands. Coptotermes niger feed on planting materials (stakes), roots, or growing plants. Attacked parts then dry or • Subterranean cutworms remain in the soil and die, particularly if climatic conditions are unfavorable, feed on the roots and underground stem parts, certain pathogens are present, or stakes are of poor causing losses in planting materials. Losses of quality. Stakes must be protected at crop young plants can reach 50%, making it establishment if shoot development is to be good and necessary to replant. the plants are to “germinate” effectively. Protection may consist of combinations of treatments, such as an The biology is similar for the three categories of application of the fungicides captan + carbendazim cutworms that attack cassava. Eggs are oviposited en (2 g of a.i./L water) with a later application of the masse on the lower side of leaves close to the soil. They insecticide lorsban in powder (3 to 4 g per site or stake) hatch in 6 to 8 days, and are fully developed within 20 to the soil. to 30 days. The pupal stage (8 to 11 days) occurs in the soil or under plant residues. Oviposition starts about a Leaf-Eating Insects week after adults emerge. One generation lasts almost 2 months and, under favorable environmental Cassava hornworm conditions, several generations may occur in 1 year. Erinnyis ello (L.), family Sphingidae, is a major cassava Cutworm attacks are sporadic and usually occur in pest in the Neotropics (Bellotti and Riis 1994; Bellotti foci or patches in the crop. They occur more frequently et al. 1992, 1994, 1999). It has a broad geographical when cassava follows maize or sorghum or when it is habitat, ranging from southeastern Brazil, Argentina, planted in lots adjacent to these crops. Longer stakes and Paraguay to the Caribbean Region and (30 cm) enable the plants to recover when under attack. southeastern USA. The migratory capacity of E. ello, its broad climatic adaptation, and wide host range These insects can be effectively controlled with comprise the probable reasons for its extensive poisoned feed applied to the soil surface (10 kg of distribution and sporadic attacks (Janzen 1987). sawdust, 8–10 L of water, 500 g of sugar or 1 L of molasses, and 100 g of trichlorform per quarter or half Other Erinnyis species also feed on cassava, hectare). They can also be controlled with applications including the subspecies E. ello encantado and a of lorsban around the stakes. closely related species, E. alope, which have been recorded in the Neotropics. The insect has not yet Crickets been reported in either Africa or Asia. As soon as they emerge, crickets, Gryllus assimilis or Biology and behavior. All hornworm larvae feed common cricket and Gryllotalpa sp. or mole-cricket, on young and mature cassava leaves and on tender cut young shoots. They also damage the plant’s base, stems and shoots. Severe attacks cause complete which then becomes more susceptible to lodging by defoliation of the plant, loss in root volume, and poor wind. Crickets are controlled by using the same root quality. Even though yield loss can be severe products as recommended for cutworms. through complete defoliation after one or several attacks, the cassava plant itself does not die. The Termites carbohydrates stored in the roots enable the plant to recover, especially during favorable conditions such as Termites—a tropical lowland pest—may attack cassava. the tropical rainy season. Repeated attacks are very They are reported as pests in various cassava-producing common when pesticides are not applied in time, as regions of the world, particularly Africa. In Madagascar, they do not destroy fifth-instar larvae or prepupae. Coptotermes voeltzkowi and C. paradoxus of the Instead, the pesticides eliminate the pest’s natural family Rhinotermitidae feed on planting materials, roots enemies (Braun et al. 1993). Large cassava plantings that have bulked, and growing plants. The principal are prone to frequent and repetitive attacks from this damage they cause appears to be stake loss, which pest. seriously affects crop establishment, especially during prolonged dry periods. Bulked roots damaged by Defoliation during the initial months of crop growth termites later rot. can cause significant yield losses. In simulation studies, 218 Insects and Mites that Attack Cassava, ... losses have been estimated to be between 10% and preoviposition period of 2 to 4 days, a female would 64%, according to the intensity of attack, number of oviposit a daily maximum of 500 eggs. Under attacks, and the ecosystem where the crop is confinement, a female may oviposit throughout her life, developed (Arias and Bellotti 1985b; CIAT 1989). producing as many as 1800 eggs. Individual couples of Severe attacks can kill young plants if the pest moths may lay an average of 850 eggs while groups of consumes all the buds. Such losses occur if the crop is couples may lay an average of 448 (CIAT 1978). These 1 to 2 months old and suffers outbreaks of the pest, high oviposition rates, combined with the adults’ with more than four larvae per plant. These studies migratory behavior, contribute to the rapid indicate that defoliation of plants younger than strengthening of hornworm populations and their 5 months will reduce yield more than defoliation of sporadic appearance (Bellotti et al. 1992; Janzen plants aged 6 to 10 months. 1987). Although each larva can consume 1107 cm2 of leaf In the pupal state, females and males differ in the area, the cassava crop can tolerate relatively high position of their genital openings. In the male, the populations. Under favorable environmental conditions, genital opening (gonopore) is located in the ninth, a crop can lose up to 80% of its leaves without enlarged, abdominal segment, leaving the eighth reductions in root yield. Of the 1107 cm2 of leaf area segment free. In the female, the genital opening is consumed during the larval period, about 75% is smooth and is found in the eighth segment, which is consumed during the fifth instar. At 15, 20, 25, and seen as a “V”. The sex ratio is about 1:1, female to 30 °C, the average duration of the larval stage is, male. respectively, 105, 52, 29, and 23 days. This indicates that the hornworm’s peak activity occurs at low This insect’s great flight ability and migratory altitudes (<1200 m) or during summer in the capacity, combined with its broad climatic adaptation subtropics (Bellotti and Arias 1988). and extensive host range (Janzen 1986, 1987) often makes effective control difficult. Pesticides may be Larvae vary in color: most commonly they are adequate if the hornworm populations are detected yellow, green, black (combined with small, lateral, white and treated during the first three instars. However, or red spots), dark gray, or cinnamon brown; farmers react to an attack of this pest by excessively occasionally, they are pink. Recently hatched larvae applying insecticides outside appropriate times, thus measure between 4 and 5 mm, and are mature triggering more severe attacks (Laberry 1997). A between 12 and 15 days. In the fifth instar, they are population of fourth and fifth instars is more difficult to 10 to 12 cm long. They drop to the soil where they control, but tolerating its presence is uneconomical pupate in a chitinous capsule that is brown with black because of the considerable defoliation they cause. streaks. Pupae are found in plant litter. Applied pesticides also affect the populations of The adult emerges after 15 to 20 days, usually in natural enemies, facilitating more frequent attacks the transitional periods between winter and summer or from the pest (Urías-López et al. 1987). Erinnyis ello summer and winter. These outbreaks are irregular and does have an associated complex of natural enemies, years may pass without their occurring. Adults of but its effectiveness is not significant, probably because E. ello are nocturnal. Females are a uniform ash color of the adult’s migratory behavior. A mass migration of and males present a longitudinal black band in the adults causes a rapid imbalance between the pest and forewings. its natural enemies because they lay large numbers of eggs—at more than 600 per plant—in only 6 or 7 days Eggs are olive green or yellow and large, having a in cassava fields. Accordingly, natural enemy 1.5-mm diameter. They are laid individually, preferably populations are too low to prevent an outbreak of on the upper surface of cassava leaves. In pest hornworm larvae and, thus, the crop’s severe outbreaks, eggs can also be found on lower leaf defoliation. surfaces, petioles, and stems. In oviposition cages placed in the field (at 25 °C and 80% rh), females lived Because their reproduction rate is limited, parasites as long as 19 days, with an average of 8.6 days, while and predators cannot recover sufficiently fast to prevent the male survived to a maximum of 15 days, with an the hornworm’s dramatic outbreaks (Bellotti et al. average of 7 days. By day 6 or 7 after emergence, 50% 1992). Hence, two or three successive attacks may of the adult population (i.e., T50) had died. After a occur if outbreaks are not detected in time. 219 Cassava in the Third Millennium: … Adequate farming practices such as weed control These light traps do not constitute a control and good soil preparation can reduce this pest’s adult method but function as a tool for discovering and pupal populations. fluctuations in the abundance of adult E. ello populations. The data obtained permit better planning Biological control with parasitoids and for applying different techniques to manage the pest. predators. The key to effectively using biological Preliminary trials led to the capture of 3094 adults in control agents is synchronize the release of a large one night, mostly between 00:00 and 02:00. This number of predators or parasites during the pest’s early information is highly useful for areas where no stages, preferably as eggs or as first to third instars. electrical power is available because traps run on More than 40 species of parasites, predators, and batteries or gasoline can then be operated at those pathogens of cassava hornworm eggs, larvae, and hours, thereby saving on resources. The difficulty is to pupae have been identified (Bellotti et al. 1999): synchronize a mass release of parasites and predators when a peak occurs in the pest population. Thus, there • Eight microhymenopteran species belonging to is need for an inexpensive and storable biological the families Trichogrammatidae, Scelionidae, pesticide. and Encyrtidae parasitize eggs of E. ello, for example, Trichogramma minutum, other Biological control with microorganisms. Trichogramma spp., Telenomus sphingis, Microbial control with sprays of Bacillus thuringiensis Tel. dilophonotae, Ooencyrtus sp., and in doses ranging from 2 to 3 g p.c. per liter of water O. submetallicus (CIAT 1989). Some provides effective control. Effectiveness increases when Trichogramma and Telenomus species have larvae are within the first three instars (Arias and been reported as parasites for 94% to 99% of Bellotti 1977; Herrera 1999). eggs (Bellotti and Schoonhoven 1978a). In 1973, CIAT found, in E. ello colonies, a virus • Dipteran parasitoids of this pest’s larvae include that attacks the pest’s larvae. The virus was identified the flies of the families Tachinidae (Thysanomia at the University of California–Berkeley, USA, by Gerard sp.), Sarcophagidae (Sarcophaga sp. and M. Thomas as a baculovirus, which identification he Oxysarcodexia innota), and Dryinidae (Drino reconfirmed in 1974 and 1977. CIAT then developed macarensis). Hymenopteran parasitoids include simple evaluation methods to discover how this virus wasps of the families Ichneumonidae could be used as a highly effective biological means for (Cryptophion sp.) and Braconidae (especially controlling the pest. Currently, this processed virus is Cotesia species [= Apanteles] such as the flag product for controlling hornworm as it can be C. americana and C. congregatus) Bellotti et al. applied conventionally and, moreover, stored for several 1992, 1994; Bellotti and Riis 1994). years without its pathogenicity altering significantly. • The most common egg predators are At a commercial level, the viral compound was first Chrysoperla spp. and Chrysopa sp. Other developed and applied to large extensions of the important larva predators are wasps cassava crop in Brazil, when larval populations were in (Hymenoptera: Vespidae) of the Polistes genus first instar. The result was complete control. Later, in such as P. erythrocephalus; stink bugs Podisus Venezuela, the virus was used instead of insecticides nigrispinus, P. obscurus, and Alceorhynchus for large plantings (7000 ha) in areas where the grandis (Hemiptera: Pentatomidae); and several hornworm was endemic. Dosage was 70 mL/ha applied spider species of the families Tomicidae and to first- and second-instar larvae. Again, the result was Salticidae (Bellotti et al. 1992). complete control. The direct costs of storage, application, processing, and collection of larvae The effectiveness of parasites and predators is amounted to U$4/ha (CIAT 1995; Laberry 1997). curtailed by their limited functional response, which lasts about 15 days during a hornworm outbreak. Thus, Fungal entomopathogens also exist, but any for control to be successful, hornworm populations collection of affected insects in cassava crops was low. must be monitored in the field to detect immigrant Of five sites evaluated, they were found in only one. adults or early instar larvae. This task requires traps Under laboratory conditions, a B. bassiana strain with black light lamps (type BL or BLB, Ref. caused a 31.6% to 87.5% mortality rate in E. ello, with T20T12BLT) to attract flying adults or to help identify the third instar being the most susceptible. Fungal eggs or larvae (CIAT 1983b, 1989). action is not transmitted from one generation to the 220 Insects and Mites that Attack Cassava, ... next. When a B. bassiana strain was mixed with a about 1 mm in diameter. Eggs are laid individually, M. anisopliae strain and applied to third instars, a 90% although sometimes in groups of 2, 4, or more eggs mortality rate was achieved without antagonism being (up to 17). Incubation takes 4 to 5 days. The average presented. The dead larvae exhibited the typical number of eggs a female lays over 14 days is 192. symptomatology for each strain (Múnera S and De los Ríos 1999). The larvae of P. sanguinea pass through five instars that together last 10 to 14 days. During this A fungus that attacks the pest’s pupae was also time, they also change colors, with each instar identified. An ascomycete of the Cordyceps genus was contrasting with the others. Larvae are covered with very aggressive in the field, controlling the third outbreak hairs that give them a furry appearance. The quantity of hornworm occurring in 1978 in the Department of and coloring of this “fur” varies according to instar. The Quindío, the only area where the fungus has been found. first instars are a yellowish, almost translucent, fawn, Cordyceps sp. can be easily reproduced on potato becoming coffee-colored and gray until they acquire dextrose agar (PDA) and, when applied to pupae in the the red color of the fifth instar. laboratory, achieves almost complete control. The first instar feeds in a circular fashion on the Mechanical control. The manual collection of lower tissues of leaf blades, leaving an intact film of larvae and pupae is highly effective for reducing upper tissues. The film dries and later falls, leaving a hornworm populations in small plantings. This practice circular perforation, which are often seen in mature is best applied to fields that the insect has only just crops and may join if many larvae eat the same leaf. begun to attack. When weeding tasks are carried out, Later instars uniformly consume the entire leaf, leaving digging the pupae up to the soil surface is sufficient for only nervures. This action converts this insect into a control, as they die from solar radiation or are destroyed potential crop pest. Evaluations of leaf consumption by with the hoe or weeding pole. P. sanguinea indicate that it can consume, on average, 78.5 cm2 of leaf blade over its life cycle. This is Cassava tiger moth caterpillar 14 times less than that consumed by E. ello (Arias and Bellotti 1983). Larvae may measure between 2.6 mm This pest (Phoenicoprocta sanguinea Walker) belongs (first instar) and 21 mm long (fifth instar) (Arias and to the family Amatidae (also called Ctenuchidae) and is Bellotti 1983). constantly found, although sporadically, within the cassava crop. Known as bicho tigre or “tiger bug” in After completing the fifth instar, the insect passes Spanish, it defoliates the plant, although not at an to the soil where it enters a prepupal state for 1 or economically significant level. However, it is considered 2 days before pupating in the soil litter, forming a as a potential pest of the crop, and has been reported in cocoon with the setae or hairs of its body. The pupal Colombia, Ecuador, Mexico, Brazil, and Suriname. state lasts 12 to 16 days. Pupae are coffee-colored and measure between 1.5 and 2.0 cm long, and between Biology and behavior. The adults of this species 0.5 and 0.7 cm wide. The insect’s life cycle from egg to are moths of diurnal habit. They are small and showy. adult averages 41.2 days at 26 °C and 70% rh (Arias Their wing span measures 30 mm and the body is and Bellotti 1983). about 12 mm long. Females have black forewings, with the smaller hindwings having transparent areas. The Biological control. Phoenicoprocta sanguinea is abdomen is colored with metallic blue spots in the a pest that, so far, does not require pesticides for its center of each abdominal segment. The bodies of control because it has not yet presented outbreaks of males have blue, red, and yellow metallic spots on a economic importance. Control should, where possible, black background. Both their forewings and hindwings be through biological control agents that would are transparent (as typical of this family). The male is maintain it at moderate to low levels in the field. showier than the female, as it also has lateral red tufts on the abdomen, separated by central blue spots, and • Eggs of P. sanguinea are parasitized by the thorax has yellow lateral tufts. The head is blue with Trichogramma sp. From each egg, five to eight black eyes. small wasps emerge, at a gender ratio ranging from 0.5:1 to 5:1, female to male. In Ecuador, a small The female lays eggs on the underside of leaves, black wasp, not yet identified, was also observed to preferably in the upper third of the plants. The eggs are parasitize P. sanguinea eggs (B Arias and semispherical, of a hyaline cream color, and measure JM Guerrero 1999, pers. comm.). 221 Cassava in the Third Millennium: … • Larvae are parasitized by an Apanteles (= Cotesia) An important crop management practice is to wasp, adults of which emerge when the pest larvae determine the time of the queens’ nuptial flights and are in a prepupal state. Hence, Apanteles pupae can capture them as they begin nest construction. This can be seen developing within the cocoon formed by the be identified by small open orifices in the soil, which pest larva. The cocoon thus becomes the wasp’s have the earth around them removed by the queens on puparium. From each puparium (cocoon) at least 6 initiating the new colonies. In some parts of the to as many as 36 small Apanteles wasps emerge, at Department of Cauca, young schoolchildren are taught a sex ratio ranging from 1:1 to 23:1, female to male. to recognize these small nests and are paid according to the number of queens they collect. In some • An unidentified wasp, possibly of the Ichneumonidae indigenous areas, these queens are collected as food. family, was once observed in a typical parasitic pose over a pupa of the pest (Arias and Bellotti 1983). Leaf-Sucking Mites Leafcutting Ants Mites are a universal pest of cassava plants, causing serious losses in crops in America and Africa (Herren In America, several ant species (Atta spp. and and Neuenschwander 1991; Bellotti et al. 1999). More Acromyrmex spp.) have been reported as feeding on the than 40 species have been reported as feeding on cassava plant. An attack on the crop by a large cassava foliage (Byrne et al. 1983), the most population of worker ants can defoliate plants. The ants frequent of which are Mononychellus tanajoa (syn. make semicircular cuts in leaves and, in severe attacks, M. progresivus), M. caribbeanae, Tetranychus buds. They take the cut parts to the anthill, where they cinnabarinus, and T. urticae (also recorded as then carry them below the soil surface. They then T. bimaculatus and T. telarius) (Bellotti 2000a, 2000b). masticate the leaf parts to form a paste on which the fungus Rhozites gongylophora grows. The queen and The cassava crop is the principal host of the ant larvae feed on this substrate. Mononychellus complex. In contrast, the Tetranychus complex has a broad range of hosts. Other mite Crop damage is usually evident as patches where species (e.g., Oligonychus peruvianus, O. biharensis, plants appear defoliated, as when they are attacked by Eutetranychus banksi, and M. mcgregori) have little hornworm. However, ant damage differs from hornworm economic importance because they feed on cassava damage by the presence of semicircular cuts and of foliage only sporadically (Byrne et al. 1983; Bellotti tracks that lead to anthills, which may be distant from 2000a). In almost all cassava-producing regions of the the site of damage. Effects on yield are not known. world, mites frequently attack the crop during dry seasons, causing severe damage. The most effective control is by insecticides. Anthills are easily recognized by the heaps of earth The mite Tetranychus urticae is universally around entrances, and colonies can be destroyed by widespread and is considered the most important fumigating with smoke of either carbon disulfide or pest in some areas of Asia. The distribution of sulfur. O. peruvianus is limited to America. When environmental conditions are optimal, mites are found • Lorsban, applied periodically to nest entrances in large numbers on the underside of cassava leaves. with a blower, is effective for reducing ant populations. Mononychellus tanajoa Bondar or the cassava green mite (CGM) • An economic and ecological control is to attack the fungus that feeds the queen. To achieve this, Although this species is native to America, it has the pH of the anthill is changed by periodically considerably reduced crop yield in several parts of East applying lime to the entrances and within the Africa after its introduction to that region and its anthill with a blower (G Sotelo 2000, pers. dissemination to other areas of the African continent. comm.). Mononychellus tanajoa is usually active around • Lime and Lorsban, mixed at a ratio of 2:1, can the plants’ growing points, buds, young leaves, and also be applied. This will attack both fungus and stems. The central and lower parts of the plant are less ants. affected by this species. In severe attacks, shoots lose their green color, and leaves show yellow points 222 Insects and Mites that Attack Cassava, ... uniformly distributed throughout the surface, so that females construct, commonly on central, secondary, the leaves acquire a mottled and bronzed appearance, tertiary, and leaf marginal nervures. Oviposition occurs as if suffering from a mosaic. Leaves are also small and under the webs, where the immature stages of the mite deformed (Byrne et al. 1983). feed and develop. As adults, the mites abandon the webs to form new colonies. In each web, 5 to 10 mites Stems become scarred, rough, and brown. are found. On the upper surface of leaves, small, Sometimes they suffer dieback, that is, a progressive brown, irregular, and necrotic areas form, necrosis from the plant’s upper parts to its lower parts. corresponding to the feeding activities of each colony Terminal points become lancet-shaped through the on the leaves’ undersides. Colonies usually form in the loss of leaves and possess a cork-like appearance. plant’s central and lower parts. When environmental Re-shooting can occur but if rains are scarce, the new conditions are favorable and if the cassava variety is leaf shoots may also be attacked (Yaninek and susceptible, the entire plant can be invaded. Animashaun 1987). If the rains return, tolerant varieties may recover their foliage. An important characteristic Yield losses caused by mites of the uniformly green Mononychellus mite is that it does not produce webs to disperse from one plant to Economically, the CGM is the most important mite another. species, with losses of cassava crops being reported in the Americas and Africa (Herren and Neuenschwander Tetranychus urticae Koch or the red spider 1991; Bellotti et al. 1999), especially in dry seasons in mite tropical lowlands (Yaninek and Animashaun 1987; Braun et al. 1989). Nyiira (1972) reported that, in The damage caused by this mite first appears in leaves Africa, reductions of yield caused by M. tanajoa were of the central and lower parts of the plant. Initially, a as much as 40%; and Bellotti (2000b) estimated that yellowing appears in the area of convergence of the yield losses in Venezuela were 30% to 40%. central nervures of leaf folioles and where the mite populations concentrate. The yellow points then extend In field trials with young crops, reductions were throughout the central nervures and become scattered 21%, 25%, and 53% during 3, 4, and 6 months of throughout the whole leaf, which then takes on a attack, respectively (Bellotti et al. [1983c]). Under field reddish or rusty brown color. The basal leaves are the conditions, a high mite population reduced yields by first to be affected. Heavily infested leaves dry up and 15% in a resistant material, 73% or more in a fall. Under normal conditions, the upper parts of plants susceptible material, and 67% in planting materials are green while the central and lower parts are affected (Byrne et al. 1982, 1983; Bellotti 2000a, 2000b). or defoliated. In severe drought, this mite can invade entire plants, killing them in susceptible varieties. The M. tanajoa mite was originally found in Northeast Brazil, in 1938. It appeared for the first time This species produces webs to move from one part in Africa (Uganda) in 1971 and, by 1985, it was of the plant to another or between neighboring plants. dispersed throughout the continent’s entire cassava- Like M. tanajoa, the mites are green, but differ by growing belt, involving 27 countries (Yaninek 1988). being a little larger and presenting on each side of the Losses ranged from 13% to 80% (Yaninek and Herren body a dark spot that is observable only under the 1988; Herren and Neuenschwander 1991; Skovgard et microscope. al. 1993; Bellotti 2000a). Tetranychus cinnabarinus Boisduval or the Controlling pest mites carmine spider mite Research on the control of M. tanajoa has taken two This reddish-colored mite produces symptoms similar principal directions: host-plant resistance (HPR) and to those of T. urticae. biological control. These two complementary strategies help reduce CGM populations and thus its level of Oligonychus peruvianus McGregor (flat economic damage. Continuous use of acaricides is not cassava mite) an economical option for low-income farmers. Nor are these products recommended because they cause In the plant, the pest manifests as small white spots on adverse effects on the pest’s natural enemies (Bellotti the underside of leaves. The spots are webs that the 2000a). 223 Cassava in the Third Millennium: … Host-plant resistance. Significant work has been nymphal mortality rates. Those that feed on resistant conducted in cassava improvement by two international materials, however, do not behave this way (Byrne et al. research centers (CIAT and IITA) and several national 1983). Instead, they have high mortality rates, long research programs, including the National Cassava and developmental periods, and less oviposition over shorter Fruits Research Center (CNPMF, coordinated by the periods. Recent laboratory studies show M. tanajoa as Brazilian Agricultural Research Corporation or strongly preferring to oviposit on susceptible varieties. EMBRAPA, its Portuguese acronym). All had tried to When resistant varieties M Ecu 72, M Per 611, and develop hybrids with resistance to CGM (Byrne et al. M Ecu 64 were compared with the susceptible CMC 40 1983; Bellotti et al. 1987; Hershey 1987). About 5000 (M Col 1468) in a free-choice test, preference for the cassava varieties held in the germplasm bank at CIAT susceptible variety was 95%, 91%, and 88%, respectively were evaluated for their resistance to CGM and the other (Arias and Guerrero 2000). mites mentioned above. Results indicated that about 6% (300 varieties) possessed low levels of resistance or Biological control. Studies were carried in tolerance of the Tetranychus genus, and moderate levels numerous cassava fields, with the experimental data of resistance to the genera Mononychellus and indicating that, despite being present in Neotropical Oligonychus (CIAT 1999). This basic work enabled the lowlands, CGM attacks rarely cause significant losses, development of varieties with moderate levels of except in some areas of Brazil. Consequently, a work-in- resistance. These varieties were then released to farmers progress, which extended from 1983 to 1990 and (Arias and Guerrero 2000). covered 2400 sites in 14 countries of the Americas, was conducted to evaluate the complex of the CGM’s natural Research carried out by CIAT on cassava resistance enemies (Byrne et al. 1983; Bellotti et al. 1987). to CGM was traditionally conducted at two sites: A reference collection of CGM predators, developed • CIAT–Palmira, located in the intermediate by CIAT and Brazil, is now held at CIAT. It includes the Andean area, at 1000 m above sea level, where acarophagous mites, known as phytoseiids, found on mite populations are moderate (Arias and cassava (Table 10-2). It also lists the various geographical Guerrero 2000). areas chosen for collection because of their ecological similarity with sites in Africa and Brazil with mite problems. • Pivijay (Magdalena), in the Colombian Atlantic Of the 87 collected and stored predatory species, Coastal Region, located in the tropical lowlands. 25 were new or had not been recorded before and This area is characterized by a dry season of 4 to 66 species (76%) were collected from cassava crops. A 6 months and high mite populations (Arias and taxonomic key of phytoseiid species associated with Guerrero 2000). cassava was then prepared as part of a collaborative project with several Brazilian colleagues. The CIAT–Brazil The cultivars selected had low to moderate levels of collection has a database that can be easily used for resistance, scoring damage values between 0 and 3.5, describing or re-describing species, listing mite types and according to a scale of 0 to 6 (Arias and Guerrero 2000), paratypes. where 0 was no damage and 6 was severe damage. Of the 66 species of phytoseiids collected from Of the 300 varieties selected as promising for cassava plants, 13 were the most common, including durable resistance (2 to 7 cropping cycles), Typhlodromalus manihoti, which was the most 72 maintained a score for damage of less than 3.0 (CIAT frequently collected species, being found in more than 1999). Most of these varieties were collected in Brazil, 50% of sampled fields. This species was followed by Colombia, Venezuela, Peru, and Ecuador. Some were Neoseiulus idaeus, T. aripo, Galendromus annectens, hybrid (Arias and Guerrero 2000). Euseius concordis, and E. ho. Phytoseiids T. aripo and N. idaeus are promising biological control agents for Mechanisms for resistance to the mite were M. tanajoa in Africa (Yaninek et al. 1991, 1993). interpreted as comprising either antixenosis (where the plant repels insects by morphological means, e.g., The explorations revealed other insects as predators pubescence) or antibiosis (where the plant adversely of the CGM, particularly the staphilinid Oligota minuta and affects insect physiology, e.g., through chemical means) the coccinellid Stethorus sp. The phytoseiids and other (Byrne et al. 1982). Mites feeding on susceptible varieties predators were carefully studied in the laboratory and field develop fast; are highly fecund; readily accept the plant; (Table 10-2), with the phytoseiid mites being verified as and have a long life span as adults, and low larval and more efficient than the predatory insects (Byrne et al. 1983). 224 Insects and Mites that Attack Cassava, ... 225 Table 10-2. Biological and ecological aspects of phytoseiids that prey on cassava mite pests.a Phytoseiid Colonies Relative Consumption of Growth period Fecundity Females predator (no., humidity Mt eggs (days) Longevity (%) 1986–1999) (24 h) Mt Tu Mc Mt Tu Mc Tu Mc Mt Tu Typhlodromalus manihoti 31 + 68.0 4.9 4.1 5.5 14.2 — 3.5 74 88 T. aripo 9 + 6.8 13.0 13.0 14.0 20.9 T. tenuiscutus 7 + 45.4 5.8 5.8 5.7 32.0 2.5 16.1 6.6 16.1 75 81 T. rapax 1 5.0 5.4 5.8 6.0 12.0 19.4 78 62 Neoseiulus idaeus 20 +++ 26.8 4.6 4.6 5.1 13.8 32.3 12.5 21.6 27.8 73 84 N. californicus 5 ++ 26.5 4.7 4.4 7.7 34.8 43.7 23.4 70 79 N. anonymus 4 4.7 5.1 5.2 14.5 34.4 27.7 39.1 12.0 73 58 Galendromus helveolus 5 + 7.4 7.0 18.7 8.0 23.0 14.2 19.0 64 66 G. annectens 6 ++ 17.8 5.7 6.1 22.4 19.0 31.0 23.0 27.7 74 85 Euseius concordis 1 5.7 5.0 12.7 75 70 a. Relative humidity: + = 75%; ++ = 60%; +++ = 40% to 50%; Mt = Mononychellus tanajoa; Tu = Tetranychus urticae; Mc = Mononychellus caribbeanae. Cassava in the Third Millennium: … The results of these studies showed that CGM Leaf-Sucking Insects density was higher in Northeast Brazil than in Colombia and that the diversity of phytoseiid species was Cassava whiteflies considerably higher in Colombia than in Brazil. Of the fields evaluated in Colombia, 92% were either not Whiteflies (Hemiptera: Aleyrodidae) feed directly on the infested with the mite pest or were infested at very low cassava plant and also serve as vectors of viruses that densities (i.e., at less than 25 mites per leaf). In attack the crop. They therefore cause significant contrast, for crops in Brazil, only 12% of fields were not damage to this crop in the agroecosystems of America, infested and 25% had intermediate or high densities of Africa, and, to a lesser extent, Asia. The Neotropical CGM (Bellotti et al. 1994). whitefly complex is enormous, with 11 species recorded as associated with cassava (Bellotti et al. 1994, 1999; Results of field experiments in Colombia (Braun et Castillo 1996; França et al. 1996): al. 1989) demonstrated the importance of the effect of various phytoseiid species associated with CGM. In Aleurotrachelus socialis Bondar Colombia, fresh and dried root production dropped by Trialeurodes variabilis Quaintance 33% when natural enemies were eliminated. In Bemisia tuberculata Bondar comparison, acaricide applications did not increase Aleurothrixus aepim Goeldi production, thus indicating that the biological control B. tabaci Gennadius was good. B. argentifolii Trialeurodes abutiloneus Haldeman Since 1984, numerous phytoseiid species were Aleurodicus disperses Russell sent to Africa from Colombia and Brazil. Of the Paraleyrodes sp. mass-released species, none from Colombia became Aleuronudus sp. established, but three species from Brazil (T. manihoti, Tetraleurodes sp. T. aripo, and N. idaeus) managed to become established (Yaninek et al. 1991, 1993; Bellotti et al. Aleurotrachelus socialis is the predominant 1999). Of the three, T. aripo seems the most species in northern South America, where it causes promising, as it dispersed rapidly and, today, is found considerable damage to crops. It is also found in Brazil, in more than 14 countries. Field evaluations indicate although in smaller numbers (Farias 1994). Small that T. aripo reduces the CGM population by 35% to populations of B. tuberculata and Trialeurodes 60%, resulting in increases of fresh matter production variabilis have been reported in Brazil, Colombia, by 30% to 37%. Venezuela, and other countries (Farias 1990; Bellotti et al. 1999). The spiralling whitefly (Aleurodicus Neozygites sp. cf. floridana (Zygomycetes: dispersus) causes damage to cassava in western Africa Entomophthorales), a pathogenic fungus, causes (Neuenschwander 1994b; D’Almeida et al. 1998). In irregular or periodic mortality in mite populations in Colombia, small populations of this species have been Colombia and Northeast Brazil (Delalibera Jr et al. found in cassava crops of the Atlantic Coast and Valle 1992). This pathogen was found in many cassava del Cauca. This whitefly also appears in some fields in several Neotropical regions. Some strains provinces of Ecuador (B Arias and JM Guerrero, pers. were specific to the Mononychellus genus (de Morães comm.). Bemisia afer has been found in Kenya et al. 1990), and was also found on CGM in Africa, (Munthali 1992) and Côte d’Ivoire (Bellotti 2000a, although no epizootics of the fungus were observed 2000b). (Yaninek et al. 1996). The fungal strain from Brazil may therefore be more virulent than that from Africa. Biology and behavior. Whitefly B. tabaci is Molecular techniques are currently being used to distributed throughout the tropics, feeding on cassava taxonomically identify the strains and in vitro plants in Africa and various regions of Asia, including methodologies are being developed to produce the India (Lal and Pillai 1981) and Malaysia. In 1990, pathogen. This fungus, which appears highly B. tabaci biotypes in America were found feeding on promising for the biological control of CGM, is also cassava. These whiteflies are known to transmit viruses being evaluated in Africa. that cause the following diseases in cassava: 226 Insects and Mites that Attack Cassava, ... • African cassava mosaic disease (ACMD), caused by vigorous. However, population levels may depend more several geminiviruses transmitted through B. on the plant’s physiological conditions than on the tabaci (Thresh et al. 1994; Bellotti 2000a). climate. • Frogskin disease, which affects cassava in the Damage and losses. Whiteflies directly damage Neotropics maybe transmitted by B. tuberculata leaves through their feeding activities. Both adults and (Angel et al. 1990; Bellotti 2000a). immature states of A. socialis are active and destructive. They feed on the phloem, the females even feeding while The absence of ACMD in the Americas is believed copulating and ovipositing. This behavior produces to be related to its vector’s (B. tabaci) inability to chlorosis and cone-like rolling of bud leaves. In colonize cassava. At the beginning of the 1990s, a new susceptible varieties, leaves of the central third of plants, B. tabaci biotype (B), which some consider as a where nymphs are found, are reduced in size and present separate species (B. argentifolii), was found in the yellowing from the margins towards the center, together Neotropics feeding on cassava. African cassava mosaic with corrugated areas that are greener than others, thus disease is now believed to be a serious threat to giving the leaves a mosaic appearance. These leaves cassava production in the Neotropics, as most usually become yellow, necrose, and eventually fall off. traditional cultivars of this region are highly susceptible to the disease. Furthermore, the biotype complex of Depending on the intensity of the attack, they may B. tabaci comprises vectors of several viruses that also become covered by the sooty black growth of a affect cultivated species that are often grown in fungal complex known as fumagina sooty mold (Arias association with cassava or in adjacent fields. The 1995). In susceptible varieties, especially if attacks start possibility that viral diseases will circulate between early in the crop’s development and last until the late these species or that new viruses will appear represents stages of vegetative growth, the plants become rachitic a potential threat to cassava production (Bellotti and their thin stems suffer from lodging. Re-shooting 2000a, 2000b). therefore occurs, but these shoots are also palatable to the adult pest. The pest thus succeeds in affecting the Females of A. socialis oviposit individual banana- production of planting materials, crop yield, and quality shaped eggs on the underside of apical leaves. of harvested roots (Arias 1995). Incubation takes about 10 days and the insect undergoes three nymphal instars and a pupal phase Populations. Research carried out in the Neotropics (fourth instar) before reaching the adult stage. During has concentrated on A. socialis and Aleurothrixus the third instar, the body changes from a cream color aepim. Populations of both species increase during dry to black and is surrounded by a waxy white layer. The seasons, but may be presented throughout the cropping black pupae make this species easy to distinguish from cycle (Farias et al. 1991; Gold et al. 1991). In the other whitefly species that feed on cassava. Department of Tolima, during summer, A. socialis Development from egg to adult in an incubator is populations increase, wheareas those of T. variabilis 32 days at 28 ± 1 °C and 70% rh (Arias 1995). Studies diminish. In the rainy seasons, the reverse occurs, with on oviposition in A. socialis indicate that a female lays the T. variabilis populations being high and those of as many as 224 eggs (Bellotti 2000b). A. socialis low (Bellotti 2000a, 2000b). A female Trialeurodes variabilis oviposits, on In the latter half of the 1990s and the first semester average, 161 eggs that have a 62% chance of survival of 2000, A. socialis populations increased considerably, from egg to adult. The female lays the bullet-shaped becoming endemic in the Departments of Cauca and eggs vertically, as do the B. tuberculata and B. tabaci Valle del Cauca and seriously affecting the farming females. The average longevity of females was economy of those areas. Populations of this whitefly 19.2 days and that of males 8.8 days. Pupae of the remained constant both in dry and rainy seasons. Bemisia species are oblongate and are normally pale Apparently, rainy days alternating with days of strong sun green. Consequently, to differentiate the morphological and high temperatures favor and stimulate the incidence characteristics of each species, microscopy should be of this pest, which even impede the presence of other carried out and differences taken into account. pests (B Arias and AC Bellotti 1998, pers. comm.). Prolonged attacks of this pest on a crop may affect the High populations of T. variabilis are usually capacity of stakes to shoot (G Jaramillo 1999, pers. associated with the rainy season when plants are more comm.). 227 Cassava in the Third Millennium: … Production losses caused by A. socialis and rainy season, the crop can be free of the pest, Aleurothrixus aepim are common. The duration of an or needs to support only small populations, in attack by whitefly correlates with losses in cassava root the first 2 to 3 months of vegetative growth, production. Attacks by A. socialis over 1, 6, and which are significant for crop development. 11 months resulted in 5%, 42%, and 79%, respectively, Timely weed control and fertilizer applications of losses in root yield in field trials conducted by (where necessary) will also prevent competition CNIA–Nataima of CORPOICA, in the Department of with other plants, giving the crop plants an Tolima, Colombia (Vargas H and Bellotti 1981; Bellotti initial vigor that will enable them to support et al. [1983c], 1999). attacks from this insect (Arias 1995). Whiteflies management. Various methods are • Researchers use yellow traps to physically used to control the pest, including pesticides, cultural control whiteflies in different crops. The pest is control, varietal resistance (i.e., HPR) and biological attracted by surfaces that reflect yellow in the control. The last two have been increasingly accepted range of 500 to 700 nm (Berlinger, cited by to complement other pest control practices. A more Arias 1995). traditional approach is crop management. These three approaches help reduce environmental pollution and Control by varietal resistance (HPR). Varietal other disadvantages that excessive use of chemical resistance offers a stable option that is low-cost and pesticides presents. long-lasting in the control of whitefly populations. Resistance to whitefly is rare in crops, although good In the Neotropics, research initially focused on sources of resistance have been identified and highly controlling whitefly in cassava crops through HPR productive resistant hybrids are being developed. The activities and crop practices. More recently, HPR studies initiated at CIAT more than 15 years ago considerable work has been conducted on identifying have systematically evaluated more than 6000 cassava natural enemies and evaluating their actions in the varieties from the germplasm bank for resistance to context of integrated pest management (IPM) (Bellotti whitefly (CIAT 1999), especially to A. socialis. In Brazil, 2000a). research was carried out with Aleurothrixus aepim (Farias 1990a, cited by Arias and Guerrero 2000). Farming practices, including traditional systems of intercalating the cassava crop with other crops, also Various sources of resistance to A. socialis have help reduce pest populations (Leihner 1983), as been identified. The cassava clone M Ecu 72 has follows: consistently shown high levels of resistance. Other varieties presenting moderate to high resistance • Egg populations of A. socialis and T. variabilis include M Ecu 64, M Per 335, M Per 415, M Per 317, in a cassava/cowpea association were lower M Per 216, M Per 221, M Per 265, M Per 266, and than those in crops under monoculture (Gold et M Per 365. These results suggest that resistance to A. al. 1990). The effects were residual, persisting socialis is found in germplasm native to Ecuador and for 6 months after harvest. Production losses in Peru, but more research is needed. Materials M Ecu 72 a cassava/maize association, a cassava and M Bra 12 (agriculturally desirable clones that monoculture, and a mixed cropping system tolerate whitefly in the field) were used in an were about 60%. In contrast, production losses improvement program to increase the production and in a cassava/beans system were only 12% (Gold resistance of clones that showed no significant et al. 1989b, 1989c). However, the cassava/ differences in production when grown in either plots maize association did not reduce egg treated with insecticides or untreated plots (CIAT 1992; populations (Gold 1993). Thus, the success of Bellotti et al. 1999). this technique depends on the crop species being intercalated, which limits effectiveness Greenhouse and field studies showed that and acceptability to farmers. With the right A. socialis, after feeding on resistant varieties, crops, however, it can reduce pest populations oviposited less, developed more slowly, were small, and in small-farmer crops (Bellotti 2000a). suffered a higher mortality rate than those that fed on susceptible clones. First-instar nymphs of A. socialis, • For agronomic control, the management of after feeding on M Ecu 72, presented a 72.5% mortality planting dates plays an important role in rate (CIAT 1994; Arias 1995) (Figure 10-1). Selected reducing pest incidence. If planted in a suitable progenies (CG 489-34, CG 489-4, CG 489-31, and 228 Insects and Mites that Attack Cassava, ... 80 N4 70 N3 60 50 N2 40 30 N1 20 10 0 H 0 5 10 15 20 25 30 35 Insect growth over time (days) M Ecu 72 CG 489-4 CG 489-34 M BRA 12 CG 489-23 CG 489-31 M Col 1505 CMC 40 Figure 10-1. Mortality of whitefly Aleurotrachelus socialis with respect to its stage of development on cassava clones that are either resistant or susceptible to the pest. H = hatching, N1 = nymph 1, N2 = nymph 2, N3 = nymph 3, N4 = nymph 4. CG 489-23) of a cross between M Ecu 72 and M Bra 12 CIAT is currently conducting research to identify had moderate levels of resistance to whitefly. Three of markers linked to genes that confer resistance to these hybrids are currently being evaluated for release A. socialis attacks to understand the genetics of to Colombian farmers in the Department of Tolima, resistance in cassava to whitefly in preparation for field Colombia (Arias and Guerrero 2000). evaluations. In Colombia, field evaluations of resistance to Building a 10-cM framework map for QTL natural populations of A. socialis have been conducted analysis and identification of candidate genes at two sites: for whitefly resistance (WFR) in cassava • In Nataima, Tolima, in cooperation with the Cassava genetic and genome resources. Colombian Corporation of Agricultural Research Cassava is an allopolyploid with 36 chromosomes (CORPOICA). Populations of A. socialis found (Magoon et al. 1969). Due to poor seed set, the in Nataima have been at moderate to high levels heterozygous nature of the crop, the high genetic load, in the last 15 years. Hence, long-term research and the high susceptibility to inbreeding depression on is possible there (Arias and Guerrero 2000). the loss of heterozygosity, shoot cuttings, thereby preserving its heterozygous nature, propagate most • In CIAT–Palmira, Valle del Cauca. Initially, the cassava. This heterozygosity provides challenges to A. socialis population was low. However, since cassava breeders but has enabled the identification of 1994, it has increased and is currently higher over 600 molecular markers (Blair et al. 2007). Simple than it is in Tolima. This sudden increase is not sequence repeat (SSR) markers were used to study the yet understood but the dynamics show an genetic diversity and structure in a large collection of outbreak of this pest in a crop that had local varieties from Africa and Latin America. CIAT previously supported its attacks (Arias and constructed the first linkage map of cassava (Fregene Guerrero 2000). et al. 1997). Since then molecular markers have been 229 Mortality (%) Cassava in the Third Millennium: … linked to the single genes conferring resistance to QTLs conferring WFR. For molecular markers to be CMD, green mites, and cassava bacterial blight (CBB), useful for integrating WFR into WFS varieties used by enhanced ß-carotene content, and early root yield smallholder farmers, the markers must be validated in (Ferreira et al. 2008; Marín Colorado et al. 2009; a second mapping population (MEcu72 x CMC40). At Ogunjobi et al. 2006). The above resources are the end of this project period, we will be poised to available at cassava database housed at CIAT. initiate MAS breeding to incorporate WFR into cassava lines preferred by smallholder farmers using the The draft cassava genome (CIAT line AM560-2) SNP/SSR markers linked to the WFR QTLs, which was released by the U.S. Department of Energy-Joint contain quantitative resistance (QR) gene(s) that confer Genome Institute (DOE-JGI) under the Community WFR. Sequencing Program (www.jgi.doe.gov/CSP). Currently, the Gates Foundation has invested $1.3 M to refine the Identification of candidate genes for resistance genome annotation and develop a robust SNP resource to whitefly using microarrays. Microarrays to enable molecular mapping in cassava (CGP 2009). technology and subtractive libraries were used to Over 47,000 protein-coding loci are currently identify differentially expressed genes in cassava during annotated on the cassava genome and 24,388 of these A. socialis attack (Bohórquez 2011). These loci are supported by ESTs (CGP 2009). Two additional methodologies allowed us to identify 405 sequences full-lenght cDNA libraries were constructed more induced by A. socialis in all stages of their life cycle. recently and are being analyzed (CIAT/RIKEN). These These sequences are involved in biological process like libraries contain cDNAs from over 23 treatments defense, cell wall modification, oxidative burst, signal including A. socialis infestation of MEcu72 (WFR) transduction, transport, primary metabolism, and leaves. photosynthesis. Some of these sequences are part of the signaling pathways regulated by jasmonic acid (JA) Genetic linkage maps are a prerequisite to studying and ethylene (ET), which are involved in defense the inheritance of both qualitative and quantitative response to pathogens and herbivores. When traits (Morgante and Salamini 2003). To identify the A. socialis feeding on leaves of genotype MEcu 72, mechanisms of WFR in cassava, we are determining the introduce their stylet, and insect-derived elicitor heritability and the number of loci that contribute to (salivary components and/or chitin) are recognized by a the antibiotic and antixenotic resistance expressed in plant receptor. In the case of chitin, it is proven that the MEcu72. To this end, it is necessary to construct a family of transcription factors AP2/ERF are induced by 10-cM framework linkage map for MEcu72 using chitin, which is a component of the insect exoskeleton. statistically well-supported EST, AFLP, SSR, and SNP This transcription factor is induced by the signaling markers. Cassava is a highly heterozygous species with cascade that begins with plasma membrane strong inbreeding depression (Blair et al. 2007). depolarization and Ca2+ flow, then are activated MAPK Homozygous lines cannot be obtained and F2 signaling cascades and subsequent induction of populations often suffer from genetic bias induced by phytohormones pathways such as JA/ET. AP2/ERF the death of some genotypes. For this reason, F1 plants transcription factors are potential mediators of the are used in cassava mapping. We are using 184 F1 synergistically induction process between JA and ET progeny from a cross between MEcu72 (♀ WFR) x and induce defense genes such as basic vacuolar MCol2246 (♂ WFS). This population size increase LOD proteins PRB1, CHIB (PR-3), as well as lectins and score estimation and hence facilitate the identification proteinase inhibitors. These proteins can have several of WFR QTL(s) explaining more than 5% of the effects against insects, such as poisoning, may target phenotypic variance. A second F1 segregating components of the insect gut that contain population with 200 individuals from the cross between carbohydrates, can inhibit the action of proteases MEcu72 (♀ WFR) and CMC40 (♂ WFS) will be used to preventing whiteflies to digest their food well, dying of validate the markers flanking the QTLs explaining the malnutrition. The defense response is complex and largest phenotypic variance. involves all the processes of cellular metabolism, some of which themselves can be effector mechanisms that Unravel the genetic mechanism of WFR using are controlling the attacker. Among these are the association genetics. Our 10-cM framework map will generation of ROS, which produces enzymes that can be used for the identification of WFR QTLs using affect insect diet or inducing plant hormone signaling composite interval mapping, which is based on mixture pathways mentioned above. Cell wall modification, models and maximum-likelihood techniques. These which may make it difficult to insect feeding and may analyses will allow us to identify the major and minor also mediate the defense response regulated by JA/ET, 230 Insects and Mites that Attack Cassava, ... and finally the protein degradation machinery in which Eretmocerus predominated in the low altitudes of the are various proteases with different roles involved in Caribbean Coast (CIAT 1999). Parasitoid species defense against pathogens. At the same time, the plant associated with each whitefly species may be represses its primary metabolism and photosynthesis, influenced by geographical region. In Valle del Cauca reallocating C and N resources to the defense. (1000 m above sea level), 99.6% of parasitism of A. socialis was from Encarsia and 0.4% from The application of functional genomics approach Eretmocerus. The most numerous species in the in the study of cassava defense responses, opens a parasitoid complex was found in association with wide range of future applications at different levels, B. tuberculata. both in silico and experimentally. Gene expression analysis, construction of physical and genetic maps, Greenhouse studies on E. hispida as a parasite of genomic sequence analysis, gene silencing, and A. socialis show that the third instar of whitefly is the production of genetically modified organisms are some preferred. Parasitism rates on different instars were of the projects will be developed in the future. 15.6%, 44.7%, 75.3%, and 43.1% on the first, second, third, and fourth instars, respectively. The average rate Biological control. In explorations carried out of parasitism was 45%, with the highest levels being recently in the Neotropics—especially in Colombia, between 72 and 96 h after exposure (CIAT 1999; Venezuela, Ecuador, and Brazil—numerous species of Ortega 2000). Encarsia hispida is the parasitoid most natural enemies have been identified as associated with frequently seen when A. socialis populations are high. the whitefly complex that attacks cassava. Not much is However, its effectiveness in regulating whitefly known of the complexes of natural enemies associated populations in the field is not known. with the different whitefly species. Thus, we cannot readily determine each complex’s effectiveness and its The way in which cassava varieties resistant to potential in biological control programs. We know sets A. socialis influence parasitoid behavior has also been of parasitoids exists, but little is known about these evaluated. The survival of E. hispida was not negatively insects’ levels of parasitism, rates of parasitism per affected by resistant cassava genotypes. However, whitefly species, the specific hosts that are chosen, and fewer parasitoids emerged from pupae of A. socialis their effects on the regulation of whitefly populations. whose larvae had previously been fed with resistant variety M Ecu 72 than from pupae of larvae fed on Since 1994, CIAT researchers have conducted susceptible variety CMC 40 (CIAT 1999). explorations to identify natural enemies in northern South America. The most representative group is that During December 2000 and the first 3 months of of the microhymenopteran parasitoids (Castillo 1996; 2001, a large number of the parasitoid Amitus Evans and Castillo 1998). An abundance of these macgowni was observed at the CIAT–Palmira species exist in Colombia. More than 10 species, some experiment station in high populations of A. socialis. not even recorded, were collected, but the genera Between 20 and 80 examples were captured per leaf that most frequently associated with A. socialis, and more than 2500 per hour (B Arias 1998, pers. B. tuberculata, and T. variabilis were Encarsia comm.). (especially E. hispida and including E. pergandiella and E. bellottii), Eretmocerus (species not yet Three fungal entomopathogens that attack whitefly identified), and Amitus (including A. macgowni) on a world level have been tried in the laboratory: (Castillo 1996; Evans and Castillo 1998). Beauveria bassiana, Verticillium lecanii, and Metarhizium anisopliae. Although these fungi have The highest levels of parasitism observed in not been found in Colombia as natural parasites, A. socialis, B. tuberculata, and T. variabilis were B. bassiana was observed to cause mortalities of 28%, 15.3%, 13.9%, and 12.1%, respectively, and varied 55%, and 39% in first, second, and third instars of according to geographical region (Castillo 1996). A. socialis, respectively. The second instar was the Parasitism was higher in the Andean Region than in the most susceptible under laboratory conditions. coastal and flat regions of eastern Colombia. Beauveria bassiana and M. anisopliae also caused mortality rates of 18.1% and 18.8%, respectively, when Studies conducted in Colombia during 1997 to introduced in the morning, and 12.4% and 5.7% when 1999 showed that Encarsia was the most frequently introduced in the afternoon (Sánchez and Bellotti collected genus in the Andean Region and that 1997). 231 Cassava in the Third Millennium: … Lace bugs (B Arias and JM Guerrero 1999, pers. comm.), unlike V. illudens and V. manihoti, which are more common in Lace bugs (Hemiptera: Tingidae) attack cassava in dry seasons. several South and Central American countries. These bugs are a pest in the Neotropics, but have not been In field trials at CIAT, natural populations of reported in Africa or Asia. Froeschner (1993) identified A. machalana led to yield losses of 39%, unlike for the several species, of which the most important for plots of plants treated with pesticides (CIAT 1990). The cassava are Vatiga illudens, V. manihotae, and literature contains little information on yield losses Amblystira machalana. Vatiga manihotae is found caused by V. illudens and V. manihotae. Populations of mainly in Colombia and Venezuela, but is also found in V. illudens in Brazil are endemic, and do appear to Cuba, Trinidad, Peru, Ecuador, Paraguay, Argentina, reduce yields, especially in the central Cerrados and, and Brazil. Vatiga illudens predominates in Brazil, but more recently, southern Brazil. Nor is much literature is also found in the Caribbean Region. Black lace bug, available on the current and potential damage of this A. machalana, attacks cassava in Colombia, pest, requiring more research (Bellotti 2000a, 2000b). Venezuela, and Ecuador (Bellotti et al. 1999; Bellotti 2000b). Controlling lace bugs. Control seems difficult, as they have very few natural enemies (Bellotti et al. 1999). Vatiga illudens and V. manihotae. These two Continuous use of insecticides is expensive and may species attack cassava mainly during dry seasons, with destroy the natural enemies of other pests. Preliminary attacks worsening in prolonged droughts. Adult Vatiga studies and evaluations made in the cassava are gray and measure about 3 mm long and 1 mm germplasm bank held at CIAT indicate that varietal wide. The average life cycle of V. illudens lasts resistance may exist, but that more research is needed 75.5 days. The female can lay, on average, 61.2 eggs, to develop the technology (CIAT 1990; Bellotti 2000a). which she inserts into leaf tissue, preferably next to central nervures where they converge near the petiole. At CIAT–Palmira, a hemipteran of the family They thus become imperceptible. The nymph is white Reduviidae (Zelus nugax) was observed preying on the and a little smaller than the adult. Both adults and nymphs and adults of the Vatiga species mentioned nymphs are found in large numbers on the underside above. It succeeded in consuming, throughout its of leaves. biological cycle, an average of 475 lace bugs. Several spider species also feed on these insects but, so far, Populations tend to concentrate on the basal and their potential as predators has not been measured. central leaves but, during severe attacks, may reach apical leaves. Damage caused in leaves is similar to Planthoppers that made by mites: small white spots of star-like appearance, giving a whitish appearance to the leaf as Thrips they join. They later acquire a reddish-brown tone (Bellotti 2000b). This damage differs from that made Several thrips species have been identified as attacking by mites by the presence of black points on the cassava: Frankliniella williamsi Hood, Scirtothrips underside of leaves, which are excrements from the manihoti, Corynothrips stenopterus, and Caliothrips bugs. Foliage can be sufficiently damaged to masculinus. All belong to the family Thripidae. Thrips extensively reduce photosynthesis and result in the are a pest in Central and South America, and have also defoliation of basal leaves (Bellotti 2000b). been reported in Africa. Amblystira machalana. This pest induces a Frankliniella williamsi and Scirtothrips manihoti. similar symptomatology to that induced by the Vatiga These two species are the most important for the spp. Adults and nymphs of A. machalana appear damage they cause to terminal buds in cassava plants, black. The female lays, on average, 93 eggs on the that is, they break the plants’ apical dominance. The underside of leaves. At first, they are white, but quickly adult of both species is uniformly yellow, with become red or orange. The life cycle of A. machalana microscopic differences. averages 42.5 days (Arias and Bellotti 2001). In the field germplasm bank held at CIAT, severe outbreaks of When these thrips attack the plant, leaves do not A. machalana have occurred during wet periods. This develop normally; the folioles become deformed and species is also found in subhumid zones of Ecuador present chlorotic yellow spots or small and irregular 232 Insects and Mites that Attack Cassava, ... tears (in the sense of “rip”). The damage done by the cassava varieties and hybrids carried by the germplasm thrips’ scraping-sucking mouth apparatus to leaves-in- bank held at CIAT are highly resistant to thrips attack, expansion causes them to deform to the point that with a large percentage presenting symptom, that is, complete leaf lobes are missing. New leaves are small damage, of little consequence (CIAT 1974; with deep clefts that run from foliole margins to central Schoonhoven 1974; Arias and Guerrero 2000). Cassava nervures. resistance to thrips is based on the villosity of its leaf buds. If leaf pubescence is increased before they are Brown lesions appear on stems and petioles, expanded, then resistance to the thrips F. williamsi is corresponding to scars, that is, to cork-like tissue that increased. Such resistance is mechanical develop as wounds heal after the insects’ scraping. (Schoonhoven 1974; Arias and Guerrero 2000). Internodes are also shortened, and terminal growing points may die, inducing the growth of lateral buds, Cassava mealybugs which then undergo attack from the pest. The result is a dwarf plant with a witches’-broom appearance. Thrips More than 15 mealybug species feed on cassava mostly attack in the dry seasons, with the affected plants in Africa and South America. Species in the plants recovering in the rainy season. Americas include Phenacoccus herreni, P. manihoti, P. madeirensis, Ferrisia virgata, and Pseudococcus Corynothrips stenopterus and Caliothrips mandioca (Bellotti et al. 1983b; Williams and Granara masculinus. These two thrips species are considered de Willink 1992). Phenacoccus herreni and P. manihoti to be of lesser importance because they prefer the are of tropical origin and are economically important. central and lower leaves of the plant. They do not break its apical dominance, thus enabling the plant to Phenacoccus manihoti was introduced into Africa develop well. If attack is severe, leaf blades become full in the early 1970s. The pest spread rapidly, causing of small cork-like wounds that disfigure the plants’ considerable losses in crop yields. This motivated the general aspect. development of a successful biological control program (Herren and Neuenschwander 1991). In the Americas, Corynothrips stenopterus is yellow with black spots P. manihoti is found in Paraguay, certain areas of in the last two abdominal segments. This coloring Bolivia, and the state of Mato Grosso in Brazil, where it easily distinguishes the insect in the field. Caliothrips is not economically significant (Lohr and Varela 1990). masculinus has a black body that generally measures Phenacoccus herreni is dispersed throughout northern 1.0 to 1.5 mm long and less than 1.0 mm wide. It is South America and Northeast Brazil, where high found on the expanded leaves of young plants, populations of the insect can cause considerable losses especially in greenhouses or screenhouses. It is rarely (Bellotti 2000a, 2000b). observed on field crops. Biology and behavior. Both species cause similar At CIAT, yield reductions from thrips attacks were damage: feeding nymphs and adults causes leaf studied. Results indicated that thrips can cause yield yellowing and curling, and a rosette formation in losses ranging from 15% to 20%, a finding that agrees growing points. High populations cause tissue with the literature. However, in highly susceptible necrosis, defoliation, stem deformation, and bud death. varieties (e.g., ‘Chiroza Gallinaza’) growing in hot Infested plants also suffer reduced rates of environments such as northern Cauca and Valle del photosynthesis and transpiration, and loss of Cauca, thrips attacks can prevent plant development, mesophyll efficiency. Moderate deficits of water which, if compounded by weed invasion, will kill the pressure occur, and levels of internal CO2 and leaf plants (B Arias 1989, pers. comm.). temperatures drop (CIAT 1992; Bellotti 2000a, 2000b). Some thrips species are fully developed within Phenacoccus manihoti is parthenogenic. In 15 to 30 days. They pass through four instars, two of contrast, males are needed for P. herreni to reproduce. which take place in the soil where they do not feed. In On the underside of leaves and around apical buds, one year, they produce five to eight generations P. herreni females deposit ovisacs that contain several (Metcalf and Flint 1972, cited by Tejada 1975). hundreds of eggs. The eggs hatch in 6 to 8 days and the insects undergo four nymphal instars, with the Control through varietal resistance. The best fourth instar being the adult. Males, however, have an control method is to plant resistant varieties, which are extra instar. The third and fourth instars occur in a readily available. Currently, more than 30% of the cocoon from which they emerge as winged adults. 233 Cassava in the Third Millennium: … Adult males live alone for 2 to 4 days. The female’s Anagyrus putonophilus average life cycle is 49.5 days, whereas that of the male An. insolitus is 29.5 days. The optimal temperature for female Aenasius vexans development is between 25 and 30 °C (Herrera et al. 1989; Bellotti 2000a, 2000b). Three encyrtid parasitoids (Ap. diversicornis, Ac. coccois, and Ae. vexans) were found to be effective for Phenacoccus herreni presents high population controlling P. herreni (Van Driesche et al. 1988, 1990). peaks during dry seasons. The beginning of the rains Aenasius vexans and Ap. diversicornis noticeably reduces these populations, allowing the crop to recover prefer P. herreni, although laboratory studies indicate (Herrera et al. 1989). Recent research indicates that, that they also parasitize other species of mealybugs when water supplies are limited, cassava leaves (Bellotti et al. 1983b, 1994; Bertschy et al. 1997). The increase the concentrations of certain metabolites, parasitoid Ac. coccois showed equal preference for which probably favor mealybug growth and reduce the either P. herreni or P. madeirensis. The three effectiveness of parasitoids (CIAT 1999; Polanía et al. parasitoids are attracted by infestations of P. herreni 1999; Calatayud et al. 2000). These results would help (Bertschy et al. 1997). Comparative studies of the three explain the rapid growth of mealybug populations parasitoids’ life cycles show that each could complete during dry seasons (Bellotti 2000a, 2000b). two cycles for every cycle of P. herreni, a favorable ratio for biological control. Control by varietal resistance. Identifying cassava resistance to the mealybug was hard, involving Apoanagyrus diversicornis prefers third-instar the evaluation of more than 3000 cultivars held in the nymphs, while Ac. coccois, which is much smaller, germplasm bank at CIAT. Only low levels of resistance parasitizes male cocoons, adult females, and second- or tolerance were identified (Porter 1988). Studies on instar nymphs with equal frequency. Oviposition of resistance made by IITA in Africa and by IRD have Ap. diversicornis caused a 13% mortality rate in obtained similar results. Low to weak levels of third-instar nymphs (Van Driesche et al. 1990). resistance to P. manihoti have also been reported (Le Aenasius vexans prefers, with equal frequency, the Ru and Calatayud 1994; Neuenschwander 1994a). second and third instars and adult females (CIAT 1990). Such low levels of resistance may therefore require increased use of natural enemies in biological control Field studies with natural populations of programs (Bellotti 2000a). Ap. diversicornis and Ac. coccois revealed a percentage of parasitism when trap plants were Biological control. Mealybug management is a established as hosts of P. herreni around the cassava well-documented example of classical biological crop (Van Driesche et al. 1988). The combined action control, especially in Africa. Phenacoccus manihoti is of the two parasitoids caused a 55% mortality rate of P. now successfully controlled by the parasitoid herreni (Van Driesche et al. 1990). Apoanagyrus lopezi after its introduction from the Neotropics. Phenacoccus herreni is distributed across Joint efforts by CIAT and EMBRAPA ensured that northern South America, but only in Northeast Brazil Ap. diversicornis, Ac. coccois, and Ae. vexans were does it cause severe yield losses. The mealybug may exported from CIAT for release in Northeast Brazil, be exotic to that region, probably originating from mainly in the states of Bahia and Pernambuco, between northern South America (Williams and Granara de 1994 and 1996. Before this introduction, EMBRAPA Willink 1992; Bellotti 2000a). scientists had conducted field studies to measure pest damage and collect natural enemies. At the end of Numerous species of parasites, predators, and 1996, more than 35,000 individuals of the three entomopathogens of P. herreni have been identified in parasitoid species had been released. In Bahia, after the Neotropics. Many are generalist predators that feed release, Ap. diversicornis had dispersed up to on numerous species of mealybugs. However, several 130 km in 6 months, 234 km in 14 months, and parasitoids prefer P. herreni, including those from 304 km in 21 months. northern South America: In the same state, Ac. coccois also established and Acerophagus coccois was recovered in large numbers at distances of less Apoanagyrus diversicornis than 180 km from the release site 9 months later. Ap. elegeri Aenasius vexans, however, was continually recaptured in its site of release in Pernambuco, dispersing only 234 Insects and Mites that Attack Cassava, ... 40 km in 5 months (Bento et al. 1999). Subsequently microscopic rice grains and hatch 4 days after the authors observed that mealybug populations were oviposition. The young larvae then tunnel into the bud, noticeably reduced in that region and that the cassava impeding the meristematic leaves from opening. A crop was returning to areas that had been abandoned milky discharge then appears and the growing point because of P. herreni infestations. dies. Several whitish larvae can be observed inside the affected terminal point, where they live for about Stem-Perforating Insects 23 days until they drop to the soil. They then pupate and, about 26 days later, the adult flies emerge. The Shoot flies flies are most active on sunny days, especially affecting cassava crops associated with banana or shade trees. Damage by shoot flies (Silba pendula and Carpolonchaea chalybea) is found in almost all This pest attacks throughout the year, although, in cassava-producing regions of America. This pest has many non-seasonal areas, they frequently appear at the not been reported in either Africa or Asia. beginning of the rainy season. At the CIAT–Palmira station, the dry climate favors the development of Damage. Damage caused by larval shoot fly is shoot-fly populations. manifested as a white exudate that flows from the growing point, which then usually dies. The exudates Trials that have confirmed a 100% loss of apical then change color from pale coffee to black as the latex buds have not yet provided data on yield losses. Nor oxidizes and dries up as the terminal point dies. Inside have the population dynamics of this pest been studied an attacked growing point, several larvae are found, in detail. For these reasons, shoot fly is considered as a which perforate the first 5 to 7 cm of the plant’s minor pest. terminal point tissue. Hence, the name “shoot fly”. Control. Because this pest does not attack the Attacks by this pest delay plant growth and break whole crop and root production is not significantly its apical dominance. This stimulates the development reduced, the few apical buds found to be infested can of lateral buds, which may also suffer attack from this be eliminated by hand, thus avoiding unnecessary fly. Sometimes, only one part of the apical bud dies applications of chemical products. However, when and the shoot continues growing. The youngest plants shoot-fly attack occurs early, affects all buds, or are the most susceptible, and repeated attacks may populations are high, application of an lead to plant dwarfism. In severe outbreaks of the pest, organophosphorus systemic insecticide is up to 86% of crop plants can be affected. recommended. A mixture of insecticide and sugar solution sprayed onto plants forms an effective bait for In studies simulating damage, between 50% and controlling adults. Also recommended are traps 100% of shoots were cut with a scalpel in each of two containing decomposed fruits, casein, or yeast. These sets of plants, one aged 2–5 months, and the other attract the insects, which can then be killed with 5–9 months. The late-branching variety M Ecu 150 was insecticide. more susceptible than the ‘Llanera’ in the first 2 to 5 months of crop growth, with yields dropping by 30%. Fruit fly Removal of shoots from plants aged 6–9 months did not affect yield in any variety. Other trials in which In Colombia and in America generally, two fruit fly damage was simulated (Arias and Bellotti 1982) species have been identified as attacking cassava: indicated that root yield in variety M Col 22 was not Anastrepha manihoti da Costa Lima and A. pickeli da reduced by shoot fly attack. However, an attack on a Costa Lima (Diptera: Tephritidae). This observation is 3-month-old crop reduced optimal quality of planting the first report of the pest attacking cassava fruit but stakes by 51% to 71%. does not cause significant economic losses. In Colombia, Venezuela, and Central America, fruit flies Biology and behavior. The adult fly is black with also cause severe damage to cassava stems. a metallic blue sheen. The female oviposits among leaves that have not, as yet, initiated expansion and in Biology and behavior. The adult fly is yellowish growing points, perforating a small cavity in the plant coffee in color and about 10 mm long. It has tissue with her ovipositor. Up to 22 eggs have been transparent wings adorned with yellowish coffee- observed in one shoot, although the average is 3 to colored bands, which gives it a showy appearance. The 8 eggs per shoot. The eggs are shaped like female’s abdomen presents a noticeable extension, 235 Cassava in the Third Millennium: … corresponding to the ovipositor, whereas the abdomen In affected stems, the rotting medulla region is in the male is rounder. either coffee-colored or brown, changing from pale to dark. Stakes obtained from these stems may lose as After oviposition, hatching takes place in the fruit. much as 16% of their capacity for shooting and may The larvae perforate and then destroy the developing take several weeks to sprout. seed. The infested fruit loses its green color, becomes soft, withers, and finally blackens (CIAT 1976). Control. At crop establishment, stakes must be Damage to fruit is important to plant-breeding selected and only those that have healthy white piths programs because seeds developed from crosses or should be planted. The most serious damage coincides hybridizations are then lost. with the rainy season, a time during which plants may recover rapidly and thus perhaps not need control If it does not find cassava fruits, the female fruit fly measures. seeks tender tissue on which to deposit her eggs. Such tissue is found in stems of young plants or in the The braconid Opius sp. parasitizes the larvae found terminal points of adult plants. The eggs are inserted in fruits by as much as 16%. However, it has not been into the tissue and can be recognized by the presence found parasitizing larvae in stems. of a respiratory siphon, which looks like a small whitish eyelash that stands up from the stem tissue. Plant Compared with other tried solutions, McPhail traps, tissue around the eggs decomposes and becomes which contain hydrolyzed maize at 2%, capture the blackish. The whitish larvae that emerge from these most adult fruit flies from developing plants. eggs soon begin boring into the stems, moving either up or down and forming brown galleries in the stem’s When adult populations are very high during the pith, which then begins to rot. Sometimes, the bud crop’s first 3 to 4 months, chemical control may dies. When the larvae reach the prepupal state, they provide an alternative. Fenthion or dimethoate controls make orifices in the stems, which are then abandoned this pest well at doses between 2 and 3 mL of p.c. per as the insects fall to pupate in the soil (Vidal and Marín liter of water. To avoid heavily contaminating the 1974). Latex then oozes out of these orifices and drips environment, chemical control should be carried out in down the length of the stems. The total life cycle of that small area of the crop from which stakes will be the fruit fly A. pickeli averages 39.5 days. obtained for the next cropping cycle. Damage. The damage caused by Anastrepha flies Stemborers is associated with the rot caused by the bacterium Erwinia carotovora pv. carotovora (Mattos 1977). The The economically most important arthropod bacterium penetrates the plant at oviposition or when stemborers belong to the orders Coleoptera and the larvae leave to pupate. Other secondary pathogens Lepidoptera. They form a complex that feeds on are also found together with this bacterium. cassava stems and branches, causing considerable damage to the crop, whether sporadically or locally, or The association between fruit fly and bacterium is mostly in adult plants. Although global in distribution, not yet fully understood. Apparently, the bacterium is stemborers are much more important in the found on the stem where it lives as an epiphyte. Neotropics, especially in the Latin American countries However, it is most unlikely that the fly itself transports of Brazil, Colombia, and Venezuela. They tend to be the bacterium. On the contrary, the bacterium highly specific to cassava, with only a few, reportedly, penetrates the stems through the openings that the feeding on alternative hosts. None can be considered larvae have dug in stem tissues under conditions of as a universal pest. They include the following species: high humidity. Under favorable conditions of precipitation and humidity, the stems rot (CIAT 1976). • The longhorned beetle (Lagocheirus spp.) is Stem rot does not favor larvae. When researchers distributed throughout the entire world, but examined rotten stems, they found that 40% of the does not cause severe damage in the field. larvae had died. Consequently, population increases of the insect may be attributed mostly to infestation of • In Brazil, several species of Coelosternus fruits of either cassava or other alternative hosts, and (Coleoptera: Curculionidae) have been reported not so much to infestation of stems (Bellotti and as reducing cassava yields and the quality of Schoonhoven 1978c). planting materials. Damage is usually sporadic 236 Insects and Mites that Attack Cassava, ... and does not significantly affect yield (Bellotti (C. alternans and C. rugicollis), and range from pale to and Schoonhoven 1978a, 1978b). dark brown, being almost totally covered with yellowish scales. Adults are active throughout the year, although • Several lepidopterans and coleopterans attack less so at some sites during cool months. cassava in Africa, with Coelosternus manihoti being considered a pest on that continent. Lagocheirus araneiformis. This insect (Coleoptera: Cerambycidae) has been found in a • Seven species of Coelosternus attack cassava diversity of places such as the USA, Caribbean Region, in America. Central and South America, the West Indies, and Indonesia. In Colombia, it is found in most cassava- The pests Coelosternus spp., Lagocheirus growing regions and is believed to be the most araneiformis, and Chilomima clarkei are presented abundant cerambycid in the country’s cacao-growing below in more detail. areas (Villegas 1984). In addition to cacao (Theobroma cacao), other host plants include an ornamental plant Coelosternus spp. This insect’s larvae vary in size known as tree spinach (Cnidoscolus aconitifolius). and form, according to species. Some measure as long as 30 mm. They are usually white, yellow, or cinnamon, Biology and behavior. The adult of this insect has and can be found tunneling into the plants’ aerial parts. antennae that are longer than its body. Its head, wide In susceptible varieties, the cassava plant’s stems and and grooved, stands out from between antennal branches may break or are reduced to sawdust. During tubercles, which are distant from each other. The dry seasons, the branches lose their leaves and may L. araneiformis body is covered by short, light brown die. If infestation is severe, young plants may die. In pubescence, with spots due to a darker or whitish infested branches, or on the soil below, waste matter pubescence. The elytra present rounded shoulders that and sawdust residues excreted or expelled by the larvae darken at the base. Each elytron has two short spiny can be found. ribs. Two spots can also be seen on the elytra: one that is more or less triangular with its middle point at the The Coelosternus female may oviposit anywhere in base on the margin; and the other is lateral, darker, and the cassava plant, although it prefers the tender parts. located on each side close to where the elytron joins For example, C. alternans oviposits near broken or cut the body at the third pair of legs. extremes of branches or under the cortex in cavities perforated by the insect with its proboscis. Three days The female insect has an average body length of after mating, the C. granicollis female will penetrate 1.64 cm and is 0.69 cm wide. The average male is the stem and oviposit white eggs. similar, at 1.60 cm long by 0.72 cm wide. Mouth parts are used for masticating, and the antennae are filiform When totally developed, C. alternans larvae and light brown in color, and possess 11 segments. measure 16 mm long and a maximum of 4 mm wide. These also enable differentiation of sexes in both adults Those of C. tardipes measure 9 × 2.5 mm. The white and pupae. or reddish-brown bodies of most of these larvae curve. Their jaws are black. For C. rugicollis, only one larva is The adult female oviposits in stems and branches found per stem, whereas other species may have at about 2.5 mm below the cortex. She first uses her several larvae per stem. The larval phase lasts from jaws to open a small perforation with a diameter of 30 to 69 days. In all species, well-developed larvae about 0.72 mm in the cortex of buds and internodes. pupate within cells they construct in the stem’s pith. A She then deposits her egg in either a horizontal or pupa can hang within its own cell because one extreme oblique position. The postures adopted are individual is attached by substances excreted by the larva to the and, occasionally, two eggs are placed at an average perforation made in the stem. The pupal phase lasts depth of 1.02 mm. The preoviposition period is usually about 1 month. 9.7 days and that of oviposition is 28.8 days (ranging from 13 to 62). During the latter period, the female lays The adult is a weevil, that is, it has a long an average of 150 eggs (ranging from 87 to 202). She proboscis. After emerging from the pupa, it remains in prefers to oviposit at night, although 10.2% of eggs are the cell for several days before abandoning the stem. laid during the day (Villegas 1984). Adults may be 6 (C. granicollis) to 12 mm long 237 Cassava in the Third Millennium: … A newly laid egg of L. araneiformis is whitish local, usually at the base of the stem, which may cream, turning yellow by the second day. Close to provoke lodging if the attack is severe. In plants that hatching, one extreme shows a dark coffee-colored have fallen, up to 30 larvae per plant have been found. spot, which corresponds to the larva’s jaws. The egg is Larvae also attack roots, forming galleries through elliptical, of hard consistency, and measures 0.76 mm which microorganisms can penetrate to cause at its equatorial and 2.04 mm at its polar diameters. secondary rots that reduce yields. Plants attacked by Incubation takes an average of 3.13 days (ranging from L. araneiformis are easily recognized in the field by the 2 to 6 days). presence of light brown or reddish brown sawdust, of rough texture, that larvae expel as they bore through The larva is apodal, cream in color, and, because stems. of its shape, is often known as gusano tornillo in Spanish. The name comes from its compressed and Control. Chemical control of this and all prognathic head, which is adhered to a very wide stemborers is difficult. The following farming practices prothorax that gives the insect a cylindrical are therefore recommended: appearance. This feature is carried to adulthood, giving rise to its name as flat-faced longicorn beetle. The • Harvest residues, which help disseminate the head is dark brown, chitinized, and carries strong jaws. insect, should be collected and burned. Dorsally, the thorax presents two, chitinized, light brown plates. The abdomen has 10 well-defined • Biological control of this insect has not yet segments, with the last one being rounded and smaller. been found. Hence, one method for regulating The larva measures 0.3 mm in the first instar, growing adult populations is to place traps made of to 37 mm by the sixth instar. packages of fresh stakes in the field, thus attracting them and enabling their capture. Pupae are exarate. When recently formed, pupae are light brown, becoming darker as they develop. • Careful selection of planting stakes. When an adult is close to emerging, its sex can be differentiated by its antennae. The male also exhibits, Chilomima clarkei. This stemborer (Lepidoptera: between the fourth and fifth joints, a wisp of hair that is Pyralidae) is a butterfly whose larvae bore or perforate not found in the female, who, in contrast, has two pairs cassava stems. Recently, this insect has greatly of spinules in the last abdominal segment. increased its populations in Colombia and Venezuela to become, currently, the most important cassava pest In the field, the life cycle of L. araneiformis lasts 86 (López et al. 1996). The pest causes root production to 194 days, with an average of 128.2 days. Adult losses of more than 60% because the stems break, females live an average of 89.7 days and males 91.6 debilitated by the attacks. In Colombia, in the late days. In the laboratory, these periods were shorter, at 1990s, C. clarkei became the most important pest in 45.8 and 71.8 days, respectively (Villegas 1984). several departments of the Atlantic Coast, destroying planting materials to the point of causing a crisis. The Damage. The larvae of L. araneiformis move pest disseminated very rapidly through the exchange of within the stem by using their jaws and contracting stakes from region to region among farmers (B Arias their bodies. Recently hatched larvae are located in the 1985, pers. comm.). In the Colombian Caribbean cortex on which they feed during the first instar. Region, 85% of planted cassava is attacked by C. Second instars partially consume the cortex but also clarkei (López et al. 1996). open galleries to tissues lying nearest to the ligneous area, where they begin the third instar. They continue This pest has also been found in Tolima, Huila, to bore through the stake or stem to its central parts, Caldas, the two Santanders, the Eastern Plains of where the last instars and pupae develop, thus Colombia, and the Western Plains of Venezuela. It has completing their life cycle. also been reported in other countries such as Argentina and Brazil (A Bellotti 1985, pers. comm.). To date, the In the field, the pest attacks both recently planted pest has not been reported in environments at altitudes stakes and already developed plants. They also attack of more than 400 to 500 m above sea level. It is very planting materials that have been stored for long important, therefore, that planting materials from these periods. When recently planted stakes are attacked, the sites are not transported to areas where the pest does seedlings die or they suffer poor sprouting. In contrast, not exist, without the necessary precautions being when already developed plants are attacked, damage is taken or without phytosanitary certification. 238 Insects and Mites that Attack Cassava, ... Females are nocturnal in habit, and live for 5 to maximum of 70, in six plants; and others an average of 6 days (males for 4 to 5 days). Oviposition takes place one hole per plant, also in six plants. CIAT will continue at night on cassava stems, usually near a node or bud, to assess varieties to tackle the pest through cassava with females laying an average of 229 eggs. The eggs plant resistance. are very small and flat, and difficult to see in the field, as they measure less than 1 mm in diameter. They are Biological control. Several biological control agents laid either individually or in small groups of 2 to 5. They have also been identified as attacking both eggs and are at first cream in color and, as they mature, take on larvae of Chilomima sp. Eggs are parasitized by a pink tinge. The eggs hatch about 6 days later (at Trichogramma microhymenopterans; and larvae by 28 °C). Bracon wasps, Brachymeria conica, and Apanteles sp. (Lohr 1983). Damage. After hatching, the first-instar larvae feed on the stem cortex or epidermis. These larvae are very Known control methods were evaluated in the mobile, seeking appropriate sites at which to feed, 1980s when research on the pest started. Applications almost always near axillary buds. They form a capsule of Bacillus thuringiensis, the fungus Spicaria sp., and for protection, living and feeding within it until they macerated larvae that had died from a probable viral reach fourth instar. At each instar, the capsule’s tissues disease were each sprayed over pest larvae, resulting stretch. A fine and abundant sawdust can then be in a mortality rate of 99%, 88%, and 100%, respectively observed, unlike for L. araneiformis. During fifth instar, (Herrera 1999). The great mobility of first instars made the larvae penetrate the stems where they complete the them much more vulnerable to several products, to the next 6 to 12 instars, pupate, and then emerge as adults point where they could be controlled with B. (Lohr 1983). The larval states take 32 to 64 days to thuringiensis. complete and the pupal state 12 to 17 days. CIAT initiated research to introduce resistance Populations of C. clarkei may be present genes to insects, using B. thuringiensis through the throughout the year and increase during rainy seasons. vector Agrobacterium to transform embryonic tissues Four to six cycles of the pest may occur during a of cassava, thereby developing cultivars resistant to cropping year, potentially increasing damage and C. clarkei. Initial results are so far promising (CIAT making control much more difficult. When the number 1999). of perforations made in the stem is already considerable (e.g., more than 20 per stem), the stem Other controls. As mentioned previously, control could break, reducing the quality and quantity of with insecticides is not practical because adult planting materials. In the field, plants with more than stemborers are difficult to kill and their larvae feed 35% of stem parts under attack suffer significant inside stems. Farming practices that reduce this pest’s reductions (45% to 62%) in root yields (Lohr 1983). populations include the removal and burning of infested plant parts and the planting of healthy Control by host-plant resistance. Once the larvae undamaged stakes (Bellotti et al. 1983a). Other useful enter the stems, control is very difficult. The capsules practices are to treat the stakes, burn harvest residues, woven by the larvae for protection against natural store stakes for short periods, and avoid exchanging enemies also protects against pesticides. However, the stakes between sites. Technical personnel and farmers great mobility of first-instar larvae makes them highly must also be trained to manage the pest and vulnerable, which means they can be controlled by disseminate the message of how important such entomopathogens such as Bacillus thuringiensis. management is. Given the pest’s generational increase, several applications will be needed, increasing production Technicians working in the Colombian Atlantic costs. Field research conducted by Gold et al. (1990) Coast have evaluated the local use of insecticides to indicated that intercropping with maize reduces manage Chilomima attacks. Among the several stemborer populations until the maize is harvested. pesticides they evaluated, they found that malathion, applied manually with “polyspray” in doses ranging In Pivijay, Department of Magdalena, nearly from 0.5 to 1.0 p.c. per liter of water and directly into 2000 cultivars held in the germplasm bank at CIAT holes containing sawdust, resulted in 100% larval were evaluated during 2 years for varietal resistance to mortality over time and even prevented the pest’s this pest. Significant differences were found among the dissemination in the locality (E Ortega 2001, pers. varieties, where some presented 20 to 30 holes, with a comm.). The practice is interesting because the 239 Cassava in the Third Millennium: … applications were not generalized but made specifically and peeled. Consequently, farmers lose the investment at the points, thus favoring both beneficial fauna and they made in cultivation tasks, time, and use of land. the environment. Furthermore, applications were easy to do, although workers must be duly protected. Populations of C. bergi are present in the soil throughout the cropping cycle and damage to roots Cassava burrower bug can be seen within the crop’s first month. At the end of the cycle, the bugs may have damaged, through their Cyrtomenus bergi Froeschner is an arthropod pest feeding action, between 70% and 80% of all roots, that feeds directly from cassava roots. The species is reducing starch content by more than 50%. Serious polyphagous and so had not coevolved with the crop. economic damage is not necessarily caused by large García and Bellotti (1980) first reported this pest C. bergi populations (Arias and Bellotti 1985a). Riis attacking cassava in Colombia in 1980. (1990) showed that, even with very small populations (close to zero), 22% of roots can be affected. The Distribution and behavior. Recently, the pest was economic threshold, where a cassava buyer would reported as causing commercial damage in Panama, reject a load of roots, is damaged parenchyma in 20% Costa Rica, and Venezuela (Riis 1997). The insect is to 30% of roots, that is, when they present “cosmetic” present in many other Neotropical regions, where it has damage due to the dark bite points, which are not been found feeding on many crops, including onion, acceptable to fresh-cassava markets (Bellotti 2000a, groundnut, maize, potato, Arachis pintoi (forage 2000b). groundnut), sorghum, sugarcane, coffee, coriander, asparagus, beans, peas, some grasses, and several Life cycle. Cyrtomenus bergi presents five weeds (Riis 1997; Bellotti et al. 1999; Bellotti 2000a, nymphal instars. The nymphs and adults may live for 2000b). more than 1 year, feeding on cassava roots (García and Bellotti 1980). In the laboratory, at 23 ºC and 65% The pest prefers certain host plants to others. ± 5% rh, when C. bergi was fed slices of cassava root Free-choice feeding tests conducted in the laboratory with low levels of cyanide (HCN), its life cycle was indicated that cassava is not the optimal host. The bug 286 to 523 days. On average, eggs took 13.5 days to prefers groundnut or maize to cassava (78% vs 22%), hatch, the five nymphal states 111.3 days to develop, growing much faster in maize. The adult life span in and the adult life span was 293.4 days. maize was 95 days, 69 in onion, 66 in sweet cassava (CMC 40), and 64 days in bitter cassava (M Col 1684) This bug is strongly attracted to moist soils. It will (Riis 1990). Optimal fecundity, survival rate, and accordingly migrate when soil moisture content is less intrinsic rate of increase in the population were than 22% and will remain in soil that has more than recorded in groundnut and Arachis pintoi but not in 31%. The rainy season therefore enormously favors the maize. Sweet cassava, sorghum, and onion were the survival of adults and nymphs and, thus, their behavior least favored hosts. It could not complete its life cycle and dispersion. In contrast, low soil moisture content in bitter cassava varieties (Riis 1997; Bellotti 2000a, during dry periods will restrict the adults from hiding 2000b). and migrating, and will increase nymph mortality (Riis 1997; Bellotti 2000a, 2000b). Damage. Nymphs and adults of C. bergi feed on cassava roots, penetrating the peel and parenchyma Effects of cyanogenic glycosides. Field trials and with their thin and strong stylets. This feeding action laboratory studies suggest that C. bergi feeding enables several soil pathogens (e.g., fungal species of preferences may be related to the levels of cyanogenic Aspergillus, Diplodia, Fusarium, Phytophthora, and glycosides in cassava roots, as follows: Pythium, and the alga Genicularia sp.) to enter the root parenchyma (Arias and Bellotti 1985a; Bellotti and • Adults and nymphs that feed on a variety with Riis 1994) and cause coffee-colored to black lesions high HCN content (i.e., more than 100 mg of that give the insect the Spanish name of chinche de la cyanide [CN-] per kilogram of roots) experience viruela or, literally, “smallpox bug”. Lesions begin longer nymphal development, reduced egg appearing in roots 24 h after feeding (Arias and Bellotti production, and increased mortality. 1985a). They may lead to reduced starch contents and hence to serious losses in the roots’ commercial value. • Oviposition on CMC 40 (43 mg CN-/kg roots) Damage is not detected until the roots are harvested was 51 eggs per female, compared with only 1.3 eggs on M Col 1684 (627 mg CN-/kg roots). 240 Insects and Mites that Attack Cassava, ... • Adult life span on CMC 40 was 235 days, that is, threshold of loss would be reduced (Castaño et al. more than double than that on M Col 1684 (112 1985). days) (Bellotti and Riis 1994). In cassava crops intercalated with Crotalaria sp., • Riis (1997) demonstrated that oviposition on damage to roots was reduced to less than 4%, as clones with a cyanogenic potential (CNP) of less opposed to monoculture where damage was 61%. than 45 ppm fw was significantly higher than on However, yields of intercalated cassava were reduced clones with a CNP of more than by 22%. Unfortunately, Crotalaria sp. has little 150 ppm. However, the rate changed commercial value and farmers therefore refuse to considerably for clones where the CNP ranged adopt this technology. between 45 and 150 ppm. Experimental data and field studies show that • Other studies have indicated that early instars varieties with high CNP values are resistant to C. bergi are more susceptible than late instars to the attack and the damage it does. However, in many roots’ CNP. Indeed, the length of the bug’s stylet cassava-producing regions, sweet varieties (or those during the first two nymphal instars probably with low CNP) are preferred for fresh consumption. restricts the insect’s feeding action mainly to the Recent studies indicate that potential for resistance or root peel (Riis 1990; Riis et al. 1995), whereas tolerance of C. bergi exists in 15 varieties with low CNP the third to fifth instars can feed directly from (Riis 1997). To take advantage of this varietal the parenchyma. In cv. CMC 40, cyanogen levels resistance, research needs to be carried out on the in root parenchyma are low, but high in the peel pest’s behavior and the plant’s mechanisms of at 707 mg CN/kg roots. Laboratory experiments resistance, both biochemical and genetic. in which the bug was fed CMC 40 resulted in a 51% mortality of first- and second-instar The potential for biological control of C. bergi is nymphs. This rate is high, even when compared being researched. Recent studies with with the 82% mortality of similar nymphs fed entomopathogenic nematodes and fungal pathogens M Col 1684. Consequently, the high level of indicate that they could be used for control. This cyanogens in the CMC 40 cortex may be research has, so far, been conducted only in the responsible for the insect’s high mortality laboratory and greenhouse. Field studies must be (Bellotti and Riis 1994; Bellotti 2000a). carried out before the most acceptable technology can be recommended. Promising technologies include: • Studies of preferential feeding conducted in cassava fields in Colombia indicated that the • The nematode Steinernema carpocapsae, level of damage was considerably higher for which has successfully parasitized C. bergi in CMC 40 (low cyanogen contents) than for M Col the laboratory. Infection was established within 1684. Clone M Mex 59, whose cyanogen content 5 to 8 days after exposure to the insect. The is intermediate at 106 mg CN-/kg roots, suffered adult was the most sensitive to infection (58.6% moderate damage (Arias and Bellotti 1985a). parasitized after 10 days). The least susceptible were the first and second instars, with 17% and These data indicate that the CNP can impede 31% parasitized, respectively (Caicedo and C. bergi survival and that any damage caused should Bellotti 1994). not be a problem when clones with a high CNP value are cultivated (e.g., in Northeast Brazil and Africa) • A native nematode, Heterorhabditis (Bellotti and Riis 1994; Bellotti 2000a). bacteriophora, found as a field parasite in Colombia, had an average rate of parasitism at Control. Controlling C. bergi is difficult because of 84% on all instars of the pest (Barberena and its polyphagous habits and adaptation to soil Bellotti 1998). environments. Measures must be adopted in the crop’s initial stages, either at planting or in the first 2 months, • Isolates of the fungal entomopathogen when initial damage may occur. The application of a Metarhizium anisopliae parasitizing C. bergi pesticide may reduce pest populations and, thus, the were collected in the field. Laboratory studies damage. However, frequent applications would be verified that the mortality rate is 61% for fifth necessary; these would be expensive, environmentally instars, which is much higher than the overall dangerous, and with no guarantee that the economic average mortality rate at 33% (CIAT 1994). 241 Cassava in the Third Millennium: … Insects that Attack Stems Externally covered with numerous fine threads. After 11 days, they molt and become immobile. After 4 days, the Scale insects adult female begins ovipositing 1 to 2 days later. A generation lasts 22 to 25 days. In most cassava-producing regions, the following species of scale insects have been identified: Scale insects are dispersed by wind, by moving Aonidomytilus albus Cockerell, Saissetia miranda around on the soil, or through infested stakes. The Cockerell et Parrott, Hemiberlesia diffinis (Newstead), environment in which scale insects spread most and Ceroplastes sp. Scale insects stay on stem readily is the area where stakes are stored, when surfaces, mostly close to buds, on which they feed. As infested stakes come into contact with healthy ones. their reproduction rate increases, the more they invade the stems. Control. Two highly effective farming practices control scale insects: planting stakes that are not These insects belong to the order Hemiptera, infested and burning infested plants to prevent suborder Homoptera, superfamily Coccoidea, family dissemination. Biological control agents include the Diaspididae. Aonidomytilus albus is commonly known following: as the white mussel scale, cassava scale, or tapioca scale. Economically, it is considered a major stem- • Chilocorus distigma (Coccinellidae), preys on sucking pest. A. albus. The family Diaspididae, the largest of the • In Cuba, two hymenopterans have been Coccoidea, includes protected scales, which reported (Aphelinidae) as parasitizing themselves include the different scales that attack A. albus: Aspidiophagus citrinus and cassava. The name “scale” comes from the dense waxy Signiphora sp. A brown, sponge-like fungus secretion that the adult secretes, adding to the exuviae (Septobasidium sp.) was also found attacking of the insect’s first two nymphal states. A. albus. Damage. When a stem is invaded by scale insects, • In Colombia, Saissetia miranda was found the leaves become yellow and fall. If the attack is being parasitized by two severe, plant growth is retarded, stems dry up, and the microhymenopterans—Anagyrus sp. and plant dies. Such damage occurs especially when the Scutellista sp.—at a level of more than 79%. attack is early, that is, when the plant is 2 to 3 months old. A generalized attack of scale early in the cropping Gall fly cycle will seriously affect yields. Attacks occur especially during dry seasons. The greatest damage In the Americas, several species of gall fly have been that scale insects cause is, apparently, the loss of reported on the cassava crop, the most frequent of planting materials. Heavily infested stakes produce few which is Jatrophobia brasiliensis Rubs. (Diptera: shoots (i.e., a low rate of germination), with a resultant Cecidomyiidae). This small fly is usually found on the deficient development of unpleasant-eating roots. The underside of leaves, where it lays its eggs. The tiny adult A. albus is shaped like a mussel and is covered larvae leave the egg and penetrate the leaf mesophyll, with a waxy white secretion. provoking a defense reaction that is manifested as an abnormal growth (hypergrowth) of the leaf cells, Life cycle. Swaine (1950) studied the biology of giving its name cassava leaf gall. A. albus in detail. The molted exoskeletons (also called exuviae) of the first and second nymphal states are Leaf galls are found on the upper leaf surface. incorporated into the scale. Unlike the females, males They range in color from yellow to red, depending on have well-developed legs and wings. The female the cassava variety, and are narrower at the base and produces, on average, 47 eggs that are oviposited are often curved. They measure up to 1 cm long and between the upper cover of the scale and the lower 0.5 mm wide. When a gall is opened, a cylindrical cottony secretion. During oviposition, the female drops tunnel, containing a small yellow larva, is found. At in size. Eggs hatch 4 days later. the base of the gall, on the underside, the tunnel is connected to a small hole from which the adult The first nymphal states are mobile and can emerges. disperse. One to four days later they become fixed and 242 Insects and Mites that Attack Cassava, ... The gall fly is believed to have little economic enables other species to degrade stored dried cassava importance and that it usually does not need to be even further, causing losses in weight and quality. controlled. In some regions of Colombia and Venezuela, galls are found almost as clusters on certain Biological cycle. The total duration of the life cycle leaves and, in isolated cases, small plants are heavily is 67.6 days at 25 °C and 56.6 days at 30 ºC. At attacked. To reduce a population of this fly, collecting 20 ºC, the larva does not completely develop. The egg and destroying affected leaves at weekly intervals is incubates for an average 3.4 and 14 days, respectively, recommended. for the same temperatures. The average oviposition period for a group of five females was 60, 95, and Pests of Dried Stored Cassava 104 days at temperatures of 20, 25, and 30 ºC, respectively. The average numbers of fertile eggs at Storage of dried cassava started in Colombia in 1981 temperatures of 20, 25, and 30 ºC were, respectively 70, when a project of natural cassava drying was 217, and 214. The rate of oviposition per female was established in the country’s Atlantic Coastal Region. 0.16, 0.39, and 0.44 eggs per day, at the same Before then, farmers handled a highly perishable respective temperatures (Motta 1994). product that, after 2 days, was no longer adequate for human consumption or animal feed. In contrast, dried Damage. The red weevil feeds on cassava dried cassava provides a more stable product (Román 1983). pieces, turning them into powder and so causing However, storage conditions sometimes permit flour economic losses. It also infests flour, with losses being and dried cassava pieces and chips to deteriorate more moderate than for dried pieces. However, product through the action of biological factors, including contamination is inevitable, degrading product quality. insect attack (Piedrahíta 1986). Pests of stored dried cassava not only reduce their quality but also consume • In flour, an initial infestation of 50 adult insects significant quantities of this product. per kilogram resulted in losses that ranged between 0.212% at 20 days and 0.875% at 90 Damaging species days. Two principal species infest cassava chips: • In dried pieces, an initial infestation of 70 adult Rhyzopertha dominica and Lasioderma serricorne. insects per kilogram resulted in losses that They infest cassava during sun-drying. After 2 months ranged between 0.462% at 30 days and 3.1% at of storage, the total weight of stored pieces may drop 90 days (Motta 1994). by as much as 16% (Motta 1994). Parker and Booth (1979) reported that, in Malaysia, the most abundant Evaluations of the type of packaging used to store insects in a trial on stored dried cassava pieces were dried cassava pieces and cassava flour have given Sitophilus zeamais, Cryptolestes klapperichi, interesting results: for example, polyethylene bags Rhyzopertha dominica, Tribolium castaneum, better preserve the quality of both pieces and flour than Stegobium paniceum, Dinoderus minutus, and cloth bags or sisal sacks. Latheticus oryzae. For the most part, damage occurred to dried cassava imported from Asia or Africa. Control and management. Practices that control dried-cassava pests are the same as those applied to CIAT scientists (CIAT 1983a) reported 38 insect pests of stored grains. In both cases, the pests are the species, mainly Coleoptera, in cassava flakes or other same and storage is usually under the same conditions. dried products. Many were polyphagous. In cassava flour, four species were found: Tribolium castaneum, The most effective measures for sanitary control are Lasioderma serricorne, T. confusum, and Rhyzopertha to clean and disinfect the storerooms before storage, dominica. In cassava pieces, three species were rapid removal of infested material, and as short a found: T. castaneum, Araecerus fasciculatus, and storage as possible, preferably less than 3 months. L. serricorne. Bitter cassava varieties are more resistant than Tribolium castaneum H. sweet varieties to these weevils, although this observation has yet to be confirmed. Fumigation is also At CIAT, scientists studied T. castaneum H, also known effective for controlling these pests, provided that all the as the red cassava weevil, which often causes serious safety standards are met to guarantee success of the damage, both as larvae and as adults. This pest control operation. 243 Cassava in the Third Millennium: … Integrated System of Pest Control Arias B; Bellotti AC. 1977. Eficiencia de Bacillus thuringiensis sobre el gusano cachón de la yuca Cassava is an ideal crop for developing a program of (E. ello), en un programa de control biológico. Rev biological pest control because its vegetative phase Colomb Entomol 3(3/4):93–97. (from 8 to 14 months) is long. The basic principles of such a program include: Arias B; Bellotti AC. 1982. Daño simulado de la mosca del cogollo, Silba pendula Bezzi (Diptera: Loncheidae), • Ready availability of some resistance to pests, en yuca (Manihot esculenta Crantz). In: Abstracts [of although high levels of resistance are not the] Proc IX Congress of SOCOLEN, Cali, Colombia. required. SOCOLEN, Bogotá, DC, Colombia. 9 p. • Inclusion of the insect–plant–environment Arias B; Bellotti AC. 1983. 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International Institute of Tropical Yaninek JS; Saizonou S; Onzo A; Zannou I; Gnanvossou Agriculture (IITA), Ibadan, Nigeria. p 59–66. D. 1996. Seasonal and habitat variability in the fungal pathogens, Neozygites cf. floridana and Hirsutella Yaninek JS; Herren HR. 1988. Introduction and spread thompsonii, associated with cassava mites in Benin, of the cassava greenmite, Mononychellus tanajoa West Africa. Biocontrol Sci Technol 6(1):23–33. (Bondar) (Acari: Tetranychidae), an exotic pest in Africa, and the search for appropriate control methods: a review. Bull Entomol Res 78(1):1–13. 250 CHAPTER 11 Insects and Mites Causing Yield Losses in Cassava* Anthony C. Bellotti1, Bernardo Arias V.2, Octavio Vargas H.3, and Jorge E. Peña4 Introduction • Those that attack fresh roots, damaging their culinary and industrial qualities (subterranean Farmers in the tropics frequently cultivate cassava for burrower bug, mealybugs, and white grubs). subsistence. This crop is regarded as hardy, as it is usually free of arthropod pests. Crop yields have • Those that attack stored dried cassava (weevils exceeded 70 t/ha in experiments at the Centro attacking flour, cassava chips, and cassava Internacional de Agricultura Tropical (CIAT)5, whereas starch). commercial production in regions of Colombia reaches 40 t/ha. World average, however, is 10 to 15 t/ha. At CIAT, studies on yield losses have been These figures indicate that several factors limit conducted for over 25 years to help identify research production, including pests as a significant constraint. priorities in the Cassava Program. This research has helped determine the true potential that key or primary Cassava pests include a broad range of arthropods pests have for causing losses, while at the same time, (Bellotti and Schoonhoven 1978a). According to the evaluate the susceptibility, resistance, or tolerance of crop’s stage of development in which they attack (crop many cultivars to pest attack. This research was phenology), pests can be divided into four categories: developed in different ecosystems, particularly in sites where the targeted pest is endemic, as in the case of • Those that attack planting materials, affecting mites in the Atlantic Coast, whiteflies in the plants in the field and stored stakes (fruit flies, Department of Tolima, and mealybugs in the Eastern stemborers, scale insects, white grubs, and Plains. This research also confirmed that less cutworms). important pests, such as fruit fly and shoot fly, do not cause significant production losses even though they • Those that attack the plant during vegetative may cause noticeable plant damage. development (leaf eaters, sap suckers, leaf deformers, and borers that attack stems, This paper discusses those results and analyzes branches, and buds). the possible physiological causes of such reductions. Although pest damage is emphasized, some results on losses caused by poor quality planting materials are also presented. Pests that defoliate or cause other * This document contains information published in the Proceedings of the XXVII Congress of the Sociedad Colombiana de damage over a short period (hornworm, fruit fly, and Entomología (SOCOLEN), 2000 shoot fly) are compared with long-term pests (mites, 1. Emeritus Scientist/Consultant, Entomologist/Agrobiodiversity, thrips, whiteflies, and scale insects) and those that IPM, Cassava Program, CIAT, Cali, Colombia. E-mail: a.bellotti@cgiar.org directly attack roots. 2. Research Associate, Plant Production, IPM, Cassava Program, CIAT. Distribution of Significant Pests E-mail: bernaarias1@gmail.com 3. Entomologist, FEDEARROZ, Bogotá, DC, Colombia. 4. Entomologist, University of Florida, Homestead, FL, USA. The widest diversity of cassava (Manihot esculenta E-mail: jepe@mail.ifas.ufl.edu Crantz) occurs in the Americas (Bellotti and 5. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, Abbreviations, and Technical Schoonhoven 1977; Bellotti 1978), the crop’s center of Terminology, this volume. origin. The cassava pests most often reported in the 251 Cassava in the Third Millennium: … Americas are hornworm (Erinnyis ello L.); thrips Relationships between Pest Damage and (Frankliniella williamsi Hood and Scirtothrips, Yield Loss manihoti); lace bugs (Vatiga manihotae Drake, V. illudens Drake, and Amblystira machalana Drake); The damage that cassava suffers is usually indirect, as whiteflies (Aleurotrachelus socialis Bondar, Bemisia most arthropod pests feed on leaves or stakes, thus tuberculata, and Trialeurodes variabilis); and fruit fly reducing leaf area, longevity, and rate of (Anastrepha pickeli Costa Lima). None of the photosynthesis. Field studies indicate that pests that aforementioned pests has been reported in Asia or attack the crop for prolonged periods (3 to 6 months), Africa. such as mites, mealybugs, thrips, whiteflies, and lace bugs, can cause severe reductions in root yield because So far, few specific cassava pests have been they feed on the cellular fluids of leaves, thus reducing disseminated to other areas. However, more than photosynthesis (Table 11-1). Many attacks can induce 20 years ago, two important pests, the cassava green premature defoliation and death of apical meristems mite (Mononychellus tanajoa Bondar), and the (Bellotti 2000). mealybug (Phenacoccus manihoti Matile-Ferrero), were accidentally introduced into Africa, where they The potential these pests have for reducing yields caused serious losses in yield (Nyiira 1976; Leuschner is greater than that of cyclic pests such as the cassava and Nwanze 1978). The mealybug is subjected to high hornworm and leafcutting ants, which cause sporadic levels of natural control in the Americas, which is why it defoliation. However, such visible pests usually induce is not reported there as causing high yield reductions. farmers to apply insecticides (Bellotti 2000). The white mussel scale, Aonidomytilus albus The subterranean burrower bug (C. bergi; Cockerell, is found in almost all cassava-growing Hemiptera: Cydnidae) is one of the few pests that regions of the world. It can cause losses in planting directly damage cassava roots. The perforations of the materials, thus reducing stake germination and, hence, stylet into roots during feeding enable pathogenic fungi yields. to penetrate roots, thus reducing their quality (García Table 11-1. Losses in cassava yields caused by major pests. Pest Yield loss References Hornworm In farm fields, natural attacks resulted in losses of 18%. Arias and Bellotti 1984; (Erinnyis ello) Studies, using simulated damage, resulted in losses ranging Bellotti et al. 1992 from 0% to 64%, depending on the number of attacks, plant age, and soil fertility. Mite Yield losses of 21%, 25%, and 53%, with attacks lasting 3, 4, Bellotti et al. [1983b]; (Mononychellus tanajoa) and 6 months, respectively; 73% for susceptible cultivars Byrne et al. 1982; versus 15% for resistant cultivars; and 13% to 80% in Africa. Herren and Neuenschwander 1991 Whitefly 1, 6, and 11 months of attack resulted in 5%, 42%, and 79% Bellotti et al. [1983b], 1999; (Aleurotrachelus socialis) losses, respectively, in field trials in Tolima, Colombia. Vargas and Bellotti 1981 Mealybugs In Colombia, 68% to 88%, depending on the cultivar’s Bellotti et al. 1999; Vargas and (Phenacoccus herreni, P. manihoti) susceptibility. Bellotti 1984; Herren and In Brazil, up to 80% of farms reported. Neuenschwander 1991 In Africa, losses of 80% were reported. Subterranean burrower bug Dark brown to black lesions make roots commercially Arias and Bellotti 1985; (Cyrtomenus bergi) unacceptable. Bellotti et al. 1999 Starch content in roots reduced by more than 50%. Lace bugs (Vatiga manihotae, Field trials with A. machalana and V. manihoti resulted in CIAT 1990 Amblystira machalana) yield losses of 39%. Stemborer In Colombia, root yield losses increase from 45% to 62% Lohr 1983 (Chilomima clarkei) when stem breakage is more than 35%. Thrips In susceptible cultivars (no pubescence on apical buds or Schoonhoven 1974; (Frankliniella williamsi) leaves), yield drops from 17% to 25% or more. Bellotti and Schoonhoven 1978a SOURCE: Bellotti 2000. 252 Insects and Mites Causing Yield Losses in Cassava and Bellotti 1980). Centipede larvae and termites are prefer young apical leaves, dry seasons tend to cause occasionally reported to feed on roots and, although major yield losses in cassava. Once the crop enters in a they damage roots and cause losses, they are usually humid cycle (rain or irrigation), new leaves sprout in minor pests (Bellotti 2000). apical parts, thus increasing the photosynthetic rate. This represents potential for recovery and compensates Biological and Physiological Bases of for yield losses caused by pest attack in the dry season Yield Losses (Bellotti 2000). The physiological bases that explain yield losses in Economically Significant Pests cassava as caused by insects and mites have been explored by Cock (1978). He established that cassava Mites may tolerate pest attack more than other crops, because it has no critical periods during production. Mites constitute a major cassava pest throughout the Once the plant is established, its growth may be world. The economically most important species completely determined in almost any stage of include Mononychellus tanajoa, Tetranychus urticae development without affecting the formation of the Koch, and Oligonychus peruvianus McGregor. Bellotti organs responsible for yield, that is, bulked roots. and Schoonhoven (1977, 1978a) detail the damage they cause, principally during dry periods, when Pests can reduce yields indirectly by (1) consuming environmental conditions favor their development and and thus reducing leaf area and therefore the permit populations to reach high levels. The duration of photosynthetic rate; (2) attacking and thus weakening an attack depends on the length of the dry periods and stems and preventing nutrient transport; and the amount of available food. Continuous feeding by (3) attacking planting materials, thus reducing their mites may lead to defoliation, which then reduces the germination rates. Direct attacks to roots may cause a photosynthetic rate. In experiment plots in Uganda, cosmetic effect (“cassava smallpox”), which may affect losses in yield caused by M. tanajoa were as high as yields and, nevertheless, makes the product 46% (Nyiira 1976; Cock 1978). unacceptable to fresh-root markets and for industrial uses. Cutworms, which attack stakes, produce lesions Four species of mites (M. tanajoa, M. macgregori or holes through which soil pathogens may enter. [Flechtmann & Baker], T. urticae, and O. peruvianus) These insects may also completely destroy the stakes’ were evaluated for their effect on yields. Depending on epidermis or buds. Other insects cut through roots or plant age and duration of attack, yield was reduced by buds of recently germinated stakes. 21% to 53% at CIAT (Table 11-2). A 3-month attack reduces yield by 21%; 4 months, by 25%; and In general, arthropod pests are more damaging to 6 months, by 53%. Damage led to necrosis and cassava crops during dry seasons than during the rains defoliation of the lower leaves, but complete defoliation (Bellotti et al. 1999). The cassava plant is well adapted did not occur. to long dry periods and takes advantage of short rainy seasons by reducing evapotranspiration from leaves by On the Atlantic Coast (Colombia), Byrne (1980) partly closing their stomata. Thus, water-use efficiency found that prolonged damage caused by mites (e.g., increases (Cock et al. 1985; El-Sharkawy et al. 1992). In Mononychellus sp.) to susceptible or resistant varieties plants suffering water stress, both the rapid defoliation has a differential effect on leaf size, rate of leaf of old leaves and the notable loss of photosynthetic formation, plant weight, and root yield. Yield losses activity enable young leaves to play a key role in ranged between 43% and 87%, with an average of 73% acquiring carbon for the plant. Because several pests for susceptible and 16% for resistant varieties. Table 11-2. Effect of populations of the mites Mononychellus spp., Oligonychus peruvianus, and Tetranychus urticae on the yield of cassava variety M Col 22. Artificial infestations of T. urticae were made. Planting Artificial Plant age Duration of Production Mites Yield loss code infestations (months) infestation (t/ha) (no./leaf) (%) (months) Treated Untreated Treated Untreated I 1 6 3 110 425 21.8 17.3 21 II 2 4 and 10 4 77 349 16.4 12.3 25 III 3 2 and 8 6 60 263 27.9 13.1 53 253 Cassava in the Third Millennium: … Production of vegetative “cuttings” (stakes) was reduced present throughout the year, but their attacks are more by 67% for susceptible and 16% for resistant varieties. severe during summer, which exacerbates conditions by intense dryness. Although the main damage caused Thrips by scale attack appears to be the loss of planting materials, studies carried out at CIAT have shown yield Thrips are cassava pests mainly in the Americas. Their reductions when populations are continuously high. For attacks are more frequent during the dry season but an evaluation, a classification system was developed, as plants recover as the rains start. Frankliniella williamsi follows: and Scirtothrips manihoti appear to be the most economically important species. The insects attack the 0 = plants have considerable foliage; scales on plants’ terminal buds. Leaves do not develop normally: stems are absent or scarce the folioles become deformed and present deep clefts 1 = reduced foliage; scales cover less than 50% of from the margins to the leaves’ central nervures. stem surfaces Irregular chlorotic spots appear. Buds may die, thus 2 = severe defoliation with death of terminal buds; destroying the apical dominance and stimulating lateral scales completely cover stem surfaces shooting. These, at their turn, may also be attacked, giving rise to a witches’-broom appearance (Bellotti and One hundred plants, corresponding to each level of Schoonhoven 1977). Thrips attack does not result in damage, were harvested and root weight measured. defoliation, even though the photosynthetic area is Damage was correlated with reduced yields. According greatly reduced. to results, loss of yield was 4% for plants scoring 1, and 19% for those scoring 2, with the latter representing a Corynothrips stenopterus prefers to attack the loss of 3 t/ha. plant’s lower and central parts and therefore does not affect apical dominance. As a result, its importance is Other species such as black scale, Saissetia less significant. miranda; gray scale, Hemiberlesia diffinis; and Ceroplastes sp. do not have economic importance, as At CIAT, thrips attacks reduced yields between 5.6% they appear only in sporadic isolated attacks on old and 28.4%, depending on the variety’s susceptibility plants. Saissetia miranda is subject to natural and (Schoonhoven and Peña 1976, 1978). One effective biological control. consequence of a 3-months’ thrips attack was an average 17.2% reduction of yield for eight varieties. Whitefly Highly susceptible varieties such as ‘Chiroza In the cassava crop, several whitefly species of variable Gallinaza’ can be totally destroyed by thrips in importance are distributed in the Americas, Africa, and ecosystems such as those found at CIAT (Valle del certain parts of Asia. Cauca) and Santander de Quilichao (northern Cauca), where varieties must be continually sprayed with The family Aleyrodidae has 126 genera that include insecticides so they may develop. In ecosystems such 1156 species, of which the most important for the as that found in Quindío, although the variety is cassava crop are Aleurotrachelus socialis, Bemisia attacked by thrips, their effect on yield is not significant tuberculata, and Trialeurodes variabilis in Colombia; (B Arias 1978, pers. comm.). Aleurothrixus aepim (Goeldi), in Brazil; and B. tabaci (Gennadius) in Africa and Asia. Scale insects Bemisia tabaci, so far, has not established well on Several species of scale insects that attack cassava cassava in Colombia. Yet, it is of particular importance, stems and branches have been identified in many as it is the vector of the virus African cassava mosaic regions of the Americas, Asia, and Africa (Bellotti and disease found in India and Africa, where it has caused Schoonhoven 1978a). The most important and yield losses of up to 80%. widespread species is Aonidomytilus albus. Recent studies conducted by scientists of the The leaves on branches become yellow and fall. In National Cassava & Fruits Research Center (CNPMF) severe attacks on young plants, when the stem is with farmers in Bahia, Northeast Brazil, demonstrated invaded, plant stunting occurs, the terminal may die, that high populations of A. aepim can cause losses of and stems may dry, causing plant death. Scales may be more than 40% of root production. 254 Insects and Mites Causing Yield Losses in Cassava In the last 6 years of the 1990s, in Colombia, large with a negative correlation (r = 0.8) occurring between outbreaks of A. socialis has alarmed farmers in duration of attack and number of stakes produced per northern Cauca, southern Valle del Cauca, Tolima, and plant. The effect of duration of attack became significant parts of the Atlantic Coast (Arias 1995). In some after 3 months of plant growth (Table 11-4). regions, the pest occurs throughout the year, obliging farmers to resort to pesticide use for control. Hornworm Damage in susceptible varieties manifests as a Erinnyis ello, in its larval stages, is a voracious consumer mottling or rolling-up of leaves, symptoms very similar of foliage and is usually considered as a highly significant to those of the African mosaic mentioned above. Leaf cassava pest in the Americas. Its ability to cause rapid yellowing and deformation of growing points may also defoliation of crops alarms cassava farmers. occur. Furthermore, fumagina, a black sooty fungus (Capnodium sp.) and a sooty-colored complex of fungi The larval stages (five instars) last about 15 days, and other pathogens, may develop on the insect’s during which time the insect consumes 1107 cm2 of leaf sugary excretions, affecting the photosynthetic rate, In area. However, 75% of this area is consumed during the severe infestations, lower leaves are defoliated. last instar, that is, in the last 3 or 4 days. Vargas and Bellotti (1981) mention that, before A Colombian commercial crop was planted with the 1978, no records existed on yield losses caused by the variety Chiroza, which has a high yield potential. whitefly’s feeding action on the cassava crop. A very severe attack occurred when the plants were 3 months old, with four plots being completely The effect of whitefly attack was evaluated on three defoliated. At harvest, when the crop was 12 months old, cassava varieties (CMC 57, CMC 40—also called the attacked plants were compared with an equal M Col 1468 —and M Mex 59), which were treated with number of those plants that had escaped attack. The monocrotophos every 10 days until harvest. Whitefly average yield of unattacked plants was 4.58 kg/plant, populations appeared throughout the year. The treated while the defoliated plants yielded 3.75 kg each. This plants showed lower densities of whitefly populations, 18% loss was equivalent to 6 t/ha on that farm. both adults and pupae, and a higher yield than did untreated plants (Table 11-3). Reductions in yield were Taking into account that the intensity of attack may 33.6% for M Mex 59, 52.0% for CMC 40, and 76.7% for be severe at any age of the crop, the effect on production CMC 57. These percentages indicate considerable varies with plant age, number of attacks, soil type, and damage to the crop. ecosystem in which the crop is grown. CIAT recently conducted research on crops with 100% defoliation In another trial, whiteflies were permitted to attack across two sites: one in Santander de Quilichao (Cauca) cassava over increasingly prolonged periods until plants that had poor soil and the other in CIAT–Palmira that were 11 months old. Correlation (r = 0.9) between the had fertile soil. Results showed that, in the poor soil, duration of attack and yield reduction was significant, yield losses could be as high as 64% with two continuous Table 11-3. Yield of three cassava varieties reduced by whitefly (Aleurotrachelus sp.) attack in Espinal (Tolima, Colombia), 1978. Average of four replications. Varietya Treated (T)b Untreated (NT) Yield (T-NT) × % per Yield Infestation Yield Infestation loss infestation (kg/plant) In With (kg/plant) In With (%) In With leavesc pupaed leavesc pupaed leavesc pupaed CMC 57 3.31 0.57 0.28 0.77 3.92 3.17 76.7 85.5 91.2 (SE) (0.41) (0.19) (0.12) (0.27) (0.27) (0.23) CMC 40 5.35 0.82 0.21 2.57 4.75 4.87 52.0 82.7 95.7 (SE) (0.60) (0.23) (0.10) (0.43) (0.17) (0.08) M Mex 9 3.63 0.71 0.17 2.41 4.70 4.65 33.6 84.9 96.4 (SE) (0.74) (0.21) (0.07) (0.67) (0.16) (0.10) a. SE = standard error. b. Monocrotophos: 1.5 cc a.i./L water. c. Population: percentage of leaves infested by adults, nymphs, and pupae, where 0 = no infestation; 1 = <20%; 2 = 21% to 40%; 3 = 41% to 60%; 4 = 61% to 80%; 5 = 81% to 100%. d. Pupae per leaf, where 0 = no pupae; 1 = <5; 2 = 6 to 10; 3 = 11 to 25; 4 = 26 to 50; 5 = >51. 255 Cassava in the Third Millennium: … Table 11-4. Relationship between the duration of whitefly (Aleurotrachelus socialis) attack and yield loss in cassava variety CMC 305-122. Duration of attack Insecticide Yield of fresh roots Reduction in yield Starch contents‡ (months) applications (no.)† (t/ha)‡ (%) 0 22 42.1 a 29.6 a 1 20 40.1 ab 4.8 29.5 a 2 18 36.1 abcd 14.3 28.7 a 3 16 37.8 abc 10.2 29.4 a 4 14 30.6 bcde 27.3 30.7 a 5 12 29.8 cde 29.2 28.7 a 6 10 24.5 ef 41.8 27.7 a 7 8 26.7 de 36.6 29.4 a 8 6 16.4 f g 61.0 27.8 a 9 4 14.3 g 66.0 27.9 a 10 2 11.5 g 72.7 28.3 a 11 0 8.6 g 79.6 27.6 a † Dimethoate was applied at 0.8 g a.i./L of water. ‡ The values within the same column followed by the same letter are not significantly different at 95%. attacks, and as high as 46% with one attack on the crop. Fruit fly In the fertile soil, these losses were, respectively, as high as 47% and 25.5% (Arias and Bellotti 1984). Fruit flies Anastrepha pickeli and A. manihoti were originally reported because they attacked the fruit. Severe attacks may also affect the production of Although the flies do not cause economic damage by planting materials: 1- and 2-month-old crops attacked in attacking fruit, in crops that are too young to fruit, they each month may lose as much as 72%, and 1-month-old deposit their eggs on the stems’ tender terminal buds. crops attacked only once may lose as much as 62% The larvae then damage the growing points by (Arias and Bellotti 1984). tunneling into them. A bacterial pathogen (Erwinia carotovora var. carotovora) is frequently found Mealybugs associated with the larvae, entering the tunnels and causing tissue rot. Severe attacks can retard and kill Throughout the tropics, the mealybug constitutes one of terminal buds, thus delaying plant growth and favoring the cassava crop’s worst pests, causing serious damage lateral bud development (Bellotti and Peña 1978). to crops in the Americas and Africa. The principal species attacking cassava in the Americas are However, cassava plants can recover rapidly from Phenacoccus herreni and P. manihoti Matile-Ferrero. In fruit-fly damage, especially when rains are well Africa, only P. manihoti causes economic losses. distributed. For example, plants that were severely attacked at 3 months old were compared with healthy The mealybug attacks both stems and leaves in plants over 6 months. Measurements of plant height cassava. Phenacoccus herreni and P. manihoti prefer showed that, at 5 months old, the attacked plants had buds, deforming and crinkling both leaves and buds, grown little (CIAT 1977), but no significant differences and giving the plant a rosette appearance. In severe in yield were found between attacked and unattacked attacks, these buds are filled with fumagina and finally plants. However, stake quality was significantly different dry up. When attacked early, plants become dwarfed, (CIAT 1980, unpublished data). Treated plots produced severely affecting root production. between 40% and 50% more stakes of good quality than the untreated plots. Cassava varieties M Col 22 and CMC 40, evaluated at CIAT, respectively lost 88.3% and 67.9% of their yields. Shoot fly Plant height was reduced by as much as 33%, thus affecting stake number and quality. Depending on Damage caused by shoot fly has been found in most variety, as much as 74% of planting materials (stakes) cassava-growing regions of the Americas, but has not may be lost (Vargas and Bellotti 1984). been reported in Africa or Asia. 256 Insects and Mites Causing Yield Losses in Cassava Several Lonchaeidae species have been described These larvae are highly mobile and usually locate but Silba pendula Bezzi and Lonchaea chalybea themselves near axillary buds, where they form a Wiedemann are the most important (Bellotti and protective capsule in which they live until the fifth Schoonhoven 1978a, 1978b). The larval stage may last instar. From there they penetrate the stem to complete from 20 to 25 days, depending on the temperature their cycle to adult emergence (Lohr 1983). The larval (Bellotti and Schoonhoven 1978a; Waddil 1978). stages last from 32 to 64 days (Bellotti 2000). Hence, the duration of the attack is relatively short. However, successive attacks may occur, when damage Populations of C. clarkei may be present the year by larval feeding manifests as a white to coffee-colored round, but are higher during the rainy season. As the discharge that flows from the terminal buds, which pest, and therefore the damage, increases, control finally die. Plant growth is therefore delayed and apical becomes more difficult. When larvae make a sufficient dominance is broken, inducing the germination of number of perforations (i.e., >20 per stem) in the lateral buds, which may then be attacked. Studies stems, these break, reducing the quality and quantity conducted in Costa Rica (Saunders 1978), Florida, USA of planting materials. Field studies indicate that fields (Waddil 1978), and at CIAT (1975) have demonstrated with more than 35% of broken stems suffer significant that such attacks do not cause yield loss. reductions (45% to 62%) in root yield (Lohr 1983). In the Colombian Caribbean Region, 85% of planted Arias and Bellotti (1982) simulated damage in cassava is attacked by C. clarkei (Vides et al. 1996). 100% of buds, with continuous damage from 1 to 5 months in clone M Col 22, and at different crop ages. The mobility of the first-instar larvae makes them Results were similar to those observed in Costa Rica. vulnerable. They can be controlled by using Bacillus No critical period exists for pest attack from the thuringiensis. Given its rapid generational increase, viewpoint of yield. However, attacks during the crop’s several applications will be needed, thus, increasing first and second months diminished planting-material production costs. Field research (Gold et al. 1990) quality by 51% to 71%. indicates that crop rotation with maize reduces stemborer populations until the maize is harvested Stemborers (Bellotti 2000). A complex of stem-boring arthropods includes species Termites of Coleoptera and Lepidoptera that feed on the interiors of cassava stems, causing damage (Bellotti In Colombia, Heterotermes tenuis Hagen has been 2000). identified as the most important termite species determined by attacking cassava. In the 1980s, CIAT Lagocheirus araneiformis. The longhorn beetle is evaluated the importance of this pest in the Atlantic found throughout the world. Its attack does not Coast and found that it can cause losses of 46% to severely damage crops in the field. These stemborers 100% of unprotected planting materials in storage. In are most important in the Neotropics, especially in the field, production may decline by 40%. These Colombia, Venezuela, and Brazil. Seven species of the studies also showed that no direct relationship exists Coelosternus genus (Coleoptera: Curculionidae) have between the percentage of plants attacked at the neck been reported as reducing cassava yields and the of the root (stump) and the percentage of damaged quality of planting materials in Brazil. However, such roots. Over 30 treatments, the percentage of attacked damage tends to be sporadic and does not imply plants was high (64% to 95%) at harvest. However, the significant reductions in yield (Bellotti 2000). percentage of damaged roots was low at 0% to 1.7% (Arias et al. 1979). When introduced cultivars were Chilomima clarkei. Populations of this stemborer evaluated, the average level of damage in roots (Lepidoptera: Pyralidae) have recently been increasing increased between 16.5% (ecosystem trial) and 25.5% dramatically in Colombia and Venezuela, currently (pest complex trial). constituting an important cassava pest (Vides et al. 1996). Females oviposit more than 200 eggs on stems Termites penetrate roots through wounds or during the night, usually near an internode or bud. The through cracks caused by climatic effects on the soil. egg stage lasts about 6 days at 28 °C. After hatching, The insects form galleries in the root parenchyma, the first instars feed on the stem’s cortex or epidermis. which then fill with sand. 257 Cassava in the Third Millennium: … Subterranean burrower bug The experiments presented in this chapter show that some arthropod pests reduce yields (e.g., whitefly, This cydnid is another root pest, although it does not Table 11-4). The magnitude of reductions is influenced directly affect root yields, but attacks the roots’ culinary by environmental conditions, soil fertility, plant age, and commercial qualities. The bug feeds on the root, type of damage, and duration of attack. using its stylet (beak) to penetrate the cassava peel to reach the parenchyma. When the affected roots are Pests that attack the plant’s aerial parts over peeled, a series of small colored spots can be seen on prolonged periods reduce yield more than those that the surface. The spots range from light to dark brown defoliate or cause damage over short periods or almost black, giving this type of damage the (Table 11-6). Cock (1978), using field data and Spanish name, meaning “cassava smallpox”. These computer simulations, suggests that “relatively minor perforations correspond to fungal pathogens of the losses in yield result from a small reduction in leaf soil, which penetrate through the wounds. Roots in area”. However, when yield is severely reduced, causes such conditions are rejected by traders and consumers relate to reductions in leaf longevity and the alike, obliging farmers to keep back production and photosynthetic rate. suffer the consequent economic losses. These roots are usually fed to farm animals. Trials at CIAT have The results of the experiments presented tend to shown that starch production may be affected by as support the following conclusions: much as 50%, can effect-lower starch content depending on the magnitude of the attack. • Attacks by pests such as fruit fly and shoot fly, which destroy the plant’s apical parts but have Other pests little or no effects on the photosynthetic rate, do not result in losses of yield (Table 11-5). Although many other pests attack cassava, little or no data are available on their effects on yields (Table 11-5). • The damage done by the hornworm through Many insects attack planting materials, causing losses consumption of foliage reduces leaf area but, in germination, thus reducing yields if as many as 30% as the attack occurs over a brief period, the of plants are destroyed. Such pests include white grubs plant produces new foliage (Figure 11-1). (Phyllophaga sp. and Leucopholis rorida [Fabricius]); and cutworms (Prodenia spp., Agrotis ipsilon, • In a field study, when the photosynthetic rate Spodoptera frugiperda (J.E. Smith), and Lagocheirus was artificially interrupted for 1 to 2 weeks over araneiformis). Pests attacking foliage include ants, lace the plant’s entire vegetative cycle, yield was bugs (Vatiga manihotae and V. illudens), and reduced by 18% after the experiment. This loss leafhoppers. was predicted (20%) by a simulated model in computer for this type of damage (Cock 1978). Discussion • Thrips reduce leaf area over about 3 months, Cassava is a crop with a growing period that may take with yield dropping by 17%. 8 to 24 months to complete, according to variety and environmental conditions. It can suffer a high level of • Scale insects cause considerable injury to the economic damage. Under certain conditions, even principal stem and branches because of their vigorous varieties may lose more than 40% of their continual feeding. At CIAT, yield loss was 19%, foliage but, in certain periods, the plant may tolerate supporting Cock’s (1978) conclusions that higher levels of defoliation without suffering significant severe damage to stems will reduce yield. reductions in yield. These two factors are important in the relationship between damage by pests and yield • Reduced photosynthetic rate throughout the reductions in cassava. The long growing period implies vegetative cycle appears to have the most that plants are subject to continuous attack from pests negative effect on yield (Table 11-1). that cause different types of damage. The most severe attacks usually occur in summer, when damage by • Mites and whiteflies attack foliage over long pests is combined with intense dryness. Although periods, in which the photosynthetic rate some pests do attack the crop during the rainy season, declines (Figure 11-2). If the duration of the the plant usually recovers in this period and grows attack increases, the yield decreases. vigorously. 258 Insects and Mites Causing Yield Losses in Cassava 259 Table 11-5. Occasional and sporadic pests or less important pests of the cassava crop. Common Important Region Type of damage Yield losses Control References name species and/or symptoms reported strategy Scale insects Aonidomytilus albus, Almost all cassava- Stems and leaves are attacked; <20% of fresh root yield; Destroy infested Bellotti and Saissetia miranda growing regions in the Leaf yellowing and defoliation; 50% to 60% loss of stakes branches; Schoonhoven 1978a; Americas, Africa, and Plants may wilt and die; Use only healthy Frison and Feliu 1991 Asia Attacked stakes have reduced stakes with no scales; germination Treat stakes with malathion Fruit flies Anastrepha pickeli, The Americas, Costa Rica, Fruits, seeds, and apical stems A. manihoti Panama, Venezuela, tunneled; Colombia, Brazil, and Fruits destroyed and stake 0% to 30% when infested Damaged stakes Bellotti and Peru quality reduced but, normally, stems are used as planting should not be used Schoonhoven 1978a, not much economic damage is materials 1978b; caused Lozano et al. 1981; Peña and Waddill 1982 Shoot flies Neosilba perezi, Throughout most of the Larvae kill the apical buds, Losses not reported for Not required Bellotti and Silba pendula Americas delay plant growth, and induce yield; Schoonhoven 1978a, sprouting Reduced stake quality 1978b; Lozano et al. 1981; Arias and Bellotti 1982 Gall fly Jatrophobia All the Americas Greenish-yellow to red galls None reported Not required Bellotti and (Eudiplosis) formed on upper leaf surface Schoonhoven 1978a, brasiliensis 1978b; Lozano et al. 1981; Samways 1980 White grubs Phyllophaga spp., The Americas, Asia, and Feeding on stakes and roots; Up to 95% of losses in Apply pesticides to Bellotti and Leucopholis rorida, Africa Possible seedling death germination soil at planting Schoonhoven 1978a, Others 1978b; Peña and Waddill 1982 Termites Coptotermes voltkevi, All regions Feeding on stakes, roots, 46% to 100% of stakes lost; Treat stakes with Bellotti and C. paradoxis, seedlings, and stems; Up to 25.6% of roots lost in pesticides; Schoonhoven 1978a, Heterotermes tenuis Wilting and/or plant death clones introduced to the Keep fields clean 1978b; Atlantic Coast CIAT 1984; Arias et al. 1979; Lal and Pillai 1981; Lozano et al. 1981 (Continued) Cassava in the Third Millennium: … 260 Table 11-5. (Continued.) Common Important Region Type of damage Yield losses Control References name species and/or symptoms reported strategy Stemborers Lagocheirus sp. All regions Tunneling in stems, leading to None reported Select healthy stakes Villegas and Bellotti breakage 1985 Coelosternus spp. The Americas, especially Tunneling in stems and None reported Select healthy stakes; Bellotti and Brazil branches, leading to breakages Keep fields clean; Schoonhoven 1978a, Destroy infested 1978b; stems Samways 1980 Leafcutting Atta spp., The Americas Defoliation Losses not reported Fumigate nests; Bellotti and ants Acromyrmex spp. Introduce poisoned Schoonhoven 1978a, baits 1978b; Samways 1980 Leafhoppers Zonocerus elegans, Mainly Africa, occasionally Defoliation, stem damage, and Losses not reported Use of Bellotti and Riis 1994; Z. variegatus the Americas branches cut entomopathogens is Bellotti and being evaluated Schoonhoven 1978a, 1978b; Lomer et al. 1990; Modder 1994 Cutworms Agrotis ipsilon, Mainly the Americas Feeding at the stem base, buds, Loss in germination of Introduce poisoned Bellotti and Prodenia eridania, and cortex of stakes and roots stakes; baits at planting Schoonhoven 1978a, Spodoptera Seedling death 1978b frugiperda SOURCE: Bellotti 2000. Insects and Mites Causing Yield Losses in Cassava Table 11-6. Yield losses to insects and mites, according to the duration of attack on the cassava crop. Pest or simulation Type of attack Duration Reduction in yield (%) Shoot fly Shoot destruction 21 days 0 Fruit fly Tunneling in branches 11 days 0 to 5 Simulation of hornworm attack Complete defoliation (for leaf consumption by the pest) 15 days 0 to 64 Thrips Leaf deformation 3 months 17 Scale insects Sap suckers on stems 3 to 4 months 19 Mites Sap suckers on leaves 3 months 21 (reduced photosynthesis) 4 months 25 6 months 53 Whitefly Sap suckers (reduced photosynthesis) 10 months 76 25 1.2 1.0 20 0.8 15 0.6 10 0.4 0.2 5 0 0 500 750 1000 1500 0 Light intensity (W/m2 per s) 10 15 20 21 22 23 24 25 26 27 28 29 30 35 40 45 12th leaf (infested) 12th leaf (clean) 4th leaf (infested) 4th leaf (clean) 4.0 Figure 11-2. Effect of high mite infestation on the photosynthetic 3.5 rate in cassava variety M Col 72 (measured in 2 leaves) (from Cock 1978). 3.0 2.5 Cock (unpublished data) suggests that computer simulations indicate that a 10% reduction in 2.0 photosynthesis over the vegetative cycle of an ideal plant type will result in a 20% smaller root production. The 1.5 plant seems to recover better from rapid defoliation or 1.0 the death of its buds than from continuous reduction of the photosynthetic rate over a long period. In this case, 0.5 pests such as the lace bug and mealybug could cause considerable yield loss (Table 11-1). However, mealybugs 0 are known to cause as much as 88% of losses in 5 10 15 20 25 30 35 40 45 50 susceptible varieties (Vargas and Bellotti 1984). Weeks after planting No attack Attacked Conclusions Figure 11-1. Effect of hornworm attack on yield and leaf area index (LAI) of a 20-week-old cassava crop Sufficient information from the field is available to (computer-simulated data) (from Cock 1978). demonstrate that insect and mite attacks can drastically 261 LAI Yield (t/ha) Rate (mg CO2 /dm 2 per h) Cassava in the Third Millennium: … reduce cassava yield. Several factors seem to influence Bellotti AC. 1978. An overview of cassava entomology. In: the pest-crop relation, among them environmental Brekelbaum T; Bellotti AC; Lozano JC. eds. Cassava conditions and soil fertility. Frequently, adequate rains protection workshop, held in Cali, Colombia, 1977. will permit the plant to recover from the damage with CIAT, Cali, Colombia. p 29–39. minimal reductions in yield. Bellotti AC. 2000. Las plagas principales del cultivo The type of damage and duration of pest attack will de la yuca: Un panorama global. In: Symposium also determine the level of reduction in yield. 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Cassava production and vegetative and the stemborer, Chilomima clarkei (Amsel) growth related to control duration of shoot flies and (Lepidoptera: Pyralidae), in Colombia. Trop Pest fruit flies. In: Brekelbaum T; Bellotti AC; Lozano Manage 36(4):362–367. JC, eds. Cassava protection workshop, held in Cali, Colombia, 1977. CIAT, Cali, Colombia. p 215–219. 263 Cassava in the Third Millennium: … Schoonhoven A van. 1974. Resistance to thrips damage in Vides OL; Sierra OD; Gómez HS; Palomino AT. 1996. El cassava. J Econ Entomol 67:728–730. barrenador del tallo de la yuca Chilomima clarkei (Lepidoptera: Pyralidae) en el CRECED, Provincia Schoonhoven A van; Peña JE. 1976. Estimation of yield del Río. Boletín. Corporación Colombiana de losses in cassava following attack from thrips. J Econ Investigación Agropecuaria (CORPOICA), Bogotá DC, Entomol 69(4):514–516. Colombia. 12 p. Schoonhoven A van; Peña JE. 1978. Thrips on cassava; Villegas GA; Bellotti AC. 1985. Biología, morfología economic importance, sources and mechanisms of y hábitos de Lagocheirus araneiformis Linne resistance. In: Brekelbaum T; Bellotti AC; Lozano (Coleoptera: Cerambycidae) barrenador de la yuca, en JC, eds. Cassava protection workshop, held in Cali, Palmira, Valle del Cauca. Acta Agron 35(4):56–67. Colombia, 1977. CIAT, Cali, Colombia. p 209–214. Waddill VH. 1978. Biology and economic importance of Vargas O; Bellotti AC. 1981. Pérdidas en rendimiento cassava shoot fly, Neosilba perezi Romero y Ruppel. causadas por moscas blancas en el cultivo de la yuca. In: Brekelbaum T; Bellotti AC; Lozano JC, eds. Rev Colomb Entomol 7(1/2):13–20. Cassava protection workshop, held in Cali, Colombia, 1977. CIAT, Cali, Colombia. p 209–214. Vargas O; Bellotti AC. 1984. Pérdidas en rendimiento causadas por Phenacoccus herreni Cox et Williams en dos clones de yuca. Rev Colomb Entomol 10:41–46. 264 CHAPTER 12 Cassava Pest Management* Anthony C. Bellotti1, Bernardo Arias V.2, and Jesús A. Reyes Q.3 Introduction Currently, accurate information exists on the pests that most reduce yields, the times and key stages of The management of cassava pests should be based on the crop when plants are more susceptible to pest biological control, host-plant resistance, and use of attack, and the precautions or suitable management cultural practices. These components of integrated actions to be taken. Some pests are known not to control have played an important role in programs for affect production, even though symptoms appear managing cassava pests during the last 35 years. Thus, severe enough to induce the application of what are, in this management model should continue to be fact, unnecessary control measures. implemented to prevent environmental degradation and possible food contamination in the future. In controlling this crop’s pests, costly inputs, especially pesticides, should be kept at a minimum. One practical objective of entomologists is to One way of achieving this objective is to increase basic maintain populations of insect pests at levels below knowledge on the biology and ecology of many of economic importance. Stated like this, the objective is these pests and their natural enemies. Advantage must clear and easy to understand but, in practice, it also be taken of the favorable factors involved in the becomes lost because its true sense is unknown. insect–plant–environment interaction, so that developing a system for cassava pest management is When speaking of maintaining destructive insects both attractive and practical. Some of these factors at low levels of economic importance, it should be are: understood that the presence and damage caused by an insect pest does not always mean reduced 1. The cassava cropping cycle is 8 to 24 months production. Almost all crops can support a certain level long. Hence, continuous use of pesticides is of damage and still recover. Hence, the mere presence costly and uneconomical with regard to of a harmful insect does not necessarily mean that profitability. insecticides must be applied. 2. Because it is a long-cycle crop, cassava is ideal The cassava plant’s ability to recover from pest for biological control programs, especially in damage is a significant quality that should always be areas where it is continuously cultivated and taken into account before resorting to the application over large extensions. Many biological control of control inputs, unless yield loss has been estimated. agents of many major pests have already been identified and studied in-depth. * This document contains information published in the Proceedings of the XXVII Congress of the Sociedad Colombiana 3. The cassava plant often recovers from the de Entomología (SOCOLEN), 2000. damage caused by insects. During seasons 1. Emeritus Scientist/Consultant, Entomologist/Agrobiodiversity, IPM, Cassava Program, CIAT, Cali, Colombia. with adequate rainfall, high levels of defoliation E-mail: a.bellotti@cgiar.org will cause little or no yield reduction. 2. Research Associate, Plant Production, IPM, Cassava Program, CIAT. E-mail: bernaarias1@gmail.com 3. Entomologist, Asociación Colombiana de Ciencias Biológicas. 4. Many pests do not disseminate widely and their Palmira, Colombia. E-mail: jesus_antonior@hotmail.com incidence is often seasonal, with dry seasons 265 Cassava in the Third Millennium: … favoring their population increase. However, the agricultural use, its lethal effect on insects was of such plant’s ability to resist long dry periods usually a magnitude that many entomologists began collecting enables it to recover when the rains start. insect species to conserve them, as the belief was that the DDT would exterminate them. However, insects 5. Cassava has a high threshold for economic have survived much more difficult situations, and damage by pests. Vigorous varieties may lose responded by developing resistance not only to DDT 40%, or even more, of their foliage without yield but also to most insecticides. being significantly affected. Newly developed varieties may possess mechanisms other than To date, 321 insect species resistant to several defoliation, resulting in higher tolerance, groups of insecticides have been recorded, meaning because of the selection methods used for both that the chemicals are no longer effective for reducing vigor and resistance to biotic and abiotic their populations. Hence, humans must seek other, factors. more rational and economic alternatives that do not continue to increase insect resistance to insecticides or 6. Very few pests can actually kill the plant. Hence, contaminate the environment at critical levels for the plant recovers from damage and can humanity. produce edible roots. Many entomologists and scientists, past and 7. The selection of healthy and vigorous planting current, have dedicated their lives to study beneficial materials, together with treatment with low-cost insects and promote their use in pest control fungicides and insecticides, permits fast and programs. These researchers are convinced that the successful germination. The plant’s initial vigor use of insecticides only would augment biological is thus ensured during this important early imbalance, which would have catastrophic phase and yield is ultimately increased. consequences for humanity. These studies are found in specialized books and bulletins that detail the methods 8. Cassava has been shown to possess adequate and recommendations for programs of integrated pest sources of resistance—at low, medium, and management (IPM). Today, the situation has changed. high levels—to prevent serious crop losses to It falls to entomologists, technical personnel, and certain pests. people generally to practice these principles and use these experiences. Not only would production problems 9. Cassava is often cultivated on small farms, be solved, but environmental contamination would also under mixed cropping conditions. This system be minimized. not only reduces pest incidence, but also prevents outbreaks in large crop extensions. The cassava crop may serve as a model for understanding some basic principles of integrated 10. Insects can reduce yields during specific control, particularly biological control by means of periods of plant development. For many beneficial insects. cassava pests, these periods have already been identified, permitting the intensification of Although pest outbreaks sometimes occur, the control during these times. cassava crop does not permanently suffer severe attacks from insects. On the contrary, it maintains an Insect Pests excellent biological equilibrium. Mortality factors also function to maintain pest populations at levels of low Insects have existed for more than 300 million years economic importance. and have survived and evolved, despite all the drastic changes derived from the Earth’s evolution. This favorable situation should be conserved. The example of the cotton crop in Colombia illustrates this Insects possess high reproductive capacity. A point: during 1977, pest control had arrived at a queen termite may oviposit 30,000 eggs daily. When “situation of catastrophe”. Heliothis larvae, the cotton dichlorodiphenyltrichloroethane (DDT)4 appeared for crop’s principal pest, had attained such a high degree of resistance to insecticides that its control was impossible. Yet, when the cotton crop was established 4. For an explanation of this and other abbreviations and acronyms, see Appendix 1: Acronyms, Abbreviations, and Technical in Colombia, more than 35 years ago, the pests that Terminology, this volume. attacked it were few and their control was relatively esay. 266 Cassava Pest Management This situation is similar to that presented by the of all available techniques, not only of biological control cassava crop 20 years ago. Thus, if cassava pests are and insecticides. These, however, form two of its basic not handled rationally and if insecticides continue to be components. indiscriminately applied, then, in the not very distant future, the same situation of despair affecting cotton Other techniques available are the use of plants growers will also develop for cassava growers. that resist or tolerate insect attack, mechanical and physical methods that attract or repel, and compliance Cassava pests have been studied in terms of their with quarantine standards. Although the available relationships with biotic and abiotic factors, crop techniques are many, their successful application is management techniques, and production of varieties more important. They must be understood and used adapted to different ecosystems. Yet, increased correctly by technical personnel and farmers. awareness of the problem is still needed if the type of management that prevents epizootics happening on a Biological control regional or national scale is to be adopted. Biological control may be defined as managing pests One epizootic—an outbreak of the cassava through the deliberate and systematic use of their stemborer (Chilomima clarkei)—occurred in the natural enemies. Parasites, predators, and pathogens Atlantic Coast of Colombia in the 1990s. Quarantine can help maintain population densities of pests at lower standards had not been observed. That is, stakes were levels than would have occurred in their absence. This exchanged from one area to another, harvest residues form of control has several advantages: were not destroyed, storage conditions for planting materials (stakes) were poor, stakes of poor quality and • It is relatively permanent infested with the pest were used, and pesticides were • It is economic inappropriately used. As a result, the pest became a • It helps maintain environmental quality social problem: the scarcity of asexual seed led many • Food is less like to be contaminated by farmers—mostly resource-poor families who depended pesticides on cassava for sustenance—into precarious situations. The idea that an insect population may be reduced A similar situation has occurred with the cassava by other insects is ancient. For example, the use of whitefly (Aleurotrachelus socialis) in northern Cauca, predator ants to control certain citrus pests probably southern Valle del Cauca, Tolima, and some areas of originated in China. This system is currently being the Atlantic Coast and Eastern Plains. This pest has followed in some areas of Asia. Insect parasitism was become endemic. Its populations have increased recorded for the first time by Vallisnieri (1661–1730) in dramatically, to the point of causing severe damage to Italy. He noted, in particular, the association between the crop over prolonged periods and thus significantly the parasitic wasp Apanteles glomeratus and the affecting root production. In response, farmers cabbage worm Pieris rapae. indiscriminately applied insecticides, exacerbating the problem. The pest is now appearing at times and in Parasites for biological control in agricultural crops areas where it had not previously been seen. were first used in Europe, mostly in France, Germany, and Italy, during the 19th century. However, the science Currently, CIAT is searching for varietal resistance of biological control was developed in USA during the and biological control to manage these pests. Future 19th and 20th centuries. results will respond positively to these problems (Bellotti et al. 1999). The project to control cottony cushion scale (Icerya purchasi) attacking citrus crops in California, Integrated Pest Management USA, was the first successful example of biological control. The scale was accidentally introduced into Integrated management appears to be the most Australia and, in 1888, entomologists brought in two of rational way of tackling insect pests. It consists of its natural enemies, one of which was the vedalia beetle combining and integrating all available techniques and (Rodolia cardinalis), a coccinellid predator. Scale applying them harmoniously to maintain insect pests at populations declined rapidly. The technique for levels where their economic damage to crops is not mass-rearing parasites and predators and releasing significant. Integrated management therefore consists them periodically for pest control was developed in 267 Cassava in the Third Millennium: … California in 1919 during a project on the coccinellid • Using predator mites of the Phytoseiidae family Cryptolaemus montrouzieri, a predator of the to control the cassava green mite mealybug. (Mononychellus spp.) in Africa and Brazil. Since then, more than 96 biological control Managing a Specific Pest: the Cassava projects have been evaluated and considered Hornworm substantially successful. Another 66 or so, conducted in many parts of the world, have been evaluated as Research conducted at CIAT on the hornworm Erinnyis partially successful (DeBach 1964). ello may be used to develop an IPM program for this insect, using the different techniques offered. Describing pest management The hornworm is attacked by several parasitic and Pest management can therefore be described as “a set predator insects, bacteria, fungi, and viruses. They can of actions that results from understanding that, instead make control of E. ello feasible, without having to of eliminating insect pests, we should learn to live with resort to insecticides that are likely to upset the balance them and to intelligently manage resources, not only that should exist between the hornworm and its natural economically but also ecologically”. enemies (Table 12-1). If insecticides are not applied, then, not only are entomophagous agents conserved, Pest management is more inclusive than integrated but the reduced number of applications will also help control (defined on page 265, this chapter) because, in prevent the appearance of other pests, especially mites, addition to the factors implicated by integrated control, that are more difficult to manage. several fundamental biological and ecological principles are also involved. Pest management recognizes that an Natural enemies of E. ello eggs insect can become a pest because of human activities such as taking pests to previously uninfested regions Parasitism of E. ello eggs by Trichogramma spp. and through the introduction of exotic plants and animals, Telenomus sp. helps reduce hornworm populations. producing varieties or races of organisms, simplifying ecosystems, or misusing pesticides. Such actions are Trichogramma is a parasite of considerable usually a result of agricultural or industrial activities. importance, as it is present throughout the year in cassava fields and has a parasitism rate of more than Controlling cassava pests 50%. Furthermore, it is easy to mass-rear in the laboratory. For release, 50 to 100 square inches per During the last 2 decades, collaborative studies of the hectare should be used over 2 or 3 work days per week, cassava crop and the control of several of its major as the parasitoids emerge. This amounts to releasing pests were carried out by institutions such as the between 150,000 and 300,000 adults per hectare. Centro Internacional de Agricultura Tropical (CIAT), the During the growing period, 5 to 10 releases International Institute of Tropical Agriculture (IITA), and (established by previous evaluations) are carried out, the Brazilian Agricultural Research Corporation costing about US$25/ha. (EMBRAPA). They successfully used biological control, involving both insects and entomopathogens. The moment at which Trichogramma adults are Examples of achievements include: released must be determined by periodically evaluating cassava plots to detect the timing of the largest • Mass release of the microhymenopterous populations of E. ello eggs. parasitoid Anagyrus lopezi to control Phenacoccus manihoti in Africa. No pattern exists to serve as a basis for determining the number of E. ello eggs with the timing • Controlling the cassava hornworm in Colombia, for release of Trichogramma spp. However, the Brazil, and Venezuela by applying a baculovirus experience of technical personnel and farmers indicates that attacks Erinnyis ello. This virus was found that if the parasite is released when the hornworm first in hornworm colonies at CIAT in 1973. It was appears, then the parasite can establish in time to applied to commercial crops in Brazil in the control the E. ello populations that may suddenly 1980s and in Venezuela in the 1990s. appear. 268 Cassava Pest Management Table 12-1. Parasites, predators, and pathogens of various stages of the life cycle of the cassava hornworm (Erinnyis ello). Agent attacking Habit Order Family Eggs Trichogramma minutum Parasite Hymenoptera Trichogrammatidae T. fasciatum Parasite Hymenoptera Trichogrammatidae T. australicum Parasite Hymenoptera Trichogrammatidae T. semifumatum Parasite Hymenoptera Trichogrammatidae Telenomus dilophonotae Parasite Hymenoptera Scelionidae T. sphingis Parasite Hymenoptera Scelionidae Chrysopa sp. Predator Neuroptera Chrysopidae Dolichoderus sp. Predator Hymenoptera Formicidae Larvae Apanteles congregatus Parasite Hymenoptera Branconidae A. americanus Parasite Hymenoptera Branconidae Euplectrus sp. Parasite Hymenoptera Eulophidae Cryptophion sp. Parasite Hymenoptera Ichneumonidae Microgaster flaviventris Parasite Hymenoptera Ichneumonidae Sarcodexia innota Parasite Diptera Sarcophagidae Chetogena (Euphorocera) scutellaris Parasite Diptera Tachinidae Thysanomyia sp. Parasite Diptera Tachinidae Belvosia sp. Parasite Diptera Tachinidae Drino macarensis Parasite Diptera Tachinidae Polistes erythrocephalus Predator Hymenoptera Vespidae P. versicolor Predator Hymenoptera Vespidae P. carnifex Predator Hymenoptera Vespidae P. canadensis Predator Hymenoptera Vespidae Polybia sericea Predator Hymenoptera Vespidae Podisus sp. Predator Hemiptera Pentatomidae Zelus sp. Predator Hemiptera Reduviidae Alcaeorrhynchus grandis Predator Hemiptera Pentatomidae Bacillus thuringiensis Pathogen Eubacteriales Bacillaceae Baculovirus erinnyis Pathogen GV Baculoviridae Prepupae and pupae Calosoma sp. Predator Coleoptera Carabidae Pupae Cordyceps sp. Pathogen Sphaeriales Hypocreaceae Trichogramma spp. should be released when Telenomus sphingis parasitizes the eggs of E. ello hornworm eggs are newly laid and are green or yellow. and E. alope and has a significant role in regulating E. ello eggs should not be left to develop much before their populations. The biological cycle of T. sphingis, releasing the parasites, because once the larvae’s from egg to adult, lasts 11 to 14 days. A female lays as cephalic capsule has started forming, the many as 228 eggs, which give rise to an average of 99 Trichogramma spp. will not parasitize them. adults. CIAT research demonstrates that Trichogramma Natural enemies of E. ello larvae austrilicum shows highly active parasitism on E. ello egg clutches (CIAT 1977). Five species of predators, several of parasitoids, and one pathogenic virus attack the larvae of this pest: 269 Cassava in the Third Millennium: … Predators. Two wasps and a bug are the most Trichogramma spp. are less effective in the used: Atlantic Coast than in the hinterland (Gallego, 1950; B Arias 1990, unpublished data). • Polistes erythrocephalus, P. canadensis, and P. carnifex. The adults’ capacity for predation The parasite can be mass-reared for use in depends on the number of their own larvae that biological control programs. they have in their nests. At CIAT, each Polistes larva was assessed as consuming 0.47 of an • Drino sp., Belvosia sp., and Chetogena E. ello larva per day (CIAT 1977; Martín 1985). (Euphorocera) scutellaris are dipterans (flies) that parasitize E. ello larvae. Chetogena • Cassava fields may be colonized with Polistes scutellaris is particularly important, as it can be nests placed in stands or huts. To establish mass-reared in the laboratory and possesses a their colonies, adults prefer cool shaded places rapid biological cycle. that are close to water. Hence, building bamboo and palm leaves are used to construct the Other biocontrol agents stands. A hut every 4 ha and 20 nests per hut are recommended. The nests should contain Hornworm larvae are also attacked by the granulosis more than 50 cells to ensure that the numbers virus Baculovirus erinnyis (EeGV) and by the of females and males are sufficient to favor the bacterium Bacillus thuringiensis. The latter is available establishment of new colonies. commercially (thus facilitating its use) under the trade names DiPel®, Thuricide, Bactospeine, and Biotrol. • Podisus spp. (Hemiptera: Pentatomidae). The most common species are P. obscurus (Dallas) Bacillus thuringiensis. Trials conducted at CIAT and P. nigrispinus. Their importance lies in the showed that this bacterium is effective against all larval ease of mass-rearing them and their capacity stages (particularly the first and second instars). It is for predation. Throughout its life, a P. obscurus applied in doses of 3 to 4 g of commercial product per bug can consume between 339 and 1023, with liter of water for soil applications, and of 800 to an average of 720, first- and second-instar 1000 g/L for aerial applications. This product has the larvae. The biological cycle lasts from 65 to advantage of not affecting natural enemies of E. ello or 119 days, averaging 97 days (Arias and Bellotti, other insects (Arias and Bellotti 1977). 1989b). Baculovirus erinnyis (EeGV). This virus is both Parasitoids. Several species have been used with highly specific and virulent for the pest. Egg parasites good results: such as Trichogramma sp. are more abundant in areas where B. erinnyis is used. These two beneficial agents • Apanteles = Cotesia americanus and are the most efficient controllers of E. ello (Arias et al. C. congregatus. These braconids attack the 1989a; Torrecilla et al. 1992). larvae, ovipositing their eggs within the hornworms’ bodies. The eggs hatch and the The baculovirus can be obtained from infected tiny larvae develop inside the host hornworms insects found in the field, or a base solution, until they pupate in the host’s epidermis, maintained in the freezer, can be used. The latter is forming a white cottony mass or cocoon. prepared from E. ello, that is, larvae that have died from the disease (Arias and Bellotti 1987; Torrecilla et • The releases of Apanteles carried out at CIAT al. 1992). resulted in increased parasitism of hornworm larvae by more than 50% (CIAT 1977). On a The baculovirus begins to act on hornworm larvae field scale, the environment influences the when these ingest contaminated leaves. After 4 days, effectiveness of the parasitoids. For example, in the sick larvae start to lose their capacity for the Atlantic Coast of Colombia, in samplings locomotion and feeding, their bodies becoming white carried out by CIAT, Apanteles spp. and and bleached. Death occurs from day 7 onwards when Telenomus sphingis were found to be more they hang, head downwards, from the leaves (Torrecilla effective than in the country’s hinterland (Valle et al. 1992). del Cauca and Quindío). In contrast, 270 Cassava Pest Management Findings obtained from different studies conducted • Avoid spraying when larvae are large. with B. erinnyis point out its advantages over most biological control agents. The latter tend to decline in • Visit the cassava plot periodically to detect the numbers when they do not have their hosts in the field. pest when it appears. The virus, however, can be stored for several years when no pest is present, to be used when the Recommendations for controlling cassava opportunity arises (Arias and Bellotti 1987; Torrecilla et hornworm al. 1992). During the first stages of their life cycle, larvae remain Usually, larvae attacked by the virus become slow, hidden under the lower sides of terminal leaves. Hence, permanently regurgitate, and present residues of when passing through the fields, these parts of the excrement adhering to the anal area. The black larvae plants must be closely examined. When 5 to 7 first- or take on a shiny tone and become extremely flaccid, second-instar larvae per plant are found, the product finally hanging from their anal pseudopodia. Green and should be applied. This level is flexible, depending on yellow larvae also develop brown spots in the folds of the abundance of natural enemies, climatic conditions, some segments or on the central parts of these, as if cassava variety, and plant age and vigor. they had been burnt with a cigarette. Finally, the dead larvae dry up (Arias and Bellotti 1987; Torrecilla et al. The number of plants to check per hectare 1992). depends on the area planted to the crop and on the availability of time. A minimum of five plants per In the field, the larvae affected by this virus break hectare would be acceptable. For plantings of more apart, thus spreading the pathogen and triggering a than 15 ha, having as a trained worker, known in disease that becomes endemic and able to wipe out the Spanish as a plaguero, to permanently check the fields pest. After the larvae have died, they decompose is most advisable. through the joint activities of other microorganisms, especially bacteria, and give off repugnant odors. We emphasize that the success of integrated Hence, larvae collected for use to prepare base control depends on the timely application of the solutions or to process or purify the virus must be different techniques. Insecticides, for example, are refrigerated (Torrecilla et al. 1992). valuable components of that control but should be resorted to only when strictly necessary. A base solution is prepared with macerated dead larvae. The solution is sprayed directly on the plants. Sometimes, beneficial insects are not sufficient to To distribute the virus effectively throughout the crop, control the hornworm or its larvae when these have 20 to 70 cc in 200 liters of water is needed per hectare reached third instar or larger. In this case, applications (Torrecilla et al. 1992). of microbial insecticides would not have the expected effectiveness. In such a case, Dipterex 80 SP To safely manage the virus, recommendations are (trichlorfon) can be applied in doses of 3 g of to (Torrecilla et al. 1992): commercial product per liter of water for soil applications, and 600 to 800 g/ha for aerial • Keep B. erinnyis in the freezer either as dead applications. larvae or in solution (liquefied mixture), using plastic bags or lidded glass bottles. Ultraviolet light traps, particularly black-light lamps (BL type) and blue-black light lamps (type BLB) can be • Withdraw from the freezer only when it is used to attract and capture adult hornworms (Bellotti et needed and in the quantities required. al. 1983). Although light traps do not constitute a control method, they allow researchers to discover the • In preparing the solution, avoid using live fluctuations in population sizes of E. ello adults and, larvae, larvae that have died from other causes, hence, better plan the application of IPM. or larvae that are already decomposing. Preliminary experiments led to the capture of as • Spray or pulverize only in the early hours of the many as 3094 adults in one night, with the largest morning. number of individuals being trapped between midnight and 2 a.m. This information is important because, in 271 Cassava in the Third Millennium: … sites where energy is not available, the traps need only control agents may exist. The situation may also arise work between midnight and 2 a.m., using batteries or in which natural controllers are limited. Fortunately, combustion motors (Bellotti et al. 1983). highly acceptable levels of resistance have been found. In fields where the pest is only beginning to attack, In most cases, the two control tools are available, manually collecting larvae and pupae is highly effective with one being more efficient than the other. For for reducing hornworm populations. successful control in this crop, the two should, ideally, be combined, together with adequate agronomic Options for Controlling Cassava Pests practices, thus minimizing pesticide use. Table 12-2 summarizes the control options currently A successful program of IPM for cassava should available for managing the principal cassava pests. harmonize with the environment. Pest management Insects normally appear as pests when the plant’s levels technologies should be available at low cost to farmers of resistance either do not exist or are very low. in developing countries (Bellotti 2000). However, for these pests, a large number of biological Table 12-2. Options to control principal cassava pests. Pest Control option References Hornworm Biocontrol: Baculovirus as pesticide; monitoring adult populations Arias and Bellotti 1987; with light traps and egg count in the field. Bellotti et al. 1992, 1999; Braun et al. 1993; Schmitt 1988 Mites HPRa: Moderate levels of resistance available in cassava clones; an Bellotti and Riis 1994; Braun et al. 1989; effective program for incorporating resistance into commercial Byrne et al. 1982, 1983; CIAT 1999; cultivars is needed. Biocontrol: A major complex of Phytoseiidae predators that can Bellotti et al. 1999; Yaninek et al. 1991 reduce mite populations is available; other entomopathogens (e.g., Neozygites and viruses) have been identified and evaluated. Whitefly Resistance: High levels have been found in some clones and hybrids. Arias 1995; Bellotti and Riis 1994; Biocontrol: Enemies, especially parasitoids, have been identified and Bellotti et al. 1999; Castillo 1996; are being evaluated; some entomopathogens give possibilities of CIAT 1999 control. Mealybugs Resistance: No adequate levels have been found in M. esculenta Bellotti et al. 1999; Bento et al. 1999; germplasm. Some wild Manihot species have potential for resistance. Van Driesche et al. 1990 Biocontrol: three parasitoids (Acerophagus coccois, Aenasius vexans, and Apoanagyrus diversicornis) provide good control for Phenacoccus herreni. (Phenacoccus The parasitoid Anagyrus lopezi provides very good control in Herren and Neuenschwander 1991; manihoti) most cassava-growing areas of Africa and Brazil. Neuenschwander 1994 Thrips HPRa: Pubescent cultivars have very good resistance and are Bellotti and Kawano 1980; available to farmers. Bellotti and Schoonhoven 1978c Subterranean HCN contents in cassava: Cultivars with high contents in roots Barberena and Bellotti 1998; burrower bug present less damage. Bellotti and Riis 1994; (Cyrtomenus Biocontrol: Natural enemies such as fungal and nematoid Bellotti et al. 1999; bergi) entomopathogens have given promising results. Caicedo and Bellotti 1994; Riis 1997 Intercropping: Intercropping cassava with Crotalaria reduces damage. Stemborers Farming practices: Keeping fields clean and destroying infested Bellotti and Schoonhoven 1978a, 1978b; (Chilomima stems. Gold et al. 1990; Lohr 1983 clarkei) Transgenesis: Possible use of transgenic plants (Bt) is being studied. Lace bug HPRa: Research indicates some level of resistance present in landrace Bellotti et al. 1999; varieties. Cavalcante and Ciociola 1993; CIAT 1990; Biocontrol: Natural enemies have been identified, but research on Farías 1985 their effectiveness is lacking. a. HPR = host-plant resistance. SOURCE: Bellotti 2000. 272 Cassava Pest Management Biotechnology However, farmers may be reluctant to adopt these practices if the intercrop species are not commercially The biotechnology tools available usually offer a acceptable or if the cassava crop yield is considerably potential to develop improved varieties resistant to reduced. In large plantings, where mechanization is a pests, thus increasing the effectiveness of natural production practice, intercropping may not be controllers, including the parasitoids and other adoptable. Other cultural practices that may reduce entomopathogens mentioned here. The new pest populations are varietal mixtures, burning of generation of genetic technologies for pest harvest residues, crop rotation, planting time, and use management is currently being integrated with of high-quality, pest-free, planting materials (Bellotti traditional IPM. It offers alternative technologies for 2000). controlling stemborers, leafcutting ants, grasshoppers, white grubs, and other pests difficult to control. This Use of natural enemies research is already under way and may be available to farmers in the near future (Bellotti 2000). In Africa, classical biological control has been highly successful for managing introduced pests. The Pesticides management of many cassava pests in the Neotropics requires greater commitment from farmers to Few pesticides are used in traditional cassava effectively implement solutions (Bellotti et al. 1999). agroecosystems, because of their high cost and the Numerous studies in cassava fields in several crop’s long cycle, which would make several Neotropical regions have revealed that complexes applications necessary. Some farmers in the Neotropics abound of natural enemies of pests important to that respond to pest outbreaks with pesticides (Bellotti crop. CIAT maintains a taxonomic reference collection, 2000). For cassava production in large plantings, the with a systematized database of cassava pests and their trend is to increasingly apply more pesticides to control natural enemies. The information is available to outbreaks, as in certain areas of Colombia, Venezuela, growers, agricultural researchers, outreach programs, and Brazil (Bellotti 2000). taxonomists, and museums (Bellotti 2000). The possibility is real that chemical pesticides can Results from explorations and research indicate be replaced with bioplaguicides in cassava pest that natural biological control frequently occurs in the management. One example is the effectiveness of the Neotropics. This phenomenon was expected because baculovirus against the hornworm and its successful the diversity of cropping systems and perenniality of implementation, especially for large plantings (Bellotti the cassava crop would induce a balanced association 2000). among pests and their natural enemies (Bellotti 2000). Entomopathogens are being found for mites, Disruption of this system (e.g., through pesticide mealybug, whitefly, hornworm, white grubs, use) may cause pest outbreaks. As described above, subterranean burrower bug, grasshoppers, and others. populations of the green cassava mite (M. tanajoa) in Research must also be conducted to develop northern South America are regulated by a complex of bioplaguicides and other methodologies for their phytoseiid predator mites. Once this complex is effective implementation. Such activity requires disturbed, yields drop (Bellotti 2000). collaboration with the bioplaguicide industry, a process that has already started in Colombia with the The virulence of natural enemies can be increased production of Baculovirus erinnyis (Bellotti 2000). through genetic engineering, thus permitting use of this abundant complex (Bellotti 2000). Agronomic practices Host-plant resistance Traditional farmers in most cassava-growing regions have depended on a set of cultural practices that The germplasm bank held at CIAT offers entomologists enable them to effectively reduce pest populations and breeders more than 6000 cassava varieties in (Lozano and Bellotti 1985). Intercropping is a common which a group of genes for pest resistance may be practice among small farmers. It reduces both the found. As mentioned above, variable levels of populations of whitefly, hornworm, and subterranean resistance to mites, whitefly, thrips, subterranean burrower bug, and the damage they cause (Bellotti burrower bug, lace bug, and stemborer have been 2000). identified (Bellotti 2000). 273 Cassava in the Third Millennium: … The innovative biotechnological tools that are and determining its objectives. The successful available allow efficient and easy access to resistant implementation of a pilot IPM project in a cassava crop genes and faster manipulation of molecular levels. developed with traditional farmers in Northeast Brazil is Numerous materials from the germplasm bank are a real example where such methodology was continually planted in the field and systematically successfully applied (Bellotti 2000). evaluated for pest resistance (Bellotti 2000). References CIAT has various techniques for mass-rearing most of the principal cassava pests. Also available are The following acronyms are used to save space: damage descriptions and population scales for identifying susceptible and resistant germplasm. Field CIAT = Centro Internacional de Agricultura Tropical evaluations of germplasm for resistance need to be SOCOLEN = Sociedad Colombiana de Entomología carried out, regardless of whether infestations are natural or artificial, because certain symptoms of Allem AC. 1994. The origin of Manihot esculenta Crantz damage caused by cassava pests are not truly (Euphorbiaceae). Genet Resour Crop Eval 41:133–150. expressed by plants maintained in the screenhouse or greenhouse (Bellotti 2000). Arias B. 1995. Estudio sobre el comportamiento de la “mosca blanca” Aleurotrachelus socialis Bondar Varieties that possess multiple resistance (i.e., (Homoptera: Aleyrodidae) en diferentes genotipos resistance to more than one pest) have been identified. de yuca, Manihot esculenta Crantz. MSc thesis. For example, M Ecu 72 contains high levels of Universidad Nacional–Palmira, Colombia. 181 p. resistance to whitefly and thrips, and moderate resistance to mites. One challenge that geneticists and Arias B; Bellotti AC. 1977. Eficiencia del Bacillius breeders may face is to include resistance to both thuringiensis sobre el gusano cachón Erinnyis ello diseases and arthropods within the one variety (Bellotti en yuca en un programa de control biológico. In: Proc 2000). IV Congress of SOCOLEN. Bogotá, DC, Colombia. The principal sources of resistance to pests may be Arias B; Bellotti AC. 1987. Control de Erinnyis ello found in the more than 100 wild Manihot species so far (L.) (Lep.: Sphingidae) gusano cachón de la yuca identified (Allem 1994). Small collections of these are (Manihot esculenta Crantz) con Baculovirus erinnyis held at some institutes, including CIAT, EMBRAPA NGV. Rev Colomb Entomol 13(2):29–35. (Brazil), and IITA (Bellotti 2000). Arias B; Bellotti AC; García F; Heredia A; Reyes JA; The genetic molecular cassava map is being Rodríguez NS. 1989a. Control de Erinnyis ello (L.) developed (Fregene et al. 1997). This will become a (gusano cachón de la yuca) mediante el uso de very useful tool for developing, using other Manihot Baculovirus erinnyis en el Patía (Cauca). Entomólogo species, transgenic cassava plants with resistance to (Bol SOCOLEN, Bogotá) 62:1–2. pests (Bellotti 2000). Arias B; Bellotti AC. 1989b. Potencial de predación de Projects on IPM in cassava are few. Guides and Podisus obscurus (Dallas) sobre Erinnyis ello (L.), el strategies for the appropriate implementation of gusano cachón de la yuca. In: Abstracts [of the] Proc alternative controls are not available for small farmers XVI Congress of SOCOLEN, Medellín, Colombia. in traditional production systems (Bellotti 2000). Such SOCOLEN, Bogotá, DC, Colombia. 166 p. a lack is also strongly felt in large cropping systems, where the implementation of an effective IPM system, Barberena MF; Bellotti AC. 1998. Parasitismo de dos razas based on biological control and resistant varieties, is del nemátodo Heterorhabditis bacteriophora sobre la decisive in maintaining high yields. This is especially chinche Cyrtomenus bergi (Hemiptera: Cydnidae) en true in the Neotropics, where a large complex of el laboratorio. Rev Colomb Entomol 24(1/2):7–11. arthropod pests and diseases exist (Bellotti 2000). Bellotti AC. 2000. Las plagas principales del cultivo An effective proposal for cassava growers is one de la yuca: Un panorama global. In: Symposium that overcomes the slow dissemination of technology, on “Avances en el Manejo de Plagas”. Proc XXVII for example, use of participatory methods with farmers Congress of SOCOLEN, Medellín, Colombia, and inclusion of the private sector in planning research July 2000. SOCOLEN, Bogotá, DC, Colombia. p 189–217. 274 Cassava Pest Management Bellotti AC; Kawano K. 1980. Breeding approaches in Caicedo AM; Bellotti AC. 1994. Evaluación del cassava. In: Maxwell FG; Jennings PR, eds. Breeding potencial del nematodo entomógeno Steinernema plants resistant to insects. Wiley, NY, USA. carpocapsae Weiser (Rhabditida: Steinernematidae) p 314–335. para el control de Cyrtomenus bergi Froeschner (Hemiptera: Cydnidae) en condiciones de laboratorio. Bellotti AC; Riis L. 1994. Cassava cyanogenic potential Rev Colomb Entomol 20(4):241–246. and resistance to pests and diseases. Acta Hortic 375:141–151. Castillo J. 1996. Moscas blancas (Homoptera: Aleyrodidae) y sus enemigos naturales sobre cultivos Bellotti AC; Schoonhoven A van. 1978a. Cassava pests de yuca (Manihot esculenta Crantz) en Colombia. and their control. CIAT, Cali, Colombia. 71 p. MSc thesis. Universidad del Valle, Cali, Colombia. 173 p. Bellotti AC; Schoonhoven A van. 1978b. Mite and insect pests of cassava. Annu Rev Entomol 23(1):39–67. Cavalcante MLS; Ciociola AI. 1993. Variabilidade quanto au grau de resistência de cultivares de mandioca Bellotti AC; Schoonhoven A van. 1978c. Plagas de la yuca ao percevejo de renda em Pacajus, CE. In: Relatório y su control. CIAT, Cali, Colombia. p 55–59. Anual de Pesquisa, 1980 a 1992, vol 2. Empresa de Pesquisa Agropecuária do Ceará (EPAC), Fortaleza, Bellotti AC; Reyes JA; Arias B. 1983. Manejo de plagas en Brazil. p 295–304. yuca. In: Reyes JA, comp. Yuca: Control integrado de plagas. CIAT, Cali, Colombia. p 265–281. CIAT. 1977. Informe Anual 1976. Cali, Colombia. Bellotti AC; Arias B; Guzmán OL. 1992. Biological control CIAT. 1990. Annual report [of the] Cassava Program, of the cassava hornworm Erinnyis ello (Lepidoptera: 1989. Cali, Colombia. 385 p. Sphingidae). Fla Entomol 75:506–515. CIAT. 1999. Annual Report: Integrated pest and disease Bellotti AC; Smith L; Lapointe SL. 1999. Recent advances management in major agroecosystems. Cali, in cassava pest management. Annu Rev Entomol Colombia. 136 p. 44:343–370. DeBach P. 1964. Biological control of insect pests and Bento JMS; Bellotti AC; Castillo JA; de Morães GJ; weeds. Reinhold Publishing, NY, USA. 844 p. Lapointe SL; Warumby JF. 1999. Introduction of parasitoids for control of cassava mealybugs in Farías ARN. 1985. Hyaliodes vitreus (Hemiptera: northeastern Brazil. Bull Entomol Res 89(5):403–410. Miridae), un predador de Vatiga illudens (Drake, 1773) (Hemiptera: Tingidae) em mandioca, na Bahia. Braun AR; Bellotti AC; Guerrero JM; Wilson LT. 1989. Rev Brasil Mandioca 4(1):123–124. Effect of predator exclusion on cassava infested with tetranychid mites (Acari: Tetranychidae). Environ Fregene M; Angel F; Gómez R; Rodríguez F; Chavarriaga Entomol 18(4):711–714. P; Roca W; Tohme J; Bonierbale M. 1997. A molecular genetic map of cassava (Manihot esculenta Crantz). Braun AR; Bellotti AC; Lozano JC. 1993. Implementation Theor Appl Genet 95:431–441. of IPM for small-scale cassava farmers. In: Altieri MA, ed. Crop protection strategies for subsistence Gallego M, L. 1950. Estudios entomólogicos: El gusano farmers. Westview, Boulder, CO, USA. p 103–115. de las hojas de la yuca (Erinnyis ello). Rev Fac Nac Agron (Colomb) 11:84–110. Byrne DH; Guerrero JM; Bellotti AC; Gracen VE. 1982. Yield and plant growth responses of Mononychellus Gold CS; Altieri MA; Bellotti AC. 1990. Effects of mite resistant and susceptible cassava cultivars intercropping and varietal mixtures on the cassava under protected vs infested conditions. Crop Sci hornworm, Erinnyis ello L. (Lepidoptera: Sphingidae), 22(5–6):486–550. and the stemborer, Chilomima clarkei (Amsel) (Lepidoptera: Pyralidae), in Colombia. Trop Pest Byrne DH; Bellotti AC; Guerrero JM. 1983. The cassava Manage 36(4):362–367. mites. Trop Pest Manage 29(4):378–394. 275 Cassava in the Third Millennium: … Herren HR; Neuenschwander P. 1991. Biological Schmitt AT. 1988. Uso de Baculovirus erinnyis para el control of cassava pests in Africa. Annu Rev Entomol control biológico del gusano cachón de la yuca. Yuca 36:257–283. Bol Inf 12:1–4. Lohr B. 1983. Biología, ecología, daño económico y Torrecilla SM; Nunes F, AR; Gómez EJ; Pegoraro RA. control de Chilomima clarkei (Amsel) (Lepidoptera, 1992. Manejo integrado del ‘marandová’ de la Pyralidae) barrenador de la yuca. In: Reyes JA, mandioca en el Cono Sur, Unidad 5. Unidades comp. Yuca: Control integrado de plagas. CIAT, Cali, de aprendizaje para la capacitación en tecnología Colombia. p 159–161. de producción de mandioca. CIAT; BID; CNPMF; EMATERS; UNESP. Cali, Colombia. Lozano JC; Bellotti AC. 1985. Integrated control of diseases and pests of cassava. In: Cock JA; Reyes JA, Van Driesche RG; Bellotti AC; Castillo JA; Herrera CJ. eds. Cassava: research, production and utilization. 1990. Estimating total losses from parasitoids CIAT, Cali, Colombia. p 575–585. for a field population of a continuously breeding insect, cassava mealybug, Phenacoccus herreni Martín CA. 1985. Biología y comportamiento de Polistes (Homoptera: Pseudococcidae) in Colombia, S.A. Fla erythrocephalus Ltr. (Hymenopotera: Vespidae), Entomol 73:133–143. predador del gusano cachón de la yuca, Erinnyis ello (L.), (Lepidoptera: Sphingidae). BSc thesis. Yaninek JS; Mégev B; de Morães GJ; Bakker F; Braun Universidad Nacional de Colombia–Palmira, A. 1991. Establishment of the Neotropical predator Colombia. 124 p. Amblyseius idaeus (Acari: Phytoseiidae) in Benin, West Africa. Biocontrol Sci Technol 1(4):323–330. Neuenschwander P. 1994. Control of cassava mealybug in Africa: lessons from a biological control project. Afr Crop Sci J 2:369–383. Riis L. 1997. Behaviour and population growth of the burrower bug, Cyrtomenus bergi Froeschner: effects of host plants and abiotic factors. Dissertation. Royal Veterinary Agricultural University, Copenhagen, Denmark. 167 p. 276 CHAPTER 13 Potential for Biological Control in the Management of Cassava Pests* Elsa Liliana Melo and Carlos Alberto Ortega1 Biological Control direct methods for using, manipulating, or conserving natural enemies. In the first phases, the fundamental Biological control, in the ecological sense, as a phase aspects studied are taxonomy, biology, physiology, of natural control, may be defined as the regulation of genetics, ecology, demography, behavior, and nutrition the population density of a pest organism by natural of pests and their enemies (DeBach 1975). enemies (parasites, parasitoids, predators, or pathogens) at a level that would be equal or greater If necessary, a pest and its enemies are identified by than would have been reached by means of another a specialist, as the organism’s name and classification alternative. Applied biological control supposes are key to all existing knowledge on it, and thus professional activity or human manipulation that understanding and controlling it if it is pest, or using it if promotes the effectiveness of natural enemies it is a natural enemy (Cave 1995b). (DeBach 1977). Natural Enemies In a broad sense, biological control may also be defined as mortality or suppression of pest organisms In biological control, various natural enemies participate, by any biotic factor. In this wider sense, it is the direct for example, parasites, parasitoids, predators, and action of parasites, parasitoids, predators, and microorganisms. These organisms must be able to pathogens (i.e., natural enemies) and of competition respond quickly to the pest’s population dynamics, so with other species for natural resources (i.e., that proportionately more natural enemies are present antagonists) that regulate an organism’s population as the pest population increases. This characterizes the density to a level lower than it would have been in the theoretically ideal natural enemy, as well as certain absence of that control. It does not include plant biological and ecological criteria (Cave 1995c). resistance, interference with the pest by semiochemicals (e.g., pheromones, allomones, Predators kairomones, and synomones), genetic engineering of the pest, natural chemical extracts, or mechanical Predators are carnivorous organisms that, in either control by humans. It does include the manipulation immature or adult state, actively seek and capture of natural enemies and antagonists through, for numerous prey, consuming them either partially or example, importation, mass-rearing, and release totally. Perhaps half of all insects and mites are (Cave 1995a). predators. As they are so numerous, determining the most effective predators is difficult. They are classified Research on biological control includes baseline as either generalists or specialists, according to eating surveys of any application of the method. These do habits and behavior. The principal arthropod predators not necessarily report immediately useful results or belong to the following orders: Odonata, Orthoptera, Dermaptera, Hemiptera, Neuroptera, Coleoptera, Diptera, Hymenoptera, Araneae, and Acari. Families that * This chapter is a revision of the version originally published in the stand out are Mantidae, Labiduridae, Pentatomidae, Proceedings of the XXVII Congress of SOCOLEN, 2000. Chrysopidae, Carabidae, Staphylinidae, Coccinellidae, 1. Advisors in Plant Health, Biotechnology Laboratories and Annexed Services (LABIOTSA), Quito, Ecuador. Elateridae, Cecidomyiidae, Syrphidae, and Phytoseiidae E-mails: meloelsa@gmail.com and caortegao@gmail.com (Banegas and Cave 1995). 277 Cassava in the Third Millennium: … Parasites controllers. According to Castillo et al. (1995), the expression “microbiological control” refers to the use of A parasite is an organism that lives at the expense of microorganisms (which, in the broad sense, includes another organism—the host (Australian Museum nematodes) to control pests. 2005). In general parasites share the following features: Recently, the use of microorganisms to effectively • Parasites are usually smaller than their host. control insect pests in different crops has increased, Parasites use both invertebrate and vertebrate most likely as a result of the discovery and development hosts. of new species and strains of entomopathogens (Lacey • Adult parasites may live on the host (e.g., lice), and Brooks 1997). Insects associate with in the host (e.g., tapeworms) or feed on a host microorganisms in diverse ways such as symbiosis, occasionally (e.g., mosquitoes). mutualism, and parasitism. Mutualism abounds among • Parasites generally do not kill the host but may insects; an example is the association of protozoa with harm the host indirectly by spreading termites, although the former are not pathogenic to the pathogens. This may affect the host’s behavior, host insects. In contrast, entomopathogens cause metabolism or its reproductive activity. infections, parasitism, or toxemia in insects (Lacey and • Many parasites have hooks, claws or suckers to Brooks 1997). attach to their host. Generally parasites have either a sucker (e.g., leeches) or piercing and Five principal groups of microbiological agents sucking type mouthparts (e.g., fleas) for exist: viruses, fungi, nematodes, bacteria, and protozoa. feeding. • Both adults and young can be parasitic. In Viruses. Entomopathogenic viruses are infectious some cases the young are parasites but the entities whose genome, constituting nucleic acid, DNA, adult is not. or RNA, is replicated in host tissues. A major viral family for insect control is the Baculoviridae. Parasitoids Baculoviruses contaminate the insect through the oral pathway. Normally, virions (infective units of viruses) A parasitoid is an organism that has young that develop are found on plant leaves and stems, and are ingested on or within another organism (the host), feeding on a by the insect as it eats. The first cells to be affected are single host and killing it at the end of their cycle. The the epithelial ones of the intestine. The virus then adult state lives free and is not parasitic. Among the attacks other tissues such as fatty bodies, intestinal characteristics that make parasitoids promising for epidermis, hemocytes, trachea, and silk glands. biological control are: Infected larvae become lethargic, stop eating, and finally become paralyzed. Dead insects become the • Specificity (e.g., Aphelinidae and Encyrtidae) most important sources of inoculum for maintaining • Ease of breeding in large quantities (e.g., the epizootic (Castillo et al. 1995). Trichogramma spp., Cotesia flavipes, Encarsia formosa, and Telenomus remus) Fungi. Entomopathogenic fungi kill the host • The power of flight, which facilitates dispersion relatively quickly by penetrating and proliferating within • High fertility, short generational time, and its body. The insect dies as the fungus either deprives it evolutionary rates that are comparable with of soluble nutrients from the hemolymph, invade or those of the pests digest its tissues, or releases toxins that poison it. Not all fungi associated with insects are pathogenic. Some Parasitoid species can be found in five of the insect pathogens are obligate, but most are facultative. orders, but most are in two: either the Hymenoptera or Saprophytic and other symbiotic fungi also exist Diptera (Díaz and Hanson 1995). Important families (Ferron 1985). include Aphelinidae, Platygastridae, Eulophidae, and Encyrtidae. More than 700 species of entomopathogenic fungi exist, distributed across different taxonomic groups, Entomopathogens and all with potential for use in regulating insects (Hajek and St Leger 1994). The most widely accepted As their name says, entomopathogens cause diseases classification system of fungi was proposed by in insects, and are grouped as microbiological Ainsworth in 1973 (cited by Tanada and Kaya 1993). It 278 Potential for Biological Control in the Management of Cassava Pests separates fungi into two divisions: Myxomycota, which spiracles, or penetrates the insect’s cuticle to reach the are plasmodial (i.e., asexual, pseudopodial, and hemocele, where it releases the symbiont. The producing masses of multinucleate protoplasm that bacterium proliferates and produces enzymes (lipases resemble amebas); and Eumycota, which are and proteases) that degrade the host’s tissues. nonplasmodial and frequently mycelial in form. Together, the nematodes and bacteria kill the insect Entomopathogenic fungi are found in the division within 48 h. The juveniles then consume the bacteria Eumycota and in the following subdivisions: and the insect’s degraded tissues. • Mastigomycotina: mobile cells or zoospores; Nematode development is favored by the perfect stage as oospores bacterium producing antibiotics, preventing the • Zygomycotina: cells not mobile; perfect stage proliferation of secondary pollutants. Between one and as zygospores three generations of the nematode are produced in the • Ascomycotina: perfect stage as ascospores host insect, depending on its size. All individuals of • Basidiomycotina: perfect stage as Steinernema are sexually differentiated. In basidiospores Heterorhabditis, however, those of the first generation • Deuteromycotina: cells not mobile; no perfect are hermaphrodite and those of the second are stage differentiated. Most entomopathogenic fungi are found in the The bacteria Xenorhabdus and Photorhabdus are subdivisions Zygomycotina, class Zygomycetes, order Gram-negative bacilli of the family Enterobacteriaceae Entomophthorales (e.g., Neozygites genus); and (Akhrust and Boemare 1990). In in vitro culture, they Deuteromycotina, class Hyphomycetes, order present two phases: Moniliales (includes the genera Aspergillus, Beauveria, Fusarium, Hirsutella, Metarhizium, Paecilomyces, and • P1, where they live in infective nematodes of Verticillium). IJ3 form, producing antibiotics and flagella • P2, where they live in cadavers of old insects or Researchers of entomopathogenic fungi have nematodes carried out studies that indicate an apparently logical way to demonstrate the virulence or pathogenicity of The bacterium-nematode association is these fungi in different insects. Thus, they can enter in mutualistic: the bacterium cannot survive alone in the an integrated pest management (IPM) program soil and the nematode cannot develop well without the (Sánchez 1996). bacterium. Through mutual assistance, they evade the host’s immune response, thus guaranteeing the Nematodes. The phylum Nematoda is, after survival of both. However, more research is needed on Arthropoda, the most diverse of the animal kingdom. this mechanism. Meanwhile, the pathogenic potential They can be found in a wide variety of habitats. They of the nematode-bacterium complex has been used for are round worms that lack respiratory and circulatory the biological control of several pests (Stock 1998). systems. The insect-nematode association ranges from accidental to obligate and from commensal to parasitic Bacteria. Bacteria are found in all dead insects, (Stock 1998). but only some are the primary cause of mortality; others sometimes cause mild infections. The bacteria Nematodes of the families Steinernematidae and enter the insect through its food and remain confined Heterorhabditidae are obligate parasites of a broad by the intestine’s peritrophic membrane. They cause range of insect species. In each family, only one genus general septicemia, but are not located in any specific exists, respectively, the Steinernema and tissue. Little is known of the role that bacterial Heterorhabditis. Their members live in mutualism with pathogens play in controlling the insect pest. Epizootics the bacteria Xenorhabdus sp. and Photorhabdus sp., occur under reported conditions of high-density respectively (Sáenz 1999). populations of the host but, under other circumstances, either occur rarely or are unrecognized. These bacteria, which are lethal for their insect hosts, make the nematodes an adequate organism for These bacteria separate into facultative and biological control. The infective state is the juvenile of obligate pathogens. Entomopathogenic bacteria the third nymphal stage (IJ3), which either enters belonging to the genus Bacillus (e.g., B. thuringiensis, through natural apertures such as the mouth, anus, or 279 Cassava in the Third Millennium: … Table 13-1. Natural enemies (no.) of cassava pests. B. cereus, B. popilliae, and B. larvae) are the most promising for controlling insect pests (Castillo et al. Pest Biocontrollers (Enemy type) 1995). Parasites/ Predators Pathogens Parasitoids Protozoa. Protozoa are considered important Mites factors in the natural regulation of the population Mononychellus density of certain insects. However, they have not been tanajoa 60 2 much applied as microbial agents, as entomophilic Tetranychus species already cause chronic or debilitating infections urticae in a wide range of hosts (Castillo et al. 1995). Hornworm 18 15 15 Whitefly 17 5 6 Biological Control of Cassava Pests Lace bug 1 Mealybug 25 46 2 The most common natural enemies of cassava pests Fruit fly 3 belong to four groups: parasites, parasitoids, predators, Stemborers and pathogens. Of these, entomopathogenic fungi, Chilomima clarkei 5 2 5 nematodes, and viruses stand out as being the most Lagochirus sp. 2 studied. At CIAT, a list of natural enemies was Scale insects compiled, which included 76 parasites/parasitoids, Aonidomytilus 138 predators, and 38 pathogens (Table 13-1). Possibly, albus 2 9 2 more species are still unreported. Saissetia miranda 2 Cydnidae 1 2 Table 13-2 shows some of the major natural Gall fly 2 1 enemies that control the cassava pests. Below are White grubs 2 discussed significant pests: cassava green mite, Total 76 138 38 cassava mealybug, cassava subterranean burrower bug, whitefly, cassava hornworm, white grubs, stemborers, and lace bugs. on agrometeorological homology of those regions in Cassava green mite the Americas and Africa affected by CGM (Bellotti et al. 1983b; Yaninek and Bellotti 1987). Agrometeorological The cassava green mite (CGM), Mononychellus tanajoa homology maps were prepared, based on the (syn.: Mononychellus progresivus), is probably native to microregional classification of the cassava crop as Northeast Brazil, where it was reported for the first time proposed by Carter et al. (1992). in 1938. The indigenous people knew its characteristic symptom of damaged young leaves and meristems, According to Braun et al. (1993), during calling it tanajoa or “plant disease or problem” (Bellotti explorations in the cassava-cropping areas of South and Schoonhoven 1978; Bellotti et al. 1999). In the America between 1983 and 1990, a total of 1970s, M. tanajoa was introduced accidentally to the 40 phytoseiid species were found in cassava and African continent, first appearing in Uganda (Nyiira neighboring plants, living in association with the 1972). This pest spread throughout the African cassava complex of phytophagous mite species. Maximum belt within 10 years, perhaps through the exchange of diversity was verified in Colombia. Of these 40 species, planting material (Yaninek and Herren 1988). This mite 18 were the most frequently found in the crop (CIAT is currently the principal cassava pest in Africa, causing 1990). Currently, CIAT has a database that stores yield losses between 13% and 80% (Herren and records belonging to 2416 samples collected from Neuenschwander 1991). different countries during various exploration periods. In all, 4300 records had been collected and identified To develop a biological control program to combat by CIAT or international taxonomists. Of these CGM—a pest of great importance in the subhumid specimens, the project conserves 2368 slides. areas of Africa and Brazil—studies were conducted on the taxonomy and geographical distribution of predator During the operation of the “CGM Biological mites of the family Phytoseiidae in the cassava crop Control” Project, 31 countries of the Americas and (Bellotti et al. 1983b). Geographical priority was other continents were sampled. In Colombia, 1576 assigned to the exploration of natural enemies based samples were recorded, meeting the project’s objective. 280 Potential for Biological Control in the Management of Cassava Pests Table 13-2. Major natural enemies of the most important cassava pests. Pest Type of natural enemies Parasitoids Predators Entomopathogens Cassava hornworm Erinnyis ello Trichogramma sp. (E)a Chrysopa sp. (E) Bacillus thuringiensis (L) Telenomus sp. (E) Podisus nigrispinus (L) Baculovirus of E. ello (L) Sphingid sp. (E) P. obscura (L) Metarhizium anisopliae (L) Cotesia americana (L) Polistes canadensis (L) Beauveria bassiana (L) Euplectrus sp. (L) P. carnifex (L) Paecilomyces sp. (L) Apanteles flaviventris (L) P. erythrocephalus (L) Nomuraea rileyi (L) Drino sp. (L) P. versicolor (L) Cordyceps sp. (P) Euphorocera sp. (L) Zelus sp. (L) Sarcodexia innota (L) Polybia emaciate (L) Thysanomia sp. (L) P. sericea (L) Belusia sp. (L) Calosoma sp. (L) Forcipomyia eriophora (L) Spiders (several species) (L) Cassava mealybug Phenacoccus herreni Apoanagyrus diversicornis Ocyptamus sp. Cladosporium sp. Anagyrus insolitus Sympherobius sp. Neozygites fumosa Anagyrus sp. ca. Hyperaspis sp. putonophilus Epidinocarsis elegeri Cleothera onerata Prochiloneurus dactylopii Nephus sp. Chartocerus sp. Acerophagus coccois P. madeirensis Eusemion sp. Kalodiplosis coccidarum Signiphora sp. Curinus colombianus Cleothera onerata P. manihoti Epidinocarsis lopezi Diomus sp. Gyranusoidea sp. Exochomus sp. Parapyrus manihoti E. flaviventris Sympherobius maculipennis Hyperaspis raynevali H. aestimabilis Diomus hennesseyi Cassava green mite Mononychellus tanajoa Insects: Stethorus sp. Hirsutella thompsonii Oligota sp. Neozygites sp. Chrysopa sp. Phytoseiidae mites: Typhlodromalus manihoti T. aripo Neoseiulus idaeus Lace bug Vatiga manihotae Zelus nugax (N-A) Whitefly complex Aleurotrachelus socialis Encarsia hispida Chrysodina sp. Fusarium sp. E. bellottii Delphastus sp. Verticillium lecanii Eretmocerus spp. Delphastus sp. pos. Beauveria bassiana quinculus Euderomphale sp. nov. D. pusillus Metarhizium anisopliae Signiphora sp. Chrysopa sp. Paecilomyces sp. Cladosporium sp. Bemisia tuberculata Eretmocerus spp. Encarsia pergandiella E. hispida Euderomphale sp. nov. Metaphycus sp. Trialeurodes variabilis Encarsia pergandiella E. hispida Eretmocerus sp. (Continued) 281 Cassava in the Third Millennium: … Table 13-2. (Continued.) Pest Type of natural enemies Parasitoids Predators Entomopathogens Aleurodicus dispersus Aleuroctonus vittatus Eretmocerus spp. Other whiteflies: Encarsia sophia E. luteola complex E. strenua complex Amitus macgowni Subterranean burrower bug Cyrtomenus bergi Nerthra sp. Heterorhabditis bacteriophora Steinernema carpocapsae Metarhizium anisopliae Beauveria bassiana Paecilomyces lilacinus White grubs Phyllophaga spp.; Heterorhabditis spp. Anomala spp. Steinernema spp. Metarhizium anisopliae Stemborers Chilomima clarkei Bracon sp. Bacillus thuringiensis Lagochirus spp. Apanteles sp. Spicaria sp. Brachymeria sp. Virus (not ident.) a. Developmental stage at which the cassava pest are attacked: E = egg; L = larva; N = Nymph; P = pupa; A = Adult. The most sampled areas were in Colombia, Venezuela, when natural enemies were eliminated. Neither did Ecuador, and Brazil. About 87 species were found, of acaricide applications increase production, thus indicating which 25 were new. On cassava, 66 phytoseiid species the effectiveness of biological control. were collected, with 13 being the most common (Melo 2000). The explorations also identified some predator insects of the CGM, especially the staphilinid Oligota Typhlodromalus manihoti was collected the most minuta and the coccinellid Stethorus sp. Oligota minuta frequently, being found in more than 50% of the has been classified as the dominant predator of M. sampled fields, followed by Neoseiulus idaeus, T. aripo, tanajoa populations. Research conducted at CIAT and in Galendromus annectens, Euseius concordis, and Uganda agrees that Oligota populations are located E. ho. To control M. tanajoa in Africa, T. aripo and among the fifth and eighth leaves, that is, where the pest N. idaeus showed the most promise (Yaninek et al. is found in highest numbers. One larva can consume 1991, 1993). Since 1984, numerous phytoseiids species from 49 to 70 mites and from 44 to 61 of their eggs. One have been sent from Colombia and Brazil to Africa. adult consumes, over 7 to 16 days, between 97 to 142 eggs and adults. Of the species that were mass released and established, none came from Colombia. However, three The other insect predator, Stethorus sp., is found successful species were from Brazil: T. manihoti, more in association with another pest: the spider mite T. aripo, and N. idaeus (Yaninek et al. 1991, 1993; Tetranychus urticae. In severe attacks in the field, 98% of Bellotti et al. 1999). Typhlodromalus aripo appeared to predators were Stethorus sp. and only 2% were Oligota be the most promising as it dispersed rapidly to more sp. (CIAT 1982). than 14 countries. Field evaluations indicated that T. aripo reduces the CGM population by 35% to 60%, These phytoseiids and predator insects are being thus increasing fresh matter production by 30% to 37%. intensively studied in the laboratory and field. So far, studies have shown that phytoseiid mites are more Field experiments conducted in Colombia (Braun efficient than predator insects (Byrne et al. 1983), et al. 1989) demonstrated the importance of diversity of although laboratory and field studies have shown that the phytoseiid species for controlling the CGM. In Colombia, neuropteran predator Chrysopa sp., which consumes the fresh and dried roots production was reduced by 33% pest at different stages, is also very effective. 282 Potential for Biological Control in the Management of Cassava Pests Other natural enemies of the pest mites are surveys to measure damage and collect natural pathogenic fungi belonging to the genera Neozygites enemies. By the end of 1996, more than 35,000 (Zygomycetes: Entomophthorales) and Hirsutella individuals of the three parasitoid species had been (Hyphomycetes: Moniliales). The former is a pathogenic released. fungus that appears sporadically in Colombia and Northeast Brazil (Neozygites sp. cf. floridana) and In Bahia, Ap. diversicornis had dispersed 130 km causes as much as 100% mortality in CGM in in 6 months, 234 km in 14 months, and 304 km in 1–2 weeks (Delalibera et al. 1992). Some strains are 21 months, after release. Acerophagus coccois had specific to the Mononychellus genus (Moraes and also established successfully, being recovered in high Delalibera 1992). numbers at distances of almost 180 km from the release site 9 months later. Aenasius vexans, however, This pathogen has been also found in Africa, but was constantly recaptured at its release site in has never been observed as causing dramatic mortality Pernambuco, having dispersed only 40 km in 5 months in this pest (Yaninek et al. 1996). This suggests that (Bento et al. 1999). Comparative studies of the life isolates from Brazil are more virulent than those of cycles of the three parasitoids show that each could Africa. Because the taxonomy of this genus is not well complete two cycles for one cycle of P. herreni, a known and it is necessary to differentiate the African favorable ratio in biological control. isolates from the candidates for release, molecular analysis of these has started. Results indicate that the Aenasius vexans and Ap. diversicornis show a isolates can be differentiated, although the technique marked preference for P. herreni, even though needs to be standardized to measure genetic distance laboratory studies indicated that they also parasitize (Bohórquez 1995). other species of mealybug (Bellotti et al. 1983a, 1994; Bertschy et al. 1997). Acerophagus coccois shows Hirsutella sp. was evaluated in Africa and shown to equal preference for either P. herreni or P. madeirensis. be very effective. Its potential is such that it could be All three parasitoids are attracted by infestations of used as a biological control agent (Odongo et al. 1988; P. herreni (Bertschy et al. 1997). Apoanagyrus Yaninek et al. 1996). diversicornis prefers third-instar nymphs, while Ac. coccois, which is much smaller, parasitizes with Cassava mealybug equal frequency male cocoons, adult females, and second-instar nymphs. Oviposition by Ap. diversicornis One way to control mealybug pests (Phenacoccus causes 13% mortality among third-instar nymphs (van herreni and P. manihoti) is to use natural enemies, Driesche et al. 1990). Aenasius vexans prefers with finding them through explorations. The management equal frequency second and third instars and adult of the cassava mealybug is an example of classical females (CIAT 1990). biological control (Herren and Neuenschwander 1991). A complex of mealybug species exists, as mentioned in Some field studies of natural populations of previous chapters, including P. herreni, which is found Ap. diversicornis and Ac. coccois determined the in the Americas. Of its parasites, two species of percentage of parasitism by using plant traps as hosts Anagyrus (Encyrtidae) stand out: A. insolitus and A. of P. herreni around the cassava crop (van Driesche sp. ca. putonophilus. Several parasitoids show a et al. 1988). With the combined action of the two specialty or preference for P. herreni. Among those parasitoids, P. herreni mortality was estimated at 55% identified in northern South America are Acerophagus (van Driesche et al. 1990). coccois, Apoanagyrus diversicornis, Ap. elegeri, Anagyrus putonophilus, A. insolitus, and Aenasius In 1980, the cassava mealybug found in the vexans. Three of these (Ap. diversicornis, Ac. coccois, Americas and that in Africa were reported as and Ae. vexans) were identified as effective for comprising different species. One presented males, controlling P. herreni (van Driesche et al. 1988, 1990). which led to the description of a new species, P. herreni. At the same time, P. manihoti was located in Collaborative efforts by CIAT and EMBRAPA Paraguay by Bellotti (Herren and Neuenschwander ensured that Ap. diversicornis, Ac. coccois, and Ae. 1991). In addition to the pest, they found 15 natural vexans were exported from CIAT and released in enemies, two of which were sent for release in Africa. Northeast Brazil, mainly in the states of Bahia and These were a coccinellid predator, Cleothera onerata, Pernambuco, during 1994 to 1996. Before which, however, had difficulties surviving the rainy introduction, EMBRAPA scientists had carried out field seasons; and the other was the parasitoid 283 Cassava in the Third Millennium: … Epidinocarsis lopezi, which was released by air and samples—300 g each—collected from 15 crops at proved to be more effective. Its establishment was 23 sites, 11 were positive for fungi, 13 for mites, and achieved in 25 countries of the cassava belt. The 17 for entomopathogenic and saprophagous mealybug is now under control in 90% of the region nematodes. From the latter, 20 subsamples were (Wigg 1994). selected according to their morphological characteristics and behavior containing only The predators reported as attacking the mealybug entomonematodes and they were sent to Germany for (Table 13-1) include Cleothera onerata (as mentioned identification. above), Sympherobius sp., the dipteran Ocyptamus sp., Hyperaspis sp., Nephus sp., and Diomus Using the PCR molecular technique, two samples hennesseyi. The only natural enemy of P. manihoti from Cauca (in Manihot esculenta) and Risaralda (in found in Zaire was the predator butterfly Spalgis Inga spp.), respectively, were identified as lemolea (Bennett and Greathead 1978; Leuschner and Steinernema kraussei Steiner (Rhabditida: Nwanze 1978). Steinernematidae). This was the first report of these nematodes for Colombia (Melo et al. 2009). Entomopathogenic fungi also have been found in association with the cassava mealybug, for example, Caicedo (1993) reported that, when she used an Cladosporium sp. and Neozygites fumosa (CIAT isolate of the S. carpocapsae strain All, the most 1990). susceptible stage of the C. bergi proved to be the adult, which presented a 60% parasitism for the entire Cassava subterranean burrower bug evaluated doses (2000, 4000, 6000, 8000, and 10,000 EPNs/ml). Over time (2, 5, 8, and 10 days), the CIAT has carried out baseline surveys on the cassava nematodes caused 100% parasitism, but mortality was subterranean burrower bug, Cyrtomenus bergi always lower than parasitism. The best dosages for (Hemiptera: Cydnidae), studying such aspects as mortality were determined to be LD50 of 193 EPNs/ml biology, behavior, population fluctuation, and host and LD90 of 403 EPNs/ml. On evaluating native preference (Arias and Bellotti 1985). Trials have also isolates found in the samples, the fifth state of the carried out on chemical control and cropping with the pest was the most susceptible, with 90% succumbing legume Crotalaria juncea (Castaño et al. 1985). to the isolate from Cauca (SQC92) and 100% to that Insecticides are not recommended, not only because from Risaralda (LFR92). The next most susceptible they are costly, but also because they destroy the state was the adult, with 85% and 100%, respectively, natural enemies that control the populations of other succumbing. cassava pests (Caicedo and Bellotti 1994). Although the nematodes were able to parasitize all Native nematodes have been found in association states of the pest, 100% parasitism by isolate LFR92 with C. bergi and are considered as an alternative to was effective only at 702 EPNs/ml and by isolate chemical and agronomic control. Eight sites around SQC92 at 826 EPNs/ml. Mortality, using LD50 and the Manizales, Pereira, and Santander of Quilichao have same strains, needed 800 and 870 EPNs/ml, been explored and, in all samples, nematodes were respectively (Barberena 1996). At the end of 2002, soil found. Geographical races of Heterorhabditis samples were collected from the same sites where the bacteriophora were identified in 37% of isolates EPN strains were initially found. The Heterorhabditis recovered from both soil and dead burrower bugs in sp. strain CIAT was found at La Colonia, Department the field under various climatic and physicochemical of Risaralda. Moreover, native and introduced strains soil conditions (Caicedo and Bellotti 1996). of Steinernema and Heterorhabditis were evaluated on stages 5 and adult of the pest (5000 EPNs/ml). In the interest of control, a search and Values of 100% parasitism and 22% mortality were identification of native isolates of entomopathogenic obtained for isolate Steinernema sp. strain SNI nematodes (EPNs) were carried out in 2003, collecting (CENICAFE) of the adult pest. soil samples from Quindío, Risaralda, Caldas, and Cauca. To extract EPNs, traps comprising larvae of the Greenhouse experiments were carried out on insect Galleria mellonella (Lepidoptera: Pyralidae) C. bergi applying S. carpocapsae, Steinernema sp. were used. The nematode larvae’s pathogenicity was strain SNI, and Heterorhabditis sp. strain HNI, using a then verified, following the Koch postulates. They were concentration of 1000 EPNs/ml. Values for parasitism then multiplied, stored, and identified. From 284 soil on the pest were 21%, 18%, and 18%, respectively, 284 Potential for Biological Control in the Management of Cassava Pests with no mortality. At a higher concentration nematode-bacterium complex probably had difficulty (25,000 EPNs/ml), parasitism was 55% for developing and thus needed more time to kill the S. carpocapsae and 45% for Heterorhabditis sp. insect. Or, this increased exposure enabled more strain HNI, and mortality 29% and 9%, respectively. In nematodes to enter and overcome the host’s defenses. another experiments, entomonematodes S. riobravis, Steinernema sp. strain SNI, and Heterorhabditis sp. Other studies have been conducted to find the best strain CIAT were evaluated against the third pest methodology for mass-rearing nematodes, using stage, with higher concentration (100,000 EPNs/ml). H. bacteriophora, which is considered as promising for Pest mortality was 33%, 28%, and 26%, respectively. its high virulence, its capacity to search, and facility to reproduce (Gaugler and Kaya 1990). Results indicated During this research, on dissecting the burrower that the best production was obtained by breeding in bugs, melanization of the EPNs was observed. With vivo and in vitro. Two races of this species were also the collaboration of the chemistry laboratory at the evaluated for their capacity to parasitize the entire University of Caldas, phenoloxidase activity was pest’s developmental stage. The fifth stage proved to detected. It is probably the pest’s immune response to be the most susceptible. On increasing nematode attack from EPNs, injecting them, whether dead or dose, parasitism also increased (Barberena 1996). alive. This finding is considered sufficiently important to further study of this line of inquiry to understand Other entomopathogens used for controlling how this humoral response, typical in Diptera, appears C. bergi are fungi. Bioassays were carried out in the in this hemipteran (CIAT 2003). laboratory and suspensions of conidia of the fungus Beauveria bassiana were evaluated, together with Two EPNs—the native S. feltiae (strain sampled at Metarhizium anisopliae and Paecilomyces lilacinus Villapinzón) and the introduced Heterorhabditis (Deuteromycotina: Hyphomycetes), combining three bacteriophora strain E-Nema—were evaluated for substrata and two inoculation methods. Immature their parasitism on six developmental stages of stages of the pest are the most susceptible to C. bergi. Results were 45.2% and 46.8% infection for M. anisopliae, which induces higher mortality rates S. feltiae and H. bacteriophora, respectively, on all than either B. bassiana or P. lilacinus (Sánchez and developmental stages of the pest at applied doses. Bellotti 1997a). Despite the lack of statistical differences between strains, the trend was greater infectivity for the fourth Isolates of M. anisopliae from CIAT applied in the instar (48.4%) and adult (46.9%). Isolates of S. feltiae laboratory also showed mortality rates ranging from induced a mortality rate of 21.4% and those of 45% to 60% (Jaramillo 2004). Results showed that H. bacteriophora 20.0%. Despite the higher infection C. bergi can be controlled by using a combination of rate, H. bacteriophora nevertheless showed a lower M. anisopliae (1E+08 conidia/ml) and sublethal doses mortality rate. (30 ppm) of Imidacloprid over 25 dai. The mortality rate was >80%. These greenhouse results were better Commercial concentrations—at 1000 and than those obtained when only the insecticide was 500 EPNs/ml of S. feltiae and H. bacteriophora, applied at commercial doses (Table 13-3). This is respectively—were applied to fifth instars and adults therefore an important alternative for IPM programs in of the pest, and destructive evaluations were made Colombia and other Latin American countries, as it 15 and 30 days after infection (dai). Only the adults would encourage farmers to reduce their use of highly were infected, at 93.9% with S. feltiae and 72.1% with toxic synthetic insecticides such as chlorpyrifos and H. bacteriophora, with no distinction of strain or carbofuran, which are heavily used in Colombia evaluation time. For mortality, at 15 dai, (Jaramillo 2004). H. bacteriophora accounted for 41.2%, and S. feltiae 8.6%. However, at 30 dai, they equalized at 62.7%. Research indicates the potential that Dissection of pest individuals revealed melanized entomopathogenic nematodes and fungi have for the EPNs, probably because of C. bergi’s immunological biological control of C. bergi, with recent studies response to the EPNs. At 30 dai, S. feltiae was shown indicating one possible solution. However, such to be more susceptible (37.5%) than H. bacteriophora research has been conducted only in laboratories or (13.17%). greenhouses. Field studies must be carried out before acceptable technologies can be recommended (AC Considering the behavior of S. feltiae isolates, Bellotti 2002, pers. comm.). which was more affected by the pest’s defense, the 285 Cassava in the Third Millennium: … Table 13.3. Mortality average corrected (CM) (%) (± SD) of Cyrtomenus bergi nymph treated with Metarhizium anisopliae (1E+08 conidia/ml) and two doses of Imidacloprid (300 y 30 ppm) alone and combined with M. anisopliae. Treatment Percentage MS (± SD) Day 5 Day 10 Day 15 Day 20 Day 25 Day 30 M. anisopliae + 9.2 ±3.6 22.4 ±6.0 34.9 ±4.0 61.2 ±5.4 79.4 ±3.5 87.1 ±2.9 Imidacloprid 30 ppm ab a* a* a* a* a* M. anisopliae 6.7 ±2.2 13.5 ±3.9 20.4 ±4.0 43.5 ±8.1 58.0 ±6.8 66.5 ±5.2 ab a* ab* ab* b* b* Imidacloprid 6.7 ±2.6 10.8 ±4.2 20.6 ±3.6 35.6 ±5.1 52.2 ±4.8 52.7 ±5.6 300 ppm ab Ab ab* bc* b* bc* Imidacloprid 30 ppm 7.6 ±1.8 15.2 ±4.0 15.2 ±4.0 18.8 ±4.0 25.1 ±5.6 37.4±5.9 a* a* b* c* c* c* MS = Mean square; SD = Standard deviation. A potential predator of C. bergi is the Nerthra (CIAT 1995). Samples of whitefly were duly collected bug (Hemiptera: Gelastocoridae), which was and processed in the laboratory, identifying and observed in a peanut field (MP Hernández 2002, analyzing each species of both parasitoids and whitefly. pers. comm.). To date, various species of whitefly and their Whitefly parasitoids have been found in different areas or sites, demonstrating the variability of parasitoids and their Recently, in Colombia, whiteflies have caused intrinsic relationship with any given whitefly species, or adverse effects in areas where cassava is cultivated. their presence as hyperparasitoids. The following Given this situation and the ignorance of the roles whiteflies were identified as being predominant in the that biological control agents play, a study was crop: Aleurotrachelus socialis, Bemisia tuberculata, begun of the parasitoid species that associate with Trialeurodes sp., and Tetraleurodes sp. this insect and their distribution. The study was conducted in different regions of Colombia: Cauca, The parasitoids found in association with whiteflies Valle del Cauca, and the Atlantic Coast (Table 13-4) were Eretmocerus sp. (Aphelinidae); the Encarsia Table 13-4. Whitefly species and their parasitoids collected from three geographical regions of Colombia. Region Whitefly species Parasitoid species Atlantic Coast Aleurotrachelus socialis Encarsia sp. Eretmocerus sp. Bemisia tuberculata Encarsia sp. Eretmocerus sp. Metaphycus sp. Trialeurodes sp. Encarsia sp. Tetraleurodes sp. Eretmocerus sp. Valle del Cauca Aleurotrachelus socialis Encarsia sp. Eretmocerus sp. Bemisia tuberculata Cauca Aleurotrachelus socialis Encarsia bellottii Eretmocerus sp. Signiphora aleyrodis Bemisia tuberculata Encarsia pergandiella Eretmocerus sp. Euderomphale sp. Signiphora aleyrodis Trialeurodes sp. Encarsia hispida Encarsia pergandiella Eretmocerus sp. 286 Potential for Biological Control in the Management of Cassava Pests pergandiella species group (Aphelinidae); E. hispida, 100 99.6 E. bellottii, Metaphycus sp. (Encyrtidae), and 80 Euderomphale sp. (Eulophidae). Signiphora aleyrodis 67 60 58 (Signiphoridae) is a possible hyperparasitoid (Trujillo et al. 1999). Other parasitoids identified were E. sophia, 40 27 26 the E. luteola species group, the E. strenua species 20 6 5 11 group (with the last two forming a species complex), 0.4 0 and Amitus macgowni (HE Trujillo 2002, pers. Atlantic Cauca Valle del comm.). Coast Cauca Not identified Signiphora aleyrodis The greatest wealth of parasitoid species in Encarsia sp. Eretmocerus sp. Colombia (mainly of the Encarsia, Eretmocerus, and Encarsia bellottii Amitus genera) was most frequently associated with Figure 13-1. Parasitoid species collected on the whitefly A. socialis, B. tuberculata, and Trialeurodes variabilis Aleurotrachelus socialis from three areas of (Castillo 1996). Colombia. Aleurotrachelus socialis, B. tuberculata, and T. variabilis are the whitefly species that usually attack preferred by the parasitoid E. hispida, which showed an the cassava crop in Colombia. Temperatures and average parasitism rate of 21.1%, 35.2%, 46.4%, and humidity were not related to populations of the three 21.9% on the first through to the fourth instar, species, although A. socialis was found primarily in respectively. The highest parasitism rate was presented those sites where temperatures were about 35 oC. More on the third instar. Evaluations were made 48, 72, 96, than 10 species of microhymenopteran parasitoids— and 216 h after the parasitoids were released. The peak natural enemies associating with whitefly species— for parasitism occurred between 72 and 96 h, with were collected and identified. Most were newly recorded 34.7% and 32.7%, respectively (Ortega 1999). for Colombia (Castillo 1996). Three were identified as Encarsia hispida, E. pergandiella, and E. bellottii Although the parasitoid demonstrates facility to (Evans and Castillo 1998). Only one Eretmocerus and parasitize under controlled conditions, results under one Amitus sp. (A. macgowni) were identified. natural conditions may be less efficient. More research Predominant species were E. hispida, Amitus sp., and is needed in this area (CIAT 1999). Eretmocerus sp. The highest levels of parasitism on whiteflies A. socialis, B. tuberculata, and T. variabilis In Colombia, entomopathogenic fungi were 15.3%, 13.9%, and 12.1%, respectively, although (B. bassiana, Verticillium lecanii, and M. anisopliae), rates varied with geographical region (Castillo 1996). recognized worldwide as whitefly pathogens, have been evaluated in the laboratory, but as yet have not been The species complex of parasitoids associated found parasitizing in the field. Laboratory results with each whitefly species was, to some extent, showed that, with B. bassiana, mortality rates were influenced by geographical area. In the Caribbean 28%, 55%, and 39% for nymphs of first, second, and coast, A. socialis was more frequently parasitized by third instars of A. socialis, respectively. The second Eretmocerus spp. (67%), whereas in Cauca and instar was the most susceptible. Beauveria bassiana Valle del Cauca, the Encarsia genus complex was and M. anisopliae caused mortality rates of 18.1% and more predominant. For example, in Valle del Cauca 18.8%, respectively, when applied in the morning, and (1000 m above sea level), 99.6% of parasitism of 12.4% and 5.7% when applied in the afternoon A. socialis was by Encarsia spp. versus 0.4% by (Sánchez and Bellotti 1997b). Eretmocerus spp. (Figure 13-1) (Trujillo et al. 1999). The most numerous complex of parasitoid species was Cassava hornworm associated with B. tuberculata. Several parasitic insects, predators, bacteria, fungi, and Greenhouse studies (Ortega 1999) showed that viruses make biological control of the cassava E. hispida preferred parasitizing the third instar of hornworm Erinnyis ello; also known as the ello sphinx A. socialis (75.3%) to the other instars, with rates being moth, possible without having to resort to insecticidal 15.6%, 44.7%, and 43.1% for the first, second, and applications that would otherwise break the balance fourth instars, respectively. Another results also existing between this pest and its natural enemies indicated that the third instar of the whitefly is also (Herrera 1999). More than 40 species of parasites, 287 Parasitoids (%) Cassava in the Third Millennium: … predators, and pathogens of the pest’s eggs, larvae, 70 ml/ha were applied to larvae of first and second and pupae have been identified (CIAT 1989; Bellotti instars. The direct expense for storing, applying, et al. 1999). processing, and collecting was U$4/ha (CIAT 1995; Laberry 1997). Eight species of microhymenopterans from the families Trichogrammatidae, Scelionidae, and Entomopathogenic fungi also exist, although Encyrtidae parasitize E. ello eggs. These include surveys showed that the number of insects affected by Trichogramma minutum, Telenomus sphingis, these in cassava crops was low, being found in only T. dilophonotae, Ooencyrtus sp., and O. submetallicus one of five areas evaluated. Under laboratory (CIAT 1989). Some Trichogramma and Telenomus conditions, a strain of B. bassiana caused the highest species have been reported as parasitizing 94% to mortality rate in E. ello (31.6% to 87.5%), with the third 99% of eggs (Bellotti and Schoonhoven 1978). The instar being the most susceptible. The fungus’s action dipteran Tachinidae flies and hymenopteran does not transmit from one generation to another. Braconidae wasps, especially the Cotesia genus, also When two strains of B. bassiana and M. anisopliae are attack the pest (Bellotti et al. 1992, 1994). mixed and applied to third-instar larvae, the mortality rate was 90%. No antagonism was presented, with The most common egg predators are the individual dead larvae showing typical symptomatology Chrysoperla spp. Other important predators, attacking (Múnera et al. 1999). larvae, include Polistes spp. (Hymenoptera: Vespidae), Podisus spp. (Hemiptera: Pentatomidae), and several In April 1979, during an outbreak of E. ello in the species of spiders (Bellotti et al. 1992). cassava-producing area of Quindío, Risaralda, and northern Valle del Cauca, pupae of this insect were For microbial control, sprays of the bacterium collected, showing infection by a fungus of the Bacillus thuringiensis, in doses of 2 to 3 g of Cordyceps genus (class Ascomycetes). In this same commercial product per liter of water, provide effective area, the pathogen had contained the attack by the control. Control is more effective with first, second, and pest’s third generation. The fungus can be cultivated third instar larvae of the pest (Arias and Bellotti 1977; under laboratory conditions in oat-agar medium (CIAT Herrera 1999). 1989). The key to effective use of biological control agents White grubs is the ability to synchronize the release of a large number of predators or parasitoids during the pest’s Nematodes Steinernema sp. strain SNI, early developmental stages, preferably the egg or first Heterorhabditis sp. strain HNI, and Heterorhabditis sp. to third instars. Parasitoids and predator efficiency is strain CIAT were evaluated under the controlled limited by poor functional response during short-term laboratory conditions. On third-instar larvae of (15 days) hornworm outbreaks. Successful control Phyllophaga menetriesi, penetration by the nematodes requires the monitoring of populations in the field to was 74.5%. The highest was for Steinernema sp. at detect immigrant adults or early instars. This can be 80.0%, compared with 52.9% for Heterorhabditis sp. done with black light lamps (type T20T12BLT) that trap strain CIAT. Overall, the mortality rate was 10.5%. adults in flight, or recognizing the presence of eggs or Further experiments were carried out with three other larvae (Braun et al. 1993). The difficulty of strains of entomonematodes (SNI, HNI, and H-CIAT), synchronizing mass releases of parasitoids and using two concentrations (7000 and 13,000 EPNs/ml) predators with peak populations of the pest suggests and two periods of evaluation (5 and 10 days). the need for an inexpensive, storable, biological Heterorhabditis strain HNI-13-5 induced the highest pesticide. mortality rate at 31.6%, and strains HNI-13-10 and H-C-7-5 both induced a rate of 21%. Treatments with A baculovirus has been identified as killing larvae, Steinernema strains SNI-13-5 and SNI-7-10 showed no as being easy to manipulate, and inexpensive to store. mortality. That is, mortality rates from treatments with This methodology was first implemented in the highest percentages of penetration (Steinernema commercial crops in Brazil, against populations of sp.) were lower than those of Heterorhabditis sp., first-instar larvae. The result was almost complete which, with less parasitism, caused higher mortality. control (Schmitt 1988). In Venezuela, the virus replaced insecticides in large plantations (7000 ha) where the Later tests with Phyllophaga sp. evaluated the hornworm is endemic. Control was 100% when infectivity and mortality produced by seven strains of 288 Potential for Biological Control in the Management of Cassava Pests EPNs: Steinernema riobravis (Sr), S. carpocapsae first strain (98.3%). No differences were observed strain All (Sc), S. arenarium (Sa), and S. feltiae (Sf); between evaluation periods for this species. The highest and Heterorhabditis bacteriophora strains Hb1 and mortality rate for P. menetriesi occurred 20 dai with Hb2, and Heterorhabditis sp. strain HNI. The strain HNI, again with L2 being the most susceptible concentration was 10,000 EPNs/ml. The highest stage (81.1%). values for infectivity occurred with the Heterorhabditis strains Hb2 (70.8%), HNI (74.0%), The susceptibility of white grubs to EPNs was and Hb1 (77.1%), whereas Steinernema strains had determined as being dependent on both the species the following rates: Sr at 12.5%, Sc at 13.5%, Sa at and strain of entomopathogen used—important 17.7%, and Sf at 35.4%. The survival rate was higher aspects, together with knowledge of the insect’s for the Steinernema strains Sf (75.0%), Sa (92.7%), dynamics, to take into account in developing biological Sr (97.9%), and Sc (98.9%) than for the control programs for white grubs (Melo et al. 2007). Heterorhabditis strains HNI (30.2%), Hb2 (35.4%), These results are relevant, as the initial stages of white and Hb1 (40.6%). grubs take place close to the soil surface, making control, using these entomonematodes, relatively easy. Three species of white grubs were also evaluated (Anomala sp., Phyllophaga sp., and P. menetriesi) More research needs to be conducted on the against three Heterorhabditis strains (H. defense mechanisms that pest larvae use, such as bacteriophora Hb1 and Hb2, and Heterorhabditis sp. physical barriers, as in the case of P. menetriesi strain HNI) and two Steinernema species (Sr and (Melolonthidae), where the cuticle is thicker than in Sc). The average rates of infection of Phyllophaga Cyclocephala (Dynastinae); external melanized sp., Anomala sp., and P. menetriesi by the five callosities that impede entry of parasitoids, as observed strains were 56.7%, 43.7%, and 22.5%, respectively. in field studies in northern Cauca (Pardo 2000); or, On comparing the average infection by the strains for movement through soil to evade antagonists the three pest species, those that stood out (M Londoño 2002, pers. comm.). significantly (P < 0.05) were HNI at 66.7% and Hb1 at 60.4%, followed by Hb2 (34.0%), Sc (25.0%), and Stemborers Sr (18.7%). The average survival rate was highest for P. menetriesi at 89.2%, followed by Anomala sp. Known control methods were first evaluated in the (70.4%) and Phyllophaga sp. (56.2%). The total 1980s, when research on the pest began. The methods average for the last pest, by strain, presented two that stand out are the treatment of planting stakes, and ranges: for the Steinernema strains 93.1% (Sr) to applications of the bacterium Bacillus thuringiensis, 86.8% (Sc), and for the Heterorhabditis strains 73.6% the fungus Spicaria sp., or a suspension of liquefied (Hb2), through 56.9% (Hb1) to 49.3% (HNI). larvae killed by disease (probably viral). The mortality rates were as follows: 100% with the solution of By other hand, it was demonstrated that certain macerated larvae, 99% with B. thuringiensis, and 88% developmental stages of the pests are more with Spicaria sp. (Lohr 1983; Herrera 1999). The high susceptible to these microorganisms. Hence, we mobility of the early larva-like instars of the stemborers evaluated the effect of the entomonematodes makes them highly vulnerable and easily controlled by Heterorhabditis sp. (HNI; from CENICAFE) and B. thuringiensis. Steinernema feltiae (Sf; from Villapinzón) on the mortality of different stages of these two species of Because adult stemborers are difficult to kill and white grubs: first-instar larva (L1), L2, L3 young, L3 larvae eat inside the stems, controlling them with mature, and prepupa. A concentration of 10,000 insecticides is not practical. Practices that will reduce EPNs/ml was applied to larvae maintained in organic pest populations are the removal and burning of soil, under controlled laboratory conditions (24.5 ºC infested plant parts. Only stakes that have no infestation and 70% ± 5% RH); evaluating its effect 10 and 20 or damage should be left to stand (Bellotti et al. 1983a). days after infection (dai). The EPN strains presented differences for Anomala inconstans (P ≤ 0.05), with Several natural enemies have been identified, the highest mortality rate achieved by strain HNI at including hymenopteran parasites and parasitoids such 84.7%, compared with Sf at 76.7%, for the different as Bracon sp., Apantales sp., and Brachymeria sp. instars. However, L2 was the most susceptible to the (Lohr 1983). 289 Cassava in the Third Millennium: … Lace bugs References At CIAT, the bug Zelus nugax (Hemiptera: Reduviidae) To save space, the acronym “CIAT” is used instead of was observed to be an excellent predator of nymphs and “Centro Internaccional de Agricultura tropical”. adults of cassava lace bugs (Vatiga spp.), consuming, during its biological cycle, an average of 496 individuals Arias B; Bellotti AC. 1977. Eficiencia de Bacillus of the pest. thuringiensis sobre el gusano cachón (Erinnyis ello) en yuca, en un programa de control biológico. 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Predators, parasites and many tasks towards controlling the pests described parasitoids. Sydney, Australia. (Available at http:// above, using natural enemies. With these tools, the australianmuseum.net.au/predators-parasites-and- conditions of such an important crop can be improved parasitoids) for millions of people around the world. Banegas JA; Cave R D. 1995. Biología y diversidad de Although the efficiency of infectivity and mortality depredadores. In: Cave R, ed. Manual para la observed in the laboratory is known to decline enseñanza del control biológico en América Latina, dramatically in the field, few studies have been applied 1st ed. Zamorano Academic Press, Zamorano, on a field scale, particularly those seeking information Honduras. p 39–49. on the effective application of biocontrol agents to better control subterranean insects such as white grubs. Barberena MF. 1996. 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Establishment of the Neotropical predator Amblyseius idaeus (Acari: Phytoseiidae) in Benin, van Driesche RG; Castillo JA; Bellotti AC. 1988. Field West Africa. Biocontrol Sci Technol 1(4):323–330. placement of mealybug-infested potted cassava plants for the study of parasitism of Phenacoccus Yaninek JS; Onzo A; Ojo JB. 1993. Continent-wide herreni. Entomol Exp Appl 46:117–123. releases of Neotropical phytoseiids against the exotic cassava green mite in Africa. Exp Appl Acarol van Driesche RG; Bellotti AC; Castillo JA; Herrera CJ. 17(1/2):145–160. 1990. Estimating total losses from parasitoids for a field population of a continuously breeding insect, Yaninek JS; Saizonou S; Onzo A; Zannou I; Gnanvossou cassava mealybug, Phenacoccus herreni (Hemiptera: D. 1996. Seasonal and habitat variability in the fungal Pseudococcidae) in Colombia, S.A. Fla Entomol pathogens, Neozygites c.f. floridana and Hirsutella 73:133–143. thompsonii, associated with cassava mites in Benin, West Africa. Biocontrol Sci Technol 6(1):23–33. Wigg D. 1994. Los revolucionarios silenciosos. Una reseña de la campaña contra el hambre que llevan a cabo los científicos agrícolas. World Bank, Washington, DC, USA. p 1–11. Yaninek JS; Bellotti AC. 1987. Exploration for natural enemies of cassava green mite based on agrometeorological critera. In: Rijks D; Mathys G, eds. Seminar on agrometeorology and crop protection in the lowland humid and subhumid tropics, held in Cotonou, Benin, July 1986. World Meteorological Organization, Geneva, Switzerland. p 69–75. 294 CHAPTER 14 Cassava’s Natural Defense against Arthropod Pests* Paul-André Calatayud1 and Diego Fernando Múnera2 Introduction compounds (e.g., linamarin and glucosinolates), and other organic compounds whose metabolic functions Higher plants develop physical and chemical within plants are not well defined (Robinson 1974; Beck mechanisms for their defense against pests. These and Reese 1976). defenses may be found within healthy plants or are induced through arthropod attack. They are variable in Whittaker (1970) proposed the term allelochemical nature, and can be modified by ecological factors. for some secondary substances that are defined, in plant-insect interactions, as substances produced by More frequently, physical mechanisms are present the plant and which markedly affect the insect’s in healthy plants, although they are sometimes induced growth, survival, and behavior or biology. An example by pests, as in the case of callus formation. These of allelochemical interactions is the production of mechanisms greatly affect the establishment of an phytoalexins, which are synthesized by the plant and arthropod on a plant, especially, those behaviors that are induced by the presence of a foreign body, usually prevail when the insect selects and establishes itself on a microorganism. Other interactions include those that a host plant. attract or repel, or are phagorepellent, inhibiting, or toxic. Chemical defense is the most effective and frequent mechanism found in plants (Bell 1974), as the Manihot esculenta Crantz (Euphorbiaceae) is substances of secondary metabolism are those that reported in the literature as presenting physical and exercise the most action on the environment. chemical mechanisms against arthropod pests (Bellotti According to Fraenkel (1969), these substances are et al. 1999). In this chapter, we present several cases composed mostly for defensive functions and tend to that have been clearly demonstrated. give the plant repellent or toxic attributes, affecting insect growth. Physical Mechanisms These substances are qualified as secondary, For cassava’s resistance to thrips, Frankliniella because each family is restricted to a limited group of williamsi (Thysanoptera, Thripidae), leaf pilosity has plants and because usually they do not appear to been clearly demonstrated as contributing to the intervene in the basic biochemical processes of most plant’s defense against these insects. Increased leaf plants. Secondary substances include alkaloids, pubescence leads to increased resistance to thrips, as steroids, terpenoids, phenolic compounds (e.g., the hairiness interferes with their progress in settling flavonoids and tannins), hydrocyanic or sulfur-derived on the plants (Schoonhoven 1974; Bellotti and Schoonhoven 1978). * This paper was first published in Spanish in the Proceedings of In contrast, cassava’s pilosity does not disturb the the XXVII Congress of SOCOLEN, held in Colombia, 2000. 1. Entomologist, Laboratory of Evolution, Genomes & Speciation, cassava mealybug (Phenacoccus manihoti Matile- IRD, c/o CNRS, Gif-sur-Yvette, France, & Université Paris-Sud, Ferrero; Sternorrhyncha: Pseudococcidae) (Calatayud Orsay, France. and Le Rü 2006). In a study on cassava and P. E-mail: calatayud@legs.cnrs-gif.fr 2. Agronomist, Cassava Entomology, CIAT, Cali, Colombia. manihoti interactions, a common and rapid reaction, E-mail: difemusa@hotmail.com also appearing in many other plant species, was 295 Cassava in the Third Millennium: … observed: callus formation (polymer of ß(1,3)-D- stems, and roots. In plant tissues, the cyano (CN)3 glucopyranose; Figure 14-1) on contact with the group links with D-glucose to form cyanogenic mealybug’s stylets (Calatayud et al. 1996). This reaction glucosides (Conn 1980), mostly linamarin (Figure 14-2) constitutes a scarring of the phloem, which thus (Butler et al. 1965). interrupts sustained feeding by this phloemphagous insect. When wounded, cassava tissues excrete hydrocyanic acid (HCN). This property, known as Another physical mechanism of plants, which cyanogenesis, results specifically from the action of an affects feeding behavior in P. manihoti, occurs in the endogenous enzyme (ß-glucosidase) on linamarase plant cell wall. An analysis of the secondary (Figure 14-2; Conn 1980). The cyanogenesis releases a compounds present in the intercellular liquids of toxic molecule, thus protecting cassava against pests. cassava leaves has shown that phenolic acids are However, such protection has yet to be clearly strongly involved in the mealybug’s establishment on demonstrated (Hruska 1988). the plant (Calatayud et al. 1994a). These acids, precursors in the synthesis of compounds associated In roots, cyanogenesis can constitute a defense with cell-wall pectins, probably constitute significant against the subterranean burrower bug, Cyrtomenus factors in interactions with the insect’s salivary bergi Froeschner (Hemiptera: Cydnidae). The HCN enzymes, thus annoying the insect and changing its released through an attack from this insect on roots feeding behavior. Moreover, the level of these phenolic was demonstrated to play a repellent role. Cassava acids declines strongly during dry times, thus partly varieties with low HCN levels are usually attacked more explaining increases in natural populations of P. severely than those with high HCN levels (Castaño et manihoti in the field during droughts (Calatayud and al. 1985; Bellotti and Riis 1994; Riis 1997; Bellotti et al. Le Rü 1995). 1999). Furthermore, high levels of HCN in artificial diets (with levels similar to those found in bitter Chemical Mechanisms cassava varieties) were clearly demonstrated to be toxic to the burrower bug (Cortés et al. 2003), indicating that An important characteristic of cassava biochemistry is cassava varieties with high levels of HCN are also toxic the presence of cyanogenic compounds in leaves, to C. bergi. However, for several reasons, cyanogenesis in (pa) cassava does not constitute a defense mechanism (ca) against the mealybug. Linamarin itself is not toxic to P. manihoti and seems more like a phagostimulant (Calatayud et al. 1994a, 1994b; Calatayud 2000). Under natural conditions, the insect has an (pw) enzymatic complex capable of hydrolyzing linamarin (Calatayud et al. 1995). However, the linamarase of P. manihoti does not seem to come from the insect itself, but from bacteria contained in its digestive tract (Calatayud 2000). The HCN levels found within their digestive tract are not toxic to the insect, as it Figure 14-1. Microphotograph of a cross-section of cassava leaf possesses an effective system of excretion or tissue infested by mealybug Phenacoccus manihoti. detoxification (Calatayud et al. 1994b). The section, which shows a phloem cell, was treated with the polyclonal antibody specific against the substance ß(1,3)-D-glucopyranose, a constituent of Furthermore, the location of linamarase in plant the callus (ca). This reaction makes visible the gold tissues differs from that of its substrate, linamarin particles carrying the antibody (black points in the (Pancoro and Hughes 1992). This, and the fact that callus). The callus results from the cell responding P. manihoti stylets, on penetrating, causes almost no to the perforation (black arrow) that the insect made in the primary cell wall (pw). The callus covers the hole and thus prevents the plasmalemma (pa) from draining and causing cell death. These elements (callus, perforation, plasmalemma) are found within 3. For an explanation of this and other abbreviations and acronyms, the insect’s feeding area. (Calatayud and Múnera see Appendix 1: Acronyms, Abbreviations, and Technical 2000; adapted from Calatayud et al. 1996.) Terminology, this volume. 296 Cassava’s Natural Defense against Arthropod Pests (A) CN CH CH 2OH O C 3 CH OH O CH 2 3 CN OH Linamarase O OH + H2O HO OH + HO C CH3 OH HO CH3 Linamarin OH (B) O CN HO C CH Hydroxynitrile lyase HCN + C CH3 3 CH CH 3 3 Figure 14-2. The chemical formula for linamarin, and cyanogenesis flow chart illustrates the release of HCN through the actions of linamarase (A) and hydroxynitrile lyase (B) (Calatayud and Múnera 2000). OH wounding (Calatayud et al. 1994a), suggests that cassava–mealybug interactions are unlikely to initiate OH cyanogenesis. Although no alkaloids were evident in cassava, O some glycosylated flavonoids were detected (Calatayud HO et al. 1994b), including rutin (Figure 14-3), the absence of which, in plants, is more significant than its presence (Harborne and Williams 1975). They were demonstrated as affecting P. manihoti growth and O–rutinose development (Calatayud et al. 1994b; Calatayud 2000). OH O One defensive response that cassava displays Rutin = quercetin (3,3’, 4’, 5,7-pentahydroxyflavone) + rutinose against P. manihoti appears to be an increase in rutin Rutinose = rhamnose + glucose levels. Such an increase varies with season and is less Figure 14-3. Chemical formula for rutin (Calatayud and Múnera pronounced during dry times. This partly explains 2000). increases in natural populations of P. manihoti in the field during drought (Calatayud et al. 1994c). However, the negative effect of rutin on P. manihoti growth and possessing a toxic molecule that works against the development does not seem to result from a toxic pests’ development and growth. This is partly action on the insect but more from being evidenced by the almost total lack of development of phagorepellent in nature (Calatayud 2000). varietal resistance to control the several arthropod pests of cassava (Bellotti and Schoonhoven 1978; Conclusions Bellotti et al. 1999). In M. esculenta, the natural defenses against arthropod However, a variety of cassava (M Ecu 72) and a wild pests described in the literature seem to affect in Manihot species (M. flabellifolia Pohl [Euphorbiaceae]) particular the establishment or sustained feeding demonstrated resistance, and may therefore be (through phagorepellence) of the pest in the plant. The promising for isolating genes for resistance to whitefly, mechanisms used are physical (pilosity and callus Aleurotrachelus socialis Bondar (Hemiptera: formation) or chemical (HCN and rutin). Aleyrodidae) (Bellotti et al. 1999; Carabalí et al. 2010). The mechanisms of resistance to this whitefly are yet to No example from the literature has clearly shown a be described, although physical factors appear cassava variety having a toxic effect on pests or as probable. 297 Cassava in the Third Millennium: … Acknowledgments Calatayud P-A; Rahbé Y; Tjallingii WF; Tertuliano M; Le Rü The authors express their gratitude to Ana Milena B. 1994a. Electrically recorded feeding behaviour of Caicedo for her critical reading and suggestions for the cassava mealybug on host and non-host plants. manuscript. Entomol Exp Appl 72(3):219–232. References Calatayud P-A; Rahbé Y; Delobel B; Khuong-Huu F; Tertuliano M; Le Rü B. 1994b. Influence of secondary Beck SD; Reese JC. 1976. Insect-plant interactions: compounds in the phloem sap of cassava on nutrition and metabolism. Recent Adv Phytochem expression of antibiosis towards the mealybug, 10:41–92. Phenacoccus manihoti. Entomol Exp Appl 72(1): 47–57. Bellotti AC; Riis L. 1994. Cassava cyanogenic potential and resistance to pests and diseases. In: Proc Calatayud P-A; Tertuliano M; Le Rü B. 1994c. Seasonal International Workshop on Cassava Safety, held in changes in secondary compounds in the phloem sap Ibadan, Nigeria, March 1994. Centro Internacional de of cassava in relation to plant genotype and Agricultura Tropical (CIAT), Cali, Colombia. WOCAS, infestation by Phenacoccus manihoti (Homoptera: ISHS, and ISTRC, Wageningen, Netherlands. Pseudococcidae). Bull Entomol Res 84:453–459. p 141–152. Calatayud P-A; Rouland C; Le Rü B. 1995. Influence of Bellotti AC; Schoonhoven A van. 1978. Mite and insect linamarin in cassava-mealybug interactions. Acta Bot pests of cassava. Annu Rev Entomol 23(1):39–67. Gall 144(4):427–432. Bellotti AC; Smith L; Lapointe SL. 1999. Recent advances Calatayud P-A; Boher B; Nicole M; Geiger JP. 1996. in cassava pest management. Annu Rev Entomol Interactions between cassava mealybug and cassava: 44:343–370. cytochemical aspects of plant cell wall modifications. Entomol Exp Appl 80:242–245. Butler GW; Bailey RW; Kennedy LD. 1965. Studies on the glucosidase “linamarase”. Phytochemistry 4(3): Carabalí A; Bellotti AC; Montoya-Lerma J; Fregene M. 369–381. 2010. Manihot flabellifolia Pohl, wild source of resistance to the whitefly Aleurotrachelus socialis Calatayud P-A. 2000. Influence of linamarin and rutin on Bondar (Hemiptera: Aleyrodidae). Crop Prot 29(1): biological performances of Phenacoccus manihoti in 34–38. artificial diets. Entomol Exp Appl 26(1):81–86. Castaño O; Bellotti AC; Vargas O. 1985. Efecto del HCN y Calatayud P-A; Le Rü B. 1995. Potential biochemical de cultivos intercalados sobre daño causado por la mechanisms used by Congolese cassava to resist chinche de la viruela Cyrtomenus bergi Froeschner al mealybug. In: Proc Second International Scientific cultivo de la yuca. Rev Colomb Entomol 11(2):24–26. Meeting of the Cassava Biotechnology Network, held in Bogor, Indonesia, Aug 1994, vol 2. Working Conn EE. 1980. Cyanogenic compounds. Annu Rev Plant Document No. 150. Centro Internacional de Physiol 31:433–451. Agricultura Tropical (CIAT), Cali, Colombia. p 485–500. Cortés ML; Sánchez T; Riis L; Bellotti AC; Calatayud P-A. 2003. A bioassay to test HCN toxicity to the Calatayud P-A; Le Rü B. 2006. Cassava-mealybug burrowing bug, Cyrtomenus bergi. Entomol Exp Appl interactions. IRD Éditions, Montpellier, France. 110 p. 109:235–239. Calatayud P-A; Múnera DF. 2000. Las defensas naturales Fraenkel G. 1969. Evaluation of our thoughts on en la yuca a las plagas artrópodas. In: Proc XXVIII secondary plant substances. Entomol Exp Appl Congress of SOCOLEN, held in Medellín, July 2000. 12:473–486. Sociedad Colombiana de Entomología (SOCOLEN), Bogotá, DC, Colombia. p 265–271. Harborne JB; Williams CA. 1975. Flavone and flavonol glycosides. In: Harborne JB; Mabry TL; Mabry H, eds. The flavonoids. Academic Press, New York. p 377–441. 298 Cassava’s Natural Defense against Arthropod Pests Hruska AJ. 1988. Cyanogenic glucosides as reference Robinson T. 1974. Metabolism and function of alkaloids in compounds: a review of the evidence. J Chem Ecol plants. Science 184:430–435. 14:2213–2217. Schoonhoven A van 1974. Resistance to thrips damage in Pancoro A; Hughes MA. 1992. In situ localization of cassava. J Econ Entomol 67(6):728–730. cyanogenic ß-glucosidase (linamarase) gene expression in leaves of cassava (Manihot esculenta Whittaker RH. 1970. The biochemical ecology of higher Crantz) using non-isotopic riboprobes. Plant J 2(5): plants. In: Sondheimer E; Simeone JB, eds. Chemical 821–827. ecology. Academic Press, New York. p 43–70. Riis L. 1997. Behaviour and population growth of the burrower bug, Cyrtomenus bergi Froeschner: effects of host plants and abiotic factors. Dissertation. Department of Ecology and Molecular Biology, Royal Veterinary and Agricultural University, Copenhagen, Denmark. 167 p. 299 Cassava in the Third Millennium: … CHAPTER 15 Biotechnology for Cassava Improvement: Genetic Modification and Clean-Seed Production Paul Chavarriaga1, Roosevelt H. Escobar2, Danilo López3, Jesús Beltrán4, William Roca5, and Joe Tohme6 In Memoriam Carlos Julio Herrera (r.i.p.) was co-author of this chapter for the first edition of this book, which was published in the Spanish language. The chapter was entitled “Biotecnología para el manejo de plagas en la producción de semilla limpia” [Biotechnology for pest control in clean-seed production]. Carlos was widely respected as an expert and teacher on insect pests of cassava. We therefore dedicate this English-language chapter to his memory. Carlos Julio Herrera leads a training session with a group from the Women Farmers’ Association of Santa Ana (ASOPROSA)7, Department of Cauca, Colombia. Themes were the production of planting materials and control of cassava pests and diseases. (Photo by R. Escobar.) 1. Research Associate, Genetic Transformation Platform, CIAT, Cali, Colombia. E-mail: p.chavarriaga@cgiar.org 2. Research Assistant, Biotechnology Unit, CIAT. E-mail: r.escobar@cgiar.org 3. Research Assistant, Genetic Transformation Platform, CIAT. E-mail: d.lopez@cgiar.org 4. Doctoral Candidate, The City University of New York, USA. E-mail: jabz81@gmail.com 5. formerly Plant Physiologist and Leader, Project on the Biodiversity and Genetic Resources of Andean Roots and Tubers, CIP, Lima, Peru. E-mail: w.roca@cgiar.org 6. Molecular Plant Breeder and Agrobiodiversity, Director, Research Area, CIAT. E-mail: j.tohme2@cgiar.org 7. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, and Abbreviations, and Technical Terminology, this volume. 300 Biotechnology for Cassava Improvement: … Introduction organs (organogenesis) directly from totipotent cells. Common agents for selecting transgenic cells include Genetic transformation technology, using antibiotics, herbicides, fluorescence, and sugars such Agrobacterium, has made possible the acquisition of as mannose. transgenic varieties of the world’s most important food crops. The varieties from first-generation transgenic Cassava is conventionally propagated in the field plants are today cultivated on 134 million hectares. by planting pieces of stems, known as stakes, obtained They contain genes that mostly confer resistance to from plants of the previous crop. This system presents herbicides and insect pests. The list of genetically relative advantages, particularly the main one of lower modified crops includes soybean, maize, cotton, colza, production costs. However, under certain alfalfa, sugar beet, tomato, and red pepper, among circumstances, the system incurs problems of others. They are cultivated in 29 countries, including transmission of pests and diseases (usually viral and/or the EU countries of Czech Republic, Germany, Poland, bacterial in nature). Such problems hinder the Portugal, Romania, Slovakia, Spain, and Sweden; and exchange of germplasm between countries, create the Central American countries of Costa Rica and seed shortages during the year’s production peaks in Mexico (James 2011). certain regions, delay distribution systems, and slow down the adaptation and/or adoption of new clones. Genetic modification technology to improve world These and other problems can be resolved by applying agriculture was also adopted for cassava in the 1980s. in vitro techniques. Somatic embryos of genetically modified cassava plants were first produced between 1993 and 1996 Implementing multiplication systems that use in (Sarria et al. 1993, 1995; Schopke et al. 1996). Since vitro tissue culture of planting materials enables the then, innovative traits have been introduced, ranging distribution of disease-free clones of interest to small from resistance to herbicides (Sarria et al. 2000), farmers or industries. CIAT has defined the basic through reduced cyanide content in the plant (Siritunga system for in vitro propagation and germplasm and Sayre 2003; Siritunga et al. 2004), to modifications cleaning, thus facilitating the consolidation of the of the amount (Ihemere et al. 2006) and quality in vitro bank held at CIAT and the exchange of genetic (Raemakers et al. 2005) of starch accumulated in materials among countries. roots. Jørgensen et al. (2005) recently demonstrated that silencing of specific genes for biosynthetic routes This chapter provides an overview of the advances in cassava is possible. For example, the quantity of made in (1) cassava transformation achieved recently, cyanogenic glycosides (cyanide) that the plant focusing on the use of genetically modified cassava to produces can be reduced, using RNA interference study genes and promoters, improve the nutritional (RNAi) technology. We can now talk of a fast- quality of roots, study leaf retention, and alter starch approaching second generation of transgenic cassava content and quality to produce biocombustibles; and by the introduction and expression of genes to improve (2) multiplication systems for planting materials at the nutritional value of the roots, i.e., increasing small-farmer and industrial levels. carotene content (Welsch et al. 2011) and protein (Abhary et al. 2011), or by introducing into cassava Cassava as a Model for Testing the genes that will help control the devastating disease Expression of Genes and Promoters caused by the African Cassava Mosaic Virus (Vanderschuren et al. 2007). A major constraint to incorporating new traits into cassava through genetic modification comprises the New genetic information has been introduced into proven availability of promoters—regulatory sequences cassava plants, essentially using Agrobacterium for gene expression—in this plant’s storage roots. tumefaciens as a natural vector of the genes of interest. Based on previous reports on the specific expression in Commonly, two types of tissues are used to generate cassava roots of a glutamic acid-rich protein (also de novo plants: totipotent cells (able to differentiate known as Pt2L4; de Souza et al. 2009), the promoter and regenerate a complete organism) derived from region (CP2) of this gene was cloned in front of the somatic embryos, and also known as friable GUSPlus reporter gene and expressed in genetically embryogenic calluses (FECs; Taylor et al. 1996); and modified plants grown in the field (Beltrán et al. 2010). the cotyledons of somatic embryos (Taylor et al. 1996). Transgenic plant regeneration is usually achieved by The expression of the reporter gene led to an inducing or germinating embryos and/or inducing intense coloration of storage roots and stem vascular 301 Cassava in the Third Millennium: … tissues. Leaves showed a less intense expression, and antibodies during infections, so that these natural killer the pith an absence of expression. Fluorometric cells carry out phagocytosis. Vitamin A is also analyses revealed that the promoter CP2 was equally attributed as having the roles of a hormone for cell active in root pulp and stems, although 3.5 times less development and gene expression, and of an active in leaves. These findings were corroborated by anticarcinogen. Cell differentiation and growth are quantitative analyses of messenger RNA (mRNA) levels, regulated by vitamin A. Today, we know that vitamins using real-time PCR developed for transgenes in and minerals, together with other food components, cassava (Beltrán et al. 2009). significantly reduce chronic diseases such as cancer, cardiovascular problems, and degenerative diseases A second, larger version of promoter CP2— related to aging (Álvarez et al. 2004). promoter CP1—was also cloned in front of the GUSPlus gene and found expression in transgenic carrot plants, When consumed in a conventional diet (i.e., at which also have roots that store carbohydrates. The 100 g of cassava per day), ß-carotene levels in cassava transformation and regeneration system in carrot is are insufficient to fulfill Required Daily Allowance (RDA) much more expeditious than that of cassava. Promoter standards. Conventional improvement would help raise CP1 seems to preferentially express in secondary these levels, but procedures are complicated because phloem and root vascular cambium, although, again, of cassava’s polyploidy, heterozygous nature, and slow expression in vascular leaf tissue was less, by six times. multiplication. Furthermore, the accumulation of ß-carotene in cassava roots involves several genes, as The results of these studies demonstrated that to be expected of a multigene synthesis route. Hence, genetically modified cassava plants grown in the field in the attempt to introduce all the “good” alleles of the provide a good model for testing genes and promoters relevant genes into a single variety, strategies for of interest. They also enabled the isolation and conventional improvement become even more characterization of regulatory sequences of cassava complicated. genes for use in directing preferential expression to the root, the most economically valuable plant organ. The international initiative HarvestPlus (www.harvestplus.org) involves interdisciplinary and Provitamin A Deficiency in Cassava and interinstitutional research to reduce micronutrient Prospects of Improving this Trait through malnutrition in humans. Within this initiative, CIAT Biotechnology collaborated with the University of Freiburg (Germany) to develop, through conventional improvement and/or The cassava plant originates in South America, where, biotechnology, cassava genotypes more able to since ancestral times, it has been consumed as a food produce and store ß-carotene in roots. This effort’s first staple providing dietary energy. The roots contain large results demonstrated that cassava genotypes vary in quantities of carbohydrates, hence its importance in accumulating carotenes in roots. Values ranged from nutrition. However, they contain little protein and few 0.102 to 1.040 mg of total carotene per 100 g of fresh micronutrients (OECD 2009), compared with sweet weight (Chávez et al. 2005). potato, potato, bean, maize, or wheat. Nevertheless, it is widely consumed because of its ability to accumulate In at least four examples of crops—rice, potato, carbohydrates and to tolerate drought and acid soils tomato, and canola—ß-carotene content has been (Kawano 2003). It is the principal dietary energy source increased substantially by inserting genes of the for more than 600 million people, especially low-income carotene synthesis route, and which are directed by populations in less developed countries, who often face promoters to express in specific organs, or food shortages (Thro et al. 1999a, 1999b). Cassava is constitutively. The genetic transformation of rice, using therefore an appropriate crop for which to use genes of the carotene route (Ye et al. 2000; Paine et al. biotechnology to produce varieties with higher levels of 2005), was successful in increasing total carotene nutrients such as ß-carotene. content in the grain by as much as 27 times to a maximum 37 μg/g. More than 80% (>30 μg/g) Beta-carotene is the fundamental source of vitamin corresponded to ß-carotene. In canola, ß-carotene was A, essential for human and animal health, and best increased by 50 times (Shewmaker et al. 1999). More known as critical in the maintenance of ocular epithelia recently, in potato, Diretto et al. (2007) demonstrated in, for example, the retina and cornea. Not so well that ß-carotene in the tuber can be increased by known, but nevertheless equally important, is the role 3600 times, reaching 47 μg/g of dry weight. Hence, on vitamin A plays in enabling T-lymphocytes to produce a diet of 250 g of potato per day, half of the RDA 302 Biotechnology for Cassava Improvement: … requirements would be supplied. Both in rice grains as fungal infections that are characteristic of PPD and potato tubers, the carotene synthesis route was (Bouvier et al. 2005). However, PPD is a highly variable sufficiently complemented to suggest that a similar characteristic. It is difficult to measure visually; it is strategy can be attempted for cassava. influenced by the environment, and depends heavily on the storage conditions of harvested roots. The first significant result that HarvestPlus obtained from its biotechnological approach was the Leaf Retention knowledge that the carotene synthesis route does operate in cassava roots. That is, the genes find One way of increasing yields of crops such as cassava expression in this organ (Arango-Mejía 2005), is to delay leaf senescence by increasing cytokinin indicating that the necessary substrata for the activity levels in the leaves. Cytokinins are plant growth factors of the route’s enzymes are present. Without this implicated in plant development, including leaf background, designing an unconventional longevity. The phenomenon of holding back leaf improvement strategy (i.e., genetic modification) to senescence is known as “stay green” (Thomas and increase ß-carotene content in cassava roots, by Howarth 2000). Millions of people use cassava as their inserting new gene combinations, would be more principal source of carbohydrates, which is why the difficult. possibility of using genetic modification to increase root yield (i.e., starch) by increasing leaf longevity is The second significant result is that transgenic being explored. The trait of “stay green” in cassava is of cassava plants were produced. They combined one or great commercial interest. Plants improved more genes from the carotene synthesis route with conventionally for foliage retention have already shown promoters that preferentially directed the expression of increases of dry matter content as high as 33% more these to roots. These plants have already been field- (Lenis et al. 2006). Moreover, delayed senescence tested (Welsch et al. 2010). The results of enables the plant to have more leaves at harvest, which overexpression of a gene for phytoene synthetase of then can be used as forage of excellent nutritional bacterial origin (crtB) in the root demonstrated that quality (Buitrago 1990). increasing total carotene content is possible. A white- root cassava (genotype 60444; transgenic event Thus, Zhang and Gruissem (2004) introduced the pCAS-Phyt-12) that normally carries ≤0.6 μg/g (dry bacterial gene ipt into cassava. This gene codes for the weight) of carotenes contained about 21 μg/g (dry enzyme isopentenyltransferase (Akiyoshi et al. 1984; weight), that is, about 35 times as much. The Barry et al. 1984). It is active during leaf senescence, ß-carotene content in this same, non-transgenic once it is activated by its promoter SAG12, itself genotype increased proportionately from 0.4 to derived from Arabidopsis thaliana (Lohman et al. 6.7 μg/g (dry weight). 1994; Weaver et al. 1998). The transgenic cassava line 60444-529-28 was selected for field evaluation at CIAT Thus, these results demonstrated that increasing in collaboration with the Institute of Plant Science (now carotene content in cassava roots is feasible. It can be the Institute of Agricultural Sciences) at ETH–Zurich, done by inserting heterologous (foreign) genes under Switzerland) and the Department of Crop and Soil the control of promoters that preferentially express in Sciences of Cornell University (Ithaca, NY, USA). storage-root tissues. Research is continuing with the Agromorphological traits were measured, together with genetic modification or transfer of transgenes to levels of cytokinins, abscisic acid (ABA), glucose, yellow-rooted genotypes that have higher carotene sucrose, and starch, all indicators of gene ipt content. These genotypes include advanced breeding expression (López 2008). lines like GM905-21 and GM905-57. Results showed that, effectively, cytokinin levels Increasing ß-carotene content in cassava roots significantly increased in basal leaves, in tandem with would bring additional advantages to the farmer, for an increase of ABA in apical leaves. Glucose and example, higher “resistance” to postharvest sucrose levels also increased in apical leaves, stems, physiological deterioration (PPD). Chávez et al. (2005) and abscission areas. No positive impact on dry matter detected a trend in roots with higher carotene contents content was apparent in this particular trial, probably to delay the beginning of PPD. Possibly, in this type of because of unexpected dry periods. Precipitation was “resistance”, molecules of the type ß-ionone, derived also more abundant and erratic than normal, which from the catabolism of ß-carotene, are involved, as probably also had an effect on root dry matter content. they play a role in the response to biotic stresses such An alternative explanation is suggested through 303 Cassava in the Third Millennium: … experiments by Medford et al. (1989), who determined when tested in the field. On the contrary, the non- that increased cytokinin levels can generate changes in transgenic wild types produced more and heavier roots the root systems of tobacco and Arabidopsis. Changes (Tables 1 in Zhang’s paper). related to these phenomena are not ruled out for cassava storage roots, despite the difficulty of observing However, as was expected, the SAG12-ipt system them. They may well have contributed to the reduced increased cytokinin levels exclusively in mature leaves. dry matter in the transgenic line 60444-529-28. The resulting delayed senescence led to extended leaf life. The retarded senescence of the mature leaves Another explanation, which also requires caused changes in source–sink relationships, as experimental verification, is that dry matter was affected reflected by the physiological symptoms associated by changes related to sugar translocation. Basal leaves with senescence (increases in sugars and ABA in apical may have made higher demands as their longevity leaves). However, these changes did not seem to be increased. However, the transgenic storage roots did reflected in the phenotype of young leaves. Larger not differ morphologically from those of the control. lobes and petioles in mature leaves could be related to the increase in cytokinins because of their participation Measuring sugars in the plant is important, as these in processes of growth and cellular division. Evaluation usually increase during senescence (Wingler et al. 1998; of the ability of the transgenic cassava line 60444-529- Stessman et al. 2002). Increase can trigger symptoms 28 to tolerate drought, while minimally affecting yield, associated with senescence such as the yellowing of may reveal the true potential of taking advantage of the leaves. Statistically, glucose and sucrose levels were SAG12-ipt system in cassava. clearly higher in the apical leaves, abscission areas, and stems of transgenic cassava plants. This suggests a Rapid Propagation of Certified Seed pattern of free-sugar remobilization from the youngest leaves towards other plant organs, or the activation of The lack of technology for producing planting materials sugar synthesis in younger leaves. in sufficient quantities, and in optimal health conditions, becomes an obstacle for the commercial The relationships between altered cytokinin levels development of cassava. Conventional plant and source-sink proportions have been studied in propagation—use of stakes—favors, among other tobacco and lettuce (McCabe et al. 2001; Cowan et al. things, the spread of diseases, thus affecting the quality 2005). Some nutrient deficiencies in young leaves relate and quantity of “seed” for planting and, hence, the to changes in cytokinin and sugar levels (Jordi et al. expected yield per production cycle. 2000). Indeed, Cowan et al. (2005) showed that the SAG12-ipt transgenic tobacco plants were slower than CIAT, in collaboration with various actors and wild plants to increase the root-to-shoot ratio and the agents in development, has implemented and adjusted specific leaf area (SLA) after drought. This was several multiplication systems at different scales. Thus, interpreted as delayed capacity to remobilize nutrients with assistance from the DGIS (Netherlands), the from source organs (leaves) towards the sink (roots). Center implemented mass propagation, using bioreactors of the type RITA® (French acronym; The protocol developed to characterize the Temporary Immersion System for Plant Tissue Culture; performance of the transgenic cassava line Teisson and Alvard 1995). This efficient multiplication 6044452928 under field conditions was sufficiently system reduces unit costs and propagation time by satisfactory and comprehensive for use as a model for about 50%, compared with the conventional stake future transgenic evaluations. This work also systems and in vitro multiplication in solid media. demonstrated that transgenesis is a viable alternative for modifying traits of agronomic importance in cassava In the RITA® system, during the immersion cycles, such as leaf longevity. Observations made in our field tissues are bathed in a liquid medium that contains experiments showed that the SAG12-ipt system did not nutrients and hormonal regulators (mainly of the obviously affect cassava yield, at least, not under our cytokinin type). The cycles alternate with dry rest evaluation conditions in Colombia. Our findings were periods and no aeration. The growth of roots, stems supported by the results of Zhang et al. (2010) who (new explants), and leaves is accelerated, and a large tested the same genotype in open fields in China quantity of buds is produced. The propagation rate, discovering that transgenic cassava plants expressing using this system, is thus increased considerably and SAG12-ipt did not improve root number, nor root weight can be used for the next micropropagation cycles. 304 Biotechnology for Cassava Improvement: … With this methodology, multiplication rates of conventional, solid-phase, in vitro systems. Such more than 1:10 can be reached, depending on the systems would benefit countries that have problems variety (Escobar et al. 2001). RITA® has also been accessing planting materials, but possess potential for successfully used for the proliferation of somatic development and have end users interested in creating embryos of coffee (Berthouly and Etienne 1999), “local banks” of pathogen-free, planting materials banana (Alvard et al. 1993), rubber (Etienne et al. (Escobar 2009). 1997), sugarcane (Lorenzo et al. 1998), and other crops. Acknowledgements The successful use of bioreactors for mass We extend our gratitude to: propagation depends on the response of the variety to management under in vitro conditions in liquid media. Willy Gruissem and Peng Zhang (ETH–Zurich) for At CIAT, this system was tested successfully for contributing cassava plants, genetically modified multiplying industrial cassava clones. Experimentally, it for leaf retention, to test in the field at CIAT; and to was also successful with yam, lulo, sugarcane, potato, Luis Duque and Tim Setter (Cornell University) for tree tomato, sweet potato, and other crops. It was also their help in analyzing cassava metabolites; successful for embryogenesis in cassava, rice, and Brachiaria. ASOPROSA, the Empresa Comunitaria San Rafael, and ASOMUDEPAS, with whom we developed and The Cassava Biotechnology Network (CBN) set up the low-cost systems for cassava; and conducted a survey of small farmers in different countries (Thro et al. 1997). It found that, in every FIDAR, CBN, PRGA, DGIS (Netherlands), and region, the principal limitation for farmers is access to MADR (Colombia) for their financial support good-quality planting materials of local and/or towards this research-and-technological improved clones in sufficient quantities at planting adjustment project. times. Thus, CIAT, with support from the CBN and the Participatory Research and Gender Analysis (PRGA) References Program, established a low-cost in vitro multiplication system at farm level (Thro et al. 1999a; Escobar et al. To save space, the acronym “CIAT” is used instead of 2006), to enable rural associations to directly access “Centro Internacional de Agricultura Tropical”. planting materials through biotechnological techniques. This system permitted the establishment Abhary M; Siritunga D; Stevens G; Taylor NJ; Fauquet of rural laboratories in the Department of Cauca (CIAT CM. 2011. Transgenic biofortification of the starchy 1999), and the Atlantic Coast (CIAT 2008), Colombia. staple cassava (Manihot esculenta) generates a novel The associations had been selected for their interest sink for protein. PLoS ONE 6(1):e16256. DOI:10.1371/ and capacity to manage and implement participatory journal.pone.0016256 laboratory processes to benefit their communities and production systems. Akiyoshi DE; Klee H; Amasino RM; Nester EW; Gordon MP. 1984. T-DNA of Agrobacterium tumefaciens The strategy on which the rural laboratories were encodes an enzyme of cytokinin biosynthesis. Proc based was the adaptation to local conditions, using Natl Acad Sci USA 81:5994–5998. infrastructure and low-cost inputs that are easily obtained from local markets. Examples of successful Alvard D; Côte F; Teisson C. 1993. Comparison of rural laboratories are those of the associations methods of liquid medium culture for banana ASOPROSA, Department of Cauca; the San Jacinto micropropagation. Effects of temporary immersion Small Farmers’ Municipal Association for Sustainable on explants. Plant Cell Tissue Organ Cult 32:55–60. Development (ASOMUDEPAS), Department of Bolívar; and the Empresa Comunitaria San Rafael in Ovejas, Álvarez MC; Uscátegui RM; López C; Baracaldo CM; Department of Sucre, all in Colombia. Castro L; Noy V. 2004. Plasma retinol concentration according to pubertal maturation in school children Alternative systems of producing planting materials and adolescents of Medellín, Colombia. 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Senescence-inducible Thro AM; Roca WM; Restrepo J; Caballero H; Poats S; expression of isopentenyl transferase extends leaf Escobar R; Mafla G; Hernández C. 1999a. in vitro life, increases drought stress resistance and alters biology have farm-level impact for small-scale cassava cytokinin metabolism in cassava. J Integr Plant Biol farmers in Latin America? In Vitro Cell Dev Biol 52(7):653–669. 35:382–387. 308 CHAPTER 16 Cassava Viral Diseases of South America Lee Calvert1, Maritza Cuervo2, and Iván Lozano3 Vegetatively propagated cassava is particularly prone to Costa 1940). It has since been found in several damage by viruses as infection tends to build up in countries of South America, and in Africa and Asia. successive cycles of propagation. At least 16 different viruses have been isolated so far from cassava, but Usually, the disease is not important in Latin there are probably others that have yet to be described America and the Caribbean. No detailed studies exist (Calvert and Thresh 2002). of affected areas in Colombia (Nolt et al. 1992). The disease is most prevalent in southern Brazil and Because the center of origin of cassava is in the Paraguay. In these regions, the disease is important Neotropics and its introduction into other regions has and phytosanitary control measures are recommended been relatively recent, only one of the viruses attacking to reduce losses. this crop in Central and South America has been found elsewhere. In addition, several Neotropical viral diseases The disease has no known vector and its are asymptomatic and do not damage plants, reflecting dissemination throughout a crop is attributed to long periods of coevolution between host and mechanical transmission. pathogens. Description The main cassava viruses causing diseases of economic importance that deserve special attention in Plants infected by CsCMD develop symptoms of plant quarantine controls are the African cassava mosaic and chlorosis in leaves. Sometimes, infected mosaic virus (ACMV), East African cassava mosaic virus leaves present clear, dark green spots, bordered by (EACMV)4, South African cassava mosaic virus (SACMV), veins. Symptoms are more severe during prolonged cassava brown streak virus (CBSV), Indian cassava and relatively cold periods—a frequent situation in the mosaic virus (ICMV), cassava common mosaic virus South American subtropics. Under these conditions, (CsCMV), cassava vein mosaic virus (CVMV), and cassava infected plants are usually dwarfed and yield losses frogskin virus (CFSV). In South and Central America, may be as high as 60% (Costa and Kitajima 1972) particular attention should be paid to the latter three. (Figure 16-1). Cassava Common Mosaic Disease Etiology and epidemiology Background and distribution Cassava common mosaic disease is caused by the virus of the same name (CsCMV) which can infect Cassava common mosaic disease (CsCMD) was first species belonging to several families of dicotyledonous reported in southern Brazil (Silberschmid 1938; plants. This virus was originally classified in the potexvirus group, that is now referred to as the genus 1. Virologist, formerly of CIAT, Cali, Colombia. Potexvirus. The virions of CsCMD are elongated, 2. Research Associate, Germplasm Health Laboratory, Genetic Resources Program, CIAT. E-mail: m.cuervo@cgiar.org semi-flexuose particles that measure 15 × 495 3. Research Associate, Virology Laboratory, CIAT. nanometers (Kitajima et al. 1965) and contain RNA. E-mail: i.lozano@cgiar.org 4. For an explanation of this and other abbreviations and acronyms, see Appendix 1: Acronyms, Abbreviations, and Technical In cassava, the virus presents the nuclear Terminology, this volume. inclusions typical of potexviruses, as found in another 309 Cassava in the Third Millennium: … Management and control Eliminating plants that express CsCMV symptoms provides adequate control. The symptoms are evident in primary leaves. If this is not done early in the cropping cycle, the plants must then be marked and the stems burned after the roots are harvested. To minimize the risk of mechanical transmission, cutting tools should be periodically disinfected (Lozano and Nolt 1989). Care in selecting healthy planting materials can eradicate CsCMV or at least mitigate, to a minimum, the economic damage it causes. Cassava Vein Mosaic Disease Background and distribution The first report on cassava vein mosaic disease (CVMD) was in 1940 (Costa 1940). The areas where the disease is prevalent are still inhabited by mainly rural communities where the lack of economic resources contributes to ignorance on this disease. Because symptoms are sporadic and usually not readily visible, the disease is unlikely to receive adequate attention at the end of the crop’s growing cycle (Figure 16-2). The disease is very common in the semiarid areas of Northeast Brazil. However, its presence in other Figure 16-1. Symptoms caused by CsCMD. regions of the country has also been reported, that is, in the States of Ceará, Pernambuco, Alagoas, Piauí, and Bahia (Calvert et al. 1995), and in some host Nicotiana benthamiana. The virus is known to neighboring regions. also systemically infect Euphorbia spp., Cnidoscolus conitifolius, and other species of the Euphorbiaceae Description family (Costa and Kitajima 1972). The first four or five leaves of infected stakes present The CsCMV viral particles contain a simple protein chlorotic veins. The chlorosis starts forming a pattern cover with a molecular weight of 26,000 Da (Nolt et al. 1991). The genome consists of single-stranded RNA, of which the complete sequence is known (Calvert et al. 1996). The organizational structure, proteins, and molecular weights are usually similar to those of other potexviruses. The principal source of inoculum is infected plant material. Because the virus spreads systemically through the plant, stakes from diseased plants are also infected. The virus is highly stable and may spread through mechanical transmission on machetes or other implements used in agricultural tasks. Although this mode of transmission is inefficient, it is the only known means of dissemination from plant to plant. Figure 16-2. Symptoms caused by CVMV. 310 Cassava Viral Diseases of South America of rings that, as they join, create a circular spot. In Brief: Viral Diseases in South America Leaves with severe symptoms commonly have deformed blades and show epinasty. Sometimes, • In South America, different viral diseases symptoms disappear and their expression is attack cassava. Some are asymptomatic and influenced by climatic conditions. Leaves of infected are not economically important to the crop. plants become prematurely old and fall, reducing leaf area. Frequently, in mature plants, observing leaves • Common mosaic has been reported in Brazil with symptoms of mosaic is difficult, as these are and other South American countries. This more pronounced in the semiarid areas than in the disease develops symptoms of mosaic and humid coastal regions of Northeast Brazil. The chlorosis in infected plants and is transmitted disease does not seem to affect plant vigor. mechanically. Etiology and epidemiology • The vein mosaic virus is found mainly in Northeast Brazil. Infected plants present Cassava vein mosaic disease is caused by a virus of chlorosis of the veins and, when symptoms are the same name (CVMV), which presents isometric severe, the leaves become deformed and particles, 50 nm in diameter (Kitajima and Costa present epinasty. These phenomena are 1966). The genome consists of double-stranded influenced by climatic conditions. The virus DNA, which has a length of 8200 base pairs. can spread from plant to plant and, although its economic importance has not been fully The CVMV virus was at first tentatively classified quantified, it can cause losses. as a member of the caulimovirus group. The complete sequence of CVMV has been determined Cassava Frogskin Disease and the genomic organization differs from that of either the caulimoviruses or badnaviruses (Calvert et Background and distribution al. 1995). The virus will probably be classified as a unique genus of the plant pararetroviruses. Cassava frogskin disease (CFSD) was first reported in 1971, in the Department of Cauca, southern Colombia Very little is known about the epidemiology and (Pineda et al. 1983). Its place of origin seems to be the control of CVMV. The only known host is cassava and Amazon Region of Brazil or Colombia, where it infects the primary mode of dissemination is by infected the different cassava varieties cultivated by indigenous planting materials. Commercial varieties are rarely communities. However, the farmers assumed that the found totally infected. Dissemination occurring disease was a physiological disorder associated with within the field suggests the existence of a vector as the varieties and, therefore, did not report it earlier. yet unidentified. However, few studies exist on the virus’s dissemination and more research is needed to In the Amazon, the disease is known as lagarto- establish the effectiveness of using virus-free jacaré because the symptoms expressed by roots material. The virus can remain in a latent state in resemble that lizard’s skin. Along the North Coast, plants, especially during the rainy seasons of the Colombia, in 1981, an allegedly new disease called Brazilian coastal regions. “Caribbean mosaic” was reported as presenting symptoms of mosaic in the leaves of cassava variety Management and control Secundina (Calvert 1994). Research demonstrated that lagarto-jacaré, caiman-lizard disease, and The disease can be effectively controlled by removing Caribbean mosaic are all the one and same CFSD. infected plant materials immediately the symptoms appear. Many infected plants seem to tolerate CVMV Of the cassava diseases, frogskin is considered to and produce stems of normal appearance that could be one of the most damaging to the crop (Lozano and be used as good planting material. Although the Nolt 1989), as it directly affects root production, economic importance of CVMD has not been fully causing yield losses of 90% or more (Figure 16-3). quantified, it can cause losses, especially if it appears at the beginning of the cropping cycle. By the 1980s, the disease had appeared in most cassava-producing regions of Colombia and was 311 Cassava in the Third Millennium: … (A) (B) Figure 16-3. General appearance of roots infected by cassava frogskin disease. steadily spreading. It has now been reported from Brazil, Costa Rica, Panama, Peru, and Venezuela. In Panama’s case, this disease was first detected in 1999, in cassava plots planted with materials that came from Costa Rica, a country that had already reported the disease. Description (C) Symptom expression is variable according to temperature and genotype. In most varieties, infected plants do not present visible signs in their aerial parts, which sometimes appear healthy and vigorous. Stems of these plants are thicker, especially at the base of the plant, as the increased thickness of stems is related to the lack of starch accumulation in roots. However, because these stems are thick, farmers tend to select them as planting materials. In the roots, symptoms range from very mild to Figure 16-4. Symptoms of frogskin disease in cassava roots: severe, depending on the plant’s age and climatic (A) healthy root; (B) root with mild symptoms; and (C) root with severe symptoms. factors (Figure 16-4). Dry or hot conditions tend to inhibit the development of symptoms, whereas cooler conditions favor expression. Even in mildly infected throughout the root’s length or may be restricted to plants, economic losses occur because of the lack of one part, mostly towards the middle. starch accumulation. The root system of infected plants usually does not Symptoms consist of small longitudinal fissures develop in the same way as healthy plants. The roots located near the callus where the roots originate. They remain thin and woody, with a thick, cork-like peel. then continue appearing along the roots’ length. As the Their starch content is very low. Sometimes, within one young roots increase in diameter, the fissures tend to plant, some roots bulk normally, although they may be scar, giving the lesions a lip-like form. As the roots more fibrous, while others are severely affected. mature, the lesions increase in size and number, and join to create the appearance of a net or honeycomb. Diagnosis The root peel or epidermis appears cork-like and easily comes off. According to the severity of symptoms, the The disease can be detected by carefully examining the lesions’ depth and number increase until the roots roots for the characteristic symptoms, whether these become deformed. All these symptoms may occur are mild or severe. 312 Cassava Viral Diseases of South America This disease is easily transmitted through grafts. Notable progress in the characterization and Hence, grafting can be used as another diagnostic detection of the virus associated with this disease has method. The test consists of grafting an indicator led to the development of a molecular diagnostic variety (such as ‘Secundina’, accession CIAT M Col method, using RT-PCR (Reverse Transcriptase-PCR). 2063) that has been duly certified as virus-free onto the Comparative studies of the two methodologies plants being evaluated (Figure 16-5). available for detecting this virus have shown that new molecular technology of detection is more effective To increase the germination rate of the grafts, buds and reliable than the symptomatology and the use of are best removed from the stocks. After 3 or 4 weeks, warning plants. the plants should be checked to confirm the presence of symptoms such as mosaic in the foliage of shoots, Etiology and epidemiology thus indicating the disease’s presence. To ensure effective appearance of symptoms, grafts must be kept Identifying the causal agent of CFSD has been a at an average temperature of 28 °C. Where they are challenge since the disease was first discovered. grown in a greenhouse or screenhouse, they may be However, based on 30 years of experimental data and placed under tables. advances made in the development and implementation of molecular techniques, the disease The disease may be eliminated through has been associated with a reovirus—the CFSV thermotherapy and in vitro meristem culture (Mafla et (Cuervo 1990; Calvert et al., 2008). al. 1984). Once treated, grafts must be made with variety Secundina to confirm the planting materials’ The presence of virus-like isometric particles of health. about 70 nm in diameter was observed through the electron microscope in tissue sections from cassava leaves, petioles, stems, and roots. So far, nine species of viral double-stranded (ds) RNA are associated with this disease, and complementary DNA (cDNA) clones to six genomic segments have been synthesized from purified viral dsRNAs. The putative proteins predicted from the sequence of the cassava viral cDNA clones obtained show similarities to the P1, P2, P3, P4, P5, and P10 proteins of rice ragged stunt (reo)virus (RRSV). Phylogenic analyses confirm that CFSV is a member of the family Reoviridae and that it is most closely related to RRSV (Calvert et al. 2008). This virus has been detected in samples collected in different regions of Colombia and has never been detected in healthy plants. To date, 30% of the reovirus’s genome has been sequenced and the existence of genetic variability in this virus was verified by examining infected plants collected from different regions of Colombia. Molecular analysis of the samples revealed at least three different strains of the virus (Calvert et al. 2008; Cuervo 2006). Field studies on transmission indicate that frogskin disease spreads from plant to plant. Although the transmission rate is relatively low, compared with many plant viruses transmitted through a vector, Figure 16-5. Detecting cassava frogskin disease through dissemination patterns suggest that the disease is grafting test. transmitted by an aerial vector. 313 Cassava in the Third Millennium: … The whitefly Bemisia tuberculata has frequently 3. As a method of integrated pest management, been associated with the disease (Angel et al. 1990), tools should be disinfected with detergent or but the insect’s efficiency in transmitting it is low. chlorine solution. Although more than 100 experiments on transmission through B. tuberculata were conducted, no 4. Heavily infected cassava plantings (i.e., at more correlations were found between the number of insects than 10%) must be burned, including both roots and the percentage of transmission. This indicates that and aerial parts. Harvest residues, particularly the vector of this disease has not yet been clearly stems, should also be eliminated because they identified. can re-sprout. When the percentage of plants infected by CFSD is 5. Systems of plant health surveillance and low, dissemination of the disease is very slow. Even so, quarantine must be strengthened to prevent the if due precautions are not taken in each cycle, the introduction of infected planting materials to incidence of CFSD increases. The higher the number national territory, or their mobilization within of infected plants in the field, the faster the rate of that territory. dissemination becomes. Use of vegetative seed (stakes) from infected cassava fields therefore becomes the Cassava frogskin disease in brief disease’s main mode of dissemination. • Frogskin disease is a serious disease for the Parallel research at CIAT has also associated CFSD cassava crop because it directly affects root with a phytoplasm (see Chapter 8). PCR techniques production and can cause yield losses of more allowed the detection of a phytoplasm in leaves than 90%. infected with frogskin disease. (Álvarez et al. 2009) • The disease has been continually spreading and Resistance already affects other regions of Colombia and other countries. Field studies have demonstrated that different levels of resistance exist among cassava varieties. The number • Symptom expression varies with temperature of lines presenting significant levels of resistance after and cassava genotype. several years of evaluation indicates that the use of resistant materials would be the most useful measure • The root system of infected plants usually does for controlling this disease. Resistant lines lose less not develop to the same extent as healthy roots. starch and suffer fewer yield losses, compared with Instead, they become thin and woody, with very susceptible lines. low starch content. Management and control • Although the causal agent has not yet been fully identified, research to date suggests that it The following recommendations are aimed at is probably of viral origin. However, its preventing the introduction and dissemination of association with a phytoplasm, or a frogskin disease in cassava-producing areas: combination of both types of organisms, has not been ruled out. 1. As the disease spreads mainly through the use of contaminated stakes, the most important • The disease spreads mainly by planting control measure is to obtain planting materials contaminated vegetative seed (stakes). It also (stakes) from healthy plantings that have been appears to be transmitted, albeit slowly, by an technically managed, with excellent plant health aerial vector. control. • Different levels of resistance exist among 2. At harvest, the stakes selected for future cassava varieties. Hence, with the use of planting should be placed beside their tolerant varieties, healthy planting materials, respective roots. Later evaluation will confirm and good plant health control, CFSD is one the absence of symptoms. disease that can be controlled. 314 Cassava Viral Diseases of South America Viral diseases in Africa (Zhang et al. 2005). Molecular markers associated with resistance to CMD have been identified and In terms of economic and social importance, perhaps successfully used (Akano et al. 2002; Okogbenin et al. the most relevant cassava diseases that are propagated 2007). More recently there have been reports on the by infected planting materials are: cassava mosaic association of at least two different satellite DNAs with disease (CMD) and cassava brown streak disease CMD (Ndunguru et al. 2008; Patil and Fauquet 2010). (CBSD), two viral diseases only present in Africa and, in the case of CMD, India and Sri Lanka as well (Monger Cassava brown streak disease, on the other hand, et al. 2001; Calvert and Thresh 2002; Thresh et al. remained a minor disease problem restricted to the 1994). Because these diseases are not present in the coastal areas of East Africa. Recently, however, it Neotropics, CIAT has not carried out much research on started to spread westbound and is now a major them. Major research achievements on these diseases concern in many regions of Africa (Hillocks et al. 2002; have been made at the International Institute of Hillocks and Jennings 2003). The disease is also Tropical Agriculture (IITA) based at Ibadan, Nigeria, transmitted by B. tabaci (Maruthi et al. 2005) and has and other collaborating institutions. been characterized from the molecular point of view (Mbanzibwa et al. 2009a, 2009b; Monger et al. 2001; Cassava mosaic disease has attracted the attention Monger et al. 2010). CBSD is named after the brown since long time ago and considerable knowledge on elongated necrotic lesions that often develop on young the disease and its vector (the whitefly Bemisia tabaci) stem tissue as well as in roots (Figure 16-7). Necrosis is available (Legg and Fauquet 2004; Legg and Thresh (A) 2000; Thresh and Cooter 2005; Patil and Fauquet 2009). Symptoms in the leaves are characteristic and easy to identify (Figure 16-6) although variable from a green mosaic to a yellow mosaic, distortion of leaflets, rupturing of tissue, and premature leaf abscission. Resistance to CMD has been identified and analyzed (Fargette et al. 1996; Hahn et al. 1980; Thresh et al. 1998) or developed through genetic transformation (B) Figure 16-6. Cassava mosaic disease (CMD) in cassava. Figure 16-7. Symptoms of cassava brown streak disease (CBSD) (Photos: Legg, Owor, and Okao-Okuja; on (A) leaves in Tanzania and (B) roots in Uganda. G. Mkamilo.) (Photos: R. Howeler.) 315 Cassava in the Third Millennium: … in the roots greatly reduces their economic value. The Calvert LA; Cuervo M; Ospina MD; Fauquet C; Ramírez degree of root necrosis and the characteristic BC. 1996. Characterization of cassava common constrictions associated is variable with some varieties mosaic virus and a defective RNA species. J Gen only expressing these symptoms late in crop growth Virol 77(3):525–530. (Calvert and Thresh 2002). Symptoms can only be observed in the leaves but are highly variable Calvert LA; Cuervo M; Lozano I; Villareal N; Arroyave (“featherly” chlorosis to yellow blotches associated to J. 2008. Identification of three strains of a virus leaf veins) and often inconspicuous. associated with cassava plants affected by frogskin disease. J Phytopathol 156:647–653. In response to the expanding relevance of CBSD, efforts to develop tolerant/resistance cultivars have Costa AS. 1940. Observações sôbre o mosaico comum increased in recent years. New sources of resistance e o mosaico das nervuras da mandioca (Manihot seem to have been found in a backcross population utilissima Pohl.). J Agron (Piracicaba) 3:239–248. involving M. esculenta subsp. flabellifolia (M Fregene 2012, pers. comm.). Costa AS; Kitajima EW. 1972. Studies on virus and mycoplasma diseases of the cassava plant in Brazil. References In: Proc Cassava Mosaic Workshop, Ibadan, Nigeria. International Institute of Tropical Agriculture (IITA), Akano A; Dixon A; Mba C; Barrera E; Fregene M. 2002. Ibadan, Nigeria. p 18–36. Genetic mapping of a dominant gene conferring resistance to cassava mosaic disease. Theor Appl Cuervo M. 1990. Caracterización de los ácidos Genet 105(4):521–525. ribonucleicos de doble cadena (dsRNA) asociados con algunas enfermedades virales en yuca. (Manihot Álvarez E; Mejía JF; Llano G; Loke JB; Calari A; Dubuk B; esculenta Crantz). Fitopat Colomb 14(1):10–17. Bertaccini A. 2009. 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International Plant Components of resistance of cassava to African Genetic Resources Institute (IPGRI), Rome. cassava mosaic virus. Eur J Plant Pathol 102(7): p 163–165. 645–654. Calvert LA; Thresh JM. 2002. The viruses and virus Hahn SK; Terry ER; Leuschner K. 1980. Breeding cassava diseases in cassava. In: Hillocks RJ; Thresh JM; for resistance to cassava mosaic disease. Euphytica Bellotti AC, eds. Cassava: biology, production and 29(3):673–683. utilization. CABI Publishing, Wallingford, UK. p 237–260. Hillocks RJ; Jennings DL. 2003. Cassava brown streak disease: A review of present knowledge and research Calvert LA; Ospina MD; Shepherd RJ. 1995. needs. Int J Pest Manage 49(3):225–234. Characterization of cassava vein mosaic virus: a distinct plant pararetrovirus. J Gen Virol 76(5): Hillocks RJ; Thresh JM; Tomas J; Botao M; Macia R; 1271–1278. Zavier R. 2002. Cassava brown streak disease in northern Mozambique. Int J Pest Manage 48(3): 178–181. 316 Cassava Viral Diseases of South America Kitajima EW; Costa AS. 1966. Particulas esferoidais Monger WA; Seal S; Isaac AM; Foster GD. 2001. associadas ao virus do mosaico das nervuras da Molecular characterization of the Cassava mandioca. Bragantia 25(18):211–221. brown streak virus coat protein. Plant Pathol 50(4): 527–534. Kitajima EW; Wetter C; Oliveira AR; Silva DM; Costa AS. 1965. Morfologia do virus do mosaico comun da Monger WAT; Alicai T; Ndunguru J; Kinyua ZM; Potts mandioca. Bragantia 24(21):247–260. M; Reeder RH; Miano DW; Adams IP; Boonham N; Glover RH; Smith J. 2010. The complete genome Legg J; Fauquet C. 2004. Cassava mosaic geminiviruses sequence of the Tanzanian strain of Cassava brown in Africa. Plant Mol Biol. 56:585–599. streak virus and comparison with the Ugandan strain sequence. Arch Virol 155:429–433. Legg J; Thresh J. 2000. 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Biológico 4(6):177–181. 317 Cassava in the Third Millennium: … Thresh JM; Fargette D; Otim-Nape GW. 1994. The viruses Thresh JM; Cooter TJ. 2005. Strategies for controlling and virus diseases of cassava in Africa. Afr Crop Sci J cassava mosaic disease in Africa. Plant Pathol. 2(4):459–478 54:587–614. Thresh JM; Otim-Nape GW; Fargette D. 1998. The Zhang P; Vanderschuren H; Fütterer J; Gruissem. 2005. components and deployment of resistance to cassava Resistance to cassava mosaic disease in transgenic mosaic virus disease. Integrated Pest Management cassava expressing antisense RNAs targeting virus Reviews 3(4):209–224. replication genes. Plant Biotechnol J 3(4):3853–97. 318 Part D Improvement and Technification 319 CHAPTER 17 Manihot Genetic Resources at CIAT (Centro Internacional de Agricultura Tropical) Gustavo Jaramillo O.1 Introduction 1. To prevent the loss of wild and cultivated species to genetic erosion, caused by pressure Among the dozens of Manihot species, cassava factors such as the adoption of modern (M. esculenta Crantz) is unique in being cultivated. Its varieties, land clearing for urbanization, and allogamous reproductive mode and its highly alteration of natural habitats. heterozygous genetic constitution are the main reasons for propagating the crop by cuttings (or stakes) instead 2. To maintain a high degree of genetic variation of by sexual seed. To preserve the visible phenotypic for use in crop improvement programs. characters, the species has been cultivated and maintained over the years by continuous vegetative Although cryopreservation techniques are currently propagation. being enhanced, conservation in the germplasm bank at CIAT is based mainly on two systems: field and The primary center of origin and diversity is the in vitro. These two modalities of ex situ conservation western Amazon Region. In pre-Columbian times, successfully maintain the status of gene combinations, cassava migrated westwards to Peru, and then that is, without change, as verified by the clones’ northwards to Colombia, and from there entered genetic stability. They also contribute important Central America. It also migrated southwards to elements for the conservation, characterization, and Paraguay and Argentina, although when this migration use of germplasm (Debouck and Guevara 1995). occurred is not precisely known (D Debouck 2001, pers. comm.). In the 1500s, cassava was taken by the This chapter compiles information from several Spanish and Portuguese to Africa and Asia, which then scientific articles and discusses collection, became secondary centers of diversity (Hershey and conservation, characterization, documentation, and Amaya 1979). distribution—all activities for managing a cassava germplasm bank. Within the system of the Consultative Group on International Agricultural Research (CGIAR)2, CIAT has Clone Codification and Nomenclature the global responsibility to conserve the genetic resources of M. esculenta. Currently, the collections According to Jaramillo (1993), the germplasm bank held at the CGIAR centers are under the auspices of the held at CIAT uses the following scheme: Food and Agriculture Organization of the United Nations (FAO), as patrimony for humanity. As with Manihot esculenta varieties other crops, the conservation of cassava germplasm is justified by the following points: For landraces collected inside and outside Colombia, CIAT assigns a three-part code: 1. Agronomist, formerly of Cassava Program, CIAT, Cali, Colombia. M + country + consecutive number E-mail: gjo97@hotmail.com 2. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, Abbreviations, and Technical • The letter “M” corresponds to the first letter of Terminology, this volume. the genus name (Manihot). 321 Cassava in the Third Millennium: … • “Country” refers to the country of origin, and is Wild Manihot species expressed as the first two or three letters of the country’s name, following the FAO code. The species collected are introduced into CIAT. Seeds are used to obtain varieties, for which the following • The consecutive number is in Arabic numerals, five-part code is proposed: and indicates the material’s order of entry at CIAT. M + abbreviation + seed population + hyphen + selected genotype For example, M Bra 383 indicates a cassava clone of Brazilian origin that had entered the collection at Examples include M alt 003-004, and CIAT as number 383. M fmt 001-001, where: Improved hybrids • The letter “M” corresponds to the first letter of the genus name (Manihot). The original identification of hybrids from the CIAT Cassava Improvement Project is conserved by assigning • The “abbreviation” consists of three letters that a four-part code: refer to the species, as according to the list proposed by Chávez et al. (1987; Table 17-2). Type of cross + record of the cross + hyphen + selected genotype • “Seed population” refers to a consecutive number given in the order in which the wild For example, CM 340-55 indicates a hybrid of species was introduced into CIAT. controlled pollination (CM). The parents crossed were M Col 22 and M Col 645, with the cross being recorded • “Selected genotype” refers to the code number as 340. The plant selected was number 55. We point of the selected plant. This number is then used out that a clone’s code never changes. Even in the event consecutively. that one disappears or dies, its code is never assigned to another clone. Cultivated cassava × wild relative hybrids Vulgar, regional, or common names for cassava A four-part code has been proposed, as follows: clones are also important. Usually, farmers give varieties simple names that relate to some characteristic of the Type of cross + record of cross + plant or to its place of origin, for example: hyphen + selected genotype Algodonas: Varieties that are easy to cook • Type of cross: Rojitas: Varieties with red petioles Open pollination = OW (open wild) Llaneras: Varieties from the Llanos (i.e., Polycross = SW Eastern Plains of Colombia) Self-pollination = AW Negritas: Varieties with dark stems or crown Controlled pollination = CW The use of common names has many limitations • Record of cross: and can be confusing, particularly as a common name This consecutive number refers to the may be used for two or more very different or parents used in the cross. A fictitious contrasting genotypes. example would be: Released materials are also given common names, Record, which usually by the institutes or agencies who do the Type refers to cross: Mother × Father releasing. These names relate to details specific to the CW 1 M Col M aes clone or release site such as Catumare, Costeña, 1505 001-002 Caribeña, and Rojita. Table 17-1 details the most common regional cassava varieties in Colombia and the • Selected genotype: materials released in the country to date. This selection number is assigned consecutively, starting at 1. Using the previous example, this would be CW 1–001, CW 1–002, and so forth. 322 Manihot Genetic Resources at CIAT Table 17-1. Examples of important cassava clones, their assigned codes, regional names, year of release in Colombia, and planting site. CIAT code Regional name Other codes assigned Year of release Planting site: country or by ICA or CIAT in Colombia locality in Colombia M Bra 356 Ornamental M Col 2264 Brazil M Col 113 Valluna Hillsides of Valle and Cauca M Col 1438 Llanera CMC 9 Eastern Plains M Col 1468 Mantiqueira Manihot ICA P-11; CMC 40 1984 Inter-Andean valleys M Col 1505 Verdecita Manihot ICA P-12; CMC 76 1984 Inter-Andean valleys M Col 1522 Algodona Caucan hillsides M Col 1684 Matasuegra Quilichao M Col 2058 Popayán Caucan hillsides M Col 2059 Sata Dovio Caucan hillsides M Col 2060 Regional Amarilla Caucan hillsides M Col 2061 Regional Morada Caucan hillsides M Col 2063 Secundina North Coast M Col 2066 Chiroza Gallinaza Quindío M Col 2215 Venezolana 1; Coñito North Coast M Col 2216 Venezolana 2; Ven. Negra North Coast M Col 2253 Blanca Mona North Coast M Col 2257 Americana Mondomo M Col 2258 Batata Mondomo M Col 2259 Selección 40 Mondomo M Col 2260 Negrita Mondomo M Col 2261 Panameña La Cumbre/Cajibío M Col 2478 Chiroza Llanera San Martín, Meta M Col 2479 Vajuna Negra Caucan hillsides M Col 2625 Vivas Cajibío M Col 2627 Chiroza Morada La Libertad, Meta M Col 2628 Chiroza Blanca La Libertad, Meta M Col 2733 Chiroza Falsa Mondomo M Col 2737 Brasilera Meta M Col 2740 Sata Caucan hillsides M Col 2752 Cogolliroja Flandes, Tolima M Col 2753 Aroma Flandes, Tolima M Col 2756 Costeña Supatá, Cundinamarca M Col 2758 Parrita Quilichao/Jamundí M Col 2759 Chiroza Manzana Alcalá, Valle M Cub 74 Señorita Falsa Cuba M Pan 139 Dayana Panama M Tai 1 Rayong 1 Thailand HMC 1 ICA Armenia Manihotica P-13 1986 Inter-Andean valleys CG 1141-1 ICA Costeña 1991 North Coast CM 523-7 ICA Catumare (Raya 7) 1990 Eastern Plains CM 2177-2 ICA Cebucán 1990 Eastern Plains CM 3306-4 ICA Negrita 1993 North Coast CM 3306-19 CORPOICA Colombia 2000-B North Coast CM 3555-6 CORPOICA Sucreña 2000-B North Coast SGB 765-2 CORPOICA Caribeña 2000-B North Coast SGB 765-4 CORPOICA Rojita 2000-B North Coast CM 6740-7 Reina 2000-B Eastern Plains CM 6438-14 Juan V Eastern Plains 323 Cassava in the Third Millennium: … Table 17-2. Manihot species, in alphabetical order and with their respective abbreviations. No. in Species Abbr. No. in Species Abbr. series series 1 M. acuminatissima Müller von Argau acu 51 M. michaelis McVaugh mic 2 M. aesculifolia (Kunth) Pohl aes 52 M. mirabilis Pax mbl 3 M. affinis Pax & K. Hoffmann alf 53 M. mossamedensis Taubert mos 4 M. alutacea Rogers & Appan alt 54 M. nana Müller von Argau nan 5 M. angustiloba Müller von Argau ang 55 M. neusana Nassar neu 6 M. anisophylla Müller von Argau aph 56 M. oaxacana Rogers & Appan oax 7 M. anomala Pohl anm 57 M. oligantha Pax & K. Hoffmann oli 8 M. attenuata Müller von Argau att 58 M. orbicularis Pohl orb 9 M. auriculata McVaugh aur 59 M. paviifolia Pohl pav 10 M. brachyandra Pax & K. Hoffmann bnd 60 M. peltata Pohl pel 11 M. brachyloba Müller von Argau blo 61 M. pentaphylla Pohl pnt 12 M. caerulescens Pohl cae 62 M. peruviana Müller von Argau per 13 M. carthaginensis (Jacq.) Müller von Argau cth 63 M. pilosa Pohl pil 14 M. catingae Ule cng 64 M. pohlii Wawra poh 15 M. caudata Greenman cdt 65 M. populifolia Pax plf 16 M. cecropiifolia Pohl cec 66 M. pringlei S. Watson pri 17 M. chlorosticta Standley & Goldman chl 67 M. procumbens Müller von Argau pcb 18 M. condensata Rogers & Appan con 68 M. pruinosa Pohl pru 19 M. corymbiflora Pax cmf 69 M. pseudoglaziovii Pax & K. Hoffmann pse 20 M. crassisepala Pax & K. Hoffmann cra 70 M. purpureocostata Pohl pur 21 M. crotalariiformis Pohl ctl 71 M. pusilla Pohl psa 22 M. davisiae Croizat dav 72 M. quinquefolia Pohl qfl 23 M. dichotoma Ule dch 73 M. quinqueloba Pohl qba 24 M. divergens Pohl dve 74 M. quinquepartita Huber ex Rogers & Appan qpt 25 M. epruinosa Pax & K. Hoffmann epr 75 M. reniformis Pohl ren 26 M. esculenta Crantz esc 76 M. reptans Pax rpt 27 M. falcata Rogers & Appan fal 77 M. rhomboidea Müller von Argau rho 28 M. filamentosa Pittier fmt 78 M. rubricaulis I.M. Johnston rub 29 M. flemingiana Rogers & Appan fgn 79 M. sagittatopartita Pohl sag 30 M. foetida (Kunth) Pohl foe 80 M. salicifolia Pohl slc 31 M. fruticulosa (Pax) Rogers & Appan fru 81 M. sparsifolia Pohl spr 32 M. glaziovii Müller von Argau gla 82 M. stipularis Pax sti 33 M. gracilis Pohl gcl 83 M. stricta Baillon str 34 M. grahamii Hooker grh 84 M. subspicata Rogers & Appan sub 35 M. guaranitica Chodat & Hassler gut 85 M. surinamensis Rogers & Appan sur 36 M. handroana Cruz han 86 M. tenella Müller von Argau ten 37 M. hassleriana Chodat hsl 87 M. tomatophylla Standley tll 38 M. heptaphylla Ule hph 88 M. tomentosa Pohl tsa 39 M. hunzikeriana Martinez-Crovetto huk 89 M. tripartita (Sprengel) Müller von Argau tpa 40 M. irwinii Rogers & Appan irw 90 M. triphylla Pohl tph 41 M. inflata Müller von Argau inf 91 M. tristis Müller von Argau tst 42 M. jacobinensis Müller von Argau jac 92 M. variifolia Pax & K. Hoffmann var 43 M. janiphoides Müller von Argau jnp 93 M. violacea Pohl vio 44 M. jolyana Cruz jol 94 M. walkerae Croizat wlk 45 M. leptophylla Pax & K. Hoffmann lph 95 M. warmingii Müller von Argau wrm 46 M. leptopoda (Müll. Arg.) Rogers & Appan da 96 M. websteri Rogers & Appan web 47 M. longipetiolata Pohl lon 97 M. weddelliana Baillon wdd 48 M. maguireana Rogers & Appan mag 98 M. xavantinensis Rogers & Appan xav 49 M. maracasensis Ule mcn 99 M. zehntneri Ule zeh 50 M. marajoara Huber mjr SOURCE: Chávez et al. (1987). 324 Manihot Genetic Resources at CIAT Collection or Acquisition Table 17-3. Number of Manihot accessions conserved in the in vitro germplasm bank held at CIAT. Accessions of germplasm banks are usually landraces Source of ISO code Number accession of in vitro or traditional varieties selected by farmers over the accessions years. Many germplasm banks also hold modern Argentina ARG 122 varieties, including those in disuse, and wild species. For JG Hawkes, University of Birmingham (pers. Bolivia BOL 7 comm.), collection is the first and fundamental stage Brazil BRA 1281 on which to develop an appropriate set of holdings. Colombia COL 2000 With it, the following can be guaranteed: China CHN 2 Costa Rica CR 102 a. An optimal collection size that is reasonable in Cuba CUB 84 terms of costs and management, and Dominican Republic DOM 5 possessing broad genetic diversity. Ecuador ECU 116 Fiji FJI 6 b. The exploration of high-priority areas. Guatemala GUA 92 Honduras HND 36 c. The exploration of areas at high risk of genetic Indonesia IND 253 erosion. Jamaica JAM 22 Malaysia MAL 61 d. The introduction of the smallest possible Mexico MEX 106 number of duplicates. Nigeria NGA 19 Nicaragua NIC 4 e. Reduced risk of introducing pests and diseases. Panama PAN 51 To achieve this, full knowledge of the species to Paraguay PAR 208 be cultivated should be available. Peru PER 421 Philippines PHI 6 To attain these objectives, as much scientific Puerto Rico PTR 17 preparation is needed as for logistics. Salvador SLV 11 Thailand TAI 37 Passport data USA USA 10 Venezuela VEN 253 This basic information is taken from both the sample Vietnam VTM 9 and collection site. Hence, for each sample collected or introduced, the respective passport information must ICA-CIAT hybrids CG; CMa be completed. For this purpose, the standard form SG; SMb 408 (Appendix 1, page 340), established by Gulick et al. (1983), should be used. The minimum data for Subtotal 5749 morphological descriptors should also be recorded on Genetic stockc 146 this format. Wild species 33 species in vitro 883 Total 6778 Passport information is of vital importance. It not only identifies each sample, but it also reduces the risk a. CG and CM = hybrids obtained through controlled pollination. b. SG and SM = hybrids obtained through open pollination. of collecting or introducing duplicates, and permits the C. Genetic stock = K family for the study of genetic mapping. recovery of materials missing in the collection. Indeed, SOURCE: www.ciat.cgiar.org/urg a sample with no passport data has no value. Status of the collection at CIAT 883 accessions (13%) correspond to 33 wild species. Of the cassava clones themselves, about 91% are Table 17-3 presents the Manihot accessions that CIAT landraces, while the rest comprise advanced (improved) conserves in the in vitro germplasm bank. This bank cultivars, hybrids, and genetic stock (K family for represents the world’s largest Manihot collection. To genetic mapping). date, it holds 6739 accessions. Of these, 5301 (i.e., about 87%) are M. esculenta clones and the other 325 Cassava in the Third Millennium: … According to Debouck and Guevara (1995), 94% of In-Field Active Genebank the cultivated cassava germplasm collection at CIAT consists of Latin American accessions, that is, from the For the CIAT Cassava Improvement Project, this region recognized as the primary center of diversity. traditional form of conservation has advantages and The introduction of about 800 accessions from the disadvantages. The advantage is one of immediate and National Cassava & Fruits Research Center (CNPMF, its almost permanent availability of stakes and leaves to Portuguese acronym), Brazil, has broadened the make evaluations, either locally or at the experiment holdings at CIAT with a highly representative sample of station, on, for example, morphology, physiology, genetic diversity, especially from Northeast Brazil. resistance to pests and diseases, and nutrient contents. Of the 61 countries where M. esculenta is important, 24 (39%) have contributed to the collection. The disadvantages include the heavy need for High-priority areas for acquiring germplasm are Central space; higher risk of losing materials to problems such America (Nicaragua, Honduras, and El Salvador); as pests, diseases, poor soils, and lack of adaptation; Amazon Region (central and western Brazil); Chaco and higher costs of maintenance and conservation. Region (Paraguay and Bolivia); Venezuela and eastern Colombia; the Guianas and the Ecuadorian mountains; Planting methods and, lastly, the Caribbean Region (Dominican Republic and Haiti, which are regarded as of moderate priority Showcase collection of existing variability. A for collection). showcase collection, highly visible to visitors from the road, is planted at the beginning of the genebank. With respect to Asia, important elite genotypes One or two furrows of five plants each are planted at were introduced into CIAT from national improvement 1 × 1 m, leaving 2 to 3 m between plots. Each plot programs, especially that of Thailand. This country, receives a placard with the clone’s name and a together with China, Vietnam, and the Philippines, has description of its main characteristics. The clones and recently become a priority area for acquiring their characteristics are studied before being chosen germplasm that would effectively represent this for this planting. secondary center of diversity. The genebank proper. All the bank’s accessions The absence of a centralized collection of African are planted in plots, with the number of plants germplasm has restricted representation of this depending on the size of the plot and maintenance continent. However, this situation will improve in the costs. A plot may be planted like a trial, with rows, or near future because the International Institute of like an observation field, with rows planted at 5 to Tropical Agriculture (IITA) is compiling information on 6 plants each and separated by a row in between to national collections and consolidating regional prevent competition between genotypes. They may collections of African germplasm. Advances in virus also be planted on plots of two furrows, with 5 to indexing techniques will also help. 10 plants per plot, leaving a space of at least 2 or 3 m between plots. To reduce the risk of losing materials, More important than country representation is that the planting should be replicated. of existing diversity, for which strategies of acquisition and collection have been established. Furthermore, major collections such as that at CIAT, where the entire collection would occupy more Germplasm Conservation Methods than 6 hectares, the accessions are best classified according to vigor or architecture. The scale used CIAT conserves the international germplasm collection ranges from 1 to 3, where 1 refers to non-branching, by using two systems: active conservation in the field, 2 to medium branching, and 3 to highly branching. and active conservation in vitro. Replication of Planting distances are therefore set according to vigor, germplasm through these two systems guarantees its thus saving area and costs. safety against unforeseen contingencies or natural disasters. Future plans are directed towards enhancing Planting for the field genebank is carried out in cryogenic conservation techniques to thereby alphabetical order of the accessions, according to guarantee long-term conservation that is safe and countries of origin (e.g., M Arg, M Bol, M Bra, and economic. M Cub) and then by number of accession within each country (e.g., M Arg 1, M Arg 2, M Arg 3, and so forth). 326 Manihot Genetic Resources at CIAT Hybrids are best planted by group, starting with vigor, Control measures for superelongation disease and following the order: CG, CM, SG, and SM. (Sphaceloma manihoticola) include the eradication of infected plants and later fumigation with cupric Renewal period fungicides such as Kocide® and copper oxychloride. To reduce the risk of losing materials to biotic and Soil problems. The field bank occupies a large area. abiotic factors, the field bank should be renewed every Some plots are therefore often affected by soil problems year at the beginning of the rainy season. Once renewal such as waterlogging and salinity. In such cases, planting is accomplished, the old bank must be kept for at least may take place elsewhere in the field or the plants may be another 6 to 8 months; it should not be immediately moved to bags that are provisionally placed in an eliminated from the field. This way, stakes for appropriate screenhouse or greenhouse. replanting the new bank are guaranteed and always available. Thus, every field bank remains standing for Excessive branching. The most vigorous clones 16 to 18 months. may close alleys with their branches and foliage, hampering personnel movement and data collection. Maintenance Unfortunately, cutting the foliage increases the possibility of attack from stemborers. Thus, pruning the foliage of A germplasm collection in the field is more highly vigorous clones must be as minimal as possible. complicated to maintain than cassava trials or other types of plots, because of, for example, wide variability Quarantine measures in plant size and adaptation to soil conditions, and the different degrees of resistance and susceptibility to The use of quarantine measures in the field bank aims to pests and diseases. Hence, to be on top of any prevent the introduction or dissemination of diseases and problem that may occur, the bank should be monitored pests. Recommendations include: every 2 or 3 weeks. Pests and diseases must be controlled by applying integrated pest-and-disease • Whenever seed (stakes) or foliage must be cut, management (IPDM), as follows: workers should each carry a recipient containing soap or commercial formalin to disinfect the Weed control. Weeds constitute the factor that machetes. most increases field management costs. Consequently, herbicide use is recommended. • Workers who come from other plots must shake out and clean their work clothes before entering Timely replanting. For a field bank, the minimum the bank. number of plants per plot must be determined. If a plot has fewer plants than this number, then a replanting • All tools and machinery to be used in the bank must be planned. The replanting must be done no later must be disinfected. than 2 months after the original planting, using stakes 40 cm long. • New clones entering the bank, even if they are from the same region, state, or country, should Controlling thrips and other pests. Pests that never be directly introduced. Instead, they should delay growth such as thrips must be controlled until be first planted within a greenhouse or the plants are at least 6 months old to ensure that screenhouse. Later, they may be planted in an these produce seed (stakes) that guarantee renewal. isolated plot and then, once their health is Thrips can be controlled with Sistemin® (a dimethoate) verified, they may enter the bank. at a dosage of 2 cc/L (commercial product). Morphological and agronomic descriptors. Controlling bacterial blight and “Morphological descriptor” is understood as that set of superelongation disease. Bacterial blight characteristics that easily identify and differentiate a (Xanthomonas axonopodis) is a disease that must not genotype, including heritability and stability before exist in a cassava field bank. If, for whatever reason, environmental changes. Descriptors are mainly used to this disease appears, commercial formalin at 5% must characterize the accessions of any given collection. be applied to both the infected plants and their neighbors. The diseased plants are then immediately For the morphological characterization of eradicated. M. esculenta, an up-to-date list of the morphological and 327 Cassava in the Third Millennium: … β-Esterase α-Esterase agronomic descriptors is used. This list was bands bands standardized for cassava by the International Plant (Origin) (Origin) Genetic Resources Institute (IPGRI, now Bioversity International) at a 1995 meeting held in Cruz das Almas Band ID no. Relative (Bahia), Brazil (Gonçalvez et al. 1996). migration (%) As Gonçalves and Guevara noted (1998), the list Band ID no. Relative 1 28.5 migration (%) comprises 13 minimal descriptors that are necessarily included in passport data, another 13 principal and 2 33.5 11 secondary descriptors, a further 21 for preliminary 3 38.5 4 41.5 5 41.5 agronomic evaluation, and 17 for complementary 6 42.5 8{ 47.5 7 45.5 evaluation (e.g., flowers, fruits, and seeds), totaling 9 46.5 10 49.5 11 51.5 75 descriptors. Wild Manihot species require a second 12 52.5 13 54.5 table with different descriptors. 14 58.5 { 15 58.5 16 62.0 17 63.5 18 63.5 To manage a given collection, all accessions must 19 68.5 be duly characterized morphologically. As Iglesias et al. 20 74.5 (1995) point out, the integration of morphological with 21 78.5 biochemical and molecular descriptors, and 22 84.5 accompanied by passport data, form a valuable tool for identifying duplicate accessions in that collection. Biochemical descriptors, using isoenzymes. Figure 17-1. Zymogram showing patterns of isoenzyme bands of Ocampo et al. (1993) indicated that, because of the α- and β-esterases obtained from cassava tissues. limitations presented by morphological markers for evaluating a collection’s materials, techniques for the electrophoresis of total seed protein must be used. was initially done, using the “restriction fragment length However, these are limited to differentiating among polymorphism” (RFLP) but several markers are now genetically close materials. The later development of available such as amplified fragment length isoenzyme electrophoresis techniques largely resolved polymorphism” (AFLP), microsatellites, simple sequence this limitation. These techniques use an electrical field repeats (SSR), or single nucleotide polymorphism (SNP). to separate enzymes present in a raw extract of a tissue. Because of their electrical charges and sizes, the The evaluation of major germplasm collections, enzymes migrate to different positions within a gel using only different types of molecular markers or matrix of either starch or polyacrylamide. isoenzymes, would be laborious and expensive, although the costs and the efficiency has improved Because enzymes catalyze specific biochemical astonishingly fast in recent years. The importance of reactions, an enzyme’s location in the gel can be seen. morphological and agronomic characterization should Through adding a substratum and appropriate not be ignored, but used to complete the first stages of cofactors, reaction products can be detected through characterization. Thus, a large collection would be color reactions. Thus, a visible band is formed at the reduced to small groups, which can then be more site where a given enzyme is located. When different efficiently and economically evaluated, using the molecular forms of an enzyme have affinity for a single isoenzyme or different molecular markers techniques. substratum, these forms make up an isoenzyme family. Duplicate identification and elimination. In a The pattern of isoenzyme bands is analyzed germplasm collection that is maintained vegetatively, quantitatively, using a laser densitometer. It is also accessions are often duplicated. Preliminary qualitatively codified according to the presence or observations of the collection at CIAT estimated that the absence of each of the 22 bands (Figure 17-1). level of duplication is between 20% and 25%. Hershey, cited by Iglesias et al. (1995), noted that the presence of Molecular characterization. According to a large number of duplicates in a germplasm collection Ocampo et al. (1995), given the limitations of has negative implications for their management and use morphological and biochemical descriptors, materials in improvement programs, such as: should be evaluated directly from their genomes. This 328 Manihot Genetic Resources at CIAT • Significant increase in the costs of conservation collection for later confirmation with RFLP and evaluation molecular markers. • Skewing of genetic variability • Narrowing of the genetic base Preliminary agronomic evaluation • Undesirable homozygosis in crosses The CIAT Cassava Improvement Project uses the Iglesias et al. (1995) pointed out that, over the years, following strategy for the preliminary agronomic the Manihot collection at CIAT has been classified by evaluation of the cassava germplasm bank: basic morphological descriptors, which had first been defined by the International Board for Plant Genetic a. Define and select edaphoclimatic areas that Resources (IBPGR, now Bioversity International). In contrast and represent cassava-producing areas. themselves, they do not reliably identify duplicates. However, if biochemical characterization is included, b. Select the group of accessions to be evaluated. based on codifying the presence or absence of 22 isoenzyme bands of α- and ß-esterases in STET gels, c. Plant according to the system “bank’s confidence levels increase greatly. observation field”, which consists of a row of six plants per accession, separated by one furrow in Given the above considerations and to eliminate between. duplicates from the international cassava collection, CIAT developed and applied a model based on the d. Select the best materials and later evaluate these following criteria: in a preliminary yield trial, followed by conventional yield trials. • Preliminary grouping of clones. Grouping is based on within-group identification, the e. Select the materials that best show integration of selection of four primary morphological adaptation, yield potential, resistance to pests characteristics, and 12 electrophoretic bands of and diseases, and root quality. high-level confidence: – Morphological characteristics: Stem f. After several cycles, followed by advanced colenchyma, stem epidermis, stem growth stages, classify the selected materials as “elite” habit, and root external color and recommend them to national programs or – Presence or absence of electrophoretic use them as parental materials in hybridization bands coded 3, 4, 9, 10, 12, 13, 14, 15, 19, schemes. 20, 21, and 22 Documentation and exchange • Secondary grouping of clones. In groups larger than 10 clones, a second level of grouping is According to Debouck and Guevara (1995), this stage made by cluster analysis, using the following encompasses the following genebank activities to group of morphological characteristics and provide information for entering institutional electrophoretic bands of secondary level of documentation system (Oracle): confidence: – Morphological characteristics: Height of first • Passport data branching, color of apical leaf, pubescence, • Morphological and isoenzymatic characterization vein color, lobe shape, lobe width, petiole • Preliminary agronomic evaluation color, cortex color, and root pulp color • Conservation methods and techniques – Presence or absence of electrophoretic • Indexing tests bands coded 1, 6, 8, 18, 2, 5, 7, and 17 • Germplasm exchange • Confirmation in the field. Clones grouped with The mandate assigned to CIAT by the CGIAR possible duplicates are planted in the field and includes not only germplasm conservation, but also its the morphological descriptors are reevaluated. distribution or exchange. Given these goals, the Clones with identical descriptors are checked for following protocol (Figure 17-2) was established for field their passport data. If these are the same, the conservation to minimize the distribution of pests and duplicates are eliminated from the field diseases: collection, but they remain in the in vitro 329 Cassava in the Third Millennium: … Introduction (acquisitions) Field genebank In vitro introduction from other countries Thermotherapy Shipping logistics: Meristems - Request or order for germplasm - Selection and testing of germplasm - Physical preparation of the shipment Indexing tests Healthy plants Micropropagation Additional information: - List of accessions and quantity of tubes sent - Passport data - Descriptive information on morphoagronomic Conservation Shipments traits - Isoenzymatic characterization - Illustrative manual on the postharvest handling of accessions National International - Special information as required by requestor (stakes or in vitro) (in vitro) Management by receptor country - Culture recovery or reconditioning Quarantine requirements: - Plant health monitoring - Plant health certificate from the sender country - Evaluation - Plant health declaration (review by plant pathologist) - Importing permit from the requestor country Propagation (traditional or rapid) or in vitro micropropagation Field Users: 1. CGIAR centers Regional trials 2. National research centers 3. Universities 4. Other germplasm banks 5. Regional organizations Farmer 6. Commercial companies 7. Others Figure 17-2. Exchange of Manihot germplasm (from Debouck and Guevara 1995). 330 Manihot Genetic Resources at CIAT • Prohibit shipments to the exterior of all • Osmotic regulators materials in the form of stakes. • Ethylene inhibitors and capturers • Only indexed stakes may be sent when the Conditions for conservation and renewal materials are for purely experimental or very specific purposes, and will be planted in the The findings of several years of research by CIAT greenhouses of non-cassava-producing scientists indicated the following growth conditions for countries of temperate areas. Furthermore, the in vitro cassava conservation: stakes must be accompanied by the exporting country’s plant health certificate and the • A constant temperature between 23 and 24 °C importing country’s previously obtained • A photoperiod of 12 h of light importing permit. • Light intensity at 1000 lux • Modified culture media (MS) (Table 17-4) • Cassava plant materials may be distributed to • Test tubes of 25 × 150 mm, covered with other countries only as meristem culture from aluminum foil and sealed with plastic plants that underwent thermotherapy and • Conservation of five tubes per clone indexing. Sexual seed may also be distributed, provided that plant health certificates and Under these conditions, the in vitro collection importing permits have been issued. presents an average period of conservation of 12.8 months, ranging from 10.3 to 18.5 months, In Vitro Active Genebank according to country of origin. Debouck and Guevara (1995) noted that the cassava Procedures for in vitro conservation in vitro active genebank (IVAG) consists of maintaining the plants under slow-growth conditions by providing Debouck and Guevara (1995) suggest the following physical and chemical conditions that extend, as far as procedures: possible, the interval before transfer to fresh media is needed. In in vitro conservation, the growth rate of • Enter the materials cultures can be controlled by managing the following • Establish the in vitro culture factors: • Evaluate and monitor the cultures’ aseptic state • Maintain and renew the materials • Temperature • Monitor viability and genetic stability • Inorganic and organic substances • Document and systematize the bank • Growth regulators Table 17-4. Culture media used for the operations of introduction, conservation, transfer to greenhouse, and exchange of in vitro cassava clones. Constituents of the medium Concentration in medium: 4E 8S 17N (for meristem initiation, (for conservation) (for transfer to micropropagation, and exchange) greenhouse) Inorganic salts MS MS 1/3 MS m-Inositol 100 mg/L 100 mg/L 100 mg/L Thiamine HCl 1 mg/L 1 mg/L 1 mg/L Sucrose 2% 2% 2% BAP 0.04 mg/L 0.02 mg/L — GA 0.05 mg/L 0.10 mg/L 0.01 mg/L ANA 0.02 mg/L 0.01 mg/L 0.01 mg/L Agar 0.7 g 0.7 g 0.7 g pH 5.7–5.8 5.7–5.8 5.7–5.8 SOURCE: Debouck and Guevara (1995). 331 Cassava in the Third Millennium: … With regard to “entering the materials”, Colombian • Vein mosaic virus (CVMV), caused by the materials may be introduced as plant materials (or Caulimovirus group stakes), whereas introductions from other countries are • Common mosaic virus (CsCMV), belonging to made only in vitro. The cultures are then multiplied or the Potexvirus group micropropagated. After micropropagation, the cultures • Frogskin disease (CFSD) complex, including are planted in 8S culture medium to conserve them Caribbean mosaic (CMD) and then placed under conditions specific to their • Colombian symptomless virus (CCSpV), establishment. belonging to the Potexvirus group Under these conditions, the cultures are left for All these viruses can be eliminated by using more than 2 weeks and then evaluated for plant thermotherapy techniques associated with meristem development and health, taking into account the culture. Figure 17-3 illustrates the general scheme for following basic aspects: state of the medium, state of eliminating viruses from cassava. The steps are: the tube’s cover and seal, seedling development, plant health, and each tube’s nomenclature and • Applying thermotherapy to meristem culture identification. Once the evaluation is completed, each (i.e., to in vitro seedlings) or to shoots that have material is registered in the database, identified by its germinated from stakes originating in the field varietal name, date of entry, culture medium, and location in the conservation room. • Thermally treated materials undergo indexing tests The materials are stored within this room at five tubes per variety. These are located on shelving and • Micropropagation of healthy clones, using are ordered according to code. Arrangement by stand, in vitro culture techniques row, shelf, and test-tube rack facilitates searching. • Virus detection Maintenance and renewal Indexing tests In vitro conservation requires that conditions in the conservation room be maintained constant, using Indexing tests for cassava viruses can be applied to equipment for regulating temperatures, relative both in vitro seedlings and greenhouse plants. The humidity, and light. Tasks for renewing materials are general methodology used to eliminate cassava viruses also carried out here. includes the following techniques: The materials coming from conservation are • Grafting with the highly susceptible clone micropropagated and then placed in 4E growth M Col 2063 or ‘Secundina’. This test is used medium for recovery and strengthening. When these mainly to detect frogskin disease. To graft, the materials are established, they are propagated again material being evaluated is the main plant and moved to 8S medium for conservation. The (stock), while Secundina is the graft (i.e., following information is recorded in the database: date grafted onto the main plant). Should the stock of exit for subculturing and cause of exit, whether be infected, symptoms will be expressed in the contamination, subculturing, elimination, or exchange. graft (Figure 17-4). With this hypersensitive Finally, genetic stability is monitored, using material, readings are normally made at morphoagronomic and biochemical criteria. 30 days. The graft must be absolutely clean to prevent the reading of false positives. Cleaning clones • The ELISA test is used for the following viruses: According to Guevara and Valderrama (1995), the African mosaic virus (ACMV), vein mosaic virus literature reports more than 50 cassava diseases (CVMV), Colombian symptomless virus produced by viruses, bacteria, fungi, and (CCSpV), and Caribbean mosaic (CMD). phytoplasmas. Among the most important viral diseases are: • Double-stranded RNA (dsRNA) is used to test for the RNA of the following cassava viruses: • African mosaic virus (ACMV), caused by viruses frogskin disease (CFSD); common mosaic virus from the Geminivirus group (CsCMV); and latent viruses. 332 Manihot Genetic Resources at CIAT In vitro clones for Disinfected stakes from field international clones from national collections exchange or from introduced materials 3 to 4 weeks recovery Change of growth medium (temperature: 26–28 °C) In vitro thermotherapy Meristem culture Materials from areas with Materials from areas presumed presence of CFSD free of CFSD Grafting of Secundina ELISA PCR onto stock clone for Negative CsCMV; CsVX; CBB; phytoplasmas; evaluation CCSpV; ACMV; CVMV CVMV Negative Positive Positive Thermotherapy Thermotherapy Thermotherapy Meristem culture Meristem culture Meristem culture Conservation in 8S medium Figure 17-3. Procedures for detecting and eliminating cassava pathogens (from Debouck and Guevara 1995). For an explanation of abbreviations and acronyms, see Appendix 1: Acronyms, Abbreviations, and Technical Terminology, this volume. 333 Cassava in the Third Millennium: … • Preculture on solid C4 medium for 3 days, in the dark, and at temperatures between 26 and 28 °C • Cryoprotection in liquid medium for 2 h on ice • Dehydration or drying for 1 h, using filter paper, at room temperature • Programmed slow cooling, using a CryoMed freezer at -40 °C • Immersion and storage in liquid nitrogen for at least 3 h • Heating to 37 °C for 45 s • Re-culturing: – R1 and R2 balance media for 2 days each – Transfer to CIAT 4E semisolid medium • Evaluation: – Tissue survival or viability – Shoot formation after 1 month Figure 17-4. The highly susceptible cassava variety Secundina (with leaves) is grafted onto the stock (stake of Studies on cryogenic conservation currently the clone being evaluated). (Photo by Norma Flor, Genetic Resources Unit, CIAT.) conducted at CIAT have led to the development of two main methodologies: • Polymerase chain reaction (PCR) is used to • For botanical seed, working with M. esculenta detect bacterial blight (CBB), phytoplasmas, and M. carthaginensis. This method permits and vein mosaic virus (CVMV). total recovery of viable plants. Cryogenic Conservation • For planting materials, which itself has two methodologies: According to Escobar et al. (1998), the in vitro base – Classical, where the varietal response is genebank (IVBG) is founded on the cryoconservation of modified. clones, that is, on the total suppression of their growth, – New, which has a practical sense in that metabolism, and other biological processes by applying active work is done, especially on the “core’” very low temperatures. Mutations are also prevented. collection. The technique is called Conservation thus becomes indefinite. encapsulation/dehydration. The method consists of isolating precultured The IVBG constitutes a basic working, but inactive meristems by using a cryoprotectant agent, completing collection that is conserved for the long term. Once the a stage of controlled cooling, and transferring to liquid technique is completely developed, this bank will be nitrogen at 196 °C. The protocol established for able to totally maintain the germplasm’s genetic cassava cryopreservation at CIAT is as follows: stability. This collection is expected to become an efficient and economic alternative for conserving • Isolation of meristems that measure 2 to 3 mm cassava clones. Thus, cryopreservation would be a safe long and had been taken from a 3 to 4-month- method for long-term storage in a reduced space. It old in vitro culture would also be free of changes and relatively low-cost. • Pretreatment in 4E medium for 3 days Debouck pointed out that cryoconservation is not envisioned as a distribution method, for which the 334 Manihot Genetic Resources at CIAT in vitro active genebank is more suitable. The main • It consists mainly of landraces, for which the activities involved in cassava germplasm exchange by passport data are complete. the CIAT in vitro bank are presented in Figure 17-2. • It does not include duplicated accessions. Nucleus or Core Collection • It has been well characterized, using The concept morphological and molecular descriptors. The concept of a “nucleus” or “core” collection was • Traits such as agronomic and physiological proposed by Frankel in 1984 (cited in Iglesias et al. characteristics, root quality, and resistance to 1992) to define a set of accessions that, with a diseases and pests have been evaluated. minimum of repetition, would represent the genetic diversity of a given species. The accessions that • Information on the crop’s evolution and become part of a core collection are selected for their different centers of genetic diversity is representativeness and ecological or genetic adequate. differences. Iglesias et al. (1992) also discuss the following points: Collection size • A core collection must be constituted in such a Brown (cited in Iglesias et al. 1992) recommends way that its genetic diversity is maximized. This selecting 5% of all accessions in large collections such means that duplicated or closely related as for maize, and 10% for small collections such as for accessions must be excluded. Normally, core cassava. Also taken into account are factors for collections for cultivated species are separated conservation and the limits imposed by sample size on from those of their wild relatives. the evaluation of certain characteristics. Hence, a core collection of 600 to 650 accessions was first proposed • For a given species, other groups of accessions as an objective for the cassava collection at CIAT. may exist for specific purposes. These can also be core collections. An example is the group of Parameters for definition elite clones within the germplasm collection held at CIAT. The general criteria for defining the cassava core collection were classified into four groups: Advantages of a core collection • Geographic origin As a representative sample, a core collection has the • Diversity of morphological characteristics following advantages: • Diversity in the band patterns of α- and ß-esterases • It increases efficiency in the use of genetic • A priori selection of accessions based on the resources by facilitating evaluation and access following requisites: to existing genetic variability. – Clones included in studies by the Cassava Biotechnology Network (CBN) • It enables the use of methodologies that can – The most frequently planted local varieties later be extended to the entire collection. – Elite clones from the cassava improvement program; these genotypes represent, with • Facilitates the possibility of duplicating high frequency, those genes that favor a accessions for other institutions. large number of characteristics Requisites To sample the main collection’s genetic diversity, emphasis was given to geographic origin. About Ideally, a core collection for a cultivated species has the two-thirds of accessions in the core collection were following characteristics: selected this way (Table 17-5). • It covers the total range of genetic variability existing in that species 335 336 Table 17-5. Parameters, including country of origin, for determining the number of accessions to be selected for the cassava core collection held at CIATa. Origin No. of Local Level of Base Importance Total diversity of Diversity of Factor of Sum of Geographic Morphological Divers. of A priori Final no. of access. cultivars duplic. number as diversity country in ecosystems correction weightsc origind diversitye esterase selectionf access.g (%) (%) of local center collection at by sizeb cultivars CIAT Score Weight 1 Score Weight 2 Score Weight 3 Argentina 16 40 10 6 1 1.00 25 0.75 2 0.40 1.00 2.15 2 4 0 3 8 Bolivia 3 100 0 3 1 1.00 5 0.95 2 0.40 1.00 2.35 1 2 0 3 3 Brazilh 1637 95 20 1244 1 1.00 40 0.60 5 1.00 0.20 0.52 110i 13 15 20 101 China 2 100 0 2 3 0.50 25 0.75 3 0.60 1.00 1.85 1 0 0 2 2 Colombia 1907 95 20 1449 1 1.00 75 0.25 5 1.00 0.20 0.45 111 15 13 14 146 Costa Rica 147 40 20 47 2 0.75 80 0.20 2 0.40 0.80 1.08 9 7 5 4 23 Cuba 74 90 20 53 2 0.75 80 0.20 2 0.40 0.80 1.08 10 5 1 2 18 Domin. Rep. 5 100 10 5 2 0.75 10 0.90 3 0.60 1.00 2.25 2 2 0 4 5 Ecuador 117 100 25 88 1 1.00 50 0.50 3 0.60 0.80 1.68 25 6 0 4 32 Fiji 6 100 10 5 3 0.50 50 0.50 1 0.20 1.00 1.20 1 0 0 2 2 Guatemala 91 100 50 46 2 0.75 80 0.20 2 0.40 0.80 1.08 8 6 0 2 15 Indonesia 51 10 15 4 3 0.50 10 0.90 3 0.60 0.80 1.60 1 0 2 5 7 Malaysia 68 70 15 40 3 0.50 50 0.50 2 0.40 0.80 1.12 8 0 1 6 15 Mexico 100 95 30 67 2 0.75 75 0.25 3 0.60 0.80 1.28 14 6 0 2 20 Panama 42 100 20 34 2 0.75 75 0.25 2 0.40 0.80 1.12 6 2 0 2 9 Paraguay 192 100 20 154 1 1.00 80 0.20 2 0.40 0.60 0.96 25 8 3 7 40 Peru 405 95 20 308 1 1.00 60 0.40 2 0.60 0.60 1.20 63 10 3 2 76 Philippines 6 30 0 2 3 0.50 5 0.95 2 0.40 1.00 1.85 1 0 0 2 2 Puerto Rico 15 40 15 5 2 0.75 60 0.40 2 0.40 1.00 1.55 1 2 0 4 7 Thailand 8 10 0 1 3 0.50 75 0.25 2 0.40 1.00 1.15 0 0 0 4 4 USA 9 0 0 0 3 0.50 100 0 1 0.20 1.00 0.70 0 0 0 4 4 Venezuela 240 95 20 182 1 1.00 60 0.40 4 0.80 0.60 1.32 41 9 3 3 55 CIAT clones 317 0 0 0 0 3 5 27 33 IITA clones 19 0 0 0 0 0 0 3 1 Total 5477 3744 440 100 51 121 630j a. Access. = accessions; duplic. = duplication; Score of a scale; divers. = diversity. b. Factor of correction according to the size of the collection, where >1000 = 0.2; 400–1000 = 0.4; 100–400 = 0.6; 20–100 = 0.8; 1–20 = 1.0. c. Sum of weights (1, 2, and 3) × factor of correction according to size of collection. d. Number of accessions for core collection = (sum of weights × base number of local cultivars × constant), where the constant = 0.17. e. Clones included in the pilot in vitro active genebank (IVAG) at CIAT/IBPGR (now Bioversity International). f. Selected by three criteria: • Included in studies conducted by the Cassava Biotechnology Network (CBN), based on the diversity of geographic origin and agronomic value • Most widespread cultivars • Elite clones held at CIAT and the International Institute of Tropical Agriculture (IITA) g. The final number may be less than the sum of the columns, given that the same clone may have been selected for different parameters. h. Includes 800 accessions introduced in 1991/92. i. Sixty accessions will be introduced, followed by another 800 new accessions, totaling 970 in all. j. The final number may be smaller after detecting and eliminating duplicates. SOURCE: Iglesias et al. (1992). Manihot Genetic Resources at CIAT Clones included in the core collection In practical terms, 70% to 80% of the core collection, as initially defined, could reasonably be The application of all the parameters mentioned expected to remain unmodifiable. The remainder may above enabled the definition of a first list of clones to be subjected to change, in accordance with new include in the core collection at CIAT (Table 17-6). information obtained over the short and medium term. Iglesias et al. (1992) also noted that, when Wild Manihot Species defining a core collection, the question arises of how flexible its structure should be in accepting changes. Few crops have such a high number of related or wild Presumably, excessive dynamism would not be good species as M. esculenta. According to Chávez (1990), if what is desired is a reference sample for the wild Manihot species constitute a valuable resource for systematic evaluation of different characteristics. improvement programs, because of their: However, such a structure should allow the incorporation of new accessions that will increase • High potential as sources of genes for even more the selected sample’s representativeness resistance to pests and diseases of the genetic diversity existing in the field. Table 17-6. Clones included in the core collection at CIAT, using different parameters. Origin Number of clones included according Final number to parameter: in core Geographic Morphological Diversity of A priori origin diversity esterases selection Argentina 2 4 0 3 8 Bolivia 1 2 0 3 3 Brazil 110 13 15 20 101 China 1 0 0 2 2 Colombia 111 15 13 14 146 Costa Rica 9 7 5 4 23 Cuba 10 5 1 2 18 Dominican Republic 2 2 0 4 5 Ecuador 25 6 0 4 32 Fiji 1 0 0 2 2 Guatemala 8 6 0 2 15 Indonesia 1 0 2 5 7 Malaysia 8 0 1 6 15 Mexico 14 6 0 2 20 Nigeria 0 0 0 3 3 Panama 6 2 0 2 9 Paraguay 25 8 3 7 40 Peru 63 10 3 2 76 Philippines 1 0 0 2 2 Puerto Rico 1 2 0 4 7 Thailand 0 0 0 4 4 USA 0 0 0 4 4 Venezuela 41 9 3 3 15 Hybrids 0 3 5 27 33 Total 440 100 51 131 590 SOURCE: Iglesias et al. (1992). 337 Cassava in the Third Millennium: … • Tolerance of most of the common abiotic represent the species, with the first letter being taken stresses from the first letter of the species’s name. No abbreviation is repeated. For the sections, the • Broad genetic variability for important abbreviations used each consists of three uppercase agronomic and biochemical characteristics letters, thus differing from the lowercase abbreviations such as low hydrocyanic acid content and high for species. protein content The list contains all the taxonomically critical wild • Highly desirable C4 photosynthetic route species of the Manihot genus as published by Rogers and Appan (1973). It also includes the new species Because of the importance of these species and recently described by Nassar (2000). Synonyms are the considerable genetic erosion they suffer, one excluded. Allem (2002) provided an update of the conservation option is to establish an ex situ origins and taxonomy of cassava. germplasm bank with these valuable materials. Possible contributions Coding and abbreviations For Chávez (1990), current studies have demonstrated Within the Manihot genus, all species studied have the that many of the wild species have potential in same number of chromosomes: 2n = 36. To date, improvement programs as sources of genes for 98 wild species plus cassava have been recognized, beneficial characteristics, including resistance to pests with five more being described. Taxonomically, the and diseases, adaptation, and tolerance of abiotic Manihot genus is separated into 18 sections. stresses. Table 17-8 details the possible contributions that some wild species may make. Chávez et al. (1987) indicated that, for coding, CIAT has developed and set up a standardized system of nomenclature for Manihot species and sections. Tables 17-2 and 17-7 list the abbreviations of all Table 17-8. Outstanding characteristics and possible benefits 99 species and 18 sections. In this system, an from wild Manihot species. abbreviation is made up of three lowercase letters to Species Characteristic and/or benefit M. pringlei Low cyanide content Table 17-7. Manihot sections in alphabetical order, with their M. glaziovii Resistance to African mosaic virus respective abbreviations. M. pseudoglaziovii Resistance to bacterial blight; Serial Section Abbreviation resistance to drought; tolerance of cold number M. reptans Resistance to bacterial blight 1 Anisophyllae Rogers & Appan ANY M. tristis High starch content 2 Brevipetiolatae Pax BRE M. angustiloba High starch content 3 Caerulescentes Rogers & Appan CAE M. neusana Resistance to stemborer 4 Carthaginenses Rogers & Appan CAR M. pohlii Resistance to stemborer 5 Crotalariaeformes Rogers & Appan CRO M. grahamii Resistance to stemborer; tolerance of cold 6 Foetidae Rogers and Appan FOE M. chlorosticta Adaptation to saline soils 7 Glaziovianae Pax GLA M. carthaginensis Resistance to drought 8 Graciles Rogers & Appan GCL M. dichotoma Resistance to drought 9 Grandibracteatae Pax GND M. irwinii Excellent adaptation to lateritic acid 10 Heterophyllae Pax HET soils 11 Manihot P. Miller MAN M. tripartita Excellent adaptation to lateritic acid 12 Parvibracteatae Pax PAR soils 13 Peltatae Pax PEL M. orbicularis Excellent adaptation to lateritic acid soils 14 Peruvianae Rogers & Appan PER M. peltata Tolerance of acid soils 15 Quinquelobae Pax QUI M. attenuata Tolerance of cold 16 Sinuatae Pax SIN M. rubricaulis Tolerance of cold 17 Tripartitae Rogers & Appan TRI M. gracilis Dwarf type 18 Variifoliae Rogers & Appan VAR SOURCE: Chávez (1990). 338 Manihot Genetic Resources at CIAT References Hershey C; Amaya A. 1979. Germoplasma de yuca: Evolución, distribución y colección. In: Manual de To save space, the acronym “CIAT” is used instead of producción de yuca. CIAT, Cali, Colombia. “Centro Internacional de Agricultura Tropical”. p E15–E26. Allem AC. 2002. The origins and taxonomy of cassava. Iglesias C; Hershey C; Iwanaga M. 1992. Importancia In: Hillocks RJ; Thresh JM; Bellotti AC, eds. Cassava: de las colecciones núcleo para la conservación y biology, production and utilization. CABI Publishing, utilización de los recursos genéticos. In: Proc Taller Wallingford, UK. p 1–16 Internacional sobre Recursos Genéticos de la Yuca, held at CIAT, Cali, Colombia, August 1992. CIAT, Cali, Chávez R; Roca W; Hershey C. 1987. Abreviatura para los Colombia. p 17–22. nombres de las especies silvestres de Manihot. Yuca Bol Inf 11(2):5–6. Iglesias C; Guevara C; Ocampo C; Jiménez A. 1995. Identificación de duplicados genéticos en la colección Chávez R. 1990. Especies silvestres de Manihot: Un de germoplasma de yuca conservada en el Centro recurso valioso. Yuca Bol Inf 14(1):2–5. Internacional de Agricultura Tropical (CIAT). CIAT, Cali, Colombia. 12 p. (Multicopied.) Debouck D; Guevara C. 1995. Unidad de Recursos Genéticos: Laboratorio de cultivo de tejidos. CIAT, Jaramillo G. 1993. Terminología, codificación y Cali, Colombia. 16 p. (Multicopied.) disponibilidad de germoplasma en mejoramiento de yuca. CIAT, Cali, Colombia. 16 p. (Multicopied.) Escobar R; Mafla G; Roca W. 1998. Cassava cryopreservation, I. In: Engelmann F; Takagi H, eds. Nassar NMA. 2000. Cytogenetics and evolution of Cryopreservation of tropical plant germplasm: current cassava (Manihot esculenta Crantz). Genet Mol Biol research progress and aplication. Japan International 23:1003–1014. Research Center for Agricultural Sciences (JIRCAS); International Plant Genetic Resources Institute Ocampo C; Hershey C; Iglesias C; Iwanaga M. 1993. (IPGRI), Rome, Italy. p 404–406. Esterase isozyme fingerprinting of the cassava germplasm collection held at CIAT. In: Roca W; Gonçalvez WMG; Costa IRS; Vilarinhos AD; Oliveira RP. Thro AM, eds. International Scientific Meeting of 1996. Banco de Germoplasma de Mandioca: Manejo, the Cassava Biotechnology Network (CBN), held conservação e caracterização. Documentos CNPMF in Cartagena, Colombia, August 1992. CIAT, Cali, No. 68. Empresa Brasileira de Pesquisa Agropecuária Colombia. p 81–89. (EMBRAPA), Cruz das Almas, Brazil. 103 p. Ocampo C; Angel F; Jiménez A; Jaramillo G; Hershey Gonçalves WM; Guevara C. 1998. Descritores C; Granados E; Iglesias C. 1995. DNA fingerprinting morfológicos e agronômicos para a caracterização to confirm possible genetic duplicates in cassava de mandioca (Manihot esculenta Crantz). In: Proc germplasm. In: Proc Second International Scientific Latin American workshop on Recursos Genéticos Meeting of the Cassava Biotechnology Network de Mandioca, held at Cruz das Almas (Bahia), Brazil, (CBN), held in Bogor, Indonesia, August 1994. CIAT, in October 1995. Centro Nacional de Pesquisa Cali, Colombia. Vol 1, p 145–151. de Mandioca e Fruticultura Tropical (CNPMF) [of the] Empresa Brasileira de Pesquisa Agropecuária Roca W; Chávez R; Marín ML; Arias D; Mafla G; Reyes R. (EMBRAPA), Cruz das Almas, Brazil. p 78–83. 1989. In vitro methods of germoplasm conservation. Genome 31(2):813–817. Guevara C; Valderrama A. 1995. Esquema de indexación para un banco de germoplasma de Manihot Rogers DJ; Appan SG. 1973. Manihot and manihotoides esculenta. Unidad de Recursos Genéticos [of] CIAT, (Euphorbiaceae). A computer-assisted study. Flora Cali, Colombia. 13 p. (Multicopied.) Neotropica. Monograph No. 13. Hafner Press, New York. 272 p. Gulick P; Hershey C; Esquinas J. 1983. Genetic resources of cassava and wild relatives. International Board for Plant Genetic Resources (IBPGR), Rome, Italy. 56 p. 339 Cassava in the Third Millennium: … Appendix 1: Form for Collecting Cassava Materials Note: The section on descriptors must be answered Genus: Species: Subspecies: Name of collectors (initials): Provisional code (collected sample) Institution responsible: Collection date (year/month/day): International code (collected sample) Country of collection: Province/State: Site: Closest municipality or town: Distance (km): Address: Latitude: degrees: minutes: North South Longitude: degrees: minutes: East West Altitude: meters above sea level: Sample’s immediate origin (encircle): Wild 1 Local market 5 Farm field 2 Commercial market 6 Local store 3 Institute 7 Household plot or garden 4 Other: 8 Sample’s status (encircle): Wild 1 Landrace 4 Weedy 2 Improved cultivar 5 Improved line 3 Other: 6 Local name: Photo (encircle): Yes No Photo code: Sample type (encircle): Plant 1 Seed 2 Both 3 Herbarium sample from the site (encircle): Yes No Amount of material (number of seeds or stakes): Primary morphological descriptors (encircle): Color of apical leaf 3 5 7 9 Color of adult leaf 3 5 7 9 Color of petiole 1 2 3 4 5 7 9 Lobe shape 1 2 3 4 5 6 7 8 9 External stem color 3 4 5 6 7 8 9 External root color 1 2 3 4 Color of root cortex 1 2 3 4 Color of root pulp 1 2 3 Growth habit (encircle): Tree 1 Shrub 2 Creeper 3 Other 4 Part of plant used (encircle): Roots 1 Foliage 2 Principal use (encircle): Human consumption (fresh) 1 Animal consumption (dried or processed) 4 Human consumption (dry or processed) 2 Starch extraction 5 Animal consumption (fresh) 3 Other: 6 340 Manihot Genetic Resources at CIAT Special qualities according to farmers (encircle): Yield 1 Resistance to diseases 5 Starch content 2 Resistance to pests 6 Culinary quality 3 Edaphic adaptation 7 Roots tolerant of PPD 4 Other: 8 Notable defects according to the farmer: Diseases or pests and their severity: (Scale of severity, where 1 = little damage; 2 = moderate damage; 3 = severe damage) Disease or pest Severity Disease or pest Severity Crops in association: Yes 1 None 2 Details: Information on wild species sample: Natural vegetation (encircle): Wet rainforest 1 Spiny forest 6 Humid rainforest 2 Desert thicket 7 Semi-humid rainforest 3 Desert 8 Dry forest 4 Other: 9 Very dry forest 5 Topography (encircle): Swampy 1 Undulating 5 Flood-prone plains 2 Hills 6 Vega 3 Mountainous 7 Plains 4 Other: 8 Soil texture (encircle): Sandy 1 Clayey 5 Loamy-sandy 2 Stony 6 Loam 3 Organic 7 Loamy-clayey 4 Other: 8 Drainage (encircle): Poor 1 Moderate 2 Good 3 Excessive 4 Slope (encircle): Flat or almost flat (<4º) 1 Moderate slope (4º–14º) 2 Steep slope (>14º) 3 Brightness (encircle): With sun 1 With shade 2 Comments: 341 Cassava in the Third Millennium: … CHAPTER 18 Cassava Genetic Improvement Hernán Ceballos1, Nelson Morante1, Fernando Calle1, Jorge Iván Lenis1, Gustavo Jaramillo O.2, and Juan Carlos Pérez2 Introduction generation after generation, without genetic segregation occurring. In this regard, cassava and A highly profitable investment in agricultural research other crops with vegetative reproduction such as sweet in terms of return to research is crop genetic potato, potato, yam, and fruit trees offer a great improvement. Increases in productivity of principal advantage over those that multiply only through grains and oil-bearing crops observed during the 20th botanical or sexual seed. century have been demonstrated to be due mostly to their genetic improvement (Fehr 1987). From the genetic viewpoint, cassava varieties are, in fact, hybrids between two selected parents. Cassava Cassava has also benefited from technological improvement starts with thousands of crosses and contributions, particularly from genetics (Kawano et al. continues with an elaborate and expensive evaluation 1998; Kawano 2003), which has enabled the process (described in more detail below) to finally development of new varieties that more adequately identify a few individuals that are genetically superior. meet the needs of farmers and consumers. Colombia Outstanding hybrids result from a cross that produces possesses one of the few cassava genetic improvement a unique and specific combination of genes that programs found in the world, thus greatly favoring confers on them the hybrid vigor that characterizes cassava growers in this country. This chapter describes them. the methodologies used by this program and its most relevant achievements. An optimal combination will give good hybrid vigor and result in a successful variety (i.e., a cultivar that Advantages and Disadvantages of farmers will plant). Very few combinations of Vegetative Reproduction progenitors stand out, which means that thousands of crosses must be evaluated every year. Once a Genotype refers to all the genetic characteristics of an genetically superior cassava plant is identified, it can be individual. To a great extent, plant breeding consists of multiplied vegetatively to deliver that genetic superiority identifying genetically desirable individuals, that is, to farmers. those that have a superior genotype. For many other crops, where reproduction is not Cassava is reproduced vegetatively. Each and every vegetative, farmers may also plant hybrid materials propagule obtained through vegetative reproduction is (e.g., maize, sorghum, and carrot). These hybrids result genetically identical, and constitutes what is known as from combinations of 2 to 4 progenitors that have been a clone. This implies that when a desirable genotype is specifically identified because when they are crossed, identified, the latter can be multiplied and perpetuated, they produce outstanding material, similar to what occurs with cassava. The seed resulting from such crosses is what farmers plant. 1. Breeder, Biologist, Agronomist, and Agronomist, respectively, Cassava Program, CIAT, Cali, Colombia. E-mails: h.ceballos@cgiar.org; n.morante@cgiar.org; These hybrids are identified genetically by the term f.calle@cgiar.org, and j.lenis@cgiar.org F1 (i.e., first filial generation). Thus, the vigor observed 2. Agronomist and Breeder, respectively, formerly of Cassava Program, CIAT. E-mails: gjo97@hotmail.com and in F1 of a commercial hybrid cannot be transmitted juanchoperezv@hotmail.com adequately to later generations. If farmers plant seed 342 Cassava Genetic Improvement harvested from F1 (technically identified as F2 or Another disadvantage of vegetative multiplication is second filial generation), “degeneration” can be the frequent accumulation of diseases, especially viral, observed. In other words, the high yield, uniformity, in planting materials. Once the plant acquires a and other desirable characteristics that farmers receive pathogen (particularly a virus), it is highly unlikely that it from the purchased hybrid seed are gradually lost in can free itself of that pathogen. Hence, all the stakes subsequent filial generations. Hence, farmers must extracted from that plant will contain the pathogen. purchase hybrid seed year after year. The scientific Good plant health management of cassava seed is basis of this “degeneration” is genetic segregation, therefore essential, and farmers must be encouraged to mentioned above. make minimal efforts to maintain the health of their planting materials. In contrast, botanical seed, resulting Technically, what occurs with genetic segregation from sexual reproduction, is usually free of viral is that the genes present in an F1 hybrid are shuffled, pathogens. in the same way as a pack of cards are before being dealt. When an individual of any species undergoes Another adverse aspect of vegetative multiplication sexual reproduction, the genes present in the individual is that stakes or trimmed stems require much more are reorganized. From the evolutionary viewpoint, this care than botanical seed. The conditions under which is critical because it enables the creation of new genetic planting materials are stored will affect plantlets vigor forms or recombinations that constitute the foundation and thus influence the crop’s general performance. of evolution. From the agricultural viewpoint, however, this is sometimes inconvenient, as the shuffling of For the above reasons, this paper gives special genes, which creates new genetic forms, destroys that attention to the management of cassava vegetative seed specific, difficult-to-obtain, yet desirable combination to achieve an optimal physiological and sanitary state of genes once a successful hybrid produces F1 seed. that maximizes returns to farmers. Once a superior hybrid is identified in crops such as maize, the problem of how to perpetuate it then has to A final drawback of vegetative multiplication is the be solved, because the option of vegetative volume that planting materials occupy. A 10-ton truck reproduction is not available. Hence, cloning would can load enough cassava seed for about 10 ha. The provide great advantage for such commercial hybrids. same truck could transport enough maize seed for about 400 ha. To multiply a hybrid and produce seed for sale to farmers, the parental lines must be “fixed” by Factors for a Successful Plant Breeding producing highly endogamous lines and later crossing Program them. This procedure complicates farmers’ access to hybrid materials and makes them much more costly. In The success of a genetic improvement program for a contrast, with cassava, once the genetically superior crop depends mainly on: plant is identified, it can be reproduced vegetatively in such a way that farmers do not need to purchase 1. Continuity over time hybrid seed year after year. However, as described later, 2. Appropriate definition of objectives the use of inbred parents allows for much more refined 3. Implementation of a good improvement scheme processes of improvement. Non-additive genetic 4. Availability of representative environments for effects (dominance and epistasis), responsible for evaluations heterosis, can be exploited more efficiently. It also enables the implementation of improvement methods Continuity over time such as backcrossing, which has been, and still is, widely used (Allard 1960; Blair et al. 2007). This is particularly important for cassava because of its prolonged selection cycle, which typically requires more Vegetative reproduction nevertheless presents than 5 years. The rest of the chapter describes this some drawbacks: the rate of vegetative multiplication issue in detail, as do other publications such as in cassava is very low—one plant produces only 6 to Ceballos et al. (2004, 2007a) and Morante et al. (2005). 10 cuttings or stakes—whereas, in sexual In contrast, a selection cycle for grains or legumes can reproduction, the rate is usually much higher. For be completed in less than one year. Crop genetic example, a maize cob normally produces about improvement is a continuous and gradual process that 400 seeds, so that the multiplication rate would requires several cycles to achieve its objectives. As a be 1:400. result, a fundamental need is to ensure that resources 343 Cassava in the Third Millennium: … will guarantee the continuous execution of the activity. Any genetic material produced should also Objectives for the process should be more or less adequately meet the needs of users or end consumers. stable, and changes introduced gradually and only when These can be described as four major destinations for their need has been convincingly confirmed. cassava in Colombia (as with the rest of the world), each of which defines specific requirements from the Adequate definition of objectives crop. Aspects of quality are becoming extremely important and are described in more detail in the next Plant breeders should adequately define the objectives section. of their programs. Usually, for most crops and, in this regard, cassava is no exception, the goal is to increase Developing a good improvement scheme yield per unit area; also to (1) maximize stability of production so that farmers will have adequate food Once defined, the improvement program’s specific security from their harvest, and (2) maintain or improve objectives should be implemented. For this, a good product quality so that this better meets the needs of improvement scheme is necessary. Because this issue end consumers. Stability of production is important and is complex, it is treated in more detail as this chapter is achieved when the developed material is genetically develops. tolerant or resistant to the main biotic and abiotic production constraints. Representative environments Because cassava is usually grown in marginal Finally, to identify superior cassava varieties that adapt environments, it is highly susceptible to natural to the environments for which they are directed, disasters such as drought or prolonged winters. A evaluations in representative sites of the targeted successful variety must necessarily have qualities that environments must be conducted. Here, a compromise enable it to bear these and other stresses. Each must be made on the number of environments that can environment where cassava is grown has its own list of be handled with the objective of maintaining the widest factors that limit production. In the North Coast of diversity of situations in which, in practice, this crop is Colombia, for example, the absence of rains and found. availability of water form the principal abiotic constraints to productivity. With regard to pests and diseases, mites For Colombia, six relevant and distinctive (Mononychellus tanajoa, M. caribbeana, Tetranychus environments can be determined for cassava: urticae, T. cinnabarinus, Oligonychus peruvianus), (1) subhumid Caribbean (Department of Atlántico), thrips (Frankliniella williamsi), and the stemborer (2) humid Caribbean (Córdoba), (3) Orinoquía (Meta), (Chilomima clarkei) pose the most common problems. (4) inter-Andean valleys (Valle del Cauca), (5) high- altitude areas of about 1800 m above sea level (Cauca), In Valle del Cauca, in contrast, the availability of and (6) humid lowlands (Putumayo). In these six water is not such a major problem, which means that, environments, most of the conditions under which instead of mites, the principal pest are whiteflies cassava is cultivated in the country are represented. (Aleurotrachelus socialis and, to a lesser extent, They are also representative of most cassava-growing Bemisia tuberculata). (In other regions of the world, environments around the world. B. tabaci is the main disease vector, including diseases such as the African cassava mosaic disease or cassava Specific Requirements for Cassava as brown streak). In some areas of Colombia, cassava Demanded by Different Industrial Uses bacterial blight (Xanthomonas axonopodis pv. manihotis) and superelongation (Sphaceloma As already mentioned, several industries base their manihoticola) are also economically significant activity on processing cassava roots. These industries constraints. need raw material at competitive prices, in constant supplies, and typically possessing good levels of dry All these observations are integrated into the matter. These requirements are constant for all process of genetic improvement for each ecoregion, so industries. However, specific requirements for certain that resulting materials will have good levels of tolerance qualitative characteristics exist for different industrial or resistance to these stresses. This activity is uses (Table 18-1). fundamental, both to maximize production and guarantee its stability, the latter of which is essential for the farmer’s economic survival. 344 Cassava Genetic Improvement Table 18-1. Differences in some of the specific requirements for cassava according to its final use. Values in parentheses indicate the relative significance of each characteristic on a scale of 1 to 3, where 1 = very important; 3 = not so important. Parameter Final use Starches, bioethanol, and Fresh-root consumption Food processing animal feed Yield (1) (2) (1) (3) (1) (1) Cyanogenic glucosides Bitter cassavas are preferred as Only “sweet” cassavas are Only “sweet” cassavas are they do not require so much acceptable acceptable surveillance (3) (1) (2) Parenchyma color For starches, it must be white; Usually white is preferred, Currently, only white roots are for balanced feeds, an orange although in some regions processed; yellow roots, color (indicating high carotene yellow roots are acceptable however, offer advantages content) is suitable (3) (1) (3) External appearance of roots An undesirable presentation The more a root looks like Industry does not need “markers” implies that less surveillance is variety ‘Chiroza’ (dark coffee- to recognize good cassava, as it needed colored peel and pink cortex), works through contract the better its price will be (2) (1) (1) Tolerance of root diseases Only where they affect yield If presentation is affected, Root smallpox disease is only and pests even if it is only a “cosmetic” a cosmetic problem, but it problem, the price will be affects prices to industry greatly affected (1) (2) (1) Dry matter contents The higher the content, the Varieties for fresh consumption High dry matter content is higher the price usually have intermediate levels usually preferred; the proportion of dry matter content of sugars can be significant (3) (1) (2) Culinary quality Poor quality material is even The basic criterion for this type Quality of the processed product preferred as field surveillance of use is more important; hence, will not be needed cassava of intermediate culinary quality can be excellent Starch production and energy source for glucosides), with usually intermediate dry matter animal feed content, and, especially, excellent culinary quality. The root appearance (e.g., form, peel color, and For these industries, the principal objective would be to parenchyma or pulp color) is fundamental. Productivity produce varieties with (1) high yield potential to enable in this case has a smaller relative weight than for the production of raw material at competitive prices, cassava destined for either starch or balanced feed and (2) high dry matter content to facilitate starch industries. extraction or the drying of roots. Yellow roots would be more suitable for animal feeds, while white roots are Food-processing industries. This growing sector preferred by the starch industry. In planta modification is represented by pre-cooked and frozen croquettes to produce varieties with special starch characteristics and fried cassava chips. In these cases, productivity is offers opportunities and advantages over the chemical essential, and root characteristics should be adjusted and/or physical modification currently carried out to to industrial requirements. For croquettes, for example, generate starches with special functional properties varieties should be “sweet”, with little fiber and levels of (Ellis et al. 1998; Davis et al. 2003). dry matter that are usually higher than for fresh consumption. Sugar levels in roots affect the quality of Fresh-root consumption. This is the traditional fried cassava chips. market for fresh roots, which are sold in both open-air markets and supermarkets. For this end use, cassava Table 18-1 describes the principal selection criteria should be “sweet” (low contents of cyanogenic according to uses given to cassava in Colombia. Other 345 Cassava in the Third Millennium: … cassava products for human consumption include gari better satisfaction of farmers’ needs as they themselves (toasted fermented cassava meal) and fufu (boiled define them (CIAT 1991). cassava pounded into a paste and eaten with stews and soups), which are consumed in Africa; and farinha A better comprehension of the needs of different (toasted cassava meal) and casabe (a flatbread), which consumers enables breeders to identify the are typical in several South American countries (Cock opportunities a given crop offers, and thus make it 1985). Another highly distinctive use of cassava, which more competitive or profitable. Such knowledge, in its is uncommon in Colombia but adopted in countries turn, permits a definition of research objectives not such as Cuba (García L and Herrera 1998), is the only from the viewpoint of genetically improving crops, harvest of young foliage. For this use, cassava is but also from other aspects that must accompany and planted at high densities and foliage is cut about every complement the release of new varieties. These 4 months. principles also are valid, and are being applied, for the cassava crop. Bioethanol. This is a growing industry, thanks to price increases in oil and oil derivatives on the one Kleese (2000) suggested several factors for hand and technology developments on the other. consideration when value is to be added to a given Research on the economic and competitive hydrolysis crop. These include: of maize endosperm (before fermentation is begun and distillation carried out) has directly benefited similar The needs of end users should be understood. processes conducted on cassava roots. Through such understanding, areas with potential for exploitation can be identified. In some areas of Adding value to crops economic activity, barriers may exist to free exchange of information, stemming from aspects of intellectual Traditionally, the production chain for the food sector property, common in many highly competitive markets. has been fractionated so that little or no interaction exists between its different components. Thus, crop Substituting values versus creating new added breeders interacted only with farmers who purchased values. The most obvious opportunities for adding their products. Communication was usually very value to a crop occur when the latter can meet needs limited between plant breeders, the sector purchasing covered by other ingredients. For cassava, the use of and selling agricultural products, processors, and, in yellow roots (high carotene content) reduces the need the final analysis, end consumers. for exogenous supplements of carotenes and/or colorings in poultry feeds. It can also be useful in a Recently, however, recognition is growing of the basic strategy to reduce the awful effects of vitamin A need for greater integration among the different deficiency in humans (Echeverri 2001). components of a given production chain. This principle is influencing policies of agricultural research Another example that stands out is that, in Colombia (CONPES 2000), including the case of sometimes, added value results by removing a given cassava within the poultry and pig-raising chains. product, as in the case of inositol in maize. This Thus, suppliers of genetic resources are interacting product links with phosphorus in such a way that it more closely with, for example, merchants of grains cannot be absorbed by monogastric species. Hence, and other agricultural products, livestock producers, the phosphorus found in chicken and pig manure from food processors, and food wholesalers and retailers to major operations is becoming a true ecological discover the specific needs of the different actors. problem. A strategic alternative, in this case, would be to improve the crop to reduce inositol content (and, In other words, crop genetic improvement has hence, the quantity of phosphorus linked to it), or, been reoriented so that its objectives aim more instead, add enzymes that will degrade it. The end precisely at the needs of end users. Thus, in well- beneficiary of these potential solutions would be the developed markets, cash crops seek to better meet the environment itself. needs of merchants, processors, and consumers of agricultural products. For less developed markets or The need to capture a new added value. Two household consumption, the end user is usually the fundamental aspects of introducing crops with added farmers themselves. In this case, specific participatory value are whether the market would pay for the new research methodologies have been developed to seek value, and how the different actors of a given 346 Cassava Genetic Improvement production chain would share the additional profits. influence the final commercial value that these crops With respect to the latter aspect, it should be have. Production by farmers benefits from the reduced remembered that, in each case, an added value to a need to apply agricultural chemicals to control insects specific crop would compete with other alternatives that are controllable by the gene Bt. The environment available on the market. Policies being implemented also benefits from fewer indiscriminate interventions by should guarantee that any additional profitability is farmers. However, public opinion has been adequately distributed among the different actors of the manipulated in such a way that, in many cases, the production chain to prevent monopolization by one or polemics of transgenic crops move away from the another. specifically technical and scientific to the more philosophical and political, distorting the true value Redefining an added value. For farmers, yield that these products may have. has been the most prevalent way of determining the value of most cash crops. Ideally, the adding of value Transgenic crops possess enormous potential for should be done without it being at the expense of a the possibilities offered, in different crops, through the crop’s productivity. For cassava, higher dry matter addition of value. For example, the quality of oil in a content and increased carotene content in roots are given oleaginous crop could be modified to benefit examples of where value can be added without human health by decreasing the proportion of the necessarily reducing productivity. Assuming the saturated fraction. Transgenesis could genetically alter simplest case where parity with productivity exists, how the rice crop to increase carotene and iron contents and who defines the magnitude of increase in the crop’s (“golden rice”) (Ye et al. 2000); and reduce amylose value? A need must be recognized for which the content in cassava starch (Munyikwa 1997) to produce consumer or processor is willing to pay extra for a waxy cassava that would have enormous potential in product that will be more useful in meeting that need. the starch industry. But, as well as the undeniable increase in the crop’s value from a biological viewpoint, If this incentive does not exist, farmers will not aspects, including psychological, must be considered necessarily adopt a new variety, as happened in the case as they intervene in the definition of the final value that of quality-protein maize (QPM)3. This maize was such a crop would have for society. improved so that, while obtaining yields and grain quality similar to normal maize, it also offered greater Preserving the added value. This is also availability of two essential amino acids: lysine and relevant. For those products whose added value is tryptophan (Vasal 2000). However, this maize was not easily detectable (e.g., the yellow color of cassava roots extensively adopted because the food industry was with high carotene content), management is simple. unwilling to pay higher prices for it, even though it better However, some characteristics are difficult to detect, as met the industry’s needs. in the case of beans with high levels of iron and zinc. In such cases, an independent marketing chain may be Can the technology function? It is clear that required to preserve the product’s identity as having crop genetic improvement can improve a crop’s added value. However, this same need would increase nutritional quality. Maize with its variants of high oil marketing costs. content (Dudley et al. 1974) or high protein quality (Vasal 2000) demonstrates this clearly. Iron and zinc can Freedom to operate. This refers, mainly, to the be added to beans (Beebe et al. 2000) and carotenes to growing quantity of legal restrictions that stem from cassava (Chávez et al. 2000). But, would such intellectual property rights for different products such modifications be sufficiently large to be reflected in as genes, procedures, and enzymes. Sometimes, a changes in the crop’s commercial value? vacuum exists in the legislation of numerous countries on the use of genetically modified organisms. In other In some specific cases, answers to these questions cases (Argentina, Canada, China, and USA), the are even more difficult to obtain. For example, in the regulation of its production and use is lax. In yet other marketing of transgenic crops (maize and cotton) that cases (mainly Europe), the production, marketing, and carry the gene from the entomotoxin of Bacillus use of food derived from genetically modified crops are thuringiensis (Bt), numerous factors intervene to highly restricted. Ironically, this situation contrasts with the production and use of drugs and medicines that are also obtained through genetic transformation 3. For an explanation of this and other abbreviations and acronyms, see Appendix 1: Acronyms, Abbreviations, and Technical techniques, but which have not generated as much Terminology, this volume. polemic as the case of agricultural products. 347 Cassava in the Third Millennium: … Flowering and the Acquisition of Botanical or Sexual Cassava Seed As described in Chapter 2 on the plant’s morphology, cassava is a monoecious species that has staminate (male) and pistillate (female) flowers on the same inflorescence (Figure 2-5, Chapter 2, this volume). Crop genetic improvement requires, as an essential stage, the development of new genotypes that are superior to those already available at the time of development. New genotypes occur through crosses between progenitors that have been selected for the purpose because they present one or more desirable characteristics. Crossing consists of facilitating the deposit of pollen from one progenitor’s male flower Figure 18-1. Clockwise, fruits at 1, 2, and 3 months after onto the stigma of a female flower of another pollination, and cassava seeds. progenitor. In controlled crosses, flowers are handled directly The production of sexual (or botanical) cassava to ensure greater control over pollination. seed at CIAT involves several stages and options. Occasionally, the researcher may decide to carry out Understanding the plant’s flowering system helps in self-pollination, whereby pollen from one plant is handling the procedure with maximum efficiency. Seed deposited on the female flowers of the same plant. production includes, in addition to parent selection, This, however, is carried out only for research hybridization or crossing, seed collection and the purposes; it very rarely gives rise to a commercial seeds’ correct coding, storage and treatment, and use variety. of an elaborate planting system. Flowering in cassava is always associated with Hybridization stem branching in such a way that those cultivars that do not branch, do not flower either. The plants flower The relatively large size of flowers ensures that preferably during the short days of the year (Jennings controlled pollination in cassava is easy and relatively 1970). Flowering in this crop is highly variable, simple. The female flowers usually open 10–14 days influenced by genetic—some varieties rarely flower, before the male ones of the same inflorescence do. while others flower abundantly—and environmental However, female and male flowers of different racemes factors—the same variety may not flower in lowlands on the same plant commonly flower at the same time, but will flower exuberantly in mid-altitudes. As a result, enabling self-pollination. Flowers usually open at the production of botanical seed in a genetic mid-day. improvement program is highly variable and depends heavily on the combination of progenitors that are to During free pollination of flowers, both self- and be crossed, as well as the sites and timing of cross-pollinated seeds may be produced, in pollinations. proportions that depend on genotype, planting design, type of insects present in the area, and timing of After pollination and subsequent fertilization, the pollination. With some practice and judging from the ovary develops, forming the fruit, which takes about flower’s color and form, predicting which female or 3 months to achieve maturity. The fruit is a dehiscent male flowers will open during the day is possible. A capsule and is either trilocular ovoid or globate. It more effective method is to loosen an unopened tepal measures 1.5 to 2.0 cm in diameter, and has six of the female flower. If a drop of nectar lies near the narrow longitudinal and prominent edges (Figure tepal’s base the flower will open that day (Figure 18-2). 18 -1). The capsule is hard and has three loculi, each of which contains a seed. Seeds are elliptical and When two different progenitors are crossed, the coffee-colored or gray, with black or coffee-colored resulting progeny constitutes a family, usually called guttae (or spots), depending on the mother variety F1. Because of cassava’s high heterozygosity (the (Figure 2-6, Chapter 2, this volume). genetic heterogeneity present in an individual), each seed produced in an F1 cross generates a genetically 348 Cassava Genetic Improvement undesirable pollen after opening. Those male flowers that are close to opening are themselves collected on the same day in the morning and deposited in plastic or glass bottles, identified with the variety’s name (Figure 18-3). The flowers will open in their bottles at mid-day. Pollination is carried out by first finding suitable female flowers and then gently rubbing their stigmas with pollen-bearing anthers (Figure 18-4). As many as three different female flowers can be pollinated by a single male flower. The pollinated flowers are then Figure 18-2. A tepal of a female flower carries a drop of nectar, which indicates that the flower is receptive to pollination. different plant, which then has the potential to produce a new variety. Consequently, great genetic variability can be easily introduced and managed through these crosses, which in their turn, permit the selection and acquisition of genetically superior individuals. However, the production of large quantities of seed is laborious and, usually, expensive. Within CIAT’s scheme of cassava improvement, two types of crosses are made for seed acquisition: controlled and open (or polycrosses). Controlled crosses For controlled crosses, both female and male progenitors are known, so that the progenies produced constitute a family of full sibs. Selected parents are organized in separated crossing blocks and pollinations are directed mostly between varieties for a single Figure 18-3. One of the plastic bottles used to store male adaptation area. However, they are also carried out flowers after their collection in the morning until their use at mid-day. between varieties from different areas to transfer and recombine specific characteristics and increase the plasticity of the materials, so that they may adapt more broadly and/or possess better stability in production. For controlled crosses, 10 to 20 plants per selected genotype are used as parental materials, planted in rows with distances between plants being 1 m and between rows 2 m. The latter distance is to facilitate circulation of the people who observe and select flowers ready for pollination each day. Pollination is carried out in the morning after female flowers, likely to be receptive that day, are chosen. They are then covered with cloth bags, measuring 20 × 25 cm, to protect them from Figure 18-4. Procedure used for controlled crosses in cassava. 349 Cassava in the Third Millennium: … Polycrosses For open pollination, only the female progenitor is known, as the pollen may come from any of the surrounding plants. In this case, the possibility exists that, occasionally, self-pollination will occur. Progeny that results from open pollination of the same female progenitor constitutes a half-sib family, as the identification of the male progenitor remains uncertain. Within such a family the plants may have some phenotypic, but fewer, similarities than do full siblings from controlled crosses. Open-pollinated seed can be collected from any cassava planting, but on the condition of having a mixture of numerous and genetically different materials. Different methods exist for increasing the possibility that the source of pollen is the desired one. The most commonly used is to plant a mixture of selected clones in isolated blocks, where they can cross exclusively with each other, while avoiding undesirable varieties. In this case, seeds from individual plants are Figure 18-5. Tags used to identify different pollinations and collected, and records of female progenitors are kept. the bags with which cassava flowers and fruits are Such a system is called polycrossing. covered. CIAT uses a system of constructing blocks of polycrosses in which a spatial arrangement is designed identified, using tags on which the crosses are detailed to favor homogeneous pollination among the varieties (thus noting the origin of the pollen, together with the involved. The field plans of the polycrossing plots follow date and number of pollinated flowers) (Figure 18-5). Wright’s methodology (1965). With this design, the Those of the raceme’s female flowers that had not same possibilities exist for crosses among selected opened by the time of pollination are eliminated to varieties. Planting distances are 1.5 m between plants prevent later confusion with those that were pollinated. and 2 m between rows. To ensure that crosses are The information of all crosses within one day is carried out among the varieties to be crossed, these tabulated and later transferred to either a card system blocks are surrounded by 8-m-wide barriers of male- or directly to an electronic system. Thus, crosses can sterile plants, planted at 1 m between plants and be organized first by the female parent and then by the between rows. These barriers reduce pollen flow from male parent, following an alphanumerical order for one block to another and reduce the possibility of each clone that was used as a progenitor. pollen from undesirable plants intervening in the pollinations. Pollinated flowers can be covered immediately with either a cloth or paper bag, but they can also be left Fruits generated by this system are collected when uncovered, as, apparently, exposed flowers are rarely, if they are sufficiently mature physiologically, at about at all, contaminated by pollen from other sources. 2 months after fertilization. At this time, the fruits lose However, flowers that are covered after pollination their natural shine, becoming opaque green in color. frequently have a low percentage of formed fruits, The peel then loosens readily from the fruit capsule, possibly because the temperature inside the bag and dehiscence begins, with the edges separating until increases sufficiently to “burn” the flower. After they are totally freed. At this moment, the peel takes on 3 weeks, the formed fruits must be covered with cloth a coffee color (Figure 18-1). bags to prevent attack from fruit fly (Anastrepha pickeli) and to collect seeds when dehiscence occurs Seed collection and coding the crosses (Figure 18-4). Fruits reach maturity at about 3 months after pollination. The dried and sectioned fruits in the bags, which were put in place earlier, are collected from the field and 350 Cassava Genetic Improvement seed is selected after all residues are removed from the thus identifies not only the female progenitor from peel. The seeds are organized; for controlled crosses, which this half-sibling family is derived, but also the first according to the female progenitor and then to the group of individuals among which the male progenitor male progenitor; and, for open-pollinated crosses, to is to be found. the female progenitor, which is the only one known. The seed is then tested for density in a solution of 2% As in controlled crosses, the code for the half- sodium hypochlorite to eliminate those with low- sibling family is followed by a hyphen and a number density or are non-viable and also to disinfect seeds of that distinguishes the different individuals composing possible pathogens adhering on their exterior. it. Thus, clone SM 1219-19 stands out among its half siblings for its superiority in mid-altitude valley To facilitate data management, a code is assigned environments. Unlike what happens for controlled to each cross according to the progenitors involved. crosses, the different individuals of an SM family may CIAT uses a code of two letters to indicate the type of have different male progenitors. cross and the progenitors involved. When the cross is controlled, different letters have been used over time Storing and treating botanical seed such as “CG” or “CM”. Currently, the letters “GM” are being used. Following the letters is a code of up to four Botanical cassava seed, stored at room temperature, numbers that represents a consecutive record of the maintains high viability for about one year after harvest. crosses done at CIAT. This number identifies the family For medium-term storage (i.e., several years), they are of the full sibs that possess progenitors in common. conserved at 5–10 ºC and 60% relative humidity. For example, the family CM 6740 identifies all progeny derived from the cross between M Col 1505 and Seeds are packed in small envelopes carrying the M Pan 51. The same cross can be made over several names of the cross and its parents, the source of seed, years. However, if the same progenitors are used, the date of harvesting the fruits, and the number of seeds progeny produced will always have the same code, in the bag. During storage, seed is treated with regardless of the year in which the cross is made. fungicides and insecticides. In addition, drying in an oven at 55–60 ºC for 10 to 14 days is sometimes As each individual of a full-sib family is genetically recommended to eliminate potential risks of pests and different from its siblings, the individuals of a single pathogens from the seed. Such treatment also helps family are distinguished by a hyphen followed by a break seed dormancy, which normally lasts 2 months consecutive number. Thus, CM 6740-7 identifies the after harvesting. clone that was recently released as ‘Reina’. In addition to CM 6740-7, numerous individuals within that family Little information exists as to the optimal storage were produced, but only the seventh one was conditions for seed. Under normal environmental superior enough to be released as a new variety. conditions, germination drops drastically 2 years after Another interesting example is that of the family seed is harvested, becoming non-existent by the third CM 3306, which produced excellent progeny that year (Kawano 1978). However, Martín and Ruberte resulted in the release of the variety ICA-Negrita (1976) found that storage under dry (in calcium (CM 3306-4). More recently, the Colombian chloride) laboratory conditions still produces a good Corporation of Agricultural Research (CORPOICA) germination rate, even after more than 2 years of released CM 3306-19. In addition, the clone CM storage. At the International Institute of Tropical 3306-9 showed exceptional performance in Guajira, Agriculture (IITA), Nigeria, germination studies (1979) despite the severe drought conditions that are typical of of seeds stored for more than 7 years at 5 ºC and 60% the region. relative humidity found that viability in seeds between 0 and 7 years old had not declined in any way. For seeds resulting from open pollination, the letters “SG” were first used but are now replaced by the Sowing sexual seed and transplanting letters “SM”. These letters are also followed by four seedlings numbers that represent a consecutive index that identifies a given polycrossing plot (i.e., a single group As mentioned earlier, the management of sexual seed of progenitors), and the mother from which seed was is not difficult, but requires special care, particularly in obtained. For example, SM 1219 identifies the whole the first stages of seedling development. The first progeny derived from the mother CG 1450-4 that consideration for sowing seed is the time at which this participated in the polycrossing plots of 1987. The code is carried out. Normally, sowing in trays should be 6 to 351 Cassava in the Third Millennium: … 8 weeks before the crop is normally planted in the area, moisture in the soil or substrate. The optimal so that transplanting to the field coincides with that temperature regime fluctuates between 25 and 35 ºC in time. If several planting times are available, one should a site where temperatures can be controlled. Otherwise, be chosen, according to convenience or relative in a greenhouse or mesh house, temperatures may importance of each time. reach as high as 38 ºC during the day. The substrate should be kept moist, but not saturated. Plants grow Seed is sown in trays, plastic bags, or in a bed best under sunlight with normal intensity and no shade. prepared in the field. The percentage of germination from sowing directly in the field tends to be low and Six to 8 weeks after sowing, or when seedling should be avoided if possible. The most preferable height averages about 20 cm, the plantlets are method is sowing in trays with individual transplanted to the field. The soil should be well compartments for each seedling. Ideally, a prepared and preferably with ridges. Planting distance compartment should be about 3 × 3 cm and 6 cm depends on the selection system implemented. In each deep (Figure 18-6). Trays without compartments are transplant site, a small hole is made. Seedlings should acceptable, but great care is needed to maintain the be extracted from the tray with minimal damage to the exact identification of each seed. roots, transplanting in the same order that the seeds were sown, that is, in ascending order of the number of The planting substrate in the trays may be soil or the cross. The easiest way to transplant all the seedlings an artificial mixture. It should be well drained and free is in serpentine form, planting down the field and of insects, pathogens, or weed seeds. For greater returning in the opposite direction. A free space is left safety, the soil should be sterilized by steaming or between different crosses where a stake is placed fumigation. The substrate should have a good balance carrying their identification. of nutrients and, especially, an adequate level of phosphorus. After preparing the trays or bags with soil, If the soil has insufficient moisture at the time of the seeds are systematically planted to a depth of transplanting, each seedling should be irrigated about 1.0–1.5 cm. Seed packets should be arranged in individually. During the first month, until the plants are ascending order according to the code, and the seeds well established, adequate soil moisture must be sown in that order, identifying each family with a plastic maintained. Also, during this establishment period, or wooden marker that carries the code and faces the seedlings are highly susceptible to damage by cutting first row. insects, slugs, and other animals, which means that protection requires continuous treatment and frequent To germinate, cassava seed has highly specific checks. In areas where thrips cause damage, the plants requirements, which, if they are not fulfilled, can lead must be protected by insecticide applications for the to a very low germination rate. The two most important first months, until they are old enough to form requirements are suitable temperature and sufficient pubescence on leaf buds (the most common form of resistance). Throughout the cycle, the normal practices of any cassava trial are carried out. Only for the first 2 or 3 months are plants from sexual seed more delicate than those derived from stakes. Once past this period, they achieve an almost normal development. The Cassava Genetic Improvement Scheme Used in Colombia Below, we briefly describe the procedures for the genetic improvement of cassava for specific environments in Colombia. In this section, the reader can better understand the complexity of the improvement system and the need for continuity of Figure 18-6. A tray is used for sowing botanical cassava seed, adequate resources. Additional information can be which is left until it germinates and the resulting found in other publications such as those by Ceballos et seedlings transplanted to the field. al. (2004, 2007a) anSd Morante et al. (2005). 352 Cassava Genetic Improvement Selecting parents for new groups of crosses In addition to materials from the Germplasm Bank, cassava clones resulting from genetic improvement A major decision to make in crop genetic improvement begun at CIAT in the early 1970s are also heavily used. is to choose the materials that will be used as parents For example, many of the genotypes selected as to produce new varieties that have higher productive parents had high dry matter productivity per hectare potential and better adaptation to the environmental (e.g., M Tai 8, SM 1565-15, and SM 1219-9). Other conditions where they will be grown. CIAT has the parents presented excellent qualities for the food- enormous privilege to be the depository for the World processing industry (M Per 183 and SM 1460-1), Cassava Germplasm Bank. With more than 6000 recognized combining ability to produce good progeny varieties from Africa, Asia, and the Americas, the Bank (SM 805-15 and SM 1565-17), or special characteristics contains a major proportion of not only the current such as resistance to root rots (CM 4574-7). An genetic variability of Manihot esculenta, but also important modification, introduced in year 2000, was a numerous wild species from which valuable genes can more frequent inclusion of materials that possess a be extracted. The materials held in the Germplasm pulp with an intense yellow color, as a result of high Bank were contributed by many countries and, carotene content. These materials may possibly have together, are considered as humanity’s patrimony. Use specific industrial uses, as they present low HCN levels of this germplasm permits development of materials (thus reducing the problem of drying cassava for the not only for Colombia, but also for the rest of the world. feed concentrate industry) while providing greater nutritional value. For the snack industry (fried cassava Not all genetic variability is usable, as many chips), an added advantage is that the product has a varieties held by the Germplasm Bank lack more attractive presentation. characteristics that make them suitable as parents. However, their conservation is considered as a way of Another new development with regard to guaranteeing the crop’s competitiveness or its future progenitors for use in producing new genotypes is the use in the event a new phenomenon occurs that the introduction, through IITA, of African materials that varieties currently disseminated are unable to possess resistance to the African cassava mosaic virus overcome, for example, when a new disease or pest (ACMV). Fortunately, this disease does not appear in makes a sudden appearance. Only then will some the Americas, but its insect vector (Bemisia tabaci) materials, which had previously not offered any has recently been detected feeding on cassava in advantages, become valuable genetic resources. Brazil, Ecuador, Dominican Republic, and Puerto Rico (Bellotti et al. 1999). Hence, to introduce resistance to A recent situation illustrates the strategic this severe disease before its eventual appearance is to importance of germplasm banks. In several regions of be prudent, particularly as American cassava varieties the Departments of Cauca, Valle del Cauca, and are highly susceptible to African mosaic. Because Tolima, a whitefly problem had been gradually but selection cannot be made for resistance (as the disease constantly evolving over recent years to the point that it is not present), molecular markers identified at CIAT became a true constraint to production in these will be used. The introduced materials were obtained regions. through embryo rescue from sexual seed to ensure there were no risks of inadvertently introducing the Responding to this growing problem, CIAT began disease into the country—as already mentioned, viral evaluating materials in the Germplasm Bank, in the diseases are not transmitted through botanical seed. In hope of finding varieties that would offer some type of addition to this precaution, special measures of plant resistance or tolerance to whiteflies. A variety from health prevention were taken. Ecuador (M Ecu 72) was identified as having excellent levels of resistance to these insects (Bellotti et al. Acquiring plants from botanical seed and 1999). In fact, the resistance present in M Ecu 72 was selecting the respective progeny later confirmed to be of the antibiosis type. Accordingly, with support from the Colombian Once recombinant cassava seeds are produced, their Government, through the Ministry of Agriculture and progeny should be evaluated to select, from the Rural Development (MADR), the resistant variety was massive number of genotypes, those few that surpass, included as progenitor in crosses for the inter-Andean in one or more characteristics, the best of the currently valley region, where this problem was most severe. The available materials. This is a slow, costly, but very antibiosis of M Ecu 72 is the first source of resistance important process. It gradually reduces the number of reported for crops affected by whiteflies. 353 Cassava in the Third Millennium: … genotypes for evaluating, while increasing the quantity utmost the probability that these materials will contain of vegetative seed available for successive evaluations communicable diseases. At 10 months, these plants and/or multiplications. are “harvested” to produce eight stakes or cuttings. All the stakes from one plant are packed together, suitably Cassava is characterized by a notable genotype-by- identified, and transported to the respective area of environment interaction that results in a marked specific adaptation (e.g., subhumid Caribbean). On specificity of adaptation of varieties to specific collecting the stakes, roots are reviewed to confirm that environmental conditions. For example, varieties for they do not have symptoms of diseases such as the subhumid Caribbean usually do not adapt to humid frogskin. The eight stakes are planted in individual Caribbean or Eastern Plains. As a result, selection must furrows of eight plants in trials known as clonal be made in each ecological region. In this regard, the evaluation trials (CET). country is seen to be highly favored by CIAT carrying out its selection activities in Colombia, as this The enormous genetic variability, based on so guarantees excellent adaptation of germplasm to many crosses among selected progenitors, can be prevalent environmental conditions. For similar appreciated in the CET. To exploit this great reasons, CIAT is highly favored by having possibly variability, several very large segregating families available such contrasting environments within a single must be evaluated. Currently, between 1500 and country. 2000 clones are being planted in these trials. As expected, many of these clones will present different, For each ecoregion, an independent evaluation possibly undesirable, characteristics. Hence, at this scheme is carried out. Figure 18-7 illustrates the way in stage, selection is highly drastic, reducing the number which these evaluations are currently conducted for of clones that will pass to the next stage of evaluation each ecoregion. The sexual or botanical seed is sown and selection to 200–300. As each genotype is in mesh houses to prevent the possibility of represented by a relatively reduced number of plants transferring diseases such as frogskin and then (up to eight) planted with one replication, selection in transplanted to the field at 2 months old (Stage F1). the CET is based mostly on highly heritable characteristics (e.g., plant type, dry matter content in These plantings are carried out in isolated plots to roots, capacity to produce storage roots, harvest index, maintain the materials as free as possible of disease and resistance to certain insects or diseases). vectors (particularly, whiteflies) and thus reduce to the Time Progenies Stage of the scheme Plot size (months) (no.) 14 10–20 parents Parents crossed and botanical or 10–20 plants per parent sexual seed obtained 16–26 2000–3000 F1 per region Sowing of botanical or sexual seed One plant per genotype (at CIAT) 27–38 1500–2000 Clonal evaluation trial Eight plants, with one replication, in the per region region of adaptation 39–50 200–300 Preliminary yield trial Each genotype, with three replications, per region in plots of 10–12 plants 51–62 30–60 per region Advanced yield trial Each genotype, with three replications, in plots of 20–25 plants 63–86 5–10 clones Regional trials Similar to the previous stage but at incorporated several sites and for 2 years every year Release of new variety Participatory research Use as progenitor Studies of industrial uses Figure 18-7. Basic cassava improvement scheme for each typical cassava-producing region in Colombia. 354 Cassava Genetic Improvement presence of biotic or abiotic factors), whereas other families maintain their leaves over longer periods. This capacity for leaf retention is a favorable influence (dry matter yield is about an extra 2 t/ha), as seen when the families were harvested 6 months later. Figure 18-9 illustrates segregation for resistance to leaf diseases (bacterial blight and superelongation) typical in the Orinoquian Region. In this particular case, stakes of highly susceptible materials were planted to separate plots, which had been planted one behind the other. The plants originating from these stakes served as sources of inoculum, that is, as “spreaders”, to ensure that disease pressure is relatively Figure 18-8. Clonal evaluation trial at Santo Tomás, Atlántico, high and uniform throughout the whole trial. Colombia, showing variation in the capacity for leaf retention. Once this first selection in the CET is made, thus reducing the number of families to evaluate and Figures 18-8 and 18-9 illustrate the type of increasing the quantity of available seed, evaluations variation that can be observed among families start with larger plots and with replications. As the evaluated in a CET. Figure 18-8 (Santo Tomás, process advances (Figure 18-7), selection focuses more Atlántico) illustrates how, in some families, at 5 months and more on characteristics of low heritability such as old, leaves tend to drop relatively quickly during plant yield. This is because, only through the use of special development (whether for genetic reasons or the experimental designs, inclusion of replications, and Resistant Susceptible Inoculum source Figure 18-9. Clonal evaluation trial at CORPOICA–La Libertad, Villavicencio, Meta, showing resistance and susceptibility to leaf diseases. 355 Cassava in the Third Millennium: … evaluations across several sites, can the environmental known as advanced yield trials (AYT). These are effects influencing the expression of low-heritability carried out, using three replications, but with plots of characteristics be satisfactorily reduced. 20–25 plants. From this stage on, harvests are carried out at the optimal and typical time (e.g., February and At typical harvest time (e.g., February and March March for the North Coast) but only for the 6 to in the North Coast) the first two plants in the furrow 9 plants in the center of the plot (Figure 18-11). These are harvested to measure dry matter content plants always have all around them other individuals of (Figure 18-10). This characteristic modifies the same clone and their harvest permits estimating their considerably according to the time at which roots are characteristics more precisely. harvested. As a result, it should be measured in the representative season. The remaining plants are left in The remaining 14 to 16 peripheral plants of each plot the field until the rains begin, when they are then that were not harvested are left as sources of planting harvested and potential yield evaluated in relation to material, and used at planting time (e.g., May for the volume of roots produced. Other variables are North Coast). These plants, located on the outside of integrated into a selection index (SI), which is each plot, are not evaluated precisely, because they are processed and analyzed by computer to quickly and competing with plants of other varieties that may, for efficiently choose the best 200 to 300 of 1500 to example, be more or less vigorous or more or less 2000 genotypes. aggressive. As these plants are affected by their neighbors, their performance is not representative of the Cuttings from the remaining six plants and from variety. They can nevertheless be used as sources of only selected materials are used in a preliminary yield planting material without problems. This distinction is trial (PYT), with three replications of plots with not made in the earlier stages of the improvement 10–12 plants each. In other environments, such as the scheme because not enough vegetative seed is available Eastern Plains or inter-Andean valleys, where the dry for planting plots with 20 to 25 plants. period is not so marked, fluctuations in dry matter content are not strong. Hence, all the plants of each Between 5 and 10 of the best genotypes from the furrow are harvested when the crop is usually planted. AYT are incorporated into regional trials (RT), which are This permits identification of the best clones while all planted in various representative sites of each ecoregion plants are also used as sources of vegetative seed. and with three replications per site. As, in each year, a Stakes from selected materials and not used in the new selection cycle is initiated, this means that, in a given three replications are planted in a separate nursery to region and at the same time, all the selection stages as serve as sources of planting material for the next described above can be found growing. Regional trials evaluation stages. are conducted continuously. They include the current best clones in each region and cover the different The best 30 to 60 clones identified in the PYT are purposes for which they may be destined (e.g., fresh selected to continue on to the next selection stage, consumption or industry). They also serve as checks. Peripheral plants as sources of seed Internal plants harvested to evaluate the clone Figure 18-10. Clonal evaluation trial at Santo Tomás, Atlántico, Colombia, after the first two plants of each Figure 18-11. Plots with internal plants harvested and the row are harvested to ascertain the correct peripheral plants left standing. These latter will be measurement of dry matter content. used as sources of planting material. 356 Cassava Genetic Improvement Those materials that do not surpass the checks are The harvest index measures the proportion of the eliminated from the RT after 2 years and new plant’s total biomass that is represented by roots. This promising genotypes planted after continual variable is particularly important in initial selection identification in the AYT. Ultimately, some new clones stages when not enough replications are available for will surpass the checks in one or more characteristics each genotype (Kawano et al. 1998). in the RT. These materials are then evaluated for eventual release as varieties. This task is typically The fourth factor included in the formula is plant carried out by CORPOICA. type. This variable is measured by using a visual scale that ranges from 1 (excellent) to 5 (highly undesirable). Results of the last regional trials held in the In this case, low values are preferred, in contrast to the Caribbean coast, Eastern Plains, and inter- first three variables where the highest values are Andean valleys ecoregions preferred. Hence, this variable receives a negative sign in the formula. Below, we briefly describe some relevant results of the last selection stages in RT held in different regions of The SI permits ranking the materials to facilitate the country. In each case, the calculation of a selection final selection. In addition to the variables included in index (SI) is included. This parameter condenses into a the index, other variables (e.g., resistance to pests or single number numerous variables that the breeder diseases) are reviewed. Sometimes, a material with an assesses. Its use permits even the consideration of excellent SI has to be discarded for other reasons that variables that may have more weight than others (Baker make them totally unacceptable. In calculating, an SI and Rodgers 1986). The index is currently frequently close to zero describes varieties of average used, as follows: performance. When SI is positive, the varieties are superior (the higher the positive value, the greater will SI = [fresh-root yield × 10] + [dry matter be the material’s genetic superiority). Similarly, a contents × 8] + [harvest index × 3] + negative SI reflects a performance that is below that of [(– plant type) × 3] the average of the materials evaluated (the higher the negative value, the worse is the material’s general To remove the problem of the units in which each performance). variable is measured (and which would influence the weight of each in the SI), each variable is standardized, Caribbean Region. Below we present data from following the statistical formula (Steel and Torrie 1988): three RT conducted in sites of the subhumid coast: Pitalito, Santo Tomás, and Molineros (Table 18-2), all in (Xi – µ)/σ the Department of Atlántico. In this table, the clones have been ordered according to their rank in relation to where, the performance of their respective selection indices in each of the three sites. Of the 60 varieties evaluated, Xi is the average of a given variety, the results of the best 15 varieties are presented, as µ is the average of all clones, and well as some checks that represent materials available σ is its standard deviation. to farmers. The coefficients of each term (10 for fresh-root Clone M Tai 8, known in Asia as ‘Rayong 60’, was yield, 8 for dry matter content, and 3 for harvest index the result of collaboration between CIAT and the Thai and plant type) reflect the relative importance of each Government (Kawano 1992). Until recently, it was the variable within the SI. These weights are subjective and best material available for industrial purposes and was may vary from one evaluation to another. planted to a large area of the country’s Atlantic Coast. Yet, in these regional trials, it occupied tenth place in The variables included in the SI formula are the regional trials, thereby suggesting that a new most important, but not the only ones to take into generation of materials could very soon surpass the account in the selection process. The materials excellent performance of M Tai 8. Some of these searched for are not only those with high yield potential materials are already being spontaneously (fresh-root yield), but also clones with high dry matter disseminated (e.g., CM 4919-1) and others have proven content (%) in roots, as this facilitates starch extraction to adapt well to other environments (e.g., SM 1411-5), and the drying of chipped cassava destined for animal which stood out in Lower Cauca, in Caucasia, feed. Antioquia). 357 Cassava in the Third Millennium: … 358 Table 18-2. Results of the 15 best of 60 genotypes, plus four local checks, from three regional trials conducted at each site in the Department of Atlántico, Colombia. Each trial consisted of three replications with plots of 25 plants each. Clone Pitalito Santo Tomás Molineros Fresh Dry matter Sel.a Rank Fresh Dry matter Sel.a Rank Fresh Dry matter Sel.a Rank roots index roots index roots index (t/ha) (t/ha) (%) (t/ha) (t/ha) (%) (t/ha) (t/ha) (%) 15 best genotypes SM 1438- 2 52.8 19.8 37.6 34.9 1 38.7 14.2 36.9 20.3 4 18.4 6.4 34.1 22.7 4 SM 1665- 2 49.9 17.3 34.7 22.9 5 47.7 15.7 32.9 23.9 1 19.2 5.5 28.7 16.3 9 SM 1669- 7 37.4 14.1 37.7 23.2 4 30.3 12.0 39.5 17.5 7 17.2 5.7 32.6 21.1 6 SM 1778-45 41.2 14.4 34.9 14.9 9 36.3 12.5 34.1 16.0 10 16.7 4.9 29.2 12.4 13 CM 4919-1 37.0 13.0 35.1 17.0 7 34.0 12.0 35.2 18.2 5 12.3 3.9 31.9 7.1 21 SM 1669- 5 31.5 11.6 36.9 8.4 16 33.8 12.3 36.5 16.8 8 15.1 4.6 30.9 15.2 10 SM 1411- 5 34.9 12.5 35.4 7.7 17 33.1 11.1 33.5 8.7 18 22.9 7.0 30.5 32.1 2 SM 1565-17 48.6 15.4 31.6 9.9 14 36.3 10.5 29.2 8.3 21 23.3 6.2 26.5 24.3 3 SM 1511- 6 34.9 12.3 35.2 7.5 18 29.9 11.5 38.5 14.6 12 15.8 4.6 29.2 14.7 11 M Tai 8 33.3 11.8 35.6 7.2 20 33.0 11.6 35.1 15.9 11 14.9 4.6 31.1 10.6 16 CM 6119-5 30.6 11.5 37.6 12.6 11 29.1 11.0 37.6 13.2 15 12.7 3.8 29.8 2.6 27 CM 3306-19 42.7 12.7 29.8 -1.5 34 33.4 10.3 30.9 8.7 19 23.8 7.6 32.2 39.0 1 SM 1778-53 34.0 11.9 35.0 3.0 23 23.5 8.5 36.3 1.2 32 19.9 5.8 29.2 21.2 5 SM 1973-25 43.6 16.7 38.1 26.0 3 36.0 13.3 37.6 16.5 9 10.2 2.8 27.4 -15.4 50 M Ven 25 32.0 11.3 35.0 0.7 31 40.8 14.4 35.2 22.3 2 12.2 3.8 30.7 1.3 29 Average 39.0 13.7 35.3 13.0 14.2 34.4 12.1 35.3 14.8 11.6 17.0 5.1 30.3 15.0 13.8 SD 7.1 2.5 2.3 10.2 10.0 5.6 1.8 2.8 6.0 8.3 4.3 1.3 2.0 13.2 13.3 Checks CG 1141-1 24.0 8.7 36.2 -7.2 43 22.0 7.6 34.7 -5.7 42 14.7 4.2 29.0 6.5 23 CM 3306-4 30.4 11.1 36.3 1.4 28 20.4 7.5 36.6 -10.7 48 12.2 3.7 30.8 -3.2 36 M Col 1505 28.3 9.6 33.9 -10.7 46 30.0 10.2 34.1 1.9 31 11.2 3.0 27.3 -7.0 41 M Col 2215 21.5 7.9 36.8 -11.8 49 19.8 7.3 36.4 -9.6 47 12.1 4.0 33.4 6.10 24.0 Average 27.2 9.7 35.6 -5.5 39.4 26.6 9.4 35.4 -0.4 34.0 12.5 3.8 30.2 0.7 30.6 SD 4.4 1.5 1.2 6.2 9.3 8.9 3.0 1.1 13.6 19.1 1.3 0.4 2.3 5.9 7.8 All 60 genotypes Average 33.7 11.7 34.8 0 30.5 26.8 9.3 34.0 0 30.5 13.1 3.8 29.1 0 30.5 SD 8.3 3.0 2.0 14.7 17.5 8.6 3.0 5.1 18.0 17.5 4.3 1.4 3.0 16.0 17.5 a. Sel. = selection. Cassava Genetic Improvement Table 18-2 also shows the poor performance of among the 60 described in Table 18-2 (but its materials in Molineros (average fresh-root yield of the performance is not shown as it was not among the best 60 materials was 13.1 t/ha), compared with Pitalito and 15). This clone performed well under subhumid Santo Tomás (33.7 and 26.8 t/ha, respectively). This Caribbean conditions, where reduced precipitations was due to a severe drought at the first site, where it limited the development of bacterial blight had begun 2 months before the rains normally cease. It (Xanthomonas axonopodis pv. manihotis). In wetter is precisely because of such variation, which frequently conditions, however, this pathogen spreads more and unpredictably affects agricultural activities, that easily, as happened in the Departments of Sucre and evaluations should be carried out in different Córdoba, where SM 1433-4 proved to be excessively environments and, if possible, for more than one cycle. susceptible to this disease. Across environments and time, genetically superior Eastern Plains. The materials adapted to this materials with stable production are gradually environment characteristically tolerate acid soils. identified. In Molineros, dry matter content (29.1%) was Bacterial blight and superelongation (caused by the considerably less than at the other sites (34.8% and fungus Sphaceloma manihoticola) are the principal 34.0%) because the rains began before the normal diseases that affect cassava in this type of time. This meant that harvest was carried out when environment. Many of the materials developed here shoot growth was already observed in the plants. Dry have performed very well in other regions of the matter content in cassava roots declines drastically country such as Quindío, Antioquia, Huila, and Tolima. when growth is reinitiated after prolonged drought, as the plant consumes part of its root reserves. Table 18-3 presents the averages of three RT conducted in Restrepo, Matazul, and La Libertad, all in On average, the 15 best clones yielded across the the Department of Meta. Because of the effects of three sites 10.3 t/ha of dry matter, while the averages genotype-by-environment interaction (i.e., differential for the total of the three experiments and for the performance of genotypes in different environments), checks were, respectively, 8.3 and 7.6 t/ha. This identifying materials that show excellent development reflects the crop’s enormous potential for genetic in the three sites was not readily possible. However, improvement. Even in advanced selection stages, not CM 6438-14 (released in 2001) and CM 6740-7 all materials were satisfactory. A fundamental aspect of (CORPOICA–Reina) performed very well, surpassing this stage is the expansion to include numerous sites. the check material (‘Brasilera’). Other clones also We emphasize that when these materials are performed well in this evaluation, as in previous transferred to farmers’ fields, productivity is usually years (SM 1363-11, SM 1821-7, and SM 1143-18). reduced because of numerous factors, many of which Clone CM 4574-7 also performed well and showed cannot not be controlled by the farmers. resistance to root rots. In these advanced stages of selection, when the Clones CM 4574-7 and CM 6438-14 are particularly number of materials to select has been considerably adapted to savanna conditions, while clone CM 6740-7 reduced, evaluations are started for characteristics that adapts better to conditions that are not as extreme can be measured only in a limited number of such as found at “La Libertad” Experiment Station progenies. For example, trials may begin on culinary (Villavicencio), and under the conditions of the quality and cyanogenic glucoside content to determine Piedemonte, a hilly region lying between the Eastern whether the cassava is “bitter” or “sweet”. Thus, when Cordillera of the Andes and the Eastern Plains. We the regional trials are finished, the excellent agronomic point out that, except for CM 6438-14, these performance and stable productivity of the genotypes experimental clones are among those materials can also be assured, as can be the information on selected to participate as parents in crosses to be different characteristics that will help define the carried out during year 2000. potential use of these materials (e.g., starch production, energy source for animal feed, and During 2001, CORPOICA released the clone fresh-root market). CM 6438-14, with a name that honors the memory of farmer Juan Vergara, who constantly promoted the Another example that illustrates the importance of cassava crop in the Orinoquia and shared his evaluating materials in different environments is that of experience and progressive vision with the team in the clone SM 1433-4. This material was included charge of this crop’s genetic improvement. CM 6438-14 (Figure 18-12) has high levels of resistance to bacterial 359 Cassava in the Third Millennium: … Table 18-3. Average of the most relevant variables of clones evaluated in three regional trials for the Orinoquian Region (Restrepo, CORPOICA–La Libertad, and Matazul, all in the Department of Meta). Order is based on the selection index across the three environments. Clone Fresh-root yield Dry matter content Dry matter yield Plant type Harvest index (t/ha) (%) (t/ha) (1–5) (0–1) SM 1363-11 24.44 36.61 8.90 3.00 0.51 SM 1152-13 23.89 35.34 8.42 4.00 0.54 SM 1794-18 22.19 36.14 8.09 3.33 0.50 CM 6438-14 20.59 35.90 7.49 3.67 0.52 SM 1821-7 23.27 33.88 7.98 3.00 0.53 SM 1143-18 21.88 32.18 7.11 4.00 0.59 SM 1854-23 22.10 32.28 7.22 3.67 0.58 M Bra 502 21.54 33.91 7.30 3.33 0.49 CM 6921- 3 18.49 34.84 6.54 4.33 0.48 CM 6740-7 18.73 34.19 6.42 3.33 0.55 Brasilera 18.80 33.90 6.49 3.67 0.52 CM 4574-7 19.38 34.03 6.58 3.00 0.53 SM 1483-1 22.93 32.07 7.42 2.67 0.48 SM 2219-11 21.64 31.48 6.84 3.00 0.53 CM 6975-14 19.14 34.80 6.70 2.00 0.47 SM 1241-12 18.89 31.08 5.82 3.67 0.58 CM 523- 7 14.54 34.03 5.09 4.00 0.54 SM 1862-25 17.07 33.31 5.56 3.33 0.51 SM 1697-1 20.32 31.09 6.46 3.33 0.48 CM 7052- 3 19.66 30.52 6.08 3.00 0.52 SM 1812-69 18.02 30.72 5.71 3.33 0.56 SM 1694-2 14.41 34.21 4.92 4.00 0.44 SM 1565-15 17.25 33.09 5.82 2.67 0.47 CM 2177- 2 16.27 32.30 5.28 4.00 0.45 SM 1674-1 14.91 32.39 5.02 3.67 0.53 SM 1859-26 19.10 30.14 5.81 2.33 0.54 CM 7073- 7 14.10 33.45 4.74 3.00 0.47 CM 5306- 8 14.85 32.44 4.76 3.33 0.42 SM 2068-3 17.01 30.65 5.27 2.00 0.45 SM 1881-17 13.86 28.91 4.11 3.33 0.42 Minimum 13.86 28.91 4.11 2.00 0.42 Maximum 24.44 36.61 8.90 4.33 0.59 Average 18.98 33.00 6.33 3.30 0.51 SD 3.10 1.91 1.19 0.58 0.04 blight and superelongation, and can thus present large ‘Brasilera’ and a higher yield potential. ‘Reina’ will serve volumes of young foliage at harvest. not only as animal feed but also for the food- processing industry. Clone CM 6740-7 or ‘Reina’ (Figure 18-13) demonstrates its extraordinary potential, both for fresh Inter-Andean valleys. This ecosystem shares roots and dry matter. In fact, being unquestionably many characteristics with the Eastern Plains. Some of superior, this material replaces the last cultivar released their sites present acid soils and share the same typical in the region (CM 523-7 or ‘Catumare’). Furthermore, diseases (bacterial blight and superelongation). ‘Brasilera’ had been used until now for the production Unsurprisingly, therefore, clone CM 6740-7 is also an of pre-cooked cassava croquettes. However, CM 6740-7 outstanding performer this region. For this type of has the advantage of a higher dry matter content than environment, high dry matter yield is a significant 360 Cassava Genetic Improvement Table 18-5 presents the results of four consecutive harvests carried out on varieties adapted to this ecosystem, in the Municipality of Jamundí, south of the City of Cali. The first harvest was carried out 7 months after stakes were planted. Even at that time, the crop’s general performance was satisfactory overall (average of 11.2 t/ha of dry matter). The consecutive harvests helped identify clones with high-yielding potential in early development. Being a perennial plant, cassava can be harvested at any time without reference to reasons of physiology or senescence to determine optimal time (except for dry matter content, which is lower when the plant renews Figure 18-12. The new cultivar for the Orinoquian Region growth after an adverse condition such as drought). (CM 6438-14). Its name honors the memory of local farmer Juan Vergara Carulla. Many farmers find it strategic to have early and late varieties, so that root production is more or less continuous. During these harvests, data on the production of young foliage were also taken. On average, this site presented small variations over time (fluctuating around 8 t/ha), but, depending on variety, foliage production ranged between 6 and 14 t/ha when roots were harvested. This information is also useful for determining optimal harvest times for each variety, taking into account the production of both roots and foliage. Variety dissemination and release When a material demonstrates genetic superiority across numerous environments and over several years, Figure 18-13. Clone 6740-7 or ‘CORPOICA–Reina’ was recently it will be profiled as a candidate for official release by released for the Colombian Orinoquia but has excellent adaptation to other regions of the institutions accredited for this purpose in the country. country. In Colombia, first the Colombian Institute of Agriculture (ICA), and later CORPOICA, traditionally fulfilled this important role. Hence, close collaboration exists criterion for selection (clone SM 1219-9 has shown between CIAT and these institutions. excellent potential). Other materials are also being looked at for good culinary quality (landraces Two modalities exist for the final evaluation of M Per 183 and M Bra 383 not only have high yield materials and to confirm their genetic advantages. The potential, but also excellent culinary quality and traditional scheme involves planting trials with characteristics for the food-processing industry). replications over several years at different sites to confirm the new varieties’ superiority. In these cases, Table 18-4 presents the yields of the best clones checks are always planted that adequately represent in the RT held at CIAT–Palmira and harvested in the best clones available to farmers at that time. A new May 2000. On average, the evaluated clones yielded variety must be superior to the checks in one or more more than 7 t/ha of dry matter. The best 10 clones characteristics and must demonstrate sufficient had dry matter yields of almost 10 tons (9.77 t/ha), stability across variable environmental conditions. whereas the five checks (including variety Catumare Hence, new varieties can only be officially released after or CM 523-7) had average dry matter yields of having been evaluated for several years and in different 6.35 t/ha. environments, thereby determining its stability and tolerance or resistance to different production constraints, whether of biotic or abiotic origin. 361 Cassava in the Third Millennium: … Table 18-4. Results of the 10 best of 48 varieties evaluated in the regional trial conducted at CIAT–Palmira, Colombia. Clone Yield (t/ha) Dry Evaluation Harvest Selection Fresh Dry matter foliage index index roots matter (%) (1–5) 10 best genotypes CM 8370-11 31.89 13.07 41.00 2.00 0.63 13.60 SM 1855-15 23.67 10.00 42.25 2.00 0.65 9.70 SM 1602-13 32.19 12.10 37.60 2.67 0.61 9.01 SM 1636-24 27.93 10.95 39.20 3.00 0.59 6.38 SM 1741-1 19.30 8.01 41.50 2.00 0.60 5.84 SM 2141-1 19.59 8.62 44.00 2.33 0.56 5.71 SM 1557-17 21.52 8.70 40.45 2.33 0.61 5.33 SM 1871-33 23.56 9.54 40.50 3.00 0.58 4.42 CM 3306-4 18.07 7.94 43.95 3.00 0.62 3.95 CM 8370-10 20.81 8.72 41.90 2.67 0.54 3.95 Average 23.85 9.77 41.24 2.50 0.60 6.79 SD 5.14 1.76 1.98 0.42 0.03 3.09 Checks CM 523-7 22.41 9.36 41.75 3.00 0.63 5.27 M Bra 12 18.19 6.66 36.65 3.00 0.58 -1.35 M Per 183 19.78 6.78 34.30 3.00 0.60 -1.49 M Col 1505 14.19 5.45 38.45 3.00 0.53 -3.22 M Col 1468 9.89 3.48 35.20 4.00 0.51 -9.75 Average 16.89 6.35 37.27 3.20 0.57 -2.11 SD 4.92 2.14 2.96 0.45 0.05 5.36 All 48 genotypes Average 18.17 7.03 38.50 2.91 0.56 0 SD 4.93 2.10 3.10 0.41 0.07 5.17 The second way to identify and validate the genetic segregating progenies. Each seed resulting from superiority of materials is through participatory pollination constitutes a new genetic entity, which research. With this methodology, segregating materials means that crossing produces great genetic variability. are delivered to farmers who will then conduct the final The more costly and slower activity is to select selection of materials according to their own selection genetically superior materials from the wide variability criteria. This system has the great advantage that, once generated by the crosses. Current technological a variety is selected by a farmer (or group of farmers), it developments enable selection to be more efficient and would then not need promoting, as it will usually be effective in terms of the use of resources at hand. immediately adopted by the farmers. It also has the Ultimately, of the thousands of crosses made every advantage of being more specific to certain more year, only some clones will be identified by CIAT as uniform environments (e.g., for a given village district being superior. Of these, only some will be released as or municipality) than the traditional improvement varieties by CORPOICA. scheme, which targets broader environments (e.g., the Caribbean or Orinoquian Region). Biotechnology Whatever the improvement system used, the The second half of the 20th century has been witness stages described in this chapter are always included. to a dizzying development of technology in the area of First, parents with desired attributes for exploitation what is now known as “biotechnology”. Perhaps the should be selected. The parents are then crossed most significant characteristic of biology is that the among themselves to produce a large number of genetic code is universal. This means that the information codified in a bacterium, for example, can 362 Cassava Genetic Improvement 363 Table 18-5. Results of four successive harvests of crops of 15 elite clones at 7, 8, 9, and 10 months old. Data are from local plots in the Municipality of Jamundí (Valle del Cauca, Colombia). Clone Age of crop in months Average 7 8 9 10 Fresh-root Dry matter Fresh-root Dry matter Fresh-root Dry matter Fresh-root Dry matter yield content yield content yield content yield content (t/ha) (%) (t/ha) (t/ha) (%) (t/ha) (t/ha) (%) (t/ha) (t/ha) (%) (t/ha) CM 7951-5 40.5 36.5 14.8 41.1 34.8 14.3 57.3 36.3 20.8 63.0 39.8 25.0 18.73 SM 1741-1 45.1 36.7 16.5 35.3 31.2 10.8 38.3 37.0 14.2 44.4 38.8 17.2 14.68 SM 1460-1 38.1 34.1 13.0 32.8 34.5 11.3 38.1 35.0 13.3 46.5 35.2 16.4 13.50 SM 1557-17 37.0 34.8 12.9 39.8 33.0 13.1 36.6 35.4 13.0 41.5 34.6 14.3 13.33 SM 909-25 33.8 34.7 11.7 34.8 30.9 10.5 42.5 35.9 15.2 39.4 37.8 14.9 13.08 M Bra 383 33.9 28.5 9.7 38.4 34.9 13.4 34.5 36.8 12.7 41.3 38.7 16.0 12.95 SM 1219-9 34.5 34.0 11.7 44.4 32.3 14.3 33.5 32.4 10.8 39.8 36.3 14.4 12.80 SM 1543-16 32.3 34.8 11.2 26.8 33.2 9.0 36.0 34.9 12.6 49.3 35.8 17.6 12.60 CM 7514-7 29.1 39.1 11.4 29.6 38.5 11.4 28.4 40.7 11.5 36.3 41.2 14.9 12.30 CM 3306-4 35.1 37.4 13.1 29.8 36.6 10.9 30.5 38.0 11.6 34.8 39.1 13.6 12.30 M Per 183 33.9 28.5 9.7 38.4 34.9 13.4 36.0 30.1 10.8 50.8 30.1 15.2 12.28 CM 6740-7 23.9 32.6 7.8 37.5 33.4 12.5 34.0 34.4 11.7 29.1 36.3 10.6 10.65 CM 523-7 29.6 34.4 10.2 33.0 34.0 11.2 36.1 35.7 12.9 23.8 34.8 8.2 10.63 CM 849-1 19.9 33.9 6.7 25.1 32.5 8.3 21.3 33.8 7.2 22.0 35.5 7.7 7.48 SM 653-14 23.9 32.6 7.8 33.9 16.9 5.8 22.5 35.0 7.8 19.8 36.4 7.3 7.18 Average 32.2 34.8 11.2 33.6 33.4 11.2 35.0 35.4 12.4 38.8 36.7 14.2 12.30 Minimum 19.9 28.5 6.7 25.1 16.9 5.8 21.3 30.1 7.2 19.8 30.1 7.3 7.18 Maximum 45.1 39.1 16.5 44.4 38.5 14.3 57.3 40.7 20.8 63.0 41.2 25.0 18.73 Cassava in the Third Millennium: … be interpreted by most living organisms of the planet, of a determined genotype, their effects cannot be because all use the same code. This has major transmitted to later generations, unlike genes that have implications for agriculture. additive effects. First, if a gene of economic interest exists in any Non-additive components of genetic variance living organism, this gene can be ultimately identified, (σ2 D and σ2 Ep) for the main characteristics of cassava multiplied, and transferred to a crop where it can be have been demonstrated to be highly significant expressed in the same way as it did in its natural (Cach et al. 2005, 2006; Calle et al. 2005; Jaramillo environment. This is the case of genes for resistance to et al. 2005; Pérez et al. 2005a, 2005b). Hence, insects or herbicides. Second, the technologies whatever method increases the proportion of additive developed for one crop can serve for another crop. effects in the selection process will greatly increase its Hence, cassava has benefited enormously from all the efficiency. Another equally valid alternative is to knowledge generated mainly for cereals (e.g., rice, implement an improvement method that can also take wheat, and maize) and legumes (e.g., soybeans and advantage of the effects of dominance and epistasis. beans). Some alternatives for improving cassava that may be implemented in the near future are presented below. The tools developed for biotechnology may be grouped into three large categories, each of which has Improvement schemes that include self-fertilizing specific uses: tissue culture, molecular markers, and stages offer some advantages that have been reported genetic transformation. This is a very dynamic field of in the literature. With successive self-fertilizations, research and a detailed description of protocols and different loci in the genome are obliged to progressively updated results goes beyond the purpose of this reach the stage of homozygosis. This is prejudicial for publication. individual performance (particularly for cross-pollinated crops such as cassava or maize), because vigor and Changes in the Implementation of the productivity will gradually diminish. However, this Cassava Genetic Improvement Scheme process has the advantage of eliminating deleterious or undesirable genes from the population that remain From the viewpoint of quantitative genetics, the “hidden” because of the generalized heterozygosity of cassava improvement scheme described earlier in this these types of crops in their natural state. The totality chapter is essentially based on the selection of of effects of these undesirable genes is known as the numerous segregating clones derived from a cross “genetic load”, which is estimated to be prominent for between two progenitors that were selected for a cassava. However, as progress is made in the degree of diversity of reasons and purposes. This selection is inbreeding of segregating populations, the proportion based on phenotypic characteristics, the variance (σ2 P) of total phenotypic variance that is additive variance of which can be separated as follows: increases (Hallauer and Miranda 1988). σ2 P = σ2 A + σ2 D +σ2 Ep + σ2 E Table 18 -6 illustrates the effects of successive self-fertilizations in the distribution of genetic variance. where, The obvious result is that, with total homozygosis, σ2 D is eliminated as a component of phenotypic σ2 A is the variance due to additive genetic effects, variance. Another obvious result is that the additive σ2 D is the variance due to the effects of genetic effects present in the F1 generation (full-sib family) now dominance, has double the influence than in the original situation. σ2 Ep is the variance due to epistatic genetic effects From the genetic viewpoint, a homozygotic line is σ2 E is the variance due to environmental effects stable (on using it as progenitor, the genetic (experimental error), as well as all the segregation mentioned previously does not occur), in components of the genotype-by-environment contrast to what happens with hybrid F1, which, even if interaction. it could reproduce vegetatively, its use as a progenitor is affected because the genetic effects of dominance Only the additive fraction of the variability observed cannot be transmitted to later generations. (on which selection of genotypes is based) can be taken advantage of by the present system of recurrent The industry of maize hybrids is based precisely on selection. Both σ2 D and σ2 E introduce a “distortion” the design of the progenitors, which, on combining, because, even though they influence the performance specifically produce a material of excellent performance 364 Cassava Genetic Improvement Table 18-6. Distribution of genetic variance between and within families when increasing inbreeding through successive self-pollinations. Family Proportion of Between families Within families homozygosis σ2 A σ2 D σ2 A σ2 D Full siblings 0 1/2 1/4 1/2 3/4 F2 50.00 1 1/4 1/2 1/2 F3 75.00 3/2 3/16 1/4 1/4 F4 87.50 7/4 7/64 1/8 1/8 F∞ 100.00 2 0 0 0 in the field. The process of self-fertilization of cassava For the reasons given above, changes are planned thus offers two very attractive advantages: (1) it for the way the cassava genetic improvement project at contributes to the automatic reduction of the genetic CIAT will be carried out in the future. Below, we briefly load in populations that have been improved in part, describe the scheme that may be implemented over the and (2) it permits the design of parents for producing next few years. We emphasize that this is only at a more competitive hybrids. Current improvement preliminary phase of definition and many changes will concentrates on producing and identifying good surely be introduced, depending on how the crop hybrids from selected progenitors. In the future, such responds at different stages. emphasis will produce individuals especially designed to be optimal progenitors and thus generate Development of homozygous progenitors outstanding hybrids. The great advantage is that this process guarantees a more sustained genetic progress, Important efforts are underway to develop a protocol for which is quick, at least from the theoretical viewpoint. the production of doubled haploids through approaches such as microspore, anther, or ovule culture or through Now, some problems exist that explain why, so far, wide crosses with Ricinus communis. these ideas have not been implemented, principally: Taking advantage of general combining ability a. The genetic load in cassava is so large that reaching high degrees of homozygosis is By definition, to eliminate deleterious genes in each difficult with plants that can survive. Although segregating population, its characteristics as progenitor this is currently a limitation, it also justifies the are improved, as the deleterious genes can no longer be urgent need to begin cleaning out the genetic transmitted to later generations. Genetic designs exist load from the crop as soon as possible. We for improving, in a systematic and efficient way, genes point out that tolerance of inbreeding can be with additive effects, those that, in an integral way, increased in cross-pollinated crops, as was define the general combining ability of each individual shown irrefutably for maize. No scientific reason or population. exists to assume that the same cannot be achieved for cassava (Contreras R et al. 2009). Defining heterotic groups and taking advantage of specific combining ability b. Because of the cassava plant’s peculiar method of reproduction, self-fertilization can be greatly Once the genetic load has been successfully reduced in delayed. To achieve a high degree of the populations, improvement can start by focusing on homozygosis, at least 4 or 5 successive self- producing progenitors that mutually complement each fertilizations are needed. In cassava, this other from the genetic viewpoint. This implies the start requires about 10 years. However, a procedure of producing materials that, when crossed with each exists that is widely used for other crops other, will produce exceptional hybrids. This is precisely whereby totally homozygotic materials, known what occurs when parents of commercial maize hybrids as doubled haploids can be immediately are crossed; the parents have been designed and obtained (Griffing 1975). This procedure gradually improved to produce, each time, more normally uses gametophytic tissue, which is productive hybrids with a more stable performance. 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Segovia1, Armando Bedoya2, William Triviño3, Hernán Ceballos4, Martin Fregene5, Guillermo Gálvez6, and Bernardo Ospina7 Introduction Hardening massive numbers of in vitro cassava Tissue culture, a technique used to micropropagate plants inevitably incurs in loss of plantlets, mainly plants, has been successfully applied in cassava when these are moved from the artificial to the natural (Manihot esculenta Crantz) for the massive environment (soil) and must adapt to new production of disease-free in vitro plants, increasing microclimatic conditions. Where the transfer is not productivity and, in certain cases, improving carried out using the appropriate technology, the longevity. In vitro micropropagation is successfully percentage of loss is very high (between 50%–95%), used to produce cassava plantlets free of pathogens which affects the crop’s agronomic progress while associated to diseases such as frogskin, cassava increasing the costs of implementing this alternative mosaic, and bacterial blight. Traditional technology. It also discourages progressive farmers micropropagation has low multiplication rates, which who would otherwise rapidly and safely produce can be improved by using more efficient disease-free planting materials or massively produce a multiplication systems such as the automated new promising variety over a short period of time. temporary immersion device known as RITA® or other automated temporary immersion systems Other drawbacks of the acclimatization process are (ATIS)8. the cost and size of the facilities needed, such as greenhouses and screenhouses. These two factors After 6 to 11 months in sterilized rooms under reduce the feasibility of applying this new technology— artificial conditions of light, temperature, moisture, and other similar ones—which could have a significant and nutrients, the plantlets produced by such systems impact on agricultural production. are like test-tube babies—weak and unadapted. As a result, they need to undergo a stage of Researchers from the Latin American and acclimatization or hardening before they can be Caribbean Consortium to Support Cassava Research transferred to their final site in the field. In cassava, and Development (CLAYUCA, its Spanish acronym), in this process is very delicate, constituting a bottleneck association with others of Biotechnology of Colombia in the massive production of cassava planting Ltd. (Biotecol, its Spanish acronym) and CIAT, have materials by tissue culture techniques. developed a methodology that enables the massive production of cassava planting materials, also known 1. Agronomist, formerly of Greenhouse Management, CIAT, Cali, as plantlets. In 2001, a large number of plants were Colombia. E-mail: rjsssegovia@gmail.com produced using ATIS. Through efforts described below, 2. Field technician, formerly of CLAYUCA, Cali, Colombia. 3. Field technician, CLAYUCA. a sustainable and economic technology for functional 4. Breeder, Cassava Program, CIAT. E-mail: h.ceballos@cgiar.org hardening was achieved, significantly minimizing the 5. Plant geneticist and molecular breeder. Director, Bio Cassava Plus percentage of plantlet loss during the hardening Program. Danforth Center, St. Louis, USA. E-mail: MFregene@danforthcenter.org process (HP). 6. Virologist, formerly of CIAT-Biotecol, Cali, Colombia. 7. Executive Director, CLAYUCA. E-mail: b.ospina@cgiar.org Stages of the Hardening Process 8. For an explanation of this and other abbreviations and acronyms, see Appendix 1: Acronyms, Abbreviations, and Technical Terminology, this volume. The six stages required for an efficient and successful HP are as follows: 369 Cassava in the Third Millennium: … Stage 1: Pre-operational activities The protective screen should be highly functional, installed on the sides of the screenhouse facing East A successful HP demands prior planning, which (sunrise) and West (sunset), at least 1 or 2 m above the includes preparing a detailed timetable of all activities tops of the bags containing the plantlets. The screen integrating the process: definition of who will carry it should be withdrawn gradually as the sun traces its out; selection and adaptation of facilities; laboratory path through the sky to let light enter the facility. The tests; purchase of equipment, materials, and inputs; aluminum foil reflects the sun’s rays and prevents the and confirmation from the biotechnology laboratory of heating of the area where the plantlets are being the number of in vitro plants that can be “hardened” hardened. per week. A good rule of thumb is that approximately 300 cassava plantlets can be hardened per square The maximum temperature within a screenhouse meter of useful area of greenhouse or screenhouse. fluctuates between 33 and 38 ºC, and the minimum between 18 and 22 ºC. For details on the design and Human resources. Labor should be qualified; if construction of a CIAT screenhouse type II, consult not, personnel should at least receive training in basic Roca and Mroginski (1991). aspects of the HP methodology. The number of workers required will depend on their experience and The greenhouse should have an automatic the number of plants entering the process. A novice microspray irrigation system installed, which is worker can handle about 200 plants per day while an controlled by a solenoid valve and control clock. This expert can handle up to 600 (see below, “Preparing for type of system reduces the cost of labor needed to Transplanting”). irrigate the plantlets by 90%. Facilities. Facilities usually consist of a work area Both the screenhouse and greenhouse should have and either a screenhouse or a greenhouse, sometimes a space set aside to acclimatize transplanted plantlets, both. Select the best of what is available, then make which can be increased by as much as three times as any necessary adaptations. the plants grow for 2 or 3 months after transplanting. The degree of increase will depend on the cassava The work area comprises a depot for soil and variety, its growth rate, and plant development. sand, a small storage shed to keep materials and inputs, a “soil patio” for mixing, and a cool site for For example, 10,000 plants are needed to plant transplanting; the latter should be protected from 1 hectare of cassava. CLAYUCA’s HP methodology direct sunlight and strong winds and should also have initially places 10,000 plantlets in an area of 25 to a washing area and table. 35 m2 in the screenhouse or greenhouse, depending on the size and type of bags used for transplanting. The screenhouse should be roofed and adapted Two months after transplanting, these 10,000 plants for automatic climate control. Microsprays should be will need an area of 50 to 70 m2. suspended either over the tables or from the roof as well as installed along the floor to control temperature Laboratory tests. To correct any potential and relative humidity, especially during the first days of problem, all soil, sand, and water to be used should be the HP. Although plantlet development is favored by first submitted to chemical and biological analyses. good light, this should not come directly from the morning, noon, or afternoon sun during the first 8 days Equipment, materials, and inputs. The following of acclimatization. elements are needed to acclimatize the cassava plantlets: A protective screen can be installed, using one of the following options: (1) sheets of polystyrene foam • Soil mill, sieve and mixer; sterilizer; fumigator; covered with aluminum foil; (2) venetian blinds protective equipment for fumigation and externally covered with aluminum foil; and pesticides (3) polypropylene meshing externally covered with • Test tubes, balance, flask washer, scissors, several sheets of aluminum foil (each 30 cm wide) and plastic or bamboo trays separated at 5-cm intervals. So far, CIAT has found the • Wide container (e.g., tray) with agar to place third option to be the best. plantlets removed from their flasks • Bucket, spade, wheelbarrow, and garden 370 Methodology for Hardening Large Numbers of In Vitro Cassava Plants spades as well as a hose and irrigator sufficient water and heat to 100 ºC. • Black plastic bags (7 x 14 cm) with • Spread a thin layer of soil over black plastic, perforations for drainage as well as cover with a piece of transparent plastic, transparent plastic bags (1 x 1 m) forming a hermetic seal between both plastics • Field book, registration forms, indelible and leave for 1 week under direct sunlight. marker, pencil, and plastic mini-stakes for identification of plantlets Preparing for transplanting. Before transplanting, make sure the facilities are fully All implements used should be disinfected to disinfected. Fill the small black plastic bags for the prevent possible contamination of plantlets. For in vitro plants with substrate, prepare the mixture of example, if roots or leaves are cut with scissors, these fertilizer and fungicide, and arrange trays and large should be disinfected in a soapy solution every time a bags for use in miniature humidity chambers. cut is made. Likewise, retrain personnel in transplanting Stage 2: Operational or technical activities procedures. This exercise will determine the personnel’s productive capacity. Skilled technicians The success of the HP depends on the comprehensive can transplant about 600 plants per working day, while management of a series of operations that range from beginners can only handle about 200 plants. receiving the in vitro plants to their transplanting in the field. Disinfecting and cleaning the site. Rigorously disinfect the entire facility with sodium hypochlorite Receiving in vitro plants. Boxes containing and organize equipment and implements to facilitate flasks with in vitro plants are received from the their use. Cleaning should also extend to the biotechnology laboratory. The flasks with plantlets are transplanting site and the screenhouse or greenhouse quickly removed from the boxes, placed at intervals in where the plantlets will be hardened. a cool place with artificial lighting or indirect sunlight, then counted and numbers recorded according to Preparing the bags. Fill either black or transparent variety. plastic bags (7 x 14 cm) with the previously prepared mixture of sand and soil (see above) to three quarters In this step, a pre-selection is also carried out, their volume. Firmly press the mixture into the bag to consisting of separating the flasks according to the obtain a compact substrate. Such compaction will later height and vigor of the in vitro plants and eliminating stimulate root growth, making them longer and thicker. those observed to be contaminated, broken, damaged, or malformed. Preparing the trays. Place the bags containing the already compacted substrate on the trays and prepare Pre-adapting the plantlets. If the transportation the following solution: mix 1 g of a soil fungicide (e.g., of the in vitro plants in closed boxes has taken several Banrot) and 2 g of a phosphorus-rich fertilizer (e.g., days, the flasks are placed as indicated in the previous formula 10-52-10) in 1 liter of deionized water (or step but left until the plantlets recover. Other option is rainwater). Immediately irrigate each bag with 10 cc of to leave the in vitro plants for 1 or 2 days at the this mixture (first irrigation). facilities where they will undergo the HP. This time can be used to make a second pre-selection of vigorous Preparing miniature humidity chambers. Introduce in vitro plants. the base of each tray into a transparent plastic bag (1 x 1 m when folded) that has been rolled down, Preparing the substrate. To prepare the concertina style, to its base in such a way that the bag substrate in which plantlets will be grown, one part of can later be quickly unfolded upwards and its opening previously pulverized and sieved black soil (i.e., from firmly tied shut. This will function as a “humidity the non-clay arable layer) is mixed with three parts of chamber”. washed and sieved coarse sand. The substrate should be steam-sterilized if the presence of nematodes and Stage 3: Transplanting fungi is suspected. If no sterilization equipment is available, then: Transplanting is traumatic for the plantlets, especially when carried out by unqualified or inexperienced • Place the sand in a metallic pipe or drum, add personnel. Plantlets undergo microclimatic stress when 371 Cassava in the Third Millennium: … moved from their flasks to the miniature humidity roots remain in their “normal position” that is, as they chambers, suffering dehydration; nutrient stress, as they were in the flask, thus preventing physical or change from a nutrient-rich substrate to one very poor physiological damage that could be caused by a change in nutrients (soil/sand mixture); and almost unavoidable of position. mechanical damage to several parts of the plantlet (e.g., root cap, absorbent hairs, roots, stem, and leaves). The Once transplanting has been achieved for all the success of the plantlets’ acclimatization and survival bags in the tray, the plantlets receive a second irrigation mainly depends on the care with which transplanting is with 10 cc of the previously used fertilizer and fungicide done. mixture. Transplanting must be performed immediately after Humidity chambers and hardening. Now the real the in vitro plants are extracted from their flasks. When process of hardening the plantlets begins: this process is carried out for the first time and the environmental conditions of the facilities are not well • Label the tray indicating the name of the variety, known, then transplanting should be carried out on a the number of bags, the date and hour of daily basis at 17:00 to prevent the plantlets from transplanting, and the transplanter’s name. dehydrating. • Place each tray at the bottom of the large transparent bag (1 x 1 m) and tie the opening Transplanting activities include: shut with a piece of rope, converting it into a miniature humidity chamber. Selection. A first selection is carried out, choosing • Transfer the humidity chambers to the facility those flasks with the most vigorous plantlets (intense where the HP will be carried out. Tie the string green color, erect, and between 5 and 7 cm tall). to a wire strung over the chambers to prevent the upper part of each chamber from folding Extracting the in vitro plants. This operation over on top of the plantlets and damaging them. consists of the following steps: Stage 4: Maintaining the transplanted plantlets • Remove the plastic tape and flask covers. • Add deionized water or rainwater to the flask to In this stage, considerable attention must be given to the moisten the agar substrate and facilitate microclimatic changes occurring within the facility, the extraction of both plantlet and agar. irrigation required by plantlets, their nutrition, and the • Hold the flask in one hand while gently presence of pests and diseases. smacking the flask with the other to loosen the agar from the flask’s walls. If it does not The bags containing the plantlets should not be separate, use a spatula, taking care not to moved during the first month after transplanting to avoid damage the roots. damaging the roots, especially the cap and absorbent • Carefully remove the plantlet by inclining the hairs. These parts are particularly fragile in this early flask; do not use tweezers because the stem stage of development. Damage or breakage in root may suffer damage. tissues increases the probability of pathogen invasion • Place the plantlet in a wide container, such as a and slows down growth and development. Such care is deep tray containing deionized water or also of considerable importance in Stages 5 and 6 of rainwater. Use your hand to gently move the the HP. water to dislodge the agar. • Gently remove particles of agar still adhered to Microclimate and humidity chambers. Between the roots with the flask washer. 8 and 12 days after transplanting (DAT), remove the • Conduct a second selection of vigorous string closing the humidity chamber—preferably in the plantlets to eliminate small, poorly formed, or afternoon—and completely open the large transparent weak plantlets. bag to allow plantlets to adapt to the microenvironment of the facility. Transplanting into bags. With one hand, place the plantlet in a bag, introducing the roots and lower part of If a tendency to wilting is observed, then reclose the the stem. This hand must be held rigid to prevent bag and continue the humidity chamber treatment. breaking the absorbent hairs and roots. With the other hand, add a fourth of the substrate, ensuring that the If plantlets have adapted well to the 372 Methodology for Hardening Large Numbers of In Vitro Cassava Plants microenvironment by the second or third day after opening the large bag (i.e., 10 to 15 DAT), the bag is A phosphorus-rich compound (e.g., formula rolled down to the tray’s base or removed altogether, 10-52-10) is first applied to enhance root development. leaving the tray exposed with its plantlets. This application is alternated at 8-day intervals with a complete fertilizer containing macro and minor During this step, plantlets must be protected from elements. If the formula 10-52-10 is not available on strong dehydrating winds. the market, it can be replaced by a combined formula including 10-30-10 and Agrimins. Fertilizer application Irrigation. If the plantlets have been irrigated with is suspended once the color of the plantlets is normal the correct amount of nutrient solution (see above) and for the varieties to which they belong. the environment within the miniature humidity chamber is appropriate, plantlets will not need irrigation. If symptoms of deficiency of any element appear, affected plantlets can be given an application of foliar However, if and only if, the first symptoms of fertilizer containing simple or complete fertilizers. Zinc physiological wilting appear in plantlets after being deficiency tends to appear in plantlets during the first removed from the humidity chamber, apply a third month and can be corrected by adding Zn to the soil in irrigation to the substrate. To reduce the risk of attack of one of the irrigations at a rate of 3 g dissolved in 1 liter pathogens, take care not to wet the leaves. Irrigate each irrigation water and applied at 10 cc per plant. plantlet with 10 cc of a nutrient solution consisting of a mixture of 2 g of phosphorus-rich fertilizer to promote Stage 5: Separating the plantlets root formation (e.g., formula 10-52-10) and 1 g of Agrimins (a fertilizer rich in minor elements) per liter of Between 30 and 34 DAT, the plantlets have now deionized water (or rainwater). become plants and therefore need more light as well as higher temperatures to grow and develop. Plants are Depending on the microclimatic conditions of the spaced at a greater distance, in an area double or triple facility and the turgor of the plantlets, schedule one or that initially occupied. two irrigations per day, each with 10 cc of water normally used to irrigate other plants. Stage 6: Transplanting plants to the field Between 21 and 25 DAT, install a microspray The plants remain in the screenhouse or greenhouse irrigation (MSI) system in the screenhouse, which for 60 to 90 days before being taken to the field. In significantly reduces labor costs. At CIAT, plantlets case of restricted space or labor, plants can be taken to receive from 2 to 3 minutes of MSI in the morning and, the field 30-40 days after transplanting. if necessary, another 2 or 3 minutes in the afternoon. Transfer. When transporting the bags from the • The use of MSI requires that plantlets be greenhouse (or screenhouse) to the field, protect plants rigorously inspected to detect any pathological from strong air currents that could cause abrasion or problems. dehydration. • The “secret” of this operation, which is crucial Adaptation and final transplanting. The plants to the success of the HP, is to apply irrigation should be grouped together and placed in the site when the first symptoms of physiological wilting chosen for planting and left for 3 to 6 days so that they are observed. This ensures an adequate can adapt to the new environment. Plants are then moisture level of the substratum, thus transplanted to their final field sites. For the next few preventing possible pathogen attack in the root days, the farmer should closely monitor the site for the area. It is important to remember that, at this appearance of any nutritional deficiency or presence of stage, cassava plantlets are highly susceptible to pests or diseases to apply the corresponding integrated excess moisture in the substrate. management practice as required. Fertilizer applications. The substrate used (1 part Reference of soil to 3 parts of sand) is of low fertility, and the application of fertilizers is therefore indispensable. Every Roca WM; Mroginski LA, eds. 1991. Cultivo de tejidos en 8 days the plantlets will receive applications of macro- la agricultura: Fundamentos y aplicaciones. Centro and micronutrients to ensure their normal development. Internacional de Agricultura Tropical (CIAT), Cali, Colombia. 970 p. 373 Cassava in the Third Millennium: … CHAPTER 20 Mechanized Systems for Planting and Harvesting Cassava (Manihot esculenta Crantz) Bernardo Ospina Patiño1, Luis Fernando Cadavid L.2, Martha García3, and César Alcalde3 Background reduction of necessary labor, production costs, time spent at each task per unit area, and the final cost of the The progress made recently in developing cassava agricultural product. Hence, the planted area can varieties with high yield potential has helped improve be increased, thereby justifying the initial investment in the crop’s productivity and competitiveness. It has machinery. facilitated its entry in various markets, especially those of balanced feeds for animals, and of industrial With the current trend towards economic applications such as starch, glues, and bioethanol. globalization, agricultural sectors of developing countries face severe competition with agricultural To compete in these markets, the costs of products imported from developed countries where they producing cassava must be kept as low as possible. were produced mostly under complex subsidy schemes The crop requires intensive labor, especially for for supporting agricultural activities. Consumers tend to planting and harvesting. In countries such as Brazil, choose the cheaper imported products, thus creating much progress has been made in developing problems in marketing agricultural products produced mechanized planting and semi-mechanized harvesting domestically and endangering the developing countries’ systems for the cassava crop. In Colombia, the Latin more fragile and vulnerable rural economies. Under America and Caribbean Consortium to Support these conditions, farmers urgently need access to Cassava Research and Development (CLAYUCA)4 has technologies that will help them reduce their production recently been evaluating and adapting models of costs and improve the productivity and competitiveness planters and harvesters for the cassava crop. These of their farming systems. models were based on those developed in southern Brazil. Mechanization of the cassava crop is priority for Colombian agriculture, if projections for that crop in This chapter describes some of the technologies national and international markets are to be taken into currently available to mechanize cassava planting and account. However, the current technological offer of harvesting. machinery in local and international markets is narrow. The adaptability of such machinery to the country’s Importance of Agricultural Mechanization conditions must first be assessed. We use the cassava crop’s recent situation in Colombia and other cassava- The principal aim of agricultural mechanization is to producing countries of Latin America and the Caribbean ensure optimal conditions for crop development at all (LAC) to illustrate this aspect. stages of its life cycle. It therefore implies the direct The continuous growth of the poultry and balanced- 1. Executive Director, CLAYUCA, Cali, Colombia. feed sectors has meant an increased demand of raw E-mail: b.ospina@cgiar.org materials, mainly cereals such as maize. National 2. Soil Agronomist, formerly of Cassava Production Systems, CLAYUCA. E-mail: luisfernandocadavidlopez@yahoo.es production is insufficient for supplying this growing 3. Formerly Agronomy Students, 2001–2002, UNIVALLE, Cali, demand, forcing countries to import, annually, massive Colombia. volumes of maize that total several millions of tons. 4. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, Abbreviations, and Technical Balanced-feed markets see cassava as an alternative Terminology, this volume. raw material that can be used as an energy source. 374 Mechanized Systems for Planting and Harvesting Cassava If cassava is to be incorporated in these markets, especially during the crop’s first months of growth, to the crop needs to be traded at prices that compete prevent erosion, which can become a serious problem, favorably with imported maize prices. Considerable particularly if the soil is also sandy (Ribeiro 1996). progress has recently been made in developing new high-yielding cassava varieties, but this was not enough Planting to significantly reduce production costs or increase competitiveness. The introduction of new technologies has modified cassava cropping practices, particularly planting method Importance of soil preparation and stake position. These two practices are fundamental for increasing yield and ensuring marketing of the As for any other crop, cassava requires good soil product (Cuadra and Rodríguez 1983). preparation as according to climate, soil type, vegetation cover, topography, the degree of mechanization the crop Cock et al. (1978) proposed several planting receives, and other agronomic practices. methods that take into account climate, soils, available equipment, topography, and farmers’ customs. These An adequately prepared soil guarantees a propitious methods are manual, semi-mechanized, and bed for the “seed” and, thus, high levels of germination mechanized. and production. The seedbed should generally be about 20 cm deep, with a loose soil that is free of lumps to In Colombia, cassava is usually planted on ridges or facilitate both horizontal and vertical root growth. on the flat. The selection of one site over another for planting depends on the area’s humidity and soil texture Soil preparation usually begins in the dry season, (Figures 20-1 and 20-2). except in regions with very humid climates, where the land is prepared at the end of the heavy rains and stakes are planted at the beginning of the dry season. Advantage is therefore taken of the remaining small but copious rains to initiate root development. In areas with less rain, plowing before the dry season is sometimes necessary to take advantage of the rains as, later, the land dries up and hardens too much for tilling. In many regions, the disk plow is being replaced by other tools such as the chisel plow, which helps conserve soil structures. Whenever this task can be mechanized, many cassava farmers prepare the soil with a simple plowing, followed by disk plowing. Thus, they obtain good conditions for planting, ventilate the soil, and control Figure 20-1. Plot in which cassava was planted on ridges. weeds. These days, soil structure and other physical properties must be evaluated to select the most suitable mechanization system. The concepts of sustainability and minimal tilling must also be applied where possible. A common practice in Brazil, wherever planting is mechanized, is to prepare furrows, 10 to 20 cm deep, to plant stakes in a horizontal position. The first pass with a disk plow is made 30 days before planting; the second just before the stakes are planted. The goal is to improve soil conditions and eliminate weeds that may compete with the crop during its establishment. Planting cassava on land that slopes at more than 15% is not recommended. If the crop is planted on such slopes, contour furrowing should be carried out, Figure 20-2. Plot in which cassava was planted on the flat. 375 Cassava in the Third Millennium: … Importance of soil type • In soils with a sandy texture, as predominate in tropical dry climates, cassava is planted on the Any method for planting cassava stakes should ensure flat. In such soils, stakes should be planted shoot growth (i.e., “germination”) and stake rooting. vertically or on a slant (Figure 20-4), burying For these to happen, the soil must have adequate them by about 5 cm (the stake itself is about moisture and be well prepared. The planting method 20 cm long). One problem is potential used will depend mainly on soil type and climate: damage caused by excessive soil heat to buried buds. These buds usually receive more heat than • In soils with a clayey texture and receiving the buds remaining above ground. Any damage more than 1200 mm of rainfall, ridges should caused affects crop yield (Cadavid L. et al. 1998). be constructed to facilitate drainage, thereby effectively improving crop establishment and Importance of planting method yield. It also facilitates manual harvesting (Lozano 1978). Four important variables must be taken into account when determining the method for planting cassava, • Conceição (1976) reports that planting whether manual or mechanized: stakes horizontally, at 10 cm deep and in furrows, facilitates commercial harvesting • planting depth (Figure 20-3). Planting on ridges gives good • stake length results if weeds do not constitute a serious • stake position problem. • spacing between plants and between furrows • In heavier and compacted soils, cassava should Each has a different value according to the soil type be planted in beds or on ridges. Such soils and climatic conditions of the region in which planting is become saturated with water in the rainy to be carried out (Figures 20-3 and 20-4). season and are thus poorly aerated. They favor the spread of root rots, which cause crop Planting depth. To encourage tuberous root losses. production, the stake should not be planted deeper than 10 to 15 cm. The fine roots responsible for taking up • However, Lulofs (1970) reported that planting essential elements and water will extend to greater on the flat in this type of soil is satisfactory, depths should the crop suffer hydric stress or drought. although planting on ridges may increase yield, better control erosion, and facilitate harvesting. Manual planting is traditional in all cassava-growing Significant differences in cassava production regions. Stakes, 20 cm long, are planted vertically or on between the two methods were not found. a slant in a furrow, whether on a ridge or on the flat, to a Planting on ridges produced fewer roots than depth of 5 to 10 cm. Planting is in the direction of bud did planting on the flat, but it also reduced the growth, ensuring that a large number of buds is buried amount of weeding needed and the physical under the soil, with the number depending on the effort required for harvesting. variety. Figure 20-3. Stake planted horizontally. Figure 20-4. Stake planted on a slant. 376 Mechanized Systems for Planting and Harvesting Cassava Several experiments have shown that the buried stake is cut at right angles to its length part of the stake should not be planted more deeply (Figure 20-6), roots are distributed consistently than 10 cm as, at greater depths, harvesting can be around the periphery of the cut. If the stake is difficult. Shallow planting (<5 cm) may mean plants planted horizontally, the roots are more separated being carried away by water, or developing surface and harvesting is easier than when stakes are roots and thus becoming prone to lodging. Shallow planted vertically or on a slant (Figure 20-7). Cock et planting will also hinder certain agronomic practices. al. (1978) found that neither the angle of the cut nor In sandy soils, planting depth should not be less than the position in which the stake is planted 5 cm, as water may settle the earth and expose the significantly affects yield. planted stake. Trials carried out at the Centro Internacional de Stake length. In any cassava production system, Agricultura Tropical (CIAT) indicate that, under field stake size and quality play a significant role in obtaining conditions, stakes planted vertically are always high yields. quicker to root and germinate. Planting them horizontally is recommended when the operation is Stake quality depends on several factors: stem age mechanized and soil moisture is appropriate. and thickness when selected for cutting, stake size, cassava variety, storage time, and mechanical damage No significant differences were found in root suffered by the stake during preparation, transport, production between stakes planted on a slant, storage, and planting. Farmers commonly use a stake vertically, or horizontally. However, continuous length that is between 15 and 25 cm. observation suggests that vertical planting favors initial growth and reduces plant lodging (Solórzano Gurnah (1974) demonstrated that, where moisture 1978). Recent data obtained by CIAT scientists in is adequate (1000 mm annual rainfall) and stakes are Honduras also suggest that vertical or slanted planted between 2 and 8 internodes deep, yield is planting helps plants maintain straight stems and higher when the number of internodes increases from 2 to 5. Beyond this number, yield did not subsequently increase. Vertical stake length therefore depends on the number of desired internodes (i.e., between 3 and 5). That number, in its turn, depends on the phenotypic characteristics of the variety being planted (Figure 20-5). A high value for shoot growth (“germination”) is guaranteed if the stake is fresh and newly cut. Stake position. In Colombia, stakes are usually planted on a slant or vertically (Figure 20-4). When the Figure 20-6. Cassava stake cut at right angles to its length. Soil surface Planting depth Direction of root growth Figure 20-5. Number of internodes in a stake, compared with Figure 20-7. Diagram shows cassava root growth according to its length, cassava variety CM 533-4 (ICA Negrita) the position in which stakes are planted. 377 Cassava in the Third Millennium: … reduce heavy adventitious rooting. Although The second system is semi-mechanized, that is, it Conceição (1976) recommends planting horizontally includes an initial step of chisel plowing that breaks the in furrows for mechanized planting, CIAT data soil and leaves lines marked with small furrows. Stakes indicate that stakes planted vertically or on a slant are then placed manually at the desired density and in a can facilitate mechanical harvesting. horizontal position within each furrow in the line. They are then covered with soil. In regions with average to heavy soils and rainfall between 1000 and 2000 mm/year, planting stakes The third system is mechanized. It involves a either horizontally or vertically makes no difference, planting machine to which a worker manually feeds as moisture is sufficient for germination. stakes that were previously cut to the desired size. A tractor is needed to move the planter. Some models In regions with sandy soils and irregular rains, integrate the application of fertilizers into the planting planting stakes vertically is safest. Furthermore, operation of cassava stakes. stake length can be reduced from 20 cm to 10–15 cm. Thus, they take better advantage of For Colombia and other South American countries, available moisture. Vertically planted stakes also the progress made in this field in southern Brazil has serve to disseminate heat. been of great importance. Brazilian machines have been evaluated under local conditions with good results, Planting density. Planting density has an including the definition of the basic requisites for their indisputable effect on crop production. It depends on adaptation. factors such as soil fertility, cassava variety, topography, stake planting method, crop’s purpose, Evaluating two Brazilian prototypes for planting time, harvesting time, and climate. Adopting mechanized cassava planting a single spacing system that responds to all these variables is therefore impossible. Performance. CLAYUCA imported two cassava planters from Brazil, one model that plants two furrows, and the Cassava plants growing in a given area compete other three. They were evaluated under the soil and among themselves for water, light, and nutrients. climatic conditions of the Department of Valle del Hence, the ideal spacing for planting each variety Cauca, Colombia. The 3-furrow model planted depends on soil fertility or planting time. Once 9.2 ha/day, using four workers (3 planters and determined, individuals can be better distributed in 1 tractor driver) over an 8-hour working day. The the field and more efficient advantage can be taken 2-furrow model could plant 6.2 ha/day, using three of production factors (Normanha and Pereira 1974). workers (2 planters and 1 tractor driver). These results compared most favorably with results obtained for the In the cassava-producing areas of Rio de Janeiro, manual planting system, which usually requires a Brazil, a spacing of 1.20 m between furrows was minimum of 7 working days to plant 1 ha. The results found to present the best results, given the region’s translated into savings of almost 50% of costs of soils. No significant differences were found between manual planting when the 2-furrow planter was used, spacing distances of 0.5, 0.7, and 0.9 m between and 57% for the 3-furrow planter. plants in terms of root production for either industrial or commercial purposes. The spacing most used in Mechanized planting is a viable alternative for Colombia is 1 m between plants and 1 m between cassava growers. However, the minimum area needed furrows. for recovering investment costs is 30 ha. The 2-furrow prototype was considered a better option, as it allows Planting systems and available machinery for variations in distances between furrows and between plants, stake length, and planting depth. The technological offer currently available for the cassava crop includes several machines that Two-furrow cassava planter, model PC-20. incorporate human activity for their correct Figure 20-8 shows the principal technical characteristics operation. Three systems exist for planting cassava: of this prototype: one is totally manual, where only farmers’ labor intervenes, as still happens in many cassava- • Hydraulic lift system producing countries of the developing world. • Stakes are cut by circular saws operated by power takeoff (PTO) 378 Mechanized Systems for Planting and Harvesting Cassava • Distance between plants is set at 90 cm • Distance between furrows is set at 1 m • Stem ends are not discarded • Two hoppers, each with a 50-kg capacity, for granulated fertilizer • Double concave disks for hilling • No depth control in furrow aperture • Approximate output: 12 ha/day Parameters evaluated for prototype performance. Prototype performance was evaluated on two principal parameters: Soil conditions. • Chemical and physical characterization of soils Figure 20-8. Two-furrow cassava planter, model PC-20. in three regions where the work was developed • Water content and apparent density (degree of soil compaction) • Distance between plants varies between 40 and 90 cm Prototype operation. The variables measured to • Distance between furrows varies between determine the operation of the two prototypes were: 0.8 and 1.2 m • Stem ends are discarded • Uniformity in planting depth • 100-kg capacity hopper for granulated fertilizer • Uniformity in length of the planted stake • Double concave disks for hilling • Uniformity in spacing between plants • Depth control in furrow aperture • Mechanical damage to stakes • Approximate output: 7 ha/day • Output in the field • Required minimum power: 70 hp • Production costs • Capacity seed deposit: 1.5 m3 Results Obtained Three-furrow cassava planter, model PMT-3. Figure 20-9 shows the principal technical characteristics Table 20-1 presents results of experimental work. Data of this prototype: obtained at each site are the average of three replications. In each case, the parameter is expressed • Hydraulic lift system as a percentage, which indicates results according to • Stakes cut by jaws operating from the steering the given conditions of the machines’ operation. For wheel’s traction example, if the desired stake length is 20 cm, the prototype is adjusted to the stake’s dimensions. The parameter’s results—uniformity of size—indicates the machine’s efficiency in planting stakes of this size. The data obtained is based on an 8-hour working day and only the workers feeding the machine are included. For manual planting, comparisons are estimated by assuming that the same number of workers who feed the planting machine is used. Discussion Uniformity of spacing between plants This parameter depends on the feeding mechanism of each prototype (Figure 20-10). It also depends on the degree of soil preparation. Overall, the functionality of Figure 20-9. Three-furrow cassava planter, model PMT-3. the 2-furrow prototype was 92%. The advantage of this 379 Cassava in the Third Millennium: … Table 20-1. Comparing the performance of mechanical cassava planters with manual planting. Parameter Site 1 Site 2 Site 3 Average Manual planting (A) The 2-furrow cassava planter Uniformity of spacing between plants (%) 91.3 92.6 94.3 92.7 97.7 Uniformity of stake length (%) 98.0 97.3 98.0 97.7 98.3 Uniformity of planting depth (%) 94.5 96.6 96.6 95.9 100.0 Mechanical damage to stakes (%) 10.0 10.0 9.6 9.98 0 Output (ha/hour) 0.42 0.39 0.38 0.39 0.02a Output (ha/day)b 6.72 6.24 6.08 6.34 1.00 i.e., a 6-fold difference (B) The 3-furrow cassava planter Uniformity of spacing between plants (%) 74.0 77.0 87.3 79.4 98.1 Uniformity of stake length (%) 96.1 96.1 95.6 95.9 98.6 Uniformity of planting depth (%) 95.6 96.6 97.6 96.6 100.0 Mechanical damage to stakes (%) 36.6 25.0 22.3 27.9 0 Output (ha/hour) 0.37 0.42 0.36 0.38 0.02a Output (ha/day)b 5.92 6.72 5.76 6.13 1.00 i.e., a 6-fold difference a. The value for this output was calculated as the number of hectares planted per hour per worker, assuming a working day of 8 hours and 6 workers. b. Assuming a working day of 16 hours. prototype is its device for discarding ends. Another advantage is that it permits different planting distances. The 3-furrow prototype does not include a device for discarding ends, and all stakes are cut to the same size. The functionality of this prototype was less than the 2-furrow type, having values of about 80%. Uniformity of stake size Although this parameter is independent of soil preparation, it plays a significant role in ensuring a high germination rate. Stake length and internode number are well known to affect sprouting. The 2-furrow prototype presented good functionality (97.7%) when 15-cm stakes were used (Figure 20-11). The 3-furrow prototype had lower results of about 95.9%. The stake length obtained was only 11 cm, which may be too short if the variety planted has few internodes. Uniformity of planting depth The two prototypes did not present major differences, as both machines obtained about 96% for this parameter, which is important for germination. Planting depth depends on soil preparation. If the planting area is not well prepared, the machine will vary in its regulation of planting depth. This effect is minimized with the 2-furrow planter, which has a device to control depth Figure 20-10. Planting distance in mechanized planting. (Figure 20-12). 380 90 cm Mechanized Systems for Planting and Harvesting Cassava Mechanical damage to stakes For the two prototypes, the degree of damage to planting materials was evaluated. Differences were a consequence of the cutting device in each machine. In the 2-furrow prototype, the cutting system comprises circular saws that operate from the tractor’s power takeoff. Damage to stakes from this device is minimal, being less than 10%. The 3-furrow planter had a lower functionality of about 28% because the cutting device uses a system of jaws that operate from the steering wheel’s traction. Prototype outputs This parameter indicates the capacity of the two prototypes to plant according to given distances between rows and between plants. The machine’s effectiveness is affected by parameters such as soil conditions (preparation and water content), the tractor’s power, and Figure 20-11. Cassava stake length in mechanized planting. the efficiency of the workers feeding the machine (Table 20-1). The 2-furrow planter had an average output of 6.3 ha/day or 0.8 ha/hour, using two people for an 8-hour working day. The 3-furrow prototype had an average output of 9.2 ha/day, employing three workers for an 8-hour working day, which corresponds to an average of 1.15 ha/hour. In neither case is the tractor driver included. The traditional planting system required six workers to plant 1 ha for an 8-hour working day. Economic impact The two prototypes evaluated did not differ significantly in operation, as the use of either one represented an important reduction in production costs. Table 20-2 illustrates the values obtained for the total operational costs of the two planters, compared with the traditional system, and the production costs of 1 ha of cassava. The use of the 2-furrow planter reduced planting costs by 51% against the traditional system. With the 3-furrow prototype, planting costs were reduced by 55.6%. Compared with the 2-furrow prototype, the Spiral spring 3-furrow planter further reduced costs by US$2.30/ha. The 2-furrow prototype was then modified by its manufacturers to improve efficiency and output. CLAYUCA validated the new 2-furrow prototype, model Bazuca 1 (Figure 20-13), which had the following characteristics: • Hydraulic lift system Figure 20-12. Planting-depth device used in the 2-furrow • Distance between furrows varies from 0.85 to planter. Note the spiral spring. 0.96 m 381 15 cm Cassava in the Third Millennium: … Table 20-2. Production costs of planting 1 hectare of cassava, Valle del Cauca, Colombia, 2000. Activity Unit Quantity Unit value Total cost (US$)a (US$) (A) Traditional manual planting Cutting stakes Workers/day 2 4.60 9.20 Chemical treatment for stakes 6.10 Labor for stake treatment Workers/day 0.5 4.60 2.30 Manual planting Workers/day 6 4.60 27.60 Replanting Workers/day 1 4.60 4.60 Total costs of planting 1 ha 49.80 Total production costs of planting 1 ha 566.00 Estimated output was 1 ha/day Planting costs as proportion of total costs 8.8% (B) Mechanized planting, using a 2-furrow prototype Cutting and stacking stems Workers/day 3 4.60 13.80 Adjusting fixed costs for planter US$/ha 1.28 9173.00 5.30 Workers for mechanized planting Workers/day 0.33 4.60 1.46 Wage for tractor driver Workers/day 0.16 9.60 1.54 Replanting Workers/day 0.5 4.60 2.30 Total costs of planting 1 ha 24.40 Total production costs of planting 1 ha 477.00 Estimated output was 6.2 ha/day Planting costs as proportion of total costs 5.1% (C) Mechanized planting, using a 3-furrow prototype Cutting and stacking stems Workers/day 3.0 4.60 13.80 Mechanized planting costs, fixed and variable US$/ha 0.87 3.94 3.42 Workers for mechanized planting Workers/day 0.33 4.60 1.50 Wage for tractor driver Workers/day 0.108 9.60 1.04 Replanting Workers/day 0.5 4.60 2.30 Total costs of planting 1 ha 22.10 Total production costs of planting 1 ha 471.00 Estimated output was 9.2 ha/day Planting costs as proportion of total costs 4.7% a. Exchange rate (year 2000) was 1 U.S. dollar = $2,100 Colombian pesos; value of wage (worker/day) was therefore 10,000 Colombian pesos or US$4.60. • Distance between plants varies from 0.30 to 0.96 m • Tractor power: 60 to 75 hp • Operational speed: 4 to 6 km/h • Stake length: 13.5 cm • Does not discard ends • Cuts stems with saws • 150-kg capacity hopper for fertilizers • Output: 5–7 ha/day The basic difference between this new model and the previous one is the device that feeds the stems to the machine. It was changed to a central hopper, contrasting with that of the previous model, which Figure 20-13. The modified 2-furrow cassava planter, Planti included a circle of multiple feeding points. Both the Center model Bazuca 1. Planti Center PC-20 and the Bazuca 1 have devices for 382 Mechanized Systems for Planting and Harvesting Cassava direct planting, which contributes to soil sustainability, as no heavy machinery is needed for soil preparation (Figure 20-14). The Brazilian metalworking sector that makes the cassava planters and harvesters is dynamic. It includes several companies that continually innovate and present new prototypes to the market. Already, new prototypes with greater efficiencies exist. For example, 4- and 6-furrow planters are already being used for cassava planted to large extensions in agroindustrial projects (Figure 20-15). WH-PM-4L Recently, a 1-furrow prototype (Figure 20-16) was launched on the market. It creates ridges, while simultaneously planting and applying fertilizers. This machine may represent a great advance for production systems where farmers operate small production areas and are limited by the lack of machinery for soil preparation. The characteristics of this new prototype are: • Hydraulic lift system • Distance between furrows vary from 0.85 to WH-PM-6L 0.96 m • Distance between plants vary from 0.31 to 0.96 m (13.5-cm stake) and 0.42–1.30 m (18.5-cm stake) • Tractor power: 45 hp • Operational speed: 4 to 6 km/h • Stake length: 13.5 cm; 18 cm (optional) • Does not discard ends • Cuts stems with saws • 150-kg capacity hopper for fertilizers • Output: 2–3 ha/day Figure 20-15. Four- (top) and six-furrow (middle and bottom) cassava planters. Figure 20-14. Two angles of the direct-planting device in the 2-furrow cassava planter, Planti Center model PC–20. 383 Cassava in the Third Millennium: … Cassava Harvesting One task in cassava cultivation that is very difficult to mechanize is harvesting. Reasons include limitations that result from the shape and distribution of roots in the soil, the depth at which they are found, the collection of foliage residues and planting materials (stakes), and the adherence of soil to roots. The best time for harvesting—the crop’s final stage—is defined by the farmer in terms of the crop’s productivity, and the roots’ starch content and culinary properties. Harvesting perhaps most influences the crop’s cost structure, as it requires many working days. In Colombia, the harvest represents more than 30% of the cassava crop’s production costs, mainly because manual, rudimentary, and, sometimes, inefficient methods are used. Hence, some Figure 20-16. One-furrow cassava planter–ridger. mechanization of the work is needed to increase operational efficiency, given that any mechanical method or device helps, even noticeably so, to reduce To decide which mechanized system is the best for not only production costs, but also energy expenditure a given case, the following factors should be taken into and fatigue on the part of the workers doing the account: harvesting (Toro M et al. 1976). • The type of tractor and its available power In northern Colombia, to obtain an average • The planting method for stakes (planting on yield of 12.5 t/ha, 25 workers are needed for an the flat or on ridges) 8-hour working day. Consequently, the daily output per • Conventional or direct planting worker is 500 kg/day. This value, however, does not include collection of planting materials or selection of Mechanized planting, by itself, does not guarantee roots and their packaging (B Ospina Patiño 2001, pers. a higher output or higher germination rate for stakes. comm.). Essential conditions are fresh, recently cut, stakes, and good soil preparation. Other tasks should be carried Manual harvesting out without exception. Certain tasks are common to any cassava harvesting, The introduction of these technologies positively whether manual and mechanical. These are carried out modifies the production cost structure for cassava. in two stages: Planted area can be increased and final costs reduced, thus leading to higher profits. Furthermore, when high • The cutting and selecting of (1) forage (cassava yields are obtained, costs are further reduced, but this leaves and other aerial parts) and (2) planting is achieved only if minimal conditions are guaranteed materials. Only 20 to 40-cm lengths of the to enable the planter to operate well. stems are left still attached to the roots underground, so that these may be more easily Table 20-3 presents CLAYUCA’s recent results extracted or pulled out of the soil. after adapting the mechanized cassava planting technology, using prototypes developed in Brazil. • The second stage is to extract, collect, clean, Farmers should, however, include in their cost and package the roots. structure those costs incurred by the machine’s depreciation and maintenance, so that calculations Manual harvesting comprises four modalities: may approach closer to reality. Using hands. In light or sandy soils, roots can be easily pulled out by hand, without need of tools. 384 Mechanized Systems for Planting and Harvesting Cassava Table 20-3. General cost structure for planting cassava, according to three methods applied to flat areas in the Department of Valle del Cauca, Colombia, 2000. Activitiesa Unitb Quantity Unit value Total value RCDc (Col$)b (Col$)b (%) (A) Manual planting Cutting stakes Working day 5 10,000 50,000 Inputs for stake treatment Global 13,410 Labor for stake treatment Working day 0.5 10,000 5,000 Manual planting Working day 6 10,000 60,000 Replanting Working day 1 10,000 10,000 Total for labor 138,410 10.38 Total cost per hectare 1,333,610 (B) Planting with a 2-furrow machine Cutting and stacking stems Working day 3 10,000 30,000 Costs of machine, F and V Col$/hour 1.28 9,174 11,761 Costs of tractor, F and V Col$/hour 1.28 12,743 16,337 Workers for mechanized planting Working day 0.32 10,000 3,200 Tractor driver Working day 0.16 21,000 3,360 Replanting Working day 0.50 10,000 5,000 Total for labor 69,658 6.41 Total cost per hectare 1,086,350 (C) Planting with a 3-furrow machine Cutting and stacking stems Working day 3 10,000 30,000 Costs of machine, F and V Col$/hour 0.87 8,600 7,482 Tractor costs, F and V Col$/hour 0.87 12,743 11,086 Workers for mechanized planting Working day 0,326 10,000 3,260 Tractor driver Working day 0,108 21,000 2,268 Replanting Working day 0.50 10,000 5,000 Total for labor 59,096 5.74 Total cost per hectare 1,029,878 a. F and V = fixed and variable costs. b. The exchange rate (year 2000) was 1 U.S. dollar = $2,100 Colombian pesos. c. RCD = ratio between the costs of planting stakes and the total direct costs of cropping, expressed in percentage. Using a lever. In soils with textures ranging from loamy to clayey and presenting problems of compaction, extraction is facilitated by tying the stem with a chain or rope to a pole that is 2.5 to 3 m long. The pole must be sufficiently straight and firm to serve as a lever against the soil. Using a puller. This technique is a modification of the previous one. The stem is subjected to a puller, comprising a claw attached to a pole 2.5 m long or more, depending on the worker’s height. The claw is fixed at 30 cm from that end of the pole supported by the soil. The claw is hooked onto the stem close to its base and leverage is applied downwards on the pole so that the claw pulls the roots upwards out of the soil, as in the previous method (Figures 20-17 and 20-18). Figure 20-17. Puller used by Thai farmers to harvest cassava. 385 Cassava in the Third Millennium: … • Planting density. These machines can loosen the soil of two furrows at once, as the blade’s “wing span” is 1.2 m. If furrows are less than 90 cm apart, losses may occur because roots may be buried or broken. If the blade is more than 1.2 m wide, then the roots will not loosen satisfactorily. • Tractor’s operational speed. This speed should be constant throughout harvesting because any sudden change, when the implement is digging, will modify the implement’s working depth, thus increasing losses through broken or buried roots. Figure 20-18. Thai farmer using a puller. To quantify yield for comparing with manual harvesting, the daily output per worker should be This tool is commonly used in cassava-producing separated from the machine’s output, which depends regions of Thailand. on tractor speed. A speed of 4 km/h is mostly used. It can be increased, however, depending on soil moisture Using a band. In the Colombian Coffee Belt, and texture. Hence, a machine’s average daily output where soils usually have a medium texture, a type of is 6.4 ha. belt or band is widely used. The farmer ties the band onto himself, then passes it over his back and shoulder, Prototype descriptions. Model P 900 Flexible and ties it to the stem. That end of the band tied to the (Figure 20-19) has the following characteristics: stem may be a strong rope or chain, which the farmer grasps and shakes to loosen the plant while his body • Weight: 200 kg acts as a lever. • Daily output: 5 to 8 ha/8-h day • Operation: harvests two furrows at the same Semi-mechanized harvesting time • Planting distances are 80 to 100 cm CLAYUCA has adapted and evaluated semi- • Includes front cutting disk, which facilitates work mechanized systems of harvesting cassava. The • Minimum soil removal, functioning as a subsoiler importance of this activity lies in the excessive costs of and leaving the soil prepared manual harvesting, which requires 25 to 35 working • Works in soils difficult for manual harvesting days to harvest an average production of 30 t/ha. • Before operation, stems must be cut at 20 to CLAYUCA imported two prototype harvesters 40 cm above soil surface developed in Brazil and evaluated their operation under • Works at depths of 40 to 60 cm, depending on the specific soil and climatic conditions of regions in tractor type being used Colombia where cassava is planted. Both the • The tractor needs more than 90 hp of power harvesters had the following components: The rigid-blade model (Figure 20-20) is similar • A disk to cut the soil crust or plant cover to the previously described model. However, instead of • An element to remove earth such as another having points or weeding hoes, it has a solid blade blade or subsoiler system in the form of a “V”. This system may generate • A device to separate roots from soil adhering to compaction, damaging the soil. the machine Parameters evaluated. The principal parameters Operation. Before a harvester is used, the for evaluating the two prototypes were: following factors should be taken into account: • Operation with each harvest method (ha/day) • Soil moisture. Dry soil makes harvesting • Root losses: entire roots (%), broken roots (%), cassava more difficult. However, soil moisture and buried roots (%) should be such that machinery can enter the • Output of manual harvesting (kilograms of roots plot without too much soil adhering to it. per day) 386 Mechanized Systems for Planting and Harvesting Cassava Figure 20-19. Prototype of a cassava harvester, model P 900 Flexible. Results obtained. For harvester output, the The greatest benefits obtained from using this results obtained during the prototype’s evaluation were machine are reduced number of working days and less as follows (values are the average of several replications labor, with workers being limited to removing rubble and trials): and packing cassava. Under the traditional system, a worker pulls up between 500 and 800 kg/8-h working • Operational speed: 7 km/h day. With semi-mechanized harvesting, CLAYUCA • Depth of work: 30–40 cm obtained yields of more than 1300 kg/worker per • Tractor power: 90 hp working day. In Brazil, harvesting systems have been • Maximum width of work: 2.4 m developed with these machines to obtain outputs as • Output: 1.1 ha/h high as 4000 kg/worker per working day. CLAYUCA also found that when semi-mechanized harvesting is Figure 20-20. Prototype of a cassava harvester with a rigid “V”-shaped blade. 387 Cassava in the Third Millennium: … incorporated into a cassava production system, processors in Brazil financed the development and harvesting costs drop by 42.8%. That is, harvesting adaptation of a prototype that was based on a potato costs are reduced by 6% in the relative harvester. The prototype eliminates all labor from the cost of labor to total production costs per hectare initial harvesting phase, using workers only for (Table 20-4). selecting and packaging roots. This prototype is now being evaluated. Preliminary results are so far highly Economic impact of semi-mechanized satisfactory. Two prototype models are being harvesting on cassava production. The importance evaluated: of using harvesters for the cassava crop lies in reducing the number of workers needed for this Model WH-15.2L. Figure 20-21 illustrates its activity. Table 20-5 presents the results obtained characteristics: when prototype P 900 Flexible was evaluated in Colombia, and compares them with those of the • Weight: 700 kg manual system. Introducing the harvester reduced • Daily output: 5 ha/8-h day total production costs by 12%. Also, total harvesting • Cutting width: 80 cm costs were reduced by 42%. Such reductions • Required power: 100 hp stemmed from a 52% cut in labor costs. Economic • Works with a mat system, where soil is impact is also created through the larger number of removed from the roots, using blades roots harvested per unit area, as the semi- • Before operation, stems must be cut at 20 to mechanical harvester removes many more roots than 40 cm above the soil surface do traditional harvesting systems. Model WH-CM 4000. Figure 20-22 shows that Mechanized harvesting this model is similar to the previous model. It also does the following: In the continual search to improve the cassava crop’s productivity and competitiveness, great progress was • Roots are mechanically taken up to a large recently made in southern Brazil to develop a sack (“big bag” type) prototype that completely mechanizes cassava • It possesses a work platform where workers harvesting. A group of cassava growers and remove roots from stems Table 20-4. General cost structure (cost/ha) for harvesting cassava, applying manual and semi-mechanized methods, in flat areas of the Department of Valle del Cauca, Colombia, 2000. Activitiesa Unit Quantity Unit value (Col$)b Total value (Col$)b RCDc (%) (A) Manual harvesting Pulling up roots Working day 25 10,000 250,000 Packaging Sack 180 90 16,200 Fique string Roll 1 5,500 5,500 Total for labor 271,700 20.4 Total cost per hectare 1,333,610 (B) Semi-mechanized harvesting Costs of machine, F and V Col$/hour 1.14 4,014 4,576 Costs of tractor, F and V Col$/hour 1.14 18,203 20,751 Workers for pulling up roots Working day 10.5 10,000 105,000 Tractor driver Working day 0.15 21,000 3,150 Packaging Sack 180 90 16,200 Fique string Roll 1 5,500 5,500 Total for labor 155,177 14.4 Total cost per hectare 1,086,350 a. F and V = fixed and variable costs. b. The exchange rate (year 2000) was 1 U.S. dollar = $2,100 Colombian pesos. c. RCD = ratio between the costs of harvesting cassava and the total direct costs of cropping, expressed in percentage. 388 Mechanized Systems for Planting and Harvesting Cassava Table 20-5. Costs per hectare of harvesting a cassava crop, Valle del Cauca, Colombia, 2000. Activity Unit Quantity Unit value Total value (US$) (US$) (A) Manual harvestinga Harvest workers Workers/day 30 4.60 138.00 Packaging Sack 180 0.04 7.20 Fique string Roll 1 2.50 2.50 Total harvest costs 147.70 Total costs per hectare 566.00 Harvest costs as proportion of total costs 26.1% (B) Semi-mechanized harvestinga Harvest workers Workers/day 14 4.60 64.40 Packaging Sack 180 0.04 7.20 Harvest costs per hectare, fixed and variable 9.50 Tractor driver 1.20 Fique string Roll 1 2.50 2.50 Total harvest costs 84.80 Total costs per hectare 498.00 Harvest costs as proportion of total costs 17.1% a. With a production of 15 to 25 t/ha. • The big-bag sack is released by a hydraulic system, enabling the machine to operate continuously • Average capacity is 7 to 10 t/h • Required power is 120 hp • Cutting width is 240 cm • The machine weighs 3500 kg For the two machines to operate adequately, the crop must first be pruned to remove all aerial parts. The machine has blades 1.80 m wide, which are located at the front. They penetrate the soil to a depth of 30 cm, pull up the roots, and send them to a mechanical mat, where plant residues and some soil are removed. The roots immediately fall into a second higher mat, where the remaining adhering soil is removed. These first two phases are totally mechanized. The roots then reach a third mat where workers remove the roots from their stems and place them in a central mat that takes them up to a big-bag sack (500-kg capacity) at the back of the machine. A worker controls the filling of this sack. When full, a device operates to deposit the sack on the ground and insert another sack, while allowing the machine to operate continuously (Figure 20-22, central right). The Figure 20-21. Prototype of a mechanical harvester, model harvester is followed by a machine that winches the WH-15.2L. sacks off the ground and into a truck. The sack’s 389 Cassava in the Third Millennium: … Figure 20-22. Prototype of mechanical harvester, model WH-CM 4000. Also shown are the use of the big-bag sack (central right) and the winch in operation (bottom right). bottom opens up, discharging the roots in their entirety 5 t/worker per day. In a traditional harvest, for the same into the truck (Figure 20-22, bottom right). volume of roots, a minimum of 40 people would be needed. This process completely eliminates the need for labor to carry roots to the truck. In some trials, this Impact of mechanizing cassava planting and machine was able to lift as much as 70 tons of harvesting. The economic impact of mechanized cassava during an 8 h working day, using 14 workers. harvesting can also be determined by the various These figures translate to an output of almost technological options available to farmers to help them 390 Mechanized Systems for Planting and Harvesting Cassava increase productivity and competitiveness. In the business is encouraged to invest in agroindustrial cassava production systems of Colombia, for example, projects involving cassava. This, in its turn, helps part of the cassava production is traded as raw material stimulate rural economies and generate jobs and for the balanced-feed market, competing in price income for farmers. against imported grains, mainly maize. Cassava production systems aim to keep production costs per On increasing the competitiveness of one segment ton of cassava as low as possible so to attract the of the cassava production chain, that is, supply, with interest of processing plants that transform cassava cassava produced at lower prices, a simultaneous chips into flour destined for balanced-feed industries. effect is generated in the segment of demand, which stimulates markets. Cassava becomes more attractive Table 20-6 summarizes cassava production costs as a raw material in many industrial fields. Benefits are for the traditional production system, where traditional thus generated for all participants in the production varieties are used and neither planting nor harvesting is chain. mechanized. Table 20-7 shows costs for a modern technology system where planting is mechanized and Environmental impact. The environmental harvesting is semi-mechanized. The traditional system impact of introducing mechanized cassava planting produces 1 ton of cassava at a 12% higher cost than and harvesting has two aspects: first, mechanized or the system with mechanized planting and harvesting. semi-mechanized harvesting leaves the soil practically This significantly higher profit, complemented by ready for planting, thus avoiding the use of heavy increased yields from high-yielding improved varieties machinery to prepare the soil before planting. Indeed, (instead of traditional varieties), can represent in some regions of Brazil, after cassava is pulled up, economic success for the farmer. direct planting is immediately carried out. The second aspect is that, by removing most of the roots from the Figure 20-23 presents an analysis carried out by earth, fewer roots remain to rot and thus become foci CLAYUCA that compares different technological of bacterial or fungal diseases. Hence, a mechanized options available to improve the efficiency of cassava cassava crop contributes to the general ecosystem by production. If the farmer maintains the traditional using fewer agricultural defenses. varieties, cost reductions are slightly less than for improved varieties. In any case, with traditional Conclusions varieties, the introduction of mechanized planting and harvesting enables farmers to reduce costs per ton of 1. The introduction of mechanized prototypes for cassava to US$21.20 (versus US$29.40 for the planting and harvesting is a practice that has high traditional system), a significant reduction of 27.9%. At potential for reducing labor costs, thus contributing this level, cassava harvesting begins to be highly to the crop’s competitiveness. competitive with imported grains. 2. The costs of the prototypes—between US$6500 The ideal situation is where farmers have easy and $15,000 for the planter and about US$4000 for access to improved varieties, and are also introduced the harvester (FOB Brazil)—is attainable. Farmer to mechanized planting and harvesting. Such a organizations (associations or cooperatives) can technology package helps farmers reduce production easily acquire and administer these prototypes to costs per ton of cassava to US$17.50 (versus US$29.40 set up cassava production systems at lower cost for the traditional system). This price represents a and improve the crop’s competitiveness. reduction of 40.5% in production costs, against the traditional production system. Such a highly 3. The operation of both planter and harvester is competitive price enables the crop to become simple and easily adapted for farmers and their incorporated into different markets. families. Social impact. The social impact of mechanizing 4. For field workers, for whom manually pulling up cassava planting and harvesting is highly significant. cassava roots is arduous work, the possibility of Field labor, especially for harvesting, becomes more using a harvester means a more comfortable and humane, as workers can more easily carry out their healthier harvest, with an improved output for work, thereby increasing their efficiency. With the labor. possibility of developing more competitive systems, 391 Cassava in the Third Millennium: … Table 20-6. Cassava production costs, using the traditional system. Activity Unit Quantity Unit cost Cost/ha (Col$) (Col$) Direct expenses Land preparation 150,000 Plowing Pass 1 50,000 50,000 Raking Pass 2 35,000 70,000 Furrowing Pass 1 30,000 30,000 Stakes and planting 353,000 Cost of stakes 20-cm stake 10,000 20 200,000 Transport Sack 12 2,000 24,000 Inputs for stake treatment 1 25,000 25,000 Labor for stake treatment Wage 1 13,000 13,000 Manual planting Wage 7 13,000 91,000 Weed control 295,000 Preemergent herbicides 1 70,000 70,000 Labor for applying preemergent herbicides Wage 1 13,000 13,000 Manual weeding Wage 13 13,000 169,000 Postemergent herbicides Liter 1 30,000 30,000 Labor for applying postemergent herbicides Wage 1 13,000 13,000 Liming 88,000 Dolomite lime Sack 10 7,500 75,000 Labor for applying lime Wage 1 13,000 13,000 Fertilizer applications 296,000 10–20–20 50-kg sack 7 33,000 231,000 Labor for applying fertilizers Wage 5 13,000 65,000 Pest and disease control 63,500 Insecticides and fungicides 1 37,500 37,500 Labor for applying pesticides Wage 2 13,000 26,000 Manual harvesting 339,200 Cutting and collection Wage 23 13,000 299,000 Packaging Sack 360 95 34,200 Fique string Roll 1 6,000 6,000 Subtotal direct costs 1,584,700 Direct production costs per ton (25 t/ha) 63,388 Indirect costs Financial costs (24%) 380,328 Lease of 1 ha land per year 300,000 Subtotal indirect costs 680,328 Total production costs per hectare 2,265,028 Total production costs per ton (25 t/ha) 90,601 5. The argument against the use of prototypes—that they are certain that production costs are they reduce labor as a source of employment— competitive. In this case, mechanized planting and needs to be analyzed according to the specific harvesting become indispensable conditions. If the context. In many cases, where the crop’s unit is in a context of small-scale cassava commercial planting is promoted, investors will not cultivation, farmer adoption of mechanized become involved with cassava as a business unless planting and harvesting would be insignificant. 392 Mechanized Systems for Planting and Harvesting Cassava Table 20-7. Cassava production costs, using a mechanized system. Activity Unit Quantity Unit cost Cost/ha (Col$) (Col$) Direct expenses Land preparation 150,000 Plowing Pass 1 50,000 50,000 Raking Pass 2 35,000 70,000 Furrowing Pass 1 30,000 30,000 Stakes and mechanized planting 289,005 Cost of stakes 20-cm stake 2000 100 200,000 Transport Sack 12 2,000 24,000 Inputs for stake treatment 1 25,000 25,000 Labor for stake treatment Wage 1 13,000 13,000 Mechanized planting Wage 0.32 13,000 4,167 Cost of machine Col$/ha 0.78 2,100 1,638 Tractor: rent + driver + fuel Day 1 8,200 8,200 Replanting Wage 1 13,000 13,000 Weed control 293,000 Preemergent herbicides 1 70,000 70,000 Labor for applying preemergent herbicides Wage 1 12,000 12,000 Manual weeding Wage 13 13,000 169,000 Post-emergent herbicide Liter 1 30,000 30,000 Labor for applying postemergent herbicides Wage 1 12,000 12,000 Liming 88,000 Dolomite lime Sack 10 7,500 75,000 Labor for applying lime Wage 1 13,000 13,000 Fertilizer applications 296,000 10–20–20 50-kg sack 7 33,000 231,000 Labor for applying fertilizers Wage 5 13,000 65,000 Pest and disease control 63,500 Insecticides and fungicides 1 37,500 37,500 Labor for applying pesticides Wage 2 13,000 26,000 Semi-mechanized harvesting 183,036 Cutting and collecting stems Wage 9 13,000 117,000 Cutting and collecting stakes Wage 1 13,000 13,000 Packaging Sack 360 95 34,200 Fique string Roll 1 6,000 6,000 Cost of machine Col$/hour 1.80 842 1,516 Tractor + driver ha 1 11,320 11,320 Subtotal direct costs 1,362,540 Direct production costs per ton (25 t/ha) 54,502 Indirect costs Financial costs (24%) 327,010 Lease of 1 ha of land per year 300,000 Subtotal indirect costs 627,010 Total production costs per hectare 1,989,550 Total production costs per ton (25 t/ha) 79,582 393 Cassava in the Third Millennium: … 35 30 29.40 25.40 26.00 25 21.20 20 17.50 15 10 5 0 Traditional Improved Mechanized Mechanized Mechanized planting system varieties planting planting and and harvesting + harvesting improved varieties Figure 20-23. Differences in cassava production costs (in US$) according to technological option. References Lozano JC. 1978. Posibles efectos del ecosistema en algunas especies de cultivos tropicales. Fitopatol Cadavid L, LF; El-Sharkawy MA; Acosta A; Sánchez T. Colomb 7(2):94–107. 1998. Long-term effects of mulch, fertilization and tillage on cassava grown in sandy soils in northern Lulofs RB. 1970. A study of method and costs for Colombia. Field Crops Res 57:45–56. commercial planting of tapioca in Kedah. In: Blencowe EK; Blencowe JW, eds. Crop diversification Cock JH; Castro M, A; Toro M, JC. 1978. Agronomic in Malaysia. Incorporated Society of Planters, Kuala implications of mechanical harvesting. In: Weber EJ; Lumpur, Malaysia. p 149–166. Cock JH; Chouinard A, eds. Proc Workshop on Cassava Harvesting and Processing held in Cali, Normanha ES; Pereira AS. 1974. Resultados e Colombia. International Development Research experiencias sobre épocas de plantío da mandioca. Centre (IDRC), Ottawa, Canada. p 60–65. Rev Agric (Piracicaba) 22 (4/6):135–142. Conceição AJ da. 1976. A mandioca. In: Curso Intensivo Ribeiro FJ. 1996. Cultura da mandioca. Escola Superior Nacional de Mandioca, Cruz das Almas, Brasil. de Agricultura [of the] Universidade Rural do Estado Empresa de Pesquisa Agropecuária de Minas Gerias de Minas Gerais, Viçosa, Brazil. 80 p. (EPAMIG); Centro Nacional de Pesquisa de Mandioca e Fruticultura (CNPMF), Cruz das Almas, Bahia, Solórzano H, A. 1978. Resultados de investigación para la Brazil. p 435–440. yuca. In: Transferencia de resultados de investigación agropecuaria a los agentes de producción de la Cuadra MA; Rodríguez MS. 1983. Estudio de diferentes Región XII–Loreto, Tarapoto, Perú, vol 2. Centro métodos de plantación de la yuca (Manihot esculenta Regional de Investigación Agropecuaria del Oriente y Crantz) y su relación con el rendimiento en el Cooperación [of] IICA–Peru, Lima. p 19–31. ecosistema de la provincia de Guantánamo. Cienc Téc Agric Viandas Trop 6(1–2):51–60. Toro M, JC; Celis E; Jaramillo E. 1976. Métodos de cosecha de yuca. In: Curso sobre producción de yuca. Gurnah AM. 1974. Effects of method of planting, the Centro Internacional de Agricultura Tropical (CIAT), length and types of cuttings on yield and some yield Cali, Colombia. p 225–232. components of cassava (Manihot esculenta Crantz) grown in the forest zone of Ghana. Ghana J Agric Sci 7(2):103–108. 394 US$/t Part E Technologies for the Postharvest Management of Cassava CHAPTER 21 Natural Cassava Drying Systems Bernardo Ospina Patiño1, Rupert Best2, and Lisímaco Alonso3 Cassava is a major tropical crop. It has high potential for are then dried, packed, and stored. Optional operations the development of agroindustries such as the may include washing the roots before chipping, or milling manufacture of balanced rations for animals. However, if the already dried chips, depending on market cassava starch is to replace cereal grains in such requirements (Figure 21-1). industries, the crop’s starchy roots must first be dried. Harvest Cassava can be dried either naturally or artificially. Methods differ not only in the technology used but also Cassava is harvested manually and is transported in in their costs. Natural drying takes advantage of solar several vehicles to the drying plant, either packed or in and wind energy, which restricts drying times to the bulk (Figure 21-2). As soon as possible, the roots are year’s dry seasons. In contrast, artificial drying demands subjected to quality control. At harvest, stem fragments a different type of energy such as fossil fuels (oil, coal, are removed, stones and accompanying lumps of earth or gas) or agricultural residues (sugarcane bagasse or are discarded, and those roots that look infested are rice husks). It does not depend on climatic conditions. separated. Despite being restricted to dry times of the year, sun Cassava roots that have low dry matter (DM)4 content and wind drying is usually economic and very useful in negatively affect the efficiency and profitability of the sites where other energy sources are limited or costly. process. They are therefore considered as being of lesser Natural cassava drying is simple and easy for farmers to quality. Dry matter content depends not only on the carry out. variety planted and on edaphoclimatic conditions, but also on the age and plant health of the crop at harvest. Farmers may organize themselves into associations and cooperatives for the integrated exploitation of the Once harvested, the roots should be taken quickly to cassava crop (i.e., production, processing, and the plant so that they are immediately processed. Roots marketing), thus creating an alternative to the instability that are processed later than 48 hours after harvest will of the fresh-cassava market. Such organization also deteriorate rapidly and their drying results in a poor presents the possibility of marketing a higher production quality product. (Best and Gómez 1983). Weighing the fresh roots Producing Dried Cassava Chips In the drying plant, cassava roots are weighed on a Dried cassava chips are produced as follows: cassava platform scale that can carry several sacks at once, thus roots are harvested, weighed, and chipped. The chips facilitating the operation (Figure 21-3). Weighing the roots before drying and the chips 1. Executive Director, CLAYUCA, Cali, Colombia. E-mail: b.ospina@cgiar.org afterwards permits the determination of “yield”, both for 2. Chemical Engineer, formerly Leader, Rural Agroenterprise Development (RAD) Project, CIAT, Cali, Colombia. E-mail: r.best@cgiar.org 4. For an explanation of this and other abbreviations and acronyms, 3. Agricultural Engineer, Postharvest Management Systems, see Appendix 1: Acronyms, abbreviations, and Technical CLAYUCA. E-mail: l.alonso@cgiar.org Terminology, this volume. 397 Cassava in the Third Millennium: … Reception and Chipping Drying Collection and Weighing and weighing packaging storage WASHING MILLING Principal operation Optional operation Figure 21-1. Obtaining dried chips from cassava roots, using natural processing. Figure 21-2. Manual harvesting of cassava roots and their transport to the drying plant. the cassava varieties used and the process itself. Washing Cassava varieties differ in their yields of dried chips. Hence, identifying the region’s best yielding varieties If soil is left adhering to fresh roots, the dried product becomes highly important. Furthermore, a given variety may have high ash content, especially of silica, which may present a certain yield in one drying process and will reduce its quality. another in a different process. To control such differences, the variety must be evaluated and weighed Soil adheres to roots when they are harvested according to the evaluation of different lots of roots. during a rainy season or from heavy soil. Hence, the 398 Natural Cassava Drying Systems Figure 21-3. Weighing sacks of cassava roots. Figure 21-5. Cassava chipping machine in operation, using a “Thailand” type disk. roots must be washed in either small troughs or achieved by cutting them into small and uniform washing machines, as shown in Figure 21-4. These pieces, that is, into chips, a task that can be carried out machines consist of a rotary drum that shakes the with a chipping machine (Figure 21-5). roots while washing them with a pressurized water jet applied inside or outside the drum. In a natural drying Drying plant, cassava roots almost never need washing because drying occurs at the same time as harvesting, The drying of cassava chips involves eliminating most that is, in summer. The roots therefore arrive from the of the moisture they contain when they are fresh. The field with little soil adhering. resulting dried product can be stored over long periods, without deterioration. The most common methods of Cassava roots destined for animal feed do not drying chips can be classified according to level of need to have the inner or outer root peel removed. technology and cost: Chipping • Continuous drying in rotary dryers or conveyor belt To dry roots more quickly, as large a root surface area • Drying by batches in dryers with static layers as possible should be exposed to the air. This is and using forced hot air (A) (B) • Natural drying, using solar and wind energy, on concrete floors or on inclined trays Selection of method depends largely on the amount of cassava roots to be dried, availability of capital, labor costs, and availability of relatively inexpensive energy sources. In this chapter, natural drying is described. Natural drying takes advantage of solar energy and of the action of air currents to evaporate moisture from cassava chips. Two technologies are available: drying on concrete floors (or in Spanish called patios) and drying on inclined trays. Figure 21-4. Washing cassava roots in troughs (A) or with a machine that features a rotary cylindrical drum (B). 399 Cassava in the Third Millennium: … Technology 1: Drying Cassava Chips on Concrete Floors With this technology, cassava chips are spread out on cover. The next morning, they are spread out again. concrete floors so that they are exposed to the direct Turning over, done with a wooden rake, should action of both solar radiation and the latent heat of continue until the chips are dried. The rake’s tines form surrounding air currents. This stage includes two basic furrows that expose moist areas of floor to direct solar operations: spreading the chips in the drying area and radiation (Figure 21.7). turning them over frequently until they are completely dry. Collecting and packing Spreading the chips When the chips’ moisture content is 10% to 12%, they are collected and packed. In drying plants, this level of A wheelbarrow is used to deposit freshly cut chips into moisture is determined by feel. If the chips are small heaps that are then raked out uniformly over the sufficiently dry, they break easily when squeezed drying floor’s surface (Figure 21-6). between fingers. They can also be used as writing chalk. Each square meter of floor should carry 8 to 12 kg of fresh chips, a load that should dry within 2 days Collecting chips requires two types of shovels: one under normal climatic conditions. A larger amount of wide and wooden, and used to pile up the dried chips chips per square meter will delay drying, thus reducing (Figure 21-8); the other is short and metal, and used to the drying plant’s efficiency and degrading the chips’ final quality. A smaller quantity, however, will not take advantage of the plant’s productive capacity. Turning the chips All the chips must be consistently dried so that the end product is of good quality. To achieve uniform drying, the chips should be turned over every 2 hours (i.e., 6 to 8 times a day), especially during the initial hours of drying, when most of the moisture is lost. At night, the chips may remain spread out on the concrete floor, unless rain is likely. In this case, the chips should be stacked at the highest level of the Figure 21-7. Cassava chips are turned over every 2 hours, using concrete floor and protected by a plastic or canvas wooden rakes. The rakes may be constructed at the plant itself, especially for this task. Figure 21-6. Wooden rakes are used to spread cassava chips Figure 21-8. Dried cassava chips are collected by piling them up over the concrete floor. in the concrete floor, using a wooden shovel. 400 Natural Cassava Drying Systems pack the heaps into bags or sacks of either polypropylene or fique (also called cabuya; from the plant Furcraea andina Trel.). For this task, two people are usually needed: one to keep the sack’s mouth open as the other shovels in the dried chips. A metal funnel can also be used, with its stem emptying into an open sack suspended from a framework (Figure 21-9). A fique sack can carry 40 to 50 kg, but if the dried chips are tamped down as the sack is filled, the weight can be higher (Figure 21-10). Milling Figure 21-11. Milling dried cassava chips. Transporting cassava chips to distant places is costly because of their low weight per unit of volume. Hence, chips are sometimes milled to obtain flour, which is However, cassava is usually marketed as chips because then packed in bags of either polypropylene, paper, or quality control of flour in consumer companies or cloth. Milling is carried out with a hammer mill, to concentrate-feed factories is not easy. which cloth filters are adapted to capture the fine powder that results from the operation (Figure 21-11). Storage The drying plant should have a storeroom where the dried chips are kept until shipped to purchasing companies. The sacks should be stacked on wooden platforms or pallets (Figure 21-12). If storage conditions are adequately controlled, the dried chips (i.e., with 10% to 12% moisture content) can be stored for as long as 6 to 12 months without their quality deteriorating. Optimal conditions are achieved if the storeroom is kept very clean and if aeration mechanisms are installed that adequately move moisture between storeroom and exterior. If storeroom humidity is too high, the dried chips Figure 21-9. A metal funnel facilitates packing the dried cassava absorb the moisture, which, together with high starch chips. content, stimulates the growth of fungi on the chips. These produce toxins that ultimately prevent the chips’ use as animal feed. Figure 21-10. Tamping down dried chips in sacks. Sacks Figure 21-12. In the storeroom, sacks of dried cassava chips weighing over 50 kg can then be obtained. should be stacked on pallets or wooden platforms. 401 Cassava in the Third Millennium: … Stored dried chips can also be attacked by insect Figure 21-14 illustrates the moisture loss curve at pests. At least 38 species of insects, mostly of the different stages of the drying procedure for cassava order Coleoptera, have been identified, although the chips, from harvest to storage, and indicates the important ones are those that can reproduce in the normal duration of each stage. chips. Studies conducted at CIAT indicate that Araecerus fasciculatus and Sitophilus oryzae can Quality standards for dried cassava chips cause major losses of dried chips (Figure 21-13). Dried chips are used mainly to totally or partially (A) (B) substitute cereal grain in the formulation of balanced feeds for animals. Their quality should therefore be adjusted to the standards required by the companies processing this product (Table 21-1). In addition to Table 21-1. Basic standards for quality as required by companies using dried cassava. Component or aspect Standard Moisture content (%) 12.0 Crude fiber, maximum (%) 5.0 Ash, maximum (%) 3.5 Fungi and yeasts, maximum count (cfu/g) 100,000 Aflatoxins and ochratoxins Absent Total cyanide (ppm) 100 Figure 21-13. The weevils Araecerus sp. (A) and Sitophilus Coliforms, total (cfu/g) 600 oryzae (B) can cause major losses to stores of dried cassava chips. Presentation Chips Chipping 70 Spreading Transport 60 Harvest Turning over 50 40 Turning over 30 20 Collection Storage 10 Packing 0 0 6 14 18 6 10 14 18 6 10 14 18 Time (hours) 0 2 14 20 26 38 44 50 Hours of drying Figure 21-14. Moisture loss curve at different stages of drying cassava chips, assuming normal conditions. The duration of each stage and of the entire process is also indicated. 402 Moisture content (%) in cassava Natural Cassava Drying Systems these standards, the product should comply with the The concrete should be a mixture of cement, following requisites: it should be fresh, have no clean sand, gravel that is free of earth and fermenting odor, and present no signs of insect attack lumps, and water. The proportions for mixing or contamination. depend on the soil’s characteristics. In general, clayey soils require a mixture of cement, sand, Infrastructure of a cassava drying plant gravel at 1:2:3, and sandy soils at 1:3:4. However, the correct proportions of these Before installing a cassava drying plant, its location components depend on the mason’s or should be carefully chosen with respect to its distance builder’s experience. Table 21-2 indicates the from sites supplying the raw material and access to quantities of the elements needed to prepare good roads. Also desirable are nearby sources of water one cubic meter of concrete according to the and electric power. The minimum infrastructure of a specified mixture. drying plant consists of a drying concrete floor, an area for chipping, and a storeroom. • The third step is to pour the concrete onto the area prepared for the floor. The area of Drying concrete floor. Cassava chips are exposed construction should be divided into slabs of to solar radiation on a surface designed to resist 2 × 2 m, leaving narrow separations in exposure to the sun, that is, it will not crack. It must between, into which “expansion joints” are also be smooth to permit easy sliding of the rakes and placed. These are simply wooden strips that are shovels used to spread, turn over, and collect cassava removed at the end of the work (Figure 21-15A). chips. The drying area should not be surrounded by To reduce the risk of the floor cracking, pieces trees, buildings, or other similar obstacles that may of iron rod should be placed between slabs, so reduce natural ventilation or shade the area. that they serve as joining elements when the Furthermore, the natural slope of the land should be slabs meld (Figure 21-15B). taken into account so that the concrete floor has a slope that allows rainwater to drain. • The fourth step, once the floor is cast, is to finish and correct it, including fixing any The construction of a drying floor is specific to remaining cracks. The wooden strips serving as each region, making it highly advisable that farmers expansion joints are then removed and the participate in its construction, as it will be built under separations between slabs filled with either a their organization. Hiring an expert mason should mortar made of cement and sand or with tar. always be recommended so that he leads the works. Figure 21-16 shows the final appearance of a Construction is as follows: drying area. • The first step is to choose the area that the The division of the drying area into 2 × 2 m slabs patio will occupy. Plant cover is removed, the has the advantage of helping workers distribute land leveled, and the exposed surface adequate amounts of cassava chips per unit of area. compacted. Good compaction guarantees the work’s quality. During compaction, the center Table 21-2. The quantities of cement, sand, gravel, and water of the concrete floor should remain at a higher needed to prepare 1 cubic meter of concrete, level than the sides. Such “crowning” will according to the proportions required. facilitate rapid drainage of rainwater. Proportions Component Cement Sand Gravel Water • The floor’s foundations are then made at the (kg)a (m3) (m3) (L) perimeter of the concrete floor. The 1:2:2 420 0.670 0.670 192 foundations should be 20 to 30 cm wide and 1:2:3 350 0.555 0.835 158 30 to 40 cm deep, and built with either poured or block concrete. The floor itself is also made 1:2:4 300 0.475 0.950 135 of either poured or block concrete. If only 1:3:3 300 0.715 0.715 135 people are passing through its area, then the 1:3:4 260 0.625 0.835 124 floor may be 10 cm thick, but if heavy motor 1:3:5 230 0.555 0.920 101 vehicles are expected to circulate on the floor, 1:3:6 210 0.500 1.000 94 then it should be 15 to 20 cm thick and a. One cubic meter of cement is sufficient for 12.5 m2 of flooring, reinforced with iron. 8 cm thick. 403 Cassava in the Third Millennium: … (A) (B) Figure 21-15. Expansion joints are placed between concrete slabs (A), together with iron rods (B). Figure 21-17. View of the roofing complex used to cover the cassava chipping machine and to protect the fresh cassava roots received for processing. Figure 21-16. Final appearance of a drying concrete floor for cassava chips. The chipping area should be close to where roots Applying the recommended load of fresh chips at are received to prevent unnecessary movement within 12.5 kg/m2 of floor, a slab of 4 m2 (2 × 2 m) should the plant. The slope of the floor in this area should be receive 50 kg. This quantity is about the same as a away from the drying area so that washing water from wheelbarrow load. Simply put, a barrow load per slab is the chipping machine and rainwater do not drain over the optimal load for the drying area. the chips being dried (Figure 21-18). Chipping area. The area where the chipping The chipping area will be subject to vibrations and machine is installed should be sufficient to allow its floor must therefore support a higher weight per unit workers to move easily and also leave room for the raw area than that of the drying area. Its floor should material to be chipped. A chipping area of 16 m2 (i.e., therefore be resistant, having foundations that are of 4 × 4 m) is adequate for plants that have 500 to poured or block concrete. The foundations should be 1000 m2 of drying floor. 40 cm deep and 40 cm wide, and the floor 15 cm thick, being composed of a mixture at 1:3:5 (Figure 21-19). This area should also have roofing to shade the A wooden framework supports this area’s roofing, which workers and prevent the chipping machine from may consist of zinc sheets, asbestos-cement tiles, or deteriorating through the action of sun and rain. In typical materials of the region (e.g., palm leaves). addition, next to this area, roofing should be built to cover the reception site for the roots, protecting them Storeroom. The storeroom guards the dried from sun and rain, and preventing their quality from cassava chips, tools, and equipment used for drying. deteriorating. This additional roofing can be The storeroom’s size depends on the drying plant’s constructed with typical materials of the region capacity, periodicity of shipping the product, and future (Figure 21-17). expansions of drying capacity. 404 Natural Cassava Drying Systems Chipping area Dryin g area Figure 21-18. The floor of the cassava chipping area must slope away from the drying area for the chips. Foundation Floor: 15 cm (1:3:5) Figure 21-20. Laying down a foundation to support the external walls of a storeroom. Upper tie beam 40 cm Figure 21-19. The cassava chipping area should have a resistant floor. Column About 350 kg of dried chips can be stored in 1 m3 Wall made of Lower of storeroom. One that is 140 m3 (10 × 4 × 3.5 m) can concrete blocks tie beam store about 30 t of dried chips, which is the production of a 1000-m2 drying concrete floor over 18 days. If the dried product is shipped from the plant every Figure 21-21. Elements of a storeroom’s basic structure. 2 weeks, the storeroom will not have problems of congestion or aeration. A 1-m space should be left between the top of the stored stack of dried chips and The storeroom should have mechanisms that the storeroom’s ceiling. control aeration or change of air. The opening of all doors for a short time is also useful. Concrete fretwork The storeroom’s foundations should be 30 to placed along the upper lengths of the walls 50 cm deep and 40 cm thick. If the walls are very long, (Figure 21-22) forms a good system for ventilating the columns should be constructed in the wall every 3 or storeroom, particularly when insecticide applications 4 m and the foundation under each column should be 60 to 70 cm (Figure 21-20). The storeroom’s basic structure consists of the following elements: • Lower tie beams placed immediately above the foundations, and perfectly joined to give the walls solid support. • Columns. • Walls made of brick or concrete blocks. • Upper tie beams to bind the columns and Figure 21-22. Wall with concrete fretwork running along its support the roofing (Figure 21-21). upper length. 405 40 cm Cassava in the Third Millennium: … are carried out. However, such fretwork is not suitable for drying and collecting chips (wheelbarrow, wooden for long-term storage. rakes, and shovels), sacks, and a plastic or canvas cover to protect the concrete floor when necessary. The roofing consists of a framework of wooden beams that support asbestos-cement tiles, zinc sheets, Platform scale. The platform scale should be able or typical materials of the region. It should be gabled, to weigh several sacks at once. A 500-kg capacity is with adequate slopes. acceptable for natural drying plants. Before constructing the storeroom floor, a cement Chipping machine. Commonly used models base must be set to serve as an initial floor to prevent are known as “Thailand” (Figure 21-23A) or moisture from creeping up to the surface of the real “Colombia” (Figure 21-23B) types. The “Thailand” floor. On this base, the final floor, consisting of a machine basically consists of a metal structure and reinforced but thin slab of concrete, is placed. It must cutting disk. The structure supports the pulleys, be as smooth as possible. The bags of dried cassava linchpin for the disk, and feed hopper. The motor’s chips must not be allowed to have direct contact with support is also coupled to the machine’s main the floor. Hence, wooden platforms or pallets that rise structure, as in the “Colombia 1” type (Herrera et al. 10 to 15 cm high from the floor should be installed and 1983), (Figure 21-23B). the sacks of dried chips stacked on these. The machine may be powered by either an electric The storeroom’s external structures should include or internal combustion (gasoline or diesel) motor. The a pathway around it and good drainage that will prevent gasoline motor should have between 8 and 10 hp rainwater from accumulating and forming muddy (Figure 21-24), whereas an electric motor may have areas. 5 hp. This motor is the most important component of the plant’s equipment because any deficiency in its Equipment for a drying plant operation alters the normal drying process. The workers must therefore be adequately trained to run it The minimum equipment for a drying plant consists of and give it rigorous maintenance. the following: platform scale, chipping machine, tools (A) (B) Figure 21-23. Cassava chipping machines, type “Thailand” (A) and type “Colombia” (B). 406 Natural Cassava Drying Systems (A) 10 cm Figure 21-24. An 8-to-10-hp internal combustion motor (gasoline) 1 m is needed to operate a cassava chipping machine. (B) Implements for drying and collectin g. The following tools are needed: • An ordinary wheelbarrow with a 50-kg capacity. It is used to distribute cassava chips into heaps on the drying concrete floor at a barrow load per area of 2 × 2 m. • Several wooden rakes to spread and turn over cassava chips. Their form and dimensions are indicated in Figure 21-25A. • Two types of shovels to manage the dried chips. One type is wooden, with the blade being wide, 1.20 m flat, rectangular, and finishing on a fine edge to Figure 21-25. Tools for cassava chip drying: (A) wooden rake to help pile up the chips (Figure 21-25B). The other spread and turn over chips; and (B) wooden type of shovel is the usual metal one. These are shovel for piling up dried chips. used to pick up and pack the chips. chips is well planned and coordinated. Having real data • A sufficient number of sacks for both on each stage is therefore indispensable when purchasing fresh cassava roots, and for storing analyzing the economic feasibility of setting up a plant. and marketing dried chips. The best sacks are The following aspects should be considered: those of fique or jute, which have a larger capacity and can be used several times over. • Production of fresh cassava roots in the plant’s Polypropylene sacks have a smaller capacity and area of influence last for less time but are less expensive. • Plant size and capacity for processing dried chips • A plastic cover to protect cassava chips in the • The correct administration and operation of the drying concrete floor from unforeseen rains. plant During winter, the plastic helps dry the chips, • The financing required albeit on a small scale. For a plant with 500 m2 • Marketing the dried cassava chips of concrete floor, a 250-m2 plastic cover is sufficient. Cassava production in the plant’s area of influence . The timely production of fresh cassava Conditions for establishing the natural drying roots—the drying plants’ raw material—is a significant plant factor to consider before installing such a plant. A drying plant will be successful if its management of Roots are usually available for processing only the production, processing, and marketing of dried when the fresh-cassava market has surpluses, as this 407 1.5 0 m 1.5 0 m cm 0.4 0 Cassava in the Third Millennium: … market is, in many places, the principal and almost Duration of the dry season. Natural drying is based exclusive channel for marketing cassava. Hence, the on the use of solar energy. Hence, the summer months offer of raw material for dried chips becomes of the region where the plant will be established must discontinuous and seasonal. To ensure a continuous be known. In the Colombian North Coast, for example, and sufficient offer, the cassava crop’s productivity must the main dry months are December to March and part increase considerably. Production costs would therefore of April. A second semester of dry climate is July to be reduced, making root prices more competitive and September. In total, the region has about 20 weeks the cassava-drying agribusiness more profitable. during which drying can take place. The organization of farmers in the region into Load of fresh chips per square meter. The optimal cooperatives or associations that produce and process load of chips (kg) for drying per square meter of floor cassava roots, and receive technical assistance and for 2 days is then determined. Two days is used for credit from official entities, is an initiative that would calculation because the most efficient advantage is ensure availability of roots for the drying plant. Hence, taken of the plant in this time, with three batches of these groups must incorporate farmers able to obtain chips being dried per week. In the Colombian North good cassava production. Otherwise, the plant would Coast, the optimal chip load is 12.5 kg/m2. On days of depend on the offer of raw material from farmers little solar radiation, during climatic transitions, smaller outside its area, thus making it dependent and loads are used. vulnerable as a company. Hence, the socioeconomic profile of a cassava drying plant’s potential owners is, Determining a plant’s capacity. A plant’s capacity perhaps, the most important factor in its establishment for processing is calculated by using the previous three and size. parameters: plant size, duration of summer, and fresh chip load (Table 21-3). In the Colombian North Coast, cassava-drying companies are constituted by farmers with little capacity Amount of fresh chips that can be dried per year. to produce cassava. They therefore have difficulties in The annual capacity for drying per square meter of achieving an acceptable level of profitability. Thus, when concrete floor would be: a cooperative or association is organized to operate a drying plant, it must establish a suitable procedure for 12 kg/m2 per batch × 3 batches/week × selecting its members to ensure supplies of the raw 20 weeks/year = 720 kg/m2 per year material needed for the plant’s efficient operation. Hence, on a 500-m2 floor, 360,000 kg, that is, Plant size and capacity. 360 t, of fresh chips could be dried per year. Plant size. Feasibility studies and experiences so far Determining the conversion factor (c.f.). The obtained indicate that the minimum area for the amount of dried chips that can be obtained from a profitable drying of cassava chips is 500 m2. To date, given batch of fresh cassava roots may be discovered plants of 1000 to 2000 m2 of drying floor have by first determining a conversion factor for the cassava functioned with good results. A new plant should variety that was harvested. To calculate it, the cassava’s therefore begin with 500 m2 to expand later when the moisture content should be determined, both at the farmers have completely mastered the drying technique beginning and end of the drying process. (Ospina and Best, 1984). To discover the size of the future plant, the area’s Table 21-3. Value of parameters determining a plant’s capacity cassava production must be calculated and the for processing dried cassava chips in the Colombian socioeconomic profile of the plant’s potential owners North Coast, 2000. described. This information should indicate the Parameter Unit probability of obtaining enough raw material and of Duration of the dry season 20 weeks maintaining the company stable. Load of fresh cassava chips 12 kg/m2 The quantity of chips that a plant can dry depends Drying time per batch 2 days on three factors: the duration of summer, the load of Batches per week 3 Drying area 500 m2 chips that can be dried per square meter, and the drying area’s capacity. 408 Natural Cassava Drying Systems Table 21-4. Quantities of dried cassava chips obtained by plants The c.f. is a parameter that relates directly with the with different-sized drying areas and summers of dry matter (DM) content in the cassava being different duration. processed. When roots have been attacked by disease Drying Dry Annual capacity for Required or a pest (e.g., cassava hornworm), DM content at area climate processing production harvest may be very low and thus the c.f. would be very (m2) (weeks/year) Fresh Dried (ha/year)b high. Climatic conditions (e.g., rain during harvest) may roots (t) chips (t) also affect a variety’s DM content and therefore its c.f. 500 12 216 87 27 16 288 115 36 Another factor that affects the c.f. is the farmers’ 20 360 144 45 management of the drying technology. For example, if 1000 12 432 174 54 they dry the chips too much (i.e., to less than 12%), the 16 576 230 72 c.f. is high. 20 720 288 90 2000 12 864 348 108 The c.f. can be calculated, using, for example, 16 1152 460 144 1000 kg of chips from recently harvested fresh cassava 20 1440 576 180 roots that had a moisture content of 65%, and were dried on a concrete floor until the final moisture a. Using a conversion factor of 2.5:1, where 2.5 t of fresh cassava roots is processed into 1 t of dried cassava chips. content was 12%. If a sample of 398 kg of chips is then b. Calculated area, assuming that the cassava variety yields 8 t/ha of taken, the c.f. would therefore be: fresh cassava roots. c.f. = 1000/398 = 2.5 plant should therefore have a manager or administrator, a treasurer, and a production head. Note that the DM should be constant. The 1000 kg of roots, which had 65% moisture content, had 650 kg • The manager or administrator is responsible of water and 350 kg of DM. On drying, most of the for the company’s general functioning. He or water was eliminated from the chips, but the DM was she coordinates all the plant’s activities and conserved. Accordingly, the 398 kg of dried chips at technical assistance services, and is also the the end of the process should contain 350 kg of DM. company’s legal representative. The manager The remaining 48 kg would represent the 12% of final must therefore be a dynamic person who is moisture content in the chips. respected by the other member farmers. Calculating dried chip production. The c.f. can be • The head of production is responsible for used to calculate the quantity of dried chips that the organizing working groups (groups of plant can produce per year. If we assume that the 360 t members or of contracted personnel) to of fresh chips (FC) that a plant of 500 m2 processes in guarantee timely supplies of raw material. He 1 year will yield 144 t of dried chips (DC), then the c.f. or she must also verify results of quality control is 2.5:1 (FC to DC), that is: of the end product. • The treasurer is in charge of making payments 360 t FC = 2.5 FC to 1 DC and collecting debts. Together with the 144 t DC manager, the treasurer is responsible for establishing an accounting system that allows The c.f. of 2.5 can then be used to calculate the members to know the outcomes of likely production of dried chips from different fresh- management. chip loads of the same variety processed at the same plant. Although these three positions (manager, production head, and treasurer) imply an administrative Table 21-4 shows the quantities of dried chips that cost for the drying plant, they help guarantee its good are obtained from processing fresh cassava roots operation. according to drying area and period of drying. Natural cassava drying plants also require a certain Administration and operational organization. A amount of labor. Each company organizes its work natural cassava drying plant functions correctly if the force according to its conditions. Sometimes, plant’s group of farmer-owners is well organized. The members or their families work at the plant but, 409 Cassava in the Third Millennium: … usually, the plant becomes a source of employment for plant construction, capital for the plant’s operation, and its rural hinterland, especially if employment production of raw material. opportunities are limited. • Plant construction. The construction costs of a Table 21-5 lists the types of labor needed for the drying plant are specific to each region or different operations of a drying plant. Note that the country, and depend on the availability and 48 working-hours and maximum of six workers required price of materials. The values listed in to process 6 t of fresh cassava roots represent one Table 21-6 indicate that a 500-m2 plant in the working day (8 working-hours) for each ton processed. Colombian North Coast needs an initial investment of about US$15,680, according to Financing. To construct and initiate a drying plant, the National Federation of Cassava Producers, investments must be made in three well-defined areas: Processors, and Traders (FEDEYUCA 2001, pers. comm.). • Plant operation. The plant needs a working Table 21-5. Labor needed to chip and dry one batch of 6 t of fresh cassava roots. capital to pay labor, acquire raw material and sacks, and pay freight and administrative costs. Tasks Workers Hours Working (no.) (no.) hours The working capital must be available when the (total) plant begins processing. Table 21-7 separates the categories comprising the working capital Weigh and chip the roots 4 3 12 underlying a plant’s operation over Spread out the cassava chips 3 3 9 30 days (FEDEYUCA 2002, pers. comm.). Turn over and mix the cassava chips 3 3 9 Collect, pack, and store the chips 6 3 18 • Production of raw material. In most cases, no Total 48 credit lines exist to finance cassava crops, but Table 21-6. The investment needed to make a 500 m2 concrete floor for a natural cassava drying plant, Colombian North Coast, 2001. Work, tool, or element Quantity Unit value Total for item Total for category (US$/m2) (US$)a (US$) Installations 11,500 Concrete floor (m2) 500 15 7500 Storeroom (m2) 40 70 2800 Wire mesh (rolls, 1 m wide) 100 2 200 Roofing for chipping machine (m2) 25 40 1000 Equipment 2,000 Chipping machine 1 900 900 5-hp electric motors 2 350 700 500-kg capacity platform scale 1 400 400 Tools 380 Wheelbarrows 4 30 120 Metal shovels 6 10 60 Wooden rakes 10 10 100 Wooden collectors 10 10 100 Others 375 Polypropylene sacks 300 0.25 75 Plastic cover (10 × 50 m, caliber 6) 1 300 300 Subtotal 14,255 Unforeseen contingencies (10%) 1,425 Working capitalb 3,940 Total investment (US$) 19,620 a. Exchange rate, January 2001: US$1 = Col$2200. b. Table 21-7 presents the distribution of the working capital by category. 410 Natural Cassava Drying Systems Table 21-7. Working capital used for 30 operational days of a drying plant with a 500m2 concrete floor having a planting high-yielding varieties and developing best load of 12 kg/m2 and 12 batches, Colombian North agronomic practices that reduce the costs of root Coast, 2001. production. If the costs stay down sufficiently, then Category or Quantity Unit value Rubric value dried cassava chips can be marketed to give an input (Col$) (Col$) adequate profit margin (Table 21-9). Fresh cassava roots (t) 72 80,000 5,760,000 Working days (units) 80 15,000 1,200,000 Sacks (units) 700 500 350,000 Table 21-8. Structure of production costs per ton of dried cassava chips for a cassava drying plant with a Freight (t, dried chips) 30 45,000 1,350,000 500m2 drying concrete floor. Total (Col$) 8,660,000 Costs Value Total (US$)a 3,940 (concept or category) (Col$) a. Exchange rate, January 2001: US$1 = Col$2200. Fixed costs 27,500 Administrationa 12,500 Depreciationb 15,000 acquiring one is a must. Credit should be timely, Variable costs 240,500 sufficient, and preferably of an association type, Raw materialc 200,000 as this will enable all company members to Labord 37,500 produce cassava and thus guarantee adequate Expensese 3,000 supplies of raw material. Marketing expenditures 53,000 Packagingf 8,000 Farmers may go to state entities or cooperatives Freightg 45,000 when searching for financing. To construct the plant, Total production cost per ton 321,000 long-term credit lines with promotional interests should of dried cassava chipsh be preferred, as the plant’s initial period of operation a. Salaries of the Administrator: Col$450,000 per month, 4 months (1 to 2 years) is critical as farmers adapt to the new period (Col$1,800,000). The total production of dry cassava agroindustrial alternative. Furthermore, farmers need to chips during the period is 144 MT. enjoy lasting institutional support that will guarantee b. Based on investment costs of US$19,620 and 20 years depreciation period. adequate training in the technical and accounting c. 2.5 t of fresh cassava roots at Col$80,000/t. aspects of the company’s effective operation. d. 2,5 man/days per MT dry cassava chips (1 man/day= Col$15,000 e. Sacks in fique, cloth, etc. Marketing dried cassava chips. The principal f. 20 clean fique sacks, each with a 50-kg capacity. market of dried chips comprises processing industries g. Transport from the drying plant to the buyer (concentrate-feed for concentrate feeds, especially for poultry and pigs. plant), maximum of 150 km. h. Exchange rate, January 2001: US$1 = Col$2200. However, most cassava-producing countries of Latin America import grains to manufacture this feed instead of using dried cassava chips to substitute imported grains. The factor that most influences Table 21-9. Calculation of net income per ton of dried cassava substitution is the price of dried chips, compared with chips produced in the previous example. that of grains such as maize and sorghum. At the time Concept Value (Col$) of writing the price of dried chips is 70% or 80% of the Costs grain price. Cassava processing 76,000 Freighta 45,000 The price of dried cassava chips depends on Raw material (fresh cassava roots) 200,000 processing costs and, mainly, on the cost of raw Total 321,000 material (Table 21-8). The next major cost is that of Sale priceb 335,250 labor (including administration), which represents almost 10% of total costs. Net earnings 14,250 a. Transport from Sincelejo to Medellín. Consequently, all possible effort must be dedicated b. Product sold in Medellín. to increasing the crop’s productivity, for example, 411 Cassava in the Third Millennium: … Technology 2: Drying Cassava Chips on Inclined Trays Trays Fresh cassava chips are spread over the trays, which are then placed on beams of bamboo or building This drying method takes maximum advantage of the (giant) bamboo supported by two rows of posts, with drying capacity of wind as it circulates through cassava the front row being shorter than the back row. The chips placed on trays. The trays have a wooden trays thus remain on a slope of 20° to 25° that takes framework, and a base of plastic mesh that holds the maximum advantage of the direction and strength of chips during drying. the wind (Figure 21-26B). Materials. The plastic mesh is strengthened by Management. Once fresh chips are obtained, the adding chicken wire netting with 1-inch-diameter holes trays are filled in at the same site where chipping took (Figure 21-26A). The dimensions shown in the figure place (Figure 21-27) before being taken to the enable the tray to be handled by two workers. Although supports. the tray’s size may vary with the cassava material available in the region, the mesh is standard at Another option is to first place the empty trays on 35 perforations per square centimeter, as anything with the supports (Figure 21-28) and then fill them with larger apertures would result in increased losses. With the use of a suitable mesh, losses are less than 3% of dried chips. (A) 0.90 m 1.85 m 0.055 m (5.5 cm) (B) Figure 21-27. A worker fills the trays with fresh cassava chips as a chipping machine operates behind him. 0.40 m 1.90 m 1.20 m 0.30 m Figure 21-26. (A) Dimensions of a tray. (B) Placement of tray on supports made from bamboo or building (giant) bamboo. (Adapted from Best 1979.) Figure 21-28. Empty trays are placed on their supports. 412 0.50 m 1.00 m Natural Cassava Drying Systems fresh chips brought by wheelbarrow. The agreed-upon The quantity of chips placed on the trays depends quantity of chips is then placed on each tray and spread largely on wind speed (Table 21-10). The higher the over the tray’s surface (Figure 21-29). wind speed, the greater will be the quantity of cassava chips that can be dried without needing to turn them The weight of cassava chips does not have to be over. However, if the load is more than 16 kg/m2, the exactly the same for each tray. An average weight is chips will need to be turned over. achieved by first measuring a suitable quantity per tray into a container and then spreading the chips over the As illustrated in Figure 21-30, drying in trays is tray. When shovels are used to directly load the trays faster than drying on floors for a given load of chips. (Figure 21-27), the amount of cassava can vary. If trays One reason for this difference is that chips in the trays have different dimensions, the chip load for each is continue losing moisture during the night, because air obtained by multiplying the tray’s area by the circulation does not stop. In contrast, when drying is appropriate figure in column 3 of Table 21-10 (tray load carried out on concrete floors, chips lose only a small in kg/m2). quantity of moisture during the night, as wind speed at floor level is low. The trays can be left on the supports overnight to take advantage of the wind’s action. If rain is predicted, Drying time the trays should be stacked horizontally (i.e., one above the other) under roofing or outside and protected with Initial stage. Initially, fresh chips lose moisture a canvas or plastic cover until the next day. The lowest rapidly and air circulation (wind) is more important tray of the stack should be sitting on two posts of than air temperature and humidity. If wind speed is bamboo (or building bamboo), thus keeping all trays off sufficient, this stage can be completed even if the sky the ground. The next morning, the trays should be is cloudy. Furthermore, drying can be carried out at moved back to their supports. Once the chips have night. As a result, in dry times, the chips may lose a attained the appropriate moisture content, they should considerable amount of moisture if left on the trays and be collected and packed. their supports during the night. To best take advantage of this period, cassava may be chipped in the afternoon hours. Table 21-11 illustrates the effect of the principal factors of drying time, especially wind speed. In contrast, fresh chips left spread on concrete floors during the night lose only a small part of their moisture, for the reasons mentioned above: low wind speed at ground level and infrequent turning over. Final stage. In the final drying stage, when moisture content is about 30%, moisture loss is very slow (Figure 21-31) and the high temperatures at mid-day are needed to complete the process. During this stage, air humidity should be less than 65% so that the chips’ final moisture content is suitable for storage. Sometimes, particularly in the rainy season, relative Figure 21-29. Fresh cassava chips are spread over trays already in position. humidity is high; drying should continue until the climate improves. Table 21-10. Relationship between cassava chip load on inclined Several trials were conducted in different sites in trays (L/T) and wind speed. Colombia to determine drying times under different Wind conditions Speed L/T (m/s) (kg/m2 climatic conditions (Table 21-12). The following ) conclusions summarize the work: Calm, smooth breeze <1 10 Constant breeze 1–2 10–13 • Drying almost always takes more than Constant wind >2 13–16 10 hours (1 day), but less than 20 hours SOURCE: Best (1979). (2 days). Only under exceptional environmental 413 Cassava in the Third Millennium: … 70 Load: 10 kg/m2 60 50 On the floor 40 30 On trays 20 MHD 10 14% Night Day Night Day 0 17 19 23 3 7 11 15 19 23 3 7 11 15 19 21 Day hours 0 4 8 12 16 20 24 28 32 36 40 44 48 52 Total time (hours) Figure 21-30. Comparison of two drying curves for cassava chips. One curve is for concrete floors and the other is for sloping trays (see text). MHD = maximum level of humidity accepted during drying. Table 21-11. Drying time for fresh cassava chips cut at different hours of the day. Site Average climatic conditions throughout trial Hours needed to dry to 14% moisture content on: Altitude Temp. r.h. Wind Solar Floor Inclined trays (load of 10 kg/m2) at: (m above (°C) (%) (m/s) radiation (5 kg/m2) sea le vel) (cal/cm 2 8:00a 11:00a 14:00a 17:00a .s) at 8:00a S evilla 125 0 2 5 73 1.1 4 0.7 4 9 14 10 9 11 Espinal 430 29 60 0.66 0.66 11 13 10 9 6 Palmira 1000 26 68 1.26 0.61 14 12 9 6 8 Caicedonia 1100 26 69 0.90 0.72 14 14 12 11 15 (16%)b El Darién 1450 23 72 1.73 0.70 13 13 12 12 11 (15%)b a. Time at which trial began. b. Percentages indicate moisture content at that hour. SOURCE: Best (1979). conditions will cassava chips dry in less than • In very moist areas, rapid drying requires a 1 day. In places where wind speed and solar high wind speed (e.g., at Sevilla, Espinal, and radiation are low, drying may take as long as El Darién). 3 days. Chip size • About the same number of hours per square meter is needed for drying, but the weight of Chip size influences drying time: the finer a chip is, the chips in trays is almost double that of those on shorter the time to release the moisture in its tissues. the concrete floor. Table 21-13 shows the range of chip dimensions used 414 Moisture content (%) Natural Cassava Drying Systems 10 65 9 60 8 55 7 50 45 6 40 5 30 20 4 14 10 0 3 2 1 0 5 6 7 8 9 10 11 12 8 9 10 11 12 1 2 3 4 5 p.m. a.m. p.m. Hours (day and night) H2O content Cassava DM Evaporated H2O Figure 21-31. Typical drying curve for cassava chips on trays. Note the moisture loss in relation to the hour of the day, starting at 5:00 p.m. and recording during the night (from Best 1979). DM: dry matter. Table 21-12. Time neededa between 8:00 and 18:00 hours to dry fresh cassava chips to 14% moisture content in five different sites. Site Climatic conditions of site Time (hours) on: Altitude Temp. r.h. Wind Solar Trays Floor (m above (°C) (%) (m/s) radiation (10 kg/m2)b (5 kg/m2)b sea level) (cal/cm2.s) Sevilla 1250 22 78 1.0 0.71 13 13 Espinal 430 30 64 0.9 0.65 12 10 Palmira 1000 26 66 1.2 0.61 13 15 Caicedonia 1100 26 67 0.8 0.58 19 17 El Darién 1450 24 70 1.9 0.73 12 11 a. Values averaged over three trials. b. The value in parentheses is the cassava chip load. SOURCE: Best (1979). 415 Chips (kg) Moisture content (%) Cassava in the Third Millennium: … by different chipping machines currently used to 25 process fresh roots. Table 21-14 lists the characteristics 20.4 20.2 of the overall material promade up of typical chips. As 20 18.8 20.2 18.9 can be observed, no machine produced more than 17.5 16.8 20.1 18.0 46% of typical chips. Reasons include imperfect 15.5 18.1 16.6 14.5 17.0 adjustment of disks with the front, variation in speed of 15 13.4 15.7 14.3 feed, and diversity of fresh-root size (Castillo and 12.2 Hernández, 1985). 10 Net drying times 5 Figures 21-32 and 21-33 show the net drying times for three types of chips in the concrete-floor systems (10, 0 10 12 14 16 18 20 12, and 14 kg/m2) and inclined trays (10, 12, 14, 16, 18, Load (kg/m2) and 20 kg/m2). Drying was carried out between 8:00 and 18:00 hours every day. The net time does not Floor, “Malaysia” cut chip Floor, “Brazil” cut chip Tray, “Malaysia” cut chip Tray, “Brazil” cut chip include the 14 hours of night. Average environmental conditions at CIAT, the site of the trials, were as follows: Figure 21-32. Net times for drying “Brazil” and “Malaysia” cut cassava chips, and dried on concrete floors or • Environmental temperature: 23.5 °C inclined trays. • Relative humidity: 75% • Solar radiation: 0.73 cal/cm2 per min 25 • Wind speed: 1.12 m/s 22.2 23.1 • Rainfall: 80 mm/month 20.4 21.8 22.4 20 20.7 17.8 19.6 20.1 18.6 18.7 17.3 17.3 For a given load, the difference between the two 17.0 15 16.0 14.6 15.2 systems is noticeable. On concrete floors, the chips 13.5 practically did not differ in drying time. “Malaysia” chips 10 tended to perform better only for loads of 10 and 12 kg/m2. For drying on inclined trays, no differences 5 were found between the finer “Malaysia” chips and the rectangular “Brazil” or “Colombia” chips. Net drying 0 times for the rougher “Thailand” chips were quicker by 10 12 14 16 18 20 2 or 3 hours than for the other chips. Figures 21-34 Load (kg/m2) Floor, “Thailand” cut chip Floor, “Brazil” cut chip Tray, “Thailand” cut chip Tray, “Brazil” cut chip Table 21-13. Range of typical sizes (in mm) expected for fresh cassava chips. Figure 21-33. Net times of drying “Thailand” and “Brazil” cut cassava chips, and dried on concrete floors or Type of chipping Length Width Thickness inclined trays. machine “Thailand” 60–80 25–30 4–7 “Brazil” 50–70 10 4–6 and 21-35 show the results in terms of dried chips per “Malaysia” 50–80 4–6 4–6 day and per each square meter of drying surface. This parameter permitted the selection of the best load for a specific site or region. Table 21-14. Percentages of different types of fresh chips produced according to type of chipping machine. Costs Type of chipping Traditionally Thinly Finely machine cut chips cut chips cut chips Drying on inclined trays is a good alternative for drying fresh chips in places where constructing concrete “Thailand” 42 34 24 floors is not possible because of inclined land or “Brazil” 46 35 19 insufficient resources. Table 21-15 compares costs of “Malaysia” 35 29 36 materials for constructing a concrete floor versus trays. 416 Net time (h) Net time (h) Natural Cassava Drying Systems 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 10 12 14 16 18 20 Load (kg/m2) Floor, “Thailand” cut chip Floor, “Brazil” cut chip Tray, “Thailand” cut chip Tray, “Brazil” cut chip Figure 21-34. Production of “Thailand” and “Brazil” cut cassava chips, dried on concrete floors or inclined trays. 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 10 12 14 16 18 20 Load density (kg/m2) Tray, “Malaysia” cut chip Tray, “Brazil” cut chip Floor, “Malaysia” cut chip Floor, “Brazil” cut chip Figure 21-35. Production of “Brazil” and “Malaysia” cut cassava chips, dried on concrete floors or inclined trays. 417 Dried chips (kg/m2 per day) Dried chips (kg/m2 per day) Cassava in the Third Millennium: … Table 21-15. Comparison of costs of materials needed for 100 m2 of drying surface, whether as a concrete floor or as trays, March 2001 Material (unit) Unit cost Units needed Total cost (Col$) (Col$) Concrete floor Cement (50-kg sacks) 13,000 40 520,000 Sand (m3) 15,000 5 75,000 Gravel (m3) 30,000 10 300,000 Tar (kg) 4,000 20 80,000 Wooden planks (2.8 × 0.24 × 0.025 m) 8,000 30 240,000 Subtotal 1,215,000 Unforeseen contingencies (10%) 130,000 Labor (60%) 805,000 Total 2,150,000 Cost per square meter of surface 21,500 Inclined trays Wood (2.8 × 0.24 × 0.025 m) 8,000 42 336,000 Chicken wire netting (roll of 1.2 × 36 m) 39,500 3.2 126,400 Plastic mesh (roll of 0.9 × 30 m) 150,000 3.8 570,000 Nails (kg) 1,500 10 15,000 Frames (3 m × 2 cm × 2 cm) 3,000 100 300,000 Subtotal 1,347,400 Unforeseen contingencies (10%) 134,740 Labor (60%) 890,000 Total 2,372,140 Cost per square meter of surface 23,700 SOURCE: Best (1979). Infrastructure. The cost per square meter of Table 21-16. Comparison of the labor needed to chip one ton of drying surface is larger for trays than for concrete cassava roots and dry on either concrete floors or inclined trays. floors. However, if the larger carrying rate of the tray system is taken into account, savings in the total Activity Working hours investment would be evident. The trays’ maintenance Floor Trays costs and their duration depend on the care with which Weigh and wash roots 3 3 they are handled. The concrete floor, in contrast, needs Chip roots 2 2 little maintenance and is long lasting. Subtotal 5 5 Spread the chips 2 2 Inclined trays notably simplify the management of Turn the chips over (4 × a day) 1.5 cassava chips, as the chips do not need turning over. Collect and cover chips at night 1 1 Moreover, the labor needed for the entire process with Spread out again in the morning 1.5 1 trays is about 25% less than that required for a Turn the chips over (4 × a day) 1.5 concrete floor (Table 21-16). Table 21-17 presents the Collect and pack chips 2 2 flow of activities for three workers who dry 3 t of Subtotal 9.5 6 cassava on 190 m2 of inclined trays (load = 16 kg/m2). Total labor 14.5 1 Total working hours spent was 19.5. If 2.5 is taken as the conversion factor, the working hours needed for SOURCE: Best (1979). producing 1 t of dried cassava would be 16.2 (about 2 working days). This is equivalent to a plant with a 500-m2 concrete Investment. Table 21-18 details the investments floor. Table 21-19 records the processing costs of a needed to install a plant with 300 m2 of inclined trays drying plant in the Colombian North Coast. Data were and a capacity to dry 5 t of fresh cassava every 2 days. provided by FEDEYUCA in August 2000. The costs 418 Natural Cassava Drying Systems Table 21-17. Timetable of activities to dry 3 t of fresh cassavaa on inclined trays. Activity Workers (no.) in hour of the day: 6 7 8 9 10 11 12 13 14 15 16 17 18 19 First day Weigh and chip roots 2 Spread out chips 1 Collect and cover 2 Second day Uncover trays 2 Collect 3 Store 3 a. Drying area = 190 m2; total working hours: 19.5; working hours per ton of cassava: 16.2; conversion factor: 2.5. Table 21-18. Investment needed for a natural drying plant with a tray area of 300 m2 and a capacity to dry 5 t of fresh cassava chips every 2 days, February 2001. Concept Unit value Total value Rubric totals (US$)a (US$)a (US$)a Installations 6,280 Trays (300 m2) 12/m2 3,600 Storeroom (40 m2) 46.80/m2 1,872 Wire mesh (100 m) 1.00/m2 100 Roofing for the chipping machine (25 m2) 28.30/m2 708 Equipment 1,700 Chipping machine, type “Colombia” 700.00 700 2 electric motors (5 hp) 300.00 600 500-kg capacity platform scale 400.00 400 Tools 180 4 wheelbarrows 30.00 120 6 metal shovels 10.00 60 Others 60 300 sacks 0.20 60 Subtotal 8,220 Unforeseen contingencies (10%) 822 Working capital (30 days)b 4,000 4,000 Total 13,042 a. Exchange rate, March 2001: US$1 = Col$2300. b. Calculation table: Working capital (Col$) needed to operate the plant normally for 30 days Fresh cassava roots = 72 t × Col$75,000 per ton 5,400,000 Working days = 80 × Col$12,000 each 960,000 Sacks = 600 × Col$300 each 180,000 Dried cassava chips = 30 t × Col$45,000 (freight per ton) 1,350,000 Total working capital (Col$) 7,890,000 419 Cassava in the Third Millennium: … Table 21-19. Cost structure of a cassava drying plant with 300 m2 of inclined trays, Colombian North Coast, include freight from Sincelejo to Medellín. For a typical August 2000. North Coast plant, processing costs is more than Concept or cost Value Col$40,000 per ton of dried chips and the profit obtained is about Col$25,000 (Table 21-20). (Col$) (%) Fixed costs Administration 3,000 Table 21-20. Costs of processing 1 t of dried cassava chips and perceived profita, Colombian North Coast. Depreciation Category Col$b Financial costs Maintenance 4,500 Raw material 187,500 Subtotal 7,500 3.5 Processing 42,000 Freight 45,000 Variable costs Raw materiala 187,500 Total production costs 274,500 Laborb Sale pricec 24,000 300,000 Expenses 3,000 Net earnings 25,500 Unforeseen contingencies a. As perceived by the Cooperativa CooproAlgarrobos, Chinú, Subtotal 214,500 78.0 Department of Córdoba, Colombia, August 2000. b. Note that the cost data offered by this table must be updated Marketing expenses when considering a specific project. c. At the concentrate-feed plant. Packaging 7,000 Commission Freightc 45,000 Subtotal 52,000 18.5 Total costs + expenses 274,500 100.0 a. From 2.5 t of fresh cassava roots, 1 t of dried cassava is obtained. b. Two working days to produce 1 t of dried cassava. c. Freight from Sincelejo to Medellín. 420 Natural Cassava Drying Systems Appendix: Determining Dry Matter Content of Fresh Roots, using the Specific Gravity Method Julio César Toro5 and Alonso Cañas6 • Several bags, either plastic or paper, that can carry 3 kg of cassava. Dry matter (DM) and starch contents, expressed as percentages in cassava roots, are often called quality • Plastic or nylon string or cord, 2 m long. factors. They vary greatly among different cassava varieties. These factors are closely related to the soil’s • An S-shaped hook. potassium content, crop’s age, and the climate (mainly rainfall and soil moisture). They also depend heavily on • A plank, 25 × 60 cm, which is large enough the absence or severity of attacks from defoliating pests to act as a small table for carrying the (e.g., thrips and hornworm) and other defoliating agents balance. The plank has a central perforation such as hail (Celis and Cadavid 1978, pers. comm.). (Ø at 5 cm) just underneath the balance’s weighing plate. To calculate the DM yield of roots at harvest from fresh root yield, the following methods are used: • A four-legged framework for the plank. The framework may be 50 cm wide and 73 cm • Conventional laboratory techniques that long. require much work and time. • A pencil or a permanent ink marker. • A hydrometer similar to that used for potato tubers. Apparently, it can be adapted to cassava • A machete or wooden spatula. roots (G Gómez 1977, pers. comm.). Conducting the specific gravity method • Specific gravity method for roots, which has been applied ever since the relationship Taking samples. Samples of recently harvested between that parameter and DM and starch roots should be collected, taking 3 or 4 samples per contents in roots was verified. variety or plot and ensuring they are representative, that is, that they include large and small roots, both Determining specific gravity (SG) is simple, useful, thick and thin. Each sample should weigh more than and within the reach of farmers on their farms or of 3 kg. The roots are cleaned with the blunt edge of a companies processing cassava flour or starch. machete or wooden spatula and the rootlets and peduncles cut off. They are then packed into Elements for determining specific gravity previously marked bags and taken to the site where measurements will be made. This site should not be The method requires the following elements: exposed to air currents, as these affect readings from the balance. • A beam balance that can weigh gram by gram to 3 kg, and has divisions in decigrams. Fresh root weight in air (FRWA). Each bagged sample is weighed individually. All samples should • A container that can carry sufficient water to have similar FRWA in that the weight is not less than submerge the sample. 3.0 kg (Figure 21A-1A). The relative uniformity of the weight helps correct possible erroneous readings, in • A metal mesh basket, with a square base, and that if a large difference is seen, then the sample can able to carry 3 kg of cassava roots. be re-weighed to immediately verify its weight. If sample weights do not vary, such repetition becomes unnecessary. Once the FRWA is obtained, the 5. Formerly, Head, Agronomy and International Cooperation, sample is re-packed into its bag. The roots in each Cassava Program, CIAT; now Researcher in fruit trees, Cali, Colombia. E-mail: frutillartor@telesat.com.co sample do not have to be entire. 6. Agricultural Technologist, Medellín, Colombia. 421 Cassava in the Third Millennium: … Fresh root weight in water (FRWW). The metal (“density”, in the table). The original table was later mesh basket, tied to a nylon cord, is introduced into a expanded with new entries and densities ranging from container full of water in such a way that it remains 1.0200 to 1.1900. The following regression equation balanced. The other end of the cord is tied to the S led to Table 21A-1. hook, which, in its turn, is hung by its upper curl from the lower extremity of the balance’s linchpin, which DM (%) = 158.26 (SG) - 142.05 (2) passes downwards through the perforation in the plank (Figure 21A-1B). The basket should remain totally These tables are applied to cassava varieties submerged. Neither the basket nor the cord should harvested 10 to 12 months after planting, under touch or even brush against any object. normal cassava production conditions in Colombia (CIAT 1978). Once assembled, the balance is calibrated to zero to eliminate the weight of the elements described Table 21A-1 was used to prepare another, even above, and the sample of roots is then placed into the shorter, table (Table 21A2) for finding only the most basket (Figure 21A-1C). Figure 21A-1D gives an overall usual DM values (%) for roots (i.e., between 20% and view of the equipment as it weighs the sample in water. 46%), knowing the corresponding FRWW. This is The FRWW is noted beside the respective FRWA. Once expressed in grams and takes only one decimal figure. the weights of all the samples are obtained, the SG is The FRWA of 3.0 kg is taken because the table can calculated for each case, using the following formula: then be summarized, and a correct reading of the FRWW is more likely. Cours (1951) verified that a FRWA variation of 16.7 g in the FRWW can indeed alter the SGC = (1) DM content value by 1%. FRWA - FRWW Determining DM content (%) in cassava roots The result should have four decimal figures. through the SG method is an easily adoptable practice Table 21A-1 was developed by Wania G. Fukuda (cited that can be very useful for identifying those cassava in Toro and Cañas 1983) to obtain percentages of DM varieties that have higher DM content. from cassava roots as derived from specific gravity (A) (B) (C) (D) Figure 21A-1. Measuring the values for “weight in air” (FRWA) and “weight in water” (FRWW) of cassava roots. From these data, the specific gravity is calculated and, from a table, the percentage of dry matter in the sample roots is obtained. (A) Balance for weighing in air. (B) Plank with perforation, its supporting framework, and the water container. (C) Balance, cord, S-shaped hook, and metal basket containing cassava roots. (D) Overall view of the equipment used for measuring “weight in water”. 422 Natural Cassava Drying Systems Table 21A-1. Determining dry matter (DM) content in cassava roots, using the specific gravity (or density) method. Density (SG) DM (%) Density (SG) DM (%) Density (SG) DM (%) 1.0200 19.53 30 23.12 65 26.79 05 19.61 35 23.20 70 26.87 10 19.69 40 23.28 75 26.95 15 19.76 45 23.36 80 27.03 20 19.84 50 23.43 85 27.10 25 19.92 55 23.51 90 27.18 30 20.00 60 23.59 95 27.26 35 20.08 65 23.67 1.0700 27.34 40 20.15 70 23.75 05 27.42 45 20.23 75 23.82 10 27.50 50 20.31 80 23.90 15 27.57 85 23.98 1.0255 20.39 20 27.65 90 24.06 60 20.47 25 27.73 95 24.14 65 20.54 30 27.81 70 20.62 1.0500 24.22 35 27.89 75 20.70 05 24.29 40 27.96 80 20.78 10 24.37 45 28.04 85 20.86 15 24.45 50 28.12 90 20.93 20 24.53 55 28.20 95 21.01 25 24.61 60 28.28 30 24.68 65 28.35 1.0300 21.09 35 24.76 70 28.43 05 21.17 40 24.84 75 28.51 1.0310 21.25 45 24.92 80 28.59 15 21.33 50 25.00 85 28.67 20 21.40 55 25.07 90 28.74 25 21.48 60 25.15 95 28.82 30 21.56 65 25.23 1.0800 28.90 35 21.64 70 25.31 05 28.98 40 21.72 75 25.39 10 29.06 45 21.79 80 25.46 15 29.14 50 21.87 85 25.54 55 21.95 90 25.62 1.0820 29.22 60 22.03 25 29.30 1.0595 25.70 30 29.37 1.0365 22.11 1.0600 25.78 35 29.45 70 22.18 05 25.86 40 29.53 75 22.26 10 25.93 45 29.61 80 22.34 15 26.01 50 29.69 85 22.42 20 26.09 55 29.77 90 22.50 25 26.17 60 29.84 95 22.57 30 26.25 65 29.92 1.0400 22.65 35 26.32 70 30.00 05 22.73 40 26.40 75 30.08 10 22.81 45 26.48 80 30.16 15 22.89 50 26.56 85 30.23 20 22.97 55 26.64 90 30.31 25 23.04 60 26.71 95 30.39 (Continued) 423 Cassava in the Third Millennium: … Table 21A-1. (Continued.) Density (SG) DM (%) Density (SG) DM (%) Density (SG) DM (%) 1.0900 30.47 35 34.14 70 37.80 05 30.55 40 34.22 75 37.88 10 30.62 45 34.29 80 37.96 15 30.70 50 34.37 85 38.04 20 30.78 55 34.45 90 38.12 25 30.86 60 34.53 95 38.19 30 30.94 65 34.61 1.1400 38.27 35 31.01 70 34.69 05 38.35 40 31.09 75 34.76 10 38.43 45 31.17 80 34.84 15 38.51 50 31.25 85 34.92 20 38.59 55 31.33 90 35.00 25 38.66 60 31.41 95 35.08 30 38.74 65 31.48 1.1200 35.15 35 38.82 70 31.56 05 35.23 40 38.90 75 31.64 10 35.31 45 38.98 80 31.72 15 35.39 50 39.05 85 31.80 20 35.46 55 39.13 90 31.87 25 35.54 60 39.21 95 31.95 30 35.62 65 39.29 1.1000 32.03 35 35.70 70 39.37 05 32.11 40 35.77 75 39.44 10 32.19 45 33.85 80 39.52 15 32.26 50 35.93 85 39.60 20 32.34 55 36.01 90 39.68 25 32.42 60 36.09 95 39.76 30 32.50 65 36.16 1.1500 39.84 35 32.58 70 36.24 05 39.91 40 32.65 75 36.32 45 32.73 1.1510 39.99 1.1280 36.40 15 40.07 1.1050 32.81 85 36.48 20 40.15 55 32.89 90 36.55 25 40.23 60 32.97 95 36.63 30 40.30 65 33.05 1.1300 36.71 35 40.38 70 33.12 05 36.79 40 40.46 75 33.20 10 36.87 45 40.54 80 33.28 15 36.95 50 40.62 85 33.36 20 37.02 55 40.69 90 33.44 25 37.10 60 40.77 95 33.51 30 37.18 65 40.85 1.1100 33.59 35 37.26 70 40.93 05 33.67 40 37.34 75 41.01 10 33.75 45 37.41 80 41.08 15 33.83 50 37.49 85 41.16 20 33.90 55 37.57 90 41.24 25 33.98 60 37.65 95 41.32 30 34.06 65 37.73 (Continued) 424 Natural Cassava Drying Systems Table 21A-1. (Continued.) Density (SG) DM (%) Density (SG) DM (%) Density (SG) DM (%) 1.1600 41.40 10 43.12 15 44.76 05 41.48 15 43.19 20 44.83 10 41.55 20 43.27 25 44.91 15 41.63 25 43.35 30 44.99 20 41.71 30 43.43 35 45.07 25 41.79 35 43.51 40 45.15 30 41.87 45 45.22 1.1740 43.59 35 41.94 45 43.66 1.1850 45.30 40 42.02 50 43.74 55 45.38 45 42.10 55 43.82 60 45.46 50 42.18 60 43.90 65 45.54 55 42.26 65 43.98 70 45.61 60 42.33 70 44.06 75 45.69 65 42.41 75 44.13 80 45.77 70 42.49 80 44.21 85 45.85 75 42.57 85 44.29 90 45.93 80 42.65 90 44.37 95 46.00 85 42.72 90 42.80 1.1795 44.45 1.1900 46.08 95 42.88 1.1800 44.52 1.1700 42.96 05 44.60 05 43.04 10 44.68 SOURCE: CIAT (1978). Table 21A-2. Calculation of dry matter (DM) content in cassava roots, using the value “fresh root weight in water” References (FRWW)a. FRWW DM (%) FRWW DM (%) To save space, the acronym “CIAT” is used instead of “Centro Internacional de Agricultura Tropical”. 58.8 20 296.0 34 77.4 21 311.8 35 Best R. 1979. Cassava drying. CIAT, Cali, Colombia. 24 p. 95.8 22 327.4 36 112.6 23 342.8 37 Best R; Gómez G. [1983]. Procesamiento de las raíces de 130.6 24 359.0 38 yuca para alimentación animal. In: Domínguez CE, 148.3 25 371.9 39 ed. Yuca: Investigación, producción y utilización. 165.8 26 386.7 40 CIAT; United Nations Development Programme (UNDP), Cali, Colombia. 183.1 27 401.5 41 198.9 28 416.0 42 Castillo C; Hernández W. 1985. Estudio del secado natural 215.8 29 430.4 43 de tres tipos de trozos de yuca. BSc thesis. Faculty 232.5 30 443.5 44 of Agronomy, Universidad del Valle, Cali, Colombia. 248.9 31 457.6 45 119 p. 265.2 32 471.5 46 280.1 33 CIAT. 1978. Método para la determinación del contenido a. Assuming that the “weight in air” (FRWA) of each sample is equal de materia seca y almidón en la yuca por el sistema to 3000 g. The specific gravity method is applied indirectly. de gravedad específica. In: CIAT. Curso de producción SOURCE: CIAT (1979). de yuca. Cali, Colombia. Vol 1, p 352–356. 425 Cassava in the Third Millennium: … CIAT. 1979. Manual de producción de yuca. Cali, Ospina Patiño B; Gómez G; Best R. 1983. El secado Colombia. (Multicopied.) de la yuca para la alimentación animal. CIAT, Cali, Colombia. 12 p. Cours G. 1951. Le manioc á Madagascar. Mem Inst Sci Madagascar Ser B 3(2):203–416. Toro JC; Cañas A. [1983]. Determinación del contenido de materia seca y almidón en yuca por el sistema de Herrera C, A; Arias CA; Muñoz H. 1983. Guía para la gravedad específica. In: Domínguez CE, ed. Yuca: construcción de una trozadora de yuca. CIAT, Cali, Investigación, producción y utilización. CIAT; Colombia. 35 p. United Nations Development Programme (UNDP), Cali, Colombia. Ospina Patiño B; Best R. 1984. Manual de construcción y operación de una planta de secado natural de yuca. CIAT, Cali, Colombia. 41 p. 426 CHAPTER 22 Artificial Cassava Drying Systems Lisímaco Alonso1, Miguel Angel Viera2, Rupert Best3, Sonia Gallego4, and José Alberto García5 Introduction aspects in the dried cassava production should be considered within the socioeconomic situation of the Great potential exists in tropical Latin America for developing countries that produce cassava. using dried cassava in animal feed. Good prospects also exist for including it in human food as a source of Among the different drying systems there are two calories in processed foodstuffs, together with other that require relatively low investment and are simple to raw materials. Examples include composite flours for manage. They therefore create interest, and have been soups, beverages, breads, and pastas. These end uses included in CIAT’s research programs. The two have created a need to develop drying methods that systems are natural drying and artificial fixed-bed are efficient, reliable in terms of product quality, and drying. technically and economically feasible. These three Technology 1: Case Study of Artificial Cassava Drying in the Colombian Atlantic Coast6 Lisímaco Alonso, Miguel Angel Viera, and Rupert Best In the 1970s, CIAT adapted a technology to naturally establishing small rural businesses that produced dried dry cassava and applied it on a commercial scale in the cassava for animal feed. In 2000, more than Colombian Atlantic Coast in a collaborative project with 180 cassava drying plants were established in Colombia. the Fund for Integrated Rural Development (DRI, its Spanish acronym)7. The project was directed towards Natural drying depends completely on climatic conditions, which restricts its use during rainy seasons. 1. Agricultural Engineer, Postharvest Management Systems, Thus, to prolong the drying period and ensure CLAYUCA, Cali, Colombia. E-mail: l.alonso@cgiar.org 2. Chemical Engineer, formerly of the Cassava Utilization Section, continuous supplies of dried cassava, a fixed-bed dryer Cassava Program, CIAT, Cali, Colombia. with artificial circulation of hot air was chosen. This 3. Chemical Engineer, formerly Leader of the RAD Project, CIAT. system was evaluated, using different sources of heat E-mail: rupertbest@gmail.com 4. Chemical Engineer, Postharvest Management Systems, such as diesel, propane gas, coal, and a solar collector. CLAYUCA. E-mail: s.gallego@cgiar.org 5. Mechanical Engineer, Postharvest Management Systems, In this chapter, the results of this evaluation are CLAYUCA. E-mail: albertogarcia@mailworks.org 6. The text of this section of the chapter, written by L. Alonso, presented and the usefulness of artificial drying M.A. Viera, and R. Best, was published in Revista ACOGRANOS discussed for the current conditions of cassava (Colombia), no. 3, 1987. production and marketing in the Colombian Atlantic 7. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, Abbreviations, and Technical Coast. This method is also studied as an alternative in Terminology, this volume. the production of dried cassava for human consumption. 427 Cassava in the Third Millennium: … Research history • Toh (1973) studied the drying of grated cassava pulp at several temperatures, air flows, and load The most economical drying method that humans densities in a continuous tunnel dryer. Pulp had have used since remote times is natural drying. This been dried previously to a moisture content of method of drying cassava was studied by several 50% (wet basis) in a filter press. A kerosene researchers, using both concrete floors and vertical or burner was used to heat the air. Fuel sloping trays during the 1970s (Roa 1974; Best 1978; consumption varied exponentially with load Thanh et al. 1979). These studies led to better density, and increased (to a lesser extent) when understanding of the factors most affecting the process flow was increased. Toh found that, for the such as the size and shape of cassava chips, load experimental conditions, heating air to density, and environmental conditions. temperatures of more than 70 °C was unsuitable because of high fuel consumption. Despite the best efforts to improve natural drying techniques and the advantages that these offer over • With this same material (pressed grated pulp), artificial drying in terms of investment and operational Seng (1976) evaluated the use of a rotary and costs, they cannot be used in regions where continuous dryer. The fuel used accounted for environmental conditions are unfavorable. For these 55% of the operation’s total cost. Even so, this areas, the use of batch dryers, involving the circulation system could compete, in terms of costs, with of ambient or hot air or a combination of both, directly traditional sun drying under Malaysian through a layer or fixed bed carrying the product to be conditions, where the study was developed. dried. The use of continuous artificial dryers of large capacity is economically the most favorable alternative • A study on the economic feasibility of for Latin America (Crown 1981; Freivalds 1982). establishing an artificial drying plant for dried cassava chips was carried out by the National In parallel to research on natural drying, studies on Center for Food Science and Technology (CITA, fixed-bed drying were carried out to improve its Spanish acronym) in 1974, in Costa Rica. The operational parameters, bed height, and air project was found feasible, with returns of 11% on temperature and speed for drying cassava chips. the total investment and 16% on the fixed investment, if the plant was operated at a • Chirife and Cachero (1970) found that beds of minimum capacity of 10 t/ha for 20 h per day up to 12 cm high do not appreciably reduce and 200 days per year. Based on this study, a drying time with air flows at more than plant was installed, but it failed because of poor 5000 kg/h per m2. The temperature at which location and the inability of the area to supply the chips are toasted to low moisture content necessary raw material. (<35%) is more than 84 °C. These authors also found that constant speed was not present and The studies mentioned above indicate that, when that the internal movement of moisture within attempting to minimize operating costs and obtain good the chips is the mechanism that controls the quality dried cassava, control parameters are fineness of process from the beginning. These findings chipping the material, temperature, and air flow. were later confirmed by Webb and Gill (1974) Furthermore, to ensure the feasibility of the process, a and Akhtar (1978). continuous and adequate supply of raw material must be guaranteed. • On a larger scale, Rossi and Roa (1980) and Ospina (1980) experimented with a dryer that Research CIAT plan had a 15-m2 drying area and was coupled to a solar collector with 100 m2 of absorbent area. Our study in Colombia was carried out in two phases: The authors used mathematical models to determine the minimum air flow that should be • First, a 6-m2 dryer, coupled to a flat solar applied as temperature and relative humidity collector with a 30-m2 surface, was evaluated. vary. They reported that, for 30-cm-high beds, The dryer and collector were constructed in the the applied flow ranged between 47.5 and Municipality of San Juan de Betulia, Department 102.5 m3/min per ton of cassava chips, with air of Sucre, in a region known as the Colombian temperatures ranging between 20 and 40 °C, Atlantic Coast. and relative humidity between 25% and 55%. 428 Artificial Cassava Drying Systems • Second, at CIAT (Palmira, Department of Valle Drying systems del Cauca, southern Colombia), two dryers were used. One had 2 m2 of drying area and was First phase. For trials in the first phase, the system coupled to a coal burner. The other dryer had 6 shown in Figure 22-2 was used. It consisted of a 6-m2 m2 and was coupled, independently, to two dryer, with a centrifugal fan and a 30-m2, flat, solar burners, one of propane gas and the other of collector. The dryer was a chamber constructed from diesel. materials available in the region. It measured 3 m long by 2 m wide. The drying area was a false floor formed To evaluate the dryers with the three sources of of galvanized steel sheets, which were perforated with heat, the quantity of chips placed in them was modified 3-mm-diameter holes for 3% of their total area. The to obtain different air flows per ton of fresh cassava sheets, measuring 1 × 2 m, were supported 60 cm off chips. Air temperature was reduced to the values the ground by wooden beams. obtained with the solar collector and was set at 50 and 60 °C for the two fuels used. A Dayton fan (reference no. 3CO73) circulated the air through the system by means of blades that curved Raw materials backwards. The machine was operated by a 1-hp electric motor. Roots were harvested from cassava (Manihot esculenta Crantz) crops that were 8 to 10 months old. The The solar collector had a 30-m2 absorbent surface. varieties used were, for the first phase, the local It was constructed on a 6-cm-thick concrete floor ‘Venezolana’, planted in the Atlantic Coast, and, for the edged with concrete blocks. The medium used for second phase, ‘Manihoica P-12’, a variety planted at absorbing solar radiation consisted of corrugated zinc CIAT. sheets painted in matte black. These sheets were placed inside the collector, between the floor and a Cassava roots were chipped in a machine prototype, plastic cover (caliber 6), itself supported by a structure known as “Thailand” type. It consisted of a metal of wood and chicken mesh (Figure 22-2). structure with a feed hopper and a vertical turning disk. The disk had six rows of holes with diameters of about Second phase. This phase of the experiment was 25 mm (Figure 22-1), and sliced the cassava into chips carried out at CIAT, where two dryers were used. The that measured 60 to 80 mm long, 25 to 30 mm wide, one with a 2-m2 drying area was coupled, through a and 7 to 10 mm thick. These standard chips were Dayton centrifugal fan (reference no. 3CO73), to a unit produced at a rate of 42%, together with smaller chips comprising a coal burner and heat exchanger (at 34%), and fine particles (at 24%). (Figure 22-3). The coal burner for the air oven was basically a combustion chamber or housing with a stationary grill. The heat exchanger was a double concentric tube, with longitudinal blades on both sides Figure 22-2. The solar collector used to heat air for a cassava Figure 22-1. Cassava chipping machine of the type “Thailand”. chip dryer. 429 Cassava in the Third Millennium: … Figure 22-3. An artificial fixed-bed dryer that uses a coal burner Figure 22-5. A propane gas heating system coupled to an to heat the air. artificial fixed-bed dryer. of the interior tube by which the combustion gases Air flow was determined with a blade anemometer, flowed. The drying air circulated through the annular a pitot tube, and an inclined-tube manometer with a space formed by the two tubes. scale 0 to 2.4 inches of water and a ±0.02 accuracy. In the dryers’ plenum, the air temperature was measured The 6-m2 dryer was coupled independently to two with a mercury thermometer, calibrated from 0 to heating units, one of propane gas and the other of 120 °C and a ±1 °C accuracy. diesel. The diesel unit consisted of a Lister 7.5-hp motor (model LT1), coupled directly to a Lister axial Evaluating the artificial drying systems fan. Through a transmission belt, the unit ran a Markon generator, producing an electric current of The solar collector. The solar collector was studied in 1.5 kilovolt-amperes (kVA), which provided the current February and March 1984. Results were classified into needed to operate the diesel burner (Nu-way Benson). two groups: one evaluating the solar collector’s The propane gas unit (Farm Fans, model 116SH) performance, and the other the dryer’s capacity when consisted of an axial fan and gas burner. Figures 22-4 the collector was used to heat the air. Results are and 22-5 show the heating units (diesel and gas) that presented in Table 22-1. were coupled to the dryer. The collector operated daily from 7:00 to The coal and diesel burners heated the air 19:00 hours, during which time it heated an air flow of indirectly, that is, they did not mix the air with the fuel 106 m3/min at an average temperature of 36 °C. The gases. The burners were connected to the dryers by initial temperature of ambient air averaged 31 °C. means of AMCA measuring ducts (Ashrae 1977). Relative humidity of the air dropped from 62% to 46%. The collector’s efficiency was defined as the ratio between the average amount of energy absorbed by the air and the energy of incident solar radiation. The result was 63%, a standard value, according to Rossi and Roa (1980) for this type of collector. Table 22-2 shows the results obtained when the dryer was coupled to the solar collector. On applying various air flows, different drying times were obtained, which were expressed as net daylight hours between 7:00 and 20:00 hours. Nocturnal hours, during which the process was suspended, were included. The number of batches that could be dried per week, considering drying time, was determined on the basis Figure 22-4. A diesel heating system coupled to an artificial that new batches were not processed after the one that fixed-bed dryer. finished after mid-day. 430 Artificial Cassava Drying Systems Table 22-1. Valuea of parameters by which a flat solar collector with a 30-m2 absorbent surfaceb operates. Ambient air Solar radiation Air flow Temperature (°C) Efficiency Temp. (°C) r.h. (%)c (cal/cm2 per min) (m3/min) Increase Final (%) 31 62 0.62 106 5 36 63 a. Average values over 43 days of observations between 7:00 and 19:00 hours. b. Absorbent surface was constructed with corrugated zinc sheets, painted in matte black and placed under a cover of polyethylene sheeting. c. r.h. refers to relative humidity. Table 22-2. Effect of air flow applied over time within an replacing the plastic cover and consuming electric artificial fixed-bed drying system that is coupled to a flat solar collector.a power. As a result, this system does not compete with the natural system, even though this latter system is Applied air flow Drying time Capacity per week dependent on environmental conditions. (m3/min per t) Netb Productionc Batches Dried chips (h) (days) (no.) (kg) The use of a solar collector to artificially dry 78 41 3.2 1.5 810 cassava chips, a product whose initial moisture is high 88 42 3.3 1.5 720 (60% to 65%) at relatively low temperatures (34 to 100 29 2.2 2.0 840 38 °C), requires high air flows. This affects the size of 118 26 1.6 3.0 1077 both collector and fan, and limits the system’s capacity 141 20 1.3 3.0 480 to 2.5 to 3 t of dried product per batch. a. Average values of three replications by level of applied air flow. General trial conditions were as follows: • Moisture content of cassava chips = initial: 64.5% ± 2%; Using three fuels. Table 22-4 gives the results of final = 12.3% (interpolated). artificial drying, using three available fuels: coal, • Air: temperature = 36 ± 2 °C; relative humidity = 43.5% ± propane gas, and diesel. The Table also shows the 6.5%; flow = 106 m3/min. • Solar radiation (cal/cm2) = 0.60% ± 10%. overall efficiency of the process for different operating b. Daylight drying period = 7:00 to 20:00 hours. conditions and the operating costs generated c. Includes nocturnal hours during which drying was suspended. according to fuel. With the air flows applied and given temperatures, cassava chips can be dried to a moisture content of 12.3% over 5.5 to 10 hours in a normal This standard was adopted because the product’s workday. Fuel consumption was greater for coal than final quality could not otherwise be guaranteed. The for propane gas. When the temperature or air flow was chips deteriorated if their drying was interrupted and increased, drying time was reduced but fuel their moisture content did not drop below 35% on the consumption and, therefore costs, were higher. first day. If this occurred, the chips appeared yellowish—a general sign of inadequate processing that Propane gas was the most efficient, followed by had left them with a poor appearance. The same thing diesel and coal. Few differences were seen between the also happened when drying time continued for more latter two fuels. The propane gas’s higher efficiency was than 2 days. due to the air being directly heated, as it is mixed with the fuel’s gases. Although drying can continue after 20:00 hours, this time was not used for reducing moisture content in the chips, because the low temperatures obtained with Table 22-3. Costs of investment and production of batch-drying the collector during those hours did not sufficiently systems with a capacity to produce 2.4 t of dried cassava chips, 1985. justify expenditure on electric power. Drying system Cost of: Table 22-2 shows that the largest capacity for Investment Production (US$)a drying per week was obtained when an air flow of (US$/t) 118 m3/min per ton of fresh chips was applied. Natural: on concrete floor (500 m2) 183.6 11.9 Artificial: fixed-bed and solar collectorb 566.7 12.6 Table 22-3 shows the value of investment and Difference 383.1 0.7c production costs of a natural system, compared with a. US$1.00 = Col$1800 in 2010. those of an artificial system with a solar collector. The b. Costs of system elements: chamber (30 m2) = US$111.1; solar artificial system has higher initial costs to pay for the collector = US$122.2; motorized fan = US$333.3 c. This difference in production costs is due to the replacement of motor-fan unit, and higher production costs to pay for the plastic cover and consumption of electric power in artificial drying. 431 Cassava in the Third Millennium: … Table 22-4. Effect of temperature and air flow on drying time and fuel consumption, and on two parameters (efficiency and costs) of the artificial cassava drying system with three different sources of heat.a Air Air flow Net Fuel consumptionc Overall efficiency (%) with: Costd (US$/tc) temp.b (m3/min drying Coal Propane Diesel Coal Propane Diesel Coal Propane Diesel (°C) per tc) time (h) (kg/t) gas (gal/t) (kg/t) gas gas 50 130 10.0 250 105 65 38 70 36 1625 3150 7150 190 7.5 390 110 70 32 72 36 2535 3300 7750 60 130 7.5 300 100 35 65 1950 3000 190 5.5 350 130 25 54 3575 3900 a. Average of three values per treatment. General trial conditions were as follows: • Average temperature of ambient air = 26 °C. • Moisture content of cassava chips (%) initial = 61% ± 2%; final = 12% (interpolated). • Heat value of fuels (kcal/kg): coal = 6,700; propane gas = 14,000; diesel = 41,000 • Efficiency of burners: coal = 60% ± 5%; propane gas = 95% ± 2%; diesel = 76% ± 2%. • Fuel prices in 1985: coal = US$0.004 per kg; propane gas = US$0.02 per kg; diesel = US$6.1 per gallon. b. The diesel heating system, on its own, provides a temperature of 50 °C. c. t refers to tons of fresh cassava chips. d. US$1.00 = Col$1800 in 2010. Although drying with coal was the least efficient • Production capacity is determined according to and consumed the most fuel, operating costs were the the capacity of a model plant in the Atlantic lowest because its price per kilogram was relatively low. Coast, and is calculated as 538 t of dried Higher air flows and temperatures meant higher cassava chips per year. operating costs. In this regard, the difference between coal and propane gas diminished. Accordingly, • Price of raw material is US$4.44/t of fresh choosing between them has to be based on the cassava roots, the value reported by drying availability of fuel and costs of combustion and heating plants during the operational year 1985. equipment. Table 22-5 presents these costs, together with those of the burners, heat exchangers, fans, and • Conversion factor of fresh roots to dried chips is controls that form each unit. The end result tends to 2.5. That is, 2.5 t of fresh cassava roots are favor the coal option, which presents lower costs of needed to produce 1 t of dried cassava chips. both investment and operation. • Sale price per ton of cassava chips dried to a Economic analysis moisture content of 12.3% was US$15.11. (This is 85% of the price for sorghum in 1985.) Burners form the heat transfer equipment in artificial dryers, with coal having advantages over propane gas • Coal consumption costs US$0.004/kg per or diesel. Hence, an economic study of the four 450 kg/t of fresh cassava chips. alternatives for investment was carried out, using the conditions of production and marketing of dried • Workdays per week: 6. cassava chips in the Atlantic Coast, where dried cassava technology is supported. Cost data are • Drying methods: expressed in American dollar (US$). The principal – Natural, on concrete floors assumptions of this analysis are presented below: – Artificial, fixed-bed, with air heated to 60 °C, using coal. Table 22-5. Cost of combustion equipment, using diesel, The prices of fresh roots and dried chips can vary propane gas, or coal, with a capacity of 70,000 kcals per hour, 1985. over the project’s life. For this analysis, the prices are assumed to be in constant currency, that is, they are System Investment cost (US$)a deflated by the same index. Table 22-6 describes the four investment alternatives: Coal 261.1 Diesel 680.6 • Alternative 1 corresponds to a model plant in Propane gas 358.3 the Atlantic Coast. It operates during summer a. US$1.00 = Col$1800 in 2010. (December to April) over 20 weeks per year. 432 Artificial Cassava Drying Systems Table 22-6. Description of four alternative investment structures for drying cassava chips. Parameter Alternative 1 2 3 4 Drying method Natural Natural Natural/Artificial Artificial Annual operational period (no. of weeks) 20 35 20/30 50 Drying system On 2000 m2 On 1300 m2 On 1000 m2 20-m2 of concrete floor of concrete floor of concrete floor/ fixed-bed 20-m2 fixed-bed dryer dryer MCPa by batch (t) 24 13 12/4 4 a. MCP = maximum capacity for processing fresh cassava chips. • Alternative 2 is the same as Alternative 1, but Table 22-8. Production costs (US$) a per ton of dried cassava chipsb according to four alternative investment operates for an extra 15 weeks, during the structures, 1985. transitions from winter to summer and summer Parameter Alternative to winter, or in regions where summer is longer, as in the northeastern departments of 1 2 3 4 the Atlantic Coast, where warm spells occur. Raw material (fresh cassava 11.1 11.1 11.1 11.1 roots) • Alternative 3 operates for 50 weeks of the year, Processing 2.0 2.0 3.0 3.6 with 20 weeks with a natural drying system on Total 13.1 13.1 14.1 14.7 concrete floors, and 30 weeks of rainy season a. US$1.00 = Col$1800 in 2010. with an artificial, fixed-bed, drying system. b. Components: moisture content at 13.7%; protein, 3.5%; fat, 0.5%; fiber, 10%; carbohydrates, 78.6%. • Alternative 4 also operates for 50 weeks per year, but uses only an artificial drying system. profitability rates at 26.4%, 37%, 12.6%, and 12.4%, respectively. Alternative 2 was the most profitable Table 22-7 shows the investment needed for because it used its installations over a longer period, equipment (chipping machines, dryers, and motors), and had low operating and investment costs. tools, and working capital (the money needed to buy Alternative 4 required the least investment, but had the raw material for 1 month’s operation). It varied from highest operating costs. plant to plant, because the period of annual operation was different for each, even though their production The economic data of the analysis were valid for capacity was the same. Some plants therefore handled summer, when dried cassava chips were produced. In larger monthly volumes of fresh cassava than others. winter, dried cassava chip production was nil, given Table 22-8 gives the production costs per ton of dried that natural drying was being used. Hence, the price cassava chips. Processing costs includes labor, increased, reaching US$20.6 per ton or more, maintenance, and consumption of electric power and especially when sorghum imports were also restricted coal. and scarce on the market. With data tabulated, the profitability or rate of If the supply of dried cassava chips could be year return was calculated on a personal computer, round, then the price could be expected to stabilize to equalizing income values to payment values. The four a balance between supply and demand, or agreements alternatives were economically feasible, with their could be made to stabilize it. Hence, the same price was considered for all alternatives, even though they had functioned in different seasons of the year. Table 22-7. Value of investment and working capital for the four alternative investment structures for drying cassava chips, 1985. However, the price of collecting fresh cassava roots Parameter Alternative varies with the changeover from dry to rainy seasons; difficulties in harvesting, collection, and transport; or 1 2 3 4 scarcity. Although obtaining raw materials most affects Initial investment (US$)a 1,721 1,269 1,946 1,410 production costs, the same price was also considered Working capital (US$)a 1,196 684 478 478 for this factor when analyzing the four alternatives a. US$1.00 = Col$1800 in 2010. because no information was available for predicting a 433 Cassava in the Third Millennium: … reliable price during the rainy season. Hence, if a project the processing of the largest volumes of fresh of dried cassava chip production is to be profitable or to cassava roots to these periods. The product expand its capacity throughout the year, a drying plant becomes distributed throughout the rest of the must not only be located in a cassava-producing region, year. This increases capital costs as it requires but should also develop its infrastructure and grow its increased capacity and storage. own crops. Thus, raw material supplies will be guaranteed and at a stable price. However, the use of an artificial fixed-bed dryer, with coal as a source of energy, is the best alternative Conclusions and recommendations to enable a year-round offer of dried cassava chips. Furthermore, product quality can be improved, an The evaluation of technologies for producing dried advantage when incentives are paid for quality or the cassava chips, by creating an agroindustry in the product is marketed for human consumption, thereby Colombian Atlantic Coast, led to the introduction of achieving better sale prices. improvements to production. This could not have happened if the work had been at an experimental level. Given the study conditions, the two systems— These improvements manifested in reduced production natural drying (ND) and artificial drying (AD)—are costs and consequent increases in profits for the profitable options. ND offers higher profits than AD project. because of lower investment and operating costs. However, the two operational alternatives can be The production of dried cassava chips and their use complemented to increase production capacity. as a source of calories to substitute certain grains (especially sorghum) in animal feed has generated a A solar collector for AD is not feasible because growing demand for this product in the market. To meet considerable energy is needed to evaporate the large this demand, both the production and processing of quantity of moisture contained in fresh cassava chips. cassava chips must be developed: That energy cannot be provided with the temperatures achieved with this system. – For production, both yield per hectare and area cultivated must be increased. Thus, cassava may be A sensitivity study is recommended to establish the produced for the fresh-root market, which pays effect of the price of raw material, sale price, conversion higher prices, and for industries using dried cassava factor of fresh to dried cassava chips, and consumption chips. and price of coal on the profitability of a project to produce dried cassava chips that alternatively uses ND – For processing, the use of a natural drying system or AD. confines work to dry seasons of the year and thus Technology 2: Producing Dried Cassava Chips for Human Consumption Sonia Gallego, Lisímaco Alonso, and José Alberto García Introduction In 2000, when CLAYUCA revisited the theme of producing high-quality cassava flour, evaluations of For more than four decades, different cassava drying different artificial cassava drying systems were also systems have been studied for their efficiency, technical started (García et al. 2006). Tools, including and economical feasibility, and reliability for product mathematical modeling, were used to predict the quality. However, most of the technologies developed performance and characteristics of cassava drying focused on dried cassava chip production for animal under certain operational conditions (Gallego et al. feed, overlooking the potential of dried chips as cassava 2003). The objective was to develop a procedure for flour for human consumption. producing dried cassava chips, using artificial drying methods that would guarantee a permanent offer of the 434 Artificial Cassava Drying Systems product at competitive prices and a quality that was Reception and weighing. After harvesting, safe for human consumption. cassava roots are transported, either packed or in bulk, to the drying plant. There, they are unloaded and The quality of dried cassava chips depends largely stored for a maximum of 1 day before processing on the processing technology used. However, obtaining (Figure 22-7). The cassava is weighed to determine the raw material of excellent quality is also very important. parameter of yield or the conversion factor of fresh Adequate control must be carried out at all stages of roots to dried chips. The roots should be processed the process to guarantee the acquisition of a product without delay as, within the first 48 h after harvest, that meets the standards of quality established for raw symptoms of deterioration develop, principally as color materials used to prepare foodstuffs. changes in tissues (Figure 22-8). Thus, according to the evaluations made, a processing prototype was developed for producing dried chips of optimal quality on equipment at CLAYUCA’s pilot plant in CIAT’s facilities, Palmira, Colombia. Producing dried cassava chips The operations required for producing dried chips are described in Figure 22-6. Ideally, all equipment or parts thereof that come into direct contact with cassava chips must be constructed or lined with stainless steel sheets to guarantee the prevention of contamination. Otherwise, washing and continuous disinfection of all equipment, tools, and installations used in the process become indispensable. Fresh cassava roots Reception and weighing Wastewater, Water Washing sludges, thin Figure 22-7. Cassava roots being stored before processing into outer peel chips. NaClO solution at Disinfection 200 ppm Chipping Dry air Drying Humid air Dried cassava chips Packing and storage Figure 22-6. Flow chart of dried cassava chips production at the CLAYUCA pilot plant in CIAT. Figure 22-8. Typical symptoms of deterioration in cassava roots. 435 Cassava in the Third Millennium: … Washing. Harvested cassava roots carry a large Disinfection. When the roots are clean, they are quantity of soil and field residues, making their disinfected, using a diluted solution of sodium washing before chipping necessary to ensure the dried hypochlorite (NaClO). This solution is also applied for a product’s nutritional quality. Washing is carried out in a few minutes when the roots are in the cylinder. rotary cylinder, which moves the roots as it washes them with clean pressurized water applied inside the Chipping. To accelerate the drying rate and thus drum. The cylinder walls are perforated to permit the obtain a good quality product, roots should be cut into exit of wastewater and residues (mainly the thin outer small chips of uniform size that increase the surface peel of cassava roots). The equipment also has a area exposed to the drying air. Chipping equipment loading gate for the length of the cylinder and a feed basically consists of a chipping disk assembled hopper at one end (Figure 22-9). vertically onto a structure that supports both the disk’s axis and the feed hopper (Figure 22-10). The disk About 1 m3 of potable water is required per ton of possesses coupled blades that, as the disk spins at fresh cassava roots. For the daily washing of 600 rpm, create chips shaped as rectangular bars equipment and installations, 2 m3 are used. Overall, (Figure 22-11). the plant requires 4 m3 of water per process. Drying. The use of dryers with hot air circulating directly across a fixed bed is the most favorable alternative in terms of quality of end product. Moreover, this method can be used where environmental conditions are not conducive to natural drying. Artificial drying over a fixed bed consists basically of a uniform flow of hot air passing through a layer, 10 to 30 cm thick, of fresh cassava chips. The dryer is a compartment of simple construction. The product rests on a false floor with perforations, with a fan Figure 22-9. Cassava washing machine. Figure 22-10. Cassava chipping machine. 436 Artificial Cassava Drying Systems For these dryers, the exposed area of the product, temperature, and air flow and humidity must be taken into account, as these variables affect drying times and fuel consumption, themselves significant parameters for determining the process’s overall efficiency and operating costs. Packing and storing. Once the chips have reached a suitable moisture content (10%–12%), they are packed in polypropylene sacks (Figure 22-13). The plant should have a room built for storing dried chips. When storage conditions are adequately controlled, dried cassava chips may be conserved for 6 to 18 months without quality deteriorating. Optimal Figure 22-11. Fresh cassava chips. conditions are achieved if the storage site is kept clean, in good sanitary condition, and free of insect pests. forcing the hot air to circulate through the layer of Evaluating the artificial drying system chips. Before it makes contact with the fresh cassava chips, the air is heated in a unit that consists of a Drying is the most important operation in the burner that is connected to the dryer by ducts. So that production of dried chips because of time and fuel drying is uniform, the product must be continually requirements, especially as cassava has a high initial mixed or turned. Although mixing can be manual moisture content. To evaluate the technical and (Figure 22-12), mechanical mixers are preferable. economic feasibility of the fixed-bed dryer for producing dried chips for human consumption, different trials were carried out to determine the values of the main variables intervening in the process (García et al. 2006). The equipment used for the evaluation was a fixed-bed dryer with forced circulation of hot air, belonging to CLAYUCA and located at CIAT’s facilities in Palmira (Figure 22-14). For the trials, the operation of the equipment and burner was adjusted. Drying curves were established for different loads and operating conditions were determined to obtain a good quality dried product. Figure 22-12. Manually mixing cassava chips in the artificial Figure 22-13. Dried cassava chips packed in polypropylene fixed-bed dryer. sacks. 437 Cassava in the Third Millennium: … 70 °C, and applied at 115 to 230 m3/min per ton of fresh cassava chips. The chips’ initial moisture content ranged between 58% and 70%. Table 22-9 shows the average results of the trials carried out with the artificial fixed-bed dryer. According to the initial chip load, various air flows were used and different drying times were obtained for each. Overall, for the different flows applied, drying times ranged from 8 to 18 h. When air flow was reduced, drying time increased, but fuel consumption (in this case, diesel) was less in Figure 22-14. CLAYUCA’s artificial fixed-bed dryer at CIAT, terms of quantity of dried chips. Table 22-9 also Palmira. presents the calculated consumption of natural gas and coal for different air flows, to compare with less expensive fuels in the calculation of the production costs Loads ranging between 600 and 1200 kg of fresh of dried chips. Figure 22-15 illustrates a typical curve for chips were managed in one or two 6-m2 drying the fixed-bed dryer, for which drying time was about 8 h chambers. Air flows were heated between 60 and to reach a moisture content of 12% in the chips. Table 22-9. Drying times and average fuel consumption for trials carried out with a fixed-bed dryer.a Air flow Net Fel consumption (m3/min per ton drying time Diesel Natural gas Coal fresh chips) (h) (gal/t dried chips) (m3/t dried chips) (kg/t dried chips) 230 8 90 353 602 180 11 88 345 589 150 13 86 340 580 120 18 80 313 535 a. Average ambient temperature = 25 °C. Average air drying temperature = 65 °C. Average initial moisture content of chips = 65%. Average final moisture content of chips = 12%. 70 60 50 40 30 20 10 0 70 70 70 70 70 70 70 70 70 70 Drying time (h) Figure 22-15. Typical curve presented when cassava chips are dried, using an artificial fixed-bed dryer. 438 Moisture content (%) Artificial Cassava Drying Systems The data in Table 22-9 were used to estimate the composition. Hence, quality control should involve not production costs of dried cassava chips obtained only compliance with legal provisions but also aspects through artificial fixed-bed drying, using natural gas that determine acceptance by consumers. as fuel and an air flow of 120 m3/min per ton of fresh cassava chips. Table 22-10 shows that the total With respect to the dried chips’ final quality, not production costs of 1 t of dried cassava chips, using a only should the raw material be of good quality, but fixed-bed dryer with natural gas as fuel, would be supervision and control should also be carried out at US$361.1. However, if coal was used instead as fuel, all stages of processing. The difficulty of carrying out the cost would be US$299.1, a drop of almost 20%. such activities in practice means that the finished product, that is, the dried cassava chips, must be In conclusion, if more economical fuels are used continuously and systematically reviewed. for drying, the best quality dried cassava chips can be obtained at low production costs. In short, dried cassava chips should comply with given requirements imposed by the market. These Quality of dried cassava chips for human characteristics include chemical composition, sanitary consumption condition, physical characteristics (size, rheology, color, and viscosity), and sensory characteristics (aroma and A product’s quality is measured by the way in which flavor). its characteristics comply, among other aspects, with: Chemical composition. The usual chemical • Legal health provisions composition of dried cassava chips is presented in • Composition Table 22-11. Although composition values are usually • Taste or acceptability to consumers constant, ranges are reported, as these values depend largely on factors such as variety, sanitary quality, type A product may comply with legal provisions but of processing, and moisture content of the dried chips nevertheless be rejected by consumers for such (Alonso and Zapata 2005). attributes as color, flavor, aroma, and chemical Table 22-10. Total production costs of dried cassava chips, using an artificial fixed-bed dryer, Colombia, June 2010. I. Basic information Conversion factor for fresh to dried cassava chips = 2.6:1 II. Variable costs per ton dried chips Unit No. units/t dried Unit value Cost/t chips (US$)a (US$)a Inputs Raw materialb t 2.6 55.55 144.4 Fuel (natural gas) gal 313.0 0.39 122.1 Energy for process kWh 218.0 0.11 24.0 Washing water m3 2.5 0.49 1.2 Sacks unit 25.0 0.37 9.2 Laborc workday 2.0 13.89 27.8 Total variable costs 328.7 III. Fixed costs/ton dried chips Cost/t (US$) Depreciation and maintenanced 32.4 Total fixed costs 32.4 Total production costs/ton dried chipse (US$) 361.1 a. US$1.00 = Col$1800 in 2010. b. Price of fresh cassava roots as delivered to plant. c. Assuming a workday of 8 h. d. Depreciation over 10 years; maintenance at 4% annually; initial investment at US$27,778. e. Production costs obtained for the conditions and equipment at CLAYUCA (fixed-bed dryer). 439 Cassava in the Third Millennium: … Table 22-11. Average values for chemical constituents of dried Table 22-12. Microbiological requirements for dried cassava cassava chips destined for human consumption. chips destined for human consumption. Parameter Range Analysis Maximum limit Moisture content (% wb)a 10–13 Total count of aerobic mesophiles (cfu/g) 200,000 Starch (%) 60–85 Count of total coliforms (cfu/g) 150 Protein (%) 1–3 Count of Escherichia coli (cfu/g) 3 Crude fiber (%) 1–4 Count of Staphylococcus aureus (cfu/g) 100 Ether extract (%) 1–2 Count of fungi and yeasts (cfu/g) 2,000 Ashes (%) 1–3 Detection of Salmonella spp. in 25 g Absent Total sugars (%) 2–5 Count of Bacillus cereus (cfu/g) 1,000 Total cyanide (ppm) 10–30 a. wb refers to wet basis. Uses of dried cassava chips Overall, dried cassava chips are characterized by their low contents of protein, fiber, and ether extract The production of dried cassava chips to obtain refined (fat), but high levels of carbohydrates, which comprise flour destined for human consumption is of great mainly of starch and small amounts of sugars. The importance at national and international levels, as they peel or cortex represents 15% to 20% of the cassava may constitute a raw material of special interest for root’s total weight, with the pulp or parenchyma numerous food-processing industries. amounting to 80%–85% (Alonso and Zapata 2005). Dried cassava chips used to produce high-quality To produce refined flour, dried cassava chips are refined flour may partially substitute not only wheat ground and sieved, removing most of the peel, thin flours, but also flours of other grains such as maize outer peel, and fiber as a solid waste byproduct. Most and rice, in food formulations, including for breads, of the protein, fat, fiber, and ashes are located in the pastas, pie mixtures, confectionery, flour mixtures for cortex, the principal component of the solid waste, beverages and soups, extruded products or snacks, whereas the carbohydrates are located in the and processed meats (Ospina et al. 2009). parenchyma, the principal component of refined flour. Even with partial substitution of other flours with The standard used for quality in Colombia for dried cassava flour, food-processing companies can save cassava chips destined for human consumption is the costs as, in most cases, cassava flour can be obtained Colombian Technical Standard NTC 2716, issued by at lower prices than the other flours. the Colombian Institute of Technical Standards and Certification (ICONTEC, its Spanish acronym). At world Finally, so that an agroindustry of this type is level, the quality standard is the CODEX STAN sustainable over time, the following aspects should be 176-1989 for “edible cassava flour”, developed by the considered: a guaranteed supply of quality cassava Codex Alimentarius Commission for cassava flour roots at adequate volumes and stable prices; an obtained from dried cassava chips. efficient, economic, and reliable technology in terms of the end product’s quality; and support from food- Microbiological quality. Apart from the average processing industries that identify cassava flour as a characteristics of size, presentation, and chemical suitable raw material that will, on the one hand, bring composition, dried cassava chips for human economic benefits to their business and, on the other consumption must also meet the microbiological hand, contribute to the cassava crop’s agroindustrial requirements called for by the Ministry of Health in development and promotion in their region. each nation. Table 22-12 shows the maximum values permitted by the Colombian Government, according to References Standard NTC 2716. In short, the product must be free of microorganisms and parasites, and must not contain Akhtar J. 1978. Drying of cassava with heated air. MSc any substance derived from microorganisms in thesis. Asian Institute of Technology (AIT), Bangkok, quantities that may endanger health. Thailand. 47 p. 440 Artificial Cassava Drying Systems Alonso L; Zapata, V. 2005. Manual de producción de García JA; Gallego S; Alonso L. 2006. Establecimiento trozos secos de yuca para la alimentación animal. de una planta piloto para la producción continua de CIAT; CLAYUCA; World Vision International, Palmira, harina refinada de yuca. In: Informe de proyecto. Colombia. CLAYUCA, Palmira, Colombia. Alonso L; Viera MA; Best R. 1987. La investigación en el Ospina JE. 1980. Quantificação da deterioraçâo de secado artificial de yuca como apoyo al desarrollo mandioca durante a secagem em barcaça por agroindustrial de la Costa Atlántica de Colombia. convecção forçada de ar aquecido com coletor solar. Revista ACOGRANOS 3:24–32. MSc thesis. Universidade Estadual de Campinas (UNICAMP), Campinas, Brazil. 100 p. Ashrae H. 1977. Fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Ospina B; Alonso L; Gallego S; García JA. 2009. Engineers, Inc., New York, USA. Tecnologías para el manejo poscosecha del cultivo de la yuca—Proc Reunión Anual de Socios. CLAYUCA/ Best R. 1978. Cassava processing for animal feed. In: CIAT, Palmira, Colombia. Weber EJ; Cock JH; Chouinard A, eds. Cassava harvesting and processing—Proc workshop held in Roa G. 1974. Natural drying of cassava. Dissertation. Cali, Colombia, April 1978. International Development Department of Agricultural Engineering, Michigan Research Centre (IDRC), Ottawa, Canada. p 12–20. State University (MSU), USA. 234 p. Chirife J; Cachero RA. 1970. Through-circulation drying Rossi SJ; Roa G. 1980. Secagem e armazenamento de of tapioca root. J Food Sci 35(4):364–368. productos agropecuários com uso de energia solar e ar natural. Secretaria da Indústria, Comércio, Ciência CITA (Centro Nacional de Ciencia y Tecnología de e Tecnologia; Academia de Ciências do Estado de Alimentos). 1974. Estudio de factibilidad agrícola e Sâo Paulo (ACIESP), Sâo Paulo, Brazil. 295 p. industrial para el establecimiento de una planta de chips secos de yuca en San Carlos. San José, Costa Seng YY. 1976. 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Artificial heat drying of tapioca Valle, Cali, Colombia. (Also available in: CLAYUCA/ chips. Malays Agric Res 3:67–76. CIAT. Informe anual de actividades. Palmira, Colombia.) 441 Cassava in the Third Millennium: … CHAPTER 23 Production and Uses of Refined Cassava Flour Contributors, in order of appearance, to different sections of this chapter: José Alberto García1, Lisímaco Alonso2, Sonia Gallego3, Johanna A. Aristizábal4, Sergio Henao5, Ana Milena Bonilla6, and Andrés Giraldo7 Introduction the opening of new markets and establishing rural agribusinesses that offer small farmers opportunities Rapid urban growth in Latin American and Caribbean for increasing their income. (LAC)3 countries has increased demand for processed food, opening opportunities whereby the cassava crop In 2006, CLAYUCA, with financial support from can acquire higher added value. In Colombia, public the Ministry of Agriculture and Rural Development of and private entities are highly interested in the potential Colombia (MADR, its Spanish acronym), prospects of increasing the consumption of cassava implemented the project Establishing a pilot plant and its derived products. Accordingly, several for the continuous production of refined cassava agroindustrial projects on cassava are being promoted flour. The aim was to develop a technology to extract, in various parts of the country. One dynamic market is on an ongoing basis, refined cassava flour with high animal feed, where cassava flour or dried chips can be starch contents and low contents of fiber, ash, and used as an energy source in balanced feed formulas. protein (García et al. 2006). However, to be viable, agroindustrial cassava A modular pilot plant was therefore established projects need other alternative marketing options for to continuously produce refined cassava flour. using cassava, for example, as a partial substitute of Mechanical means (mill sieves) and pneumatic other products such as wheat, maize, and rice flours, classification (cyclones) were used to obtain granules and even sweet cassava starch. Thus, cassava can as fine as those of starch. Specifically, flour was participate in food-processing and industrial markets, refined to a maximum fineness, where particles were for which products of higher added value can be less than 50 μm in particle size. developed. The project was based on the problems industry CIAT has conducted projects to expand the has with cassava starch such as the generation of production of cassava flour and its use, thus promoting large amounts of wastewater to obtain native starch. Studies were initiated, with the collaboration of Universidad del Valle (Colombia), to obtain flours based on dried cassava chips, using a minimum 1. Mechanical Engineer, Postharvest Management Systems, quantity of water (Barona and Isaza 2003). CLAYUCA, Cali, Colombia. E-mail: albertogarcia@mailworks.org 2. Agricultural Engineer, Postharvest Management Systems, CLAYUCA. E-mail: l.alonso@cgiar.org The pilot plant 3. Chemical Engineer, Postharvest Management Systems, CLAYUCA. E-mail: s.gallego@cgiar.org 4. Formerly Chemical Engineer, Postharvest Management Systems, Dried cassava chips can be ground into high-quality CLAYUCA. flour for use as a partial substitute for wheat, maize, 5. Agroindustrial Engineer, UN–Palmira. rice, and other flours in foodstuffs such as breads; 6. Agroindustrial Engineer, Universidad de San Buenaventura, Cali, Colombia. pastas; flour mixtures for pies, beverages, and soups; 7. Agroindustrial Engineer, Universidad del Cauca, Popayán, extruded products; and processed meats. Cassava Colombia. flour can also be used as raw material in the 8. For an explanation of this and other acronyms and abbreviations, see Appendix 1: Acronyms, Abbreviations, and Technical production of glues for corrugated cardboard boxes, Terminology, this volume. biodegradable plastics, beer, and ethanol. 442 Production and Uses of Refined Cassava Flour Figure 23-1 shows the pilot plant for the plant permitted variation in operating conditions, continuous production of refined cassava flour located according to the desired refining requirements such as in the facilities of CIAT, Palmira, Colombia. The plant refined flour or a much finer flour. The pilot plant was processes 300 kg/h of dried cassava chips. The design used: took into account the different issues determining the functionality of processing dried chips into refined • To generate materials or raw materials for the flour. A simple technology was used, in which elements research and development of new products were easy to manage and accessible for maintenance. The technology was simple enough for anyone person • For the technical training of functionaries with minimal training to carry out. Furthermore, the • To manage actual costs of operation and profitability • To disseminate a new technology to cassava- processing companies interested in products of higher added value, and to companies wanting to enter new markets, using cassava flour in their processes. Principal components Figure 23-2 details the basic procedures for extracting refined cassava flour. It shows a screw conveyor for feeding raw material (dried cassava chips) to the mill sieves, three cylindrical mill-sieves with three shafts and three cylindrical sieves (screens), three fans, and Figure 23-1. The CLAYUCA modular pilot plant for producing five cyclones for pneumatic classification and flour refined flour from dried cassava chips, Palmira. collection. Filter Outlet for fine flour 2 inverse cyclones 2 collector 1 inverse (pneumatic cyclones cyclone classification) Outlet for r coarse veyo Mill flour Mill Mill con sieve 1 sieve 2 sieve 3 Dried crew 3-mm 177-μm 100-μm chips S mesh mesh mesh Gate Gate valve 1 valve 2 Raw material Fan 1 Fan 2 Fan 3 Residues Refined flour (peels & fiber) Byproduct Product Figure 23-2. Diagram showing basic procedures for extracting refined cassava flour at the CLAYUCA pilot plant, Palmira. 443 Cassava in the Third Millennium: … Screw conveyor. The feeder or screw conveyor endless screw at one end to feed dried cassava chips consists of a receiving hopper with a capacity of into the sieve. It also transmits energy for the blades 300 kg/h of dried cassava chips (Figure 23-3). The striking the chips. The four stainless steel blades are chips are deposited into the hopper and conveyed by joined to the shaft and are located at 90° to each other. the screw to the first mill sieve for processing. At its They are designed to strike the chips over the mesh, largest, the screw’s diameter is 6 inches. The shaft exercising sufficient strength to mill them and separate diameter is 2 inches, and the space between the blades the peels from the flour (Figure 23-5). is 4.5 inches. Cylindrical sieves. The sieves are built with an Cylindrical mill-sieves. Each mill sieve—a expanded mesh of ⅛ inch to form the structure of the fundamental part of the plant—consists of a feed screen, with stainless steel rings coupled to its ends, hopper, a cylindrical estructure or body where the sieve comprising a cylinder of 29.5-cm diameter and and shaft are located, and a discharge hopper with a 120.5-cm length. The screens are covered with mesh cylindrical outlet that couples to a fan (Figure 23-4). of 3 mm for grinding and 177- or 100-μm for classification of the particles (Figure 23-6). Mill shafts. Each of the three shafts measures 1½ inches diameter, 170 cm length and possesses an Fans. The fans transport fine flour from the mill sieves’ outlets to the collector cyclones. The pilot plant has three centrifugal fans with radial blades and a 12-inch-diameter rotor (Figure 23-7). Collector cyclones. The pilot plant has five cyclones, two of which collect fine particles, in this case, of refined cassava flour. The other three classify the particles. The basic structure of a collector cyclone Endless Blade screw Figure 23-3. Screw conveyor-feeder. Figure 23-5. A mill shaft. Feed hopper Cylindrical body Discharge hopper Residues discharge Figure 23-6. Sieves for milling and classification, with mesh openings of, from left to right, 3 mm, 177 μm, and Figure 23-4. Mill-sieve. 100 μm 444 Production and Uses of Refined Cassava Flour Outlet for clean air Vortex Rectangular localizer inlet to the involute Mill Air charged with particles Nucleus of the vortex Principal vortex Cylinder Figure 23-7. Centrifugal fan. Cone comprises a vertical cylinder with a conical base. It is provided with a tangential inlet, normally rectangular, and a circular discharge for clean air in its upper parts. This equipment is designed to separate particles from a fluid current, with high efficiencies for particles larger than 20 μm. Outlet for flour The cyclone’s tangential inlet creates centrifugal To the storage forces that tend to push particles towards the hopper equipment’s periphery, away from the inlet of the air, Figure 23-8. Collector cyclone. thus increasing sedimentation and making collection more effective (Figure 23-8). • Area C lies in the cyclone’s cylindrical part Classifier cyclones. These are used to separate where the air, loaded with particles, flows fine from coarser particles. It is characterized by an inside, in an axially central direction. Meeting inverse feed (central axial) that differs from that used the back pressure from area B, this air forms in conventional cyclones. Studies by CLAYUCA considerable turbulence, which lifts the finest (García 2006; Herrera et al. 2007) determined that, as particles and forces them to leave the cyclone air loaded with particles flowed into the equipment, in by a duct connected tangentially to the an axially central direction, it moved in different collector cyclone. directions in three areas inside the cyclone (Figure 23-9). Refined cassava flour production • The first area, marked as A in Figure 23-9, The stages of refined cassava flour production in the constitutes the entire periphery of the cylinder’s pilot plant are shown in Figure 23-10. The basic stages conical part. The larger particles decant parallel are feeding dried cassava chips for mill-sieving in to the axial feed, losing speed and becoming mill 1. The resulting coarse flour is then mill-sieved in deposited into the cyclone’s bottom. mill 2 to create an intermediate flour that is then mill-sieved in mill 3. The flour is classified in the three • In area B, a back pressure is formed, which classifier cyclones and the final refined flour is then helps disperse the particles entering the collected by the two collector cyclones. cylinder’s upper part. 445 Cassava in the Third Millennium: … Inlet for air charged Second mill-sieving . In this stage, the coarse with particles flour from the first mill sieve becomes the raw material for mill sieve 2, which has a mesh with 177-μm openings. In this mill, the flour is again reduced in size, and new residue is generated. F lour that passes through the mesh is extracted by fan 2 and separated into two new flours within the classifier cyclone, that is, intermediate flour that is decanted and becomes the raw material for the third mill sieve, and fine flour that is directly collected. Outlet for C fine flour Third mill-sieving . As with the previous stages, intermediate flour from the second mill sieve enters the B last stage of milling and refining in mill sieve 3. This mill has a mesh with 100-μm openings. The refined flour is extracted by fan 3 and transported to collection. Again, new residue is generated. Pneumatically classifying the flour . Classification is carried out during the intermediate stages of mill-sieving. Conventional cyclones are used, A that is, those that are normally used to collect processed products. As they already meet the requirements for classifying particles, the cyclones are being used as pneumatic classifiers. An air current, loaded with flour, is fed inversely into the cyclone, making possible the decanting of coarse particles (>100 μm) towards the mill sieve for further milling. The fine particles, however, leave the Outlet for coarse flour cyclone by its tangential outlet to be later collected. They thus avoid being re-milled. Figure 23-9. Classifier cyclone. Collecting the refined flour . The refined flour is Feeding the dried cassava chips. Unpeeled dried collected by two cyclones with tangential feed inlets cassava chips with a moisture content between 10% and that are connected in parallel for greater flour capture . 12% are deposited in the hopper by a screw conveyor to T he two cyclones are coupled to a cone that discharges feed the first mill sieve. The feed capacity is 300 kg/h of the end product into packing bags. dried chips, which are, ideally, free of peduncles. Conversion factors First mill-sieving . Dried cassava chips are fed to the first mill sieve, which has an expanded mesh with The CLAYUCA pilot plant obtained an average 3-mm openings. The chips are reduced in size and, conversion factor of 1.3:1. That is, for every 1.3 kg of according to the mesh’s openings, separated into small dried chips (12% moisture content) that entered the pieces of peel, thin outer peel, and fiber that comprise equipment, 1 kg of refined flour was extracted, and the residues. These are extracted as byproducts that are 0.3 kg was either byproduct or residues. usually converted into animal feed. Material that succeeds in passing through the mesh is extracted by If refined-flour production from fresh roots is fan 1, which transports it to the classifier cyclones. After considered, the conversion factor would range between pneumatic separation, the flour produced by mill sieve 1 3.6:1 and 4:1, depending on the cassava roots’ dry is divided into two types: fine flour that rises directly to matter content. That is, for every 3.6 or 4 kg of fresh the collector cyclones, and coarse flour that is decanted cassava, 1 kg of refined flour is extracted. through a gate valve and automatically becomes the raw material for the next stage. 446 Production and Uses of Refined Cassava Flour Cyclones in parallel for classification Coarse particles Fine particles Mill 1 Mill 2 Mill 3 Feed Collection of refined flour Figure 23-10. Production of refined cassava flour at the CLAYUCA pilot plant, Palmira, Colombia. Physicochemical description of refined cassava characteristics: 70%–75% of particles at less than flour 50 μm and 20%–25% of particles at less than 177-μm. Although less refined, the flour has important Granule analysis. As mentioned earlier, two types of applications in the baking, brewing, meat-processing, products are extracted from each mill sieve in the pilot and ethanol-producing industries. plant: refined flour as the principal product and three types of residues, which form the byproduct. These Table 23-1. Granulometric analysis of the refined cassava flour materials are separated out in the equipment, produced by the CLAYUCA pilot plant. eliminating any peel that was left over from the manual Mesh openings Fraction retained peeling of cassava roots for dried chip production. This (μm) (%) was one of the pilot plant’s most valuable contributions 150 2 to refining, because it eliminated the need for labor 106 3 (and therefore costs) to peel roots destined for 50 5 processing into flour for human consumption. <50 90 Table 23-1 lists the overall results of several granule analyses of the refined flour obtained at the CLAYUCA Chemical composition. Table 23-2 shows the pilot plant. The refined flour had a high percentage of average composition of materials present in the impalpable particles (90% at less than 50 μm). Even so, production of refined cassava flour from dried chips. in this same equipment and using only the first two The composition of native starch is provided for stages of mill-sieving, flour of bread-making quality comparison. The table shows that processing dried could be obtained. This flour had the following cassava chips in the pilot plant leads to reductions by 447 Cassava in the Third Millennium: … Table 23-2. Typical composition of materials present in the production of refined cassava flour. The composition of native starch from the same cassava variety is also included. Materials Crude protein Ash Crude fiber Ether extract Starch (%) (%) (%) (%) (%) Dried cassava chips 3.0 3.5 4.0 0.8 77.0 Refined cassava flour 1.4 1.3 1.9 0.6 85.0 Residues 5.5 6.5 52.0 1.0 24.0 Native starch 0.1 0.1 0.3 0.1 91.0 more than 50% in values for crude protein, ash, and lower gelatinization temperatures and lower maximum crude fiber. The values for native starch (extracted from viscosities. Moreover, the maximum viscosity peaks for the same cassava variety) show significant differences the flours were not reached as rapidly. This indicates with those of the refined flour, affecting various that the commercial starch is easier to cook and properties, as described below. requires less energy for cooking. Table 23-3 also presents the results for the following parameters: ease Rheological properties. The rheological characteristics of refined cassava flour were evaluated, Table 23-3. Viscosity profiles of refined flour and native starch, using amylographs or profiles of flour slurries, in which both obtained from cassava variety HMC-1. changes in the viscosity of a suspension of flour and Evaluations on were carried out with a viscoamylograph RVA series 4. water are recorded during heating and cooling (Rodríguez et al. 2006). Figure 23-11 shows the Parametera Refined flour Native starch viscosity curves, as generated by a viscograph, of Gelatinization temperature (ºC) 63 65 refined flours from cassava varieties M Col 1505, Maximum viscosity (RVA units) 146 478 M Per 183, and HMC-1, and a commercial cassava Ease of cooking (min) 4.4 1.6 starch. Gel stability (RVA units) 72 332 Gelatinization index (RVA units) 14 54 The viscosity curves show that, compared with the a. RVA units measure viscosity according to the Rapid Visco commercial starch, all the refined flours presented Analyzer. 1000 100 BU (115 cmg) 900 90 Cassava starch 800 M Col 1505 80 700 70 600 60 500 50 M Per HMC-1 400 183 40 300 30 200 20 100 10 0 0 0 5 10 15 20 25 30 35 Time (min) Figure 23-11. Micro-viscoamylograph (MVAG) profiles for flours from different cassava varieties, compared with commercial cassava starch. 448 Brabender Units (BU) Gelatinization temperature (ºC) Production and Uses of Refined Cassava Flour of cooking, gel stability, and gelatinization index or retention and bite characteristics. Refined flour can gelling for both the refined flour and the native starch also be used in extrusion to produce dietary pastes, extracted from the same cassava variety (HMC-1). snacks, and breakfast cereals (flakes). Flour was easier to cook than starch, as All types of composite flours can be used to confirmed by a slower swelling rate of granules for the prepare instantaneous beverages and infants’ refined flour. With regard to gel stability (which is beverages (Ospina et al. 2009). Tests also confirmed related to the fragility and solubility of swollen starch that cassava flour can replace or complement the granules), the native starch presented a value of various raw materials used in extruded products, widely 332 RVA units, suggesting that the refined flour used in human food. tended to form more stable gels than did the native starch. Finally, during testing in the RVA For industrial use, refined cassava flour is an viscoamylograph, the value for the gelatinization appropriate raw material in the manufacture of glues index of the refined flour indicated that pastes formed for affixing corrugated cardboard boxes, even though with cassava flour are stable, with little tendency levels of fiber, ash, and protein are not as low as those towards retrogradation. of native starch. Refined flour nevertheless also has potential because it has characteristics similar to those Uses of refined cassava flour of pearl maize starch (Bonilla and Alonso 2002). Table 23-4 presents possible applications of refined In 2006, CLAYUCA analyzed the technical viability cassava flour in different food products and industrial of including refined cassava flour as a brewing additive. use, as determined by recent research carried out by Results indicated that refined cassava flour is a CLAYUCA. These studies showed that bread prepared technically viable alternative for maltose as a raw with refined cassava flour, using 5% and 10% levels of material in beer production (Ospina and Aristizábal substitution, performs well in tests for specific volume 2006). and presents high values of water absorption. No significant differences were found for acceptance by Finally, in collaboration with the Universities of consumers, compared with pure wheat bread Cauca and Valle, research has been carried out on the (Aristizábal and Henao 2004). Partial substitution of production of thermoplastic biopolymers from cassava cassava flour also enabled bakers to save on flour. These polymers can be used as precursors in the production costs, as cassava flour can be obtained at manufacture of biodegradable plastics (e.g., bags, lower prices than wheat flour. linings, and disposable utensils). The largest difference between the plastics currently produced (based on Because of its starch’s capacity to thicken during petroleum derivatives) and those based on cassava final preparation, refined cassava flour is an excellent flour is that the latter is completely biodegradable. This raw material for beverage and soup preparation. This means that its usability as packaging, from its characteristic also allows cassava flour to be used as production, is no more than 1 year (Villada and Acosta an ingredient in meat processing, as it improves water 2003). Table 23-4. Applications of refined cassava flour. Market Product The raw material Percentage of Advantages of replaced substitution cassava flour Foodstuffs Bread Wheat flour 5–20 Lower cost Mixtures for beverages and Flours from wheat, rice, maize, and 10–40 Increased yield soups plantain Processed meats Wheat flour, starches 50 Better quality Snacks Wheat, rice, and maize flours 100 Lower cost Beer Maize starch, rice flour, maltose syrup 50–100 Lower cost Industrial uses Glues Maize and potato starches 30–100 Lower cost Biodegradable plastics Maize and potato starches 70 Better structural stability 449 Cassava in the Third Millennium: … References Herrera CA; Rosillo ME; García JA. 2007. Cassava flour separation using inverse cyclone. Rev Bras Eng Agríc Aristizábal J; Henao S. 2004. Adaptación y validación Ambient 11(5):515–520. de tecnología para utilización de harina de yuca en panificación. In: Informe de proyecto. CLAYUCA, Ospina B; Aristizábal J. 2006. Investigación para la Palmira, Colombia. evaluación técnica del uso de la harina de yuca como adjunto cervecero. In: Informe de proyecto. Barona SM; Isaza LE. 2003. Estudios para el desarrollo CLAYUCA, Palmira, Colombia. de un proceso de extracción de almidón a partir de trozos secos de yuca (Manihot esculenta Crantz) con Ospina B; Nutti M; Gallego S; Carvalho JL; Ascheri JL. mínima utilización de agua. BSc thesis in Agricultural 2009. Fichas técnicas: Productos alimenticios. In: Engineering. Universidad del Valle, Cali, Colombia. Proc of an international course on “Tecnologías para (Also available in: CLAYUCA. Informe anual de la elaboración de productos alimenticios a partir actividades. Palmira, Colombia.) de cultivos con alto contenido nutricional”, held in Palmira, Colombia. CLAYUCA; Empresa Brasileira Bonilla AM; Alonso L. 2002. Estudio de la viabilidad de Pesquisa Agropecuária (EMBRAPA), Palmira, técnica, económica y comercial de la obtención Colombia. 115 p. de adhesivos para uso en la industria de cartón corrugado, a partir de almidón de yuca extraído por Rodríguez E; Fernández A; Alonso L; Ospina B. 2006. vía seca. In: CLAYUCA. Informe anual de actividades. Reología de suspensiones preparadas con harina Palmira, Colombia. precocida de yuca. Ingeniería y Desarrollo. 19:17–30. García JA. 2006. Evaluación de ciclones en la clasificación Villada HS; Acosta H. 2003. Proyectos de desarrollo de partículas refinadas de yuca. BSc thesis in de materiales poliméricos biodegradables usando Mechanical Engineering. Universidad del Valle, Cali, extrusión simple. In: CLAYUCA Informe anual de Colombia. actividades. Palmira, Colombia. p 212–222. García JA; Gallego S; Alonso L. 2006. Establecimiento de una planta piloto para la producción continúa de harina refinada de yuca. In: Informe de proyecto. CLAYUCA, Palmira, Colombia. Technological Study of Cassava Flour in Bread-Making Johanna A. Aristizábal and Sergio Henao Introduction To help resolve this situation, much effort has been focused on the partial substitution of wheat flour with In Colombia, as in many South American countries, an indigenous crop flours. Solutions towards incorporating acute imbalance is growing between the production raw materials of local origin (cassava, rice, maize, and demand for wheat to supply domestic needs for sorghum, and millet) into popular foods such as bread bread flour. Among the factors causing this imbalance and pastas have been studied. Several studies are lack of land suitable for growing the cereal, examined the use of cassava flour as a wheat flour relatively low yields, population growth, and increasing substitute in bread-making. In Colombia, such studies per capita consumption of wheat and its derivatives. have shown promising results. From a technical This imbalance has been compensated only through viewpoint, breads comparable with those of traditional importing large quantities of the cereal at increasingly wheat breads and substituting as much as 15% with higher prices, thus generating an expensive outflow of cassava flours can be produced (Aristizábal and Henao foreign exchange from the country. 2004; Henao and Aristizábal 2009). 450 Production and Uses of Refined Cassava Flour The Government’s strategy of promoting the Reception cassava crop, complemented with efforts to link farmers to new markets for cassava, will help promote the sustainable cultivation of the crop. Thus, new employment opportunities in rural areas will be created, Weighing benefiting cassava flour producers, increasing the offer of this product, and reducing wheat flour imports. Furthermore, bread-makers will have a more Mixing of solids economical substitute for the traditional raw material. About 60% of wheat flour is destined for bread-making. Hence, if 10% were replaced with cassava flour, imports would be reduced by about 75,000 t of wheat flour per Wet mix year. Although cassava flour contains a low percentage of Resting protein (~2%), one of its important contributions is its higher fiber content (>3%), compared with wheat flour with less than 1%. Cassava flours, which can provide a bread with a high fiber content, are convenient for Kneading bread-making in a society concerned with good health and nutrition. Weighing Bread-making tests Three processing variables were defined: cassava variety, percentage of substitution, and bread type, with three levels for each. The cassava varieties—CMC-40, Dividing M Col 1505, and HMC-1—were selected for their availability, average yield of dry matter in roots, dry matter content, and HCN content. The percentages selected for substituting wheat flour with cassava flour Resting were 5%, 10%, and 15% (w/w ratio, based on quantity of wheat flour). These values were chosen from the literature, which reported that values of more than 15% Shaping affected the bread’s final quality. White bread types selected were rolls, sandwich, and hamburger, the selection being based on previous studies, which had selected the most used bread types—rolls and Fermentation sandwich—for evaluation. The bread-making trials were based on the typical Baking formulas used for rolls, sandwich, and hamburger breads by the bakery “La Estrella” located in Palmira, Colombia. To avoid modifying the preparation protocols that its workers followed daily, only the percentages of Packing substitution by cassava flour were included in the traditional mixture. For each trial, 1 kg of wheat flour Figure 23-12. Flow chart for bread production at a large bakery in Palmira. was used with its respective percentage of substitution according to cassava variety and bread type, and always preparing a 100%-wheat bread as control. The stages of time, and baking temperature and time. Thus, bread bread manufacture are illustrated in Figure 23-12. rolls was divided mechanically for later shaping. This type of bread required a fermentation chamber with a The bread types were prepared according to the constant feed of steam at 30 °C for 1.5 h. The bread proportions of components in the formula, fermentation was then baked at 200 ºC for 25 min. 451 Cassava in the Third Millennium: … Table 23-6. Physicochemical characteristics of wheat and Sandwich bread was also divided, but manually, cassava flours. and the dough then shaped and introduced into rectangular molds that gave the breads their Analysisa Flours from cassava variety: characteristic form. Fermentation was carried out in CMC-40 M Col HMC-1 Wheat closed molds at room temperature, not in the 1505 fermentation chamber. The bread was then baked at Dry matter (%, wb) 89.20 92.03 91.61 89.02 190 ºC for 45 min. Moisture (%, wb) 10.80 7.97 8.39 10.98 Protein (%, db) 1.78 2.32 1.34 14.01 Hamburger bread was divided mechanically Crude fiber (%, db) 3.45 3.21 2.96 0.84 before the dough was fermented in the chamber. The Starch content (%, db) 86.00 87.00 88.25 69.00 dough was then rested for about 20 min to soften Ash (%, db) 2.06 1.26 2.25 0.72 before being kneaded to facilitate shaping. The Cyanide, total (ppm) 6.58 9.30 13.00 — hamburger breads were baked at 200 ºC for 25 min. Cyanide, free (ppm) 0.58 1.15 0.58 — Reducing sugars (%, db) 1.73 2.30 1.37 0.94 The formulas used to prepare rolls, sandwich, Amylose (%, db) 12.02 12.15 12.31 13.87 and hamburger bread are listed in Table 23-5. Amylopectin (%, db) 87.98 87.85 87.69 86.13 WAI (g of gel/g of flour) 4.35 4.73 4.15 3.11 Analyzing cassava flour WSI (%) 7.01 7.43 8.79 13.26 a. Abbreviations wb refers to wet basis; db, dry basis; WAI, water- Cassava flours obtained at the CLAYUCA pilot plant absorption index; WSI, water-solubility index. were evaluated, using microbiological, granulometric, and physicochemical analyses (Table 23-6). The cassava flours obtained met Rheological analyses of wheat-cassava microbiological requirements and possessed the composite flours granule size required by the Colombian Technical Standard for wheat flour (NTC no. 267, as established Doughs made from wheat-cassava composite flours, by ICONTEC). More than 98% of particles passed using three substitution percentages, were evaluated. through the mesh with 212-μm openings. Testing involved a farinograph (Table 23-7), alveograph, amylograph, falling number test (Table 23-8), The water-absorption index for cassava flours was mechanical work, and water absorption during the higher than for wheat flours. This factor favors the process. former’s use in bread-making, as increased water absorption means that more bread will be obtained Except for flours made from variety HMC-1, water for the same quantity of flour. The water-solubility absorption by all composite wheat-cassava flours was, index was also higher for wheat flour, which was on average, 1% more than water absorption by wheat expected, as wheat flour presents a higher content of flour. The growth period for wheat flour is almost soluble proteins in water. double that of wheat-cassava composite flours. This factor indicates that dough prepared from wheat- cassava composite flours reaches consistency in less Table 23-5. Formulas for rolls, sandwich, and hamburger breads time. at a large bakery in Palmira. Component Percentagea Results for flour stability presented major differences between varieties, showing a ratio that is Bread Sandwich Hamburger rolls bread bread inversely proportional to the percentage of substitution. Composite flours with a 15% substitution showed less Wheat flour 85–100 85–100 85–100 tolerance of kneading. Cassava flour 5–15 5–15 5–15 Yeast 4 4 6 The degree of decay of composite flours is higher Sugar 12 8 12 than that of wheat flour. In contrast, the time to Salt 2 2.5 2 breakage for all composite flours was shorter than for Margarine 12 6 6 wheat flour. This was expected, as this period indicates Water 50–60 50–60 50–60 the strength of gluten in bread flours. Wheat flour a. Percentages given, assuming 100% as flour. therefore presents the highest resistance to breakage. 452 Production and Uses of Refined Cassava Flour Table 23-7. Characteristics of composite flours according to a farinograph. Composite floura Water Dough peak time Stability Degree of decay Break-down time absorptionb (min) (min) (FU)c (min) Wheat only (control) 63.8 3.9 17.1 11.0 18.0 Wheat+CMC-40 (5%) 64.4 2.3 16.7 23.0 10.3 Wheat+CMC-40 (10%) 64.5 2.0 10.5 39.0 4.5 Wheat+CMC-40 (15%) 64.5 2.2 9.4 48.0 3.6 Wheat+M Col 1505 (5%) 64.3 2.7 9.3 37.0 6.0 Wheat+M Col 1505 (10%) 64.7 1.9 3.0 60.0 2.9 Wheat+M Col 1505 (15%) 64.6 1.9 3.3 47.0 2.8 Wheat+HMC-1 (5%) 63.1 2.9 17.4 25.0 12.1 Wheat+HMC-1 (10%) 63.4 2.0 14.0 37.0 4.8 Wheat+HMC-1 (15%) 62.9 1.7 3.7 53.0 2.8 a. Percentages indicate levels of substitution of wheat flour with cassava flour. b. In mL/100 g of flour. c. FU refers to farinograph units. Table 23-8. Characteristics of composite flours in terms of an alveograph, falling number test, and amylograph. Composite floura Strength Tenacityb Extensibility Balance Falling number Tgel Vmax (joules) (mm) (sec) (°C) (cP) Wheat only (control) 381.87 147.40 60.80 2.42 353 59 77.40 Wheat+CMC-40 (5%) 400.96 152.90 56.00 2.73 360 66 77.45 Wheat+CMC-40 (10%) 280.30 152.90 41.49 3.69 354 68 76.90 Wheat+CMC-40 (15%) 339.55 152.90 48.20 3.17 354 68 77.90 Wheat+M Col 1505 (5%) 295.28 154.00 50.70 3.04 343 61 77.65 Wheat+M Col 1505 (10%) 335.63 151.47 45.05 3.36 349 63 77.35 Wheat+M Col 1505 (15%) 284.49 151.80 39.77 3.82 329 68 76.90 Wheat+HMC-1 (5%) 372.98 152.90 54.00 2.83 349 70 76.92 Wheat+HMC-1 (10%) 301.03 152.90 43.20 3.54 324 74 77.85 Wheat+HMC-1 (15%) 272.13 143.66 46.30 3.10 325 74 76.95 a. Percentages indicate levels of substitution of wheat flour with cassava flour. b. In water (mm). The values of strength in flours made from variety M Col 1505 (15%), and CMC-40 (10%), when these were HMC-1 tended to be inversely proportional to the prepared as sandwich bread, as the composite flours percentage of substitution. However, composite flour presented the highest balance values. with 5% substitution of flour from variety CMC-40 had a higher strength value than wheat flour. The tenacity The “falling number” values obtained for all values for all composite flours were similar to each composite flours presented acceptable values, falling other and surpassed, by a low percentage, that for into the requisite range of 250 to 400 seconds. Bread wheat flour. This datum reflects what was observed flours should not present values of more than during the process, that the tenacity of doughs made 400 seconds, as they would require the addition of with composite flours was greater. Extensibility of enzymes, thus inducing prolonged fermentation times doughs made with composite flours were less than that and creating breads with pale crumbs. of wheat flour. Gelatinization temperatures (Tgel) of composite The balance of doughs from wheat-cassava flours are higher than for wheat flour. Starch granule composite flours presented values that were higher size affects Tgel. In wheat flour, this ranges between than those of the control and showed differences 2 and 38 μm, whereas, in cassava flour, it ranges between themselves. In the bread-making tests, between 5 and 35 μm. Hence, wheat flour presenting problems occurred during kneading and in the bread’s smaller granules may reach Tgel in less time. final appearance for flours from varieties HMC-1 (10%), 453 Cassava in the Third Millennium: … Wheat flour presents constant viscosity over time prepared from composite flours with substitutions of once it reaches maximum viscosity. In contrast, 5% and 10% were higher than that of wheat bread. All cassava flours tend to continue increasing in viscosity breads prepared with 15% of substitution presented over time after reaching maximum viscosity, thus lower specific volumes than wheat bread. Flour from demonstrating higher instability, compared with wheat variety M Col 1505 performed best in the specific flour. Composite flours tend to form more stable gels, volume tests. whereas cassava flour of the same variety, after being gelatinized and reaching maximum viscosity, tends to The sensory tests included 50 surveys (hedonic continue increasing in viscosity over time. test) to evaluate four samples (the three percentages of substitution and the control) from each variety. The Composite flours need to absorb more water surveys were directed at people who regularly during processing, the need increasing as the consumed bread. They ranged in age from 14 to percentage of substitution increases. This fact is 70 and in social strata from 2 to 6. The people verified by the higher value of water absorption that surveyed only made one evaluation, so that panelists composite flours presented during the farinograph test were not repeated in the evaluation. (Table 23-7). Composite flour made from variety M Col 1505 required the largest volume of water. Results suggested that bread prepared from composite wheat-cassava flour from variety M Col 1505 Analyzing prepared breads did not present differences in acceptability to consumers, whether for aroma, flavor, crumb texture, Prepared breads (Figure 23-13) were evaluated for their and general acceptability. As a result, this variety specific volume, shelf life, and sensory tests of produced flour with the best baking quality of the three acceptance (aroma, crumb texture, flavor, and varieties evaluated. The 5% substitution was the most acceptability). acceptable overall, presenting an equal scoring or higher than the control. The 15% substitution To evaluate the presence of mold, four samples of presented the lowest values for most of the tests. each treatment were stored in individual polyethylene bags, under the same conditions (away from direct Bread rolls performed best in the acceptability light, moisture, and sources of contamination) and at tests as, according to the consumers, it presented room temperature. While the breads did not harden, minimal or no differences to wheat bread, probably most samples showed mold 7 to 9 days after because this type of bread had the highest amounts of preparation. These values were closely similar to those fat and sugar in its formula. These factors helped mask obtained for wheat bread, which showed mold after the effects of including cassava flour. The lowest values 9 days. were for the hamburger bread, where flours from most of the varieties did not please the respondents. This Results also indicated that an inverse ratio exists bread had the fewest ingredients in its formula, which between the percentage of substitution of wheat flour meant that the effects of adding cassava flour were and specific volume. The specific volumes of breads more noticeable. CONTROL 5% 10% 15 15% HMC-1 HMC-1 HMC-1 HMC-1 C0NTROL HMC-1 Sandwich Sandwich Sandwich Sandwich bread bread bread bread 5% 10% 15% CONTROL CMC-40 CMC-40 CMC-40 5% 10% HMC-1 HMC-1 Figure 23-13. Samples of sandwich, rolls, and hamburger breads prepared with composite flours, substituting 5%, 10%, and 15% of wheat flour with cassava flour. 454 Production and Uses of Refined Cassava Flour Conclusions As a result, flour from this variety presents the best baking quality of the three varieties evaluated, The microbiological quality of cassava flour can be particularly when a 5% substitution is used. improved by ensuring prior cleaning of the washing and chipping equipment and drying trays. This should be Economic indicators determined that, for the followed by efficiently washing cassava roots, processing conditions of a large bakery such as the one immersing them for 20 min in tanks containing sodium in which the experiment was developed, savings hypochlorite at 20 ppm. obtained by using a 10% substitution were about US$8,055 per year (US$1.00 = Col$1800 in 2010). From a technical viewpoint, the use of wheat- cassava composite flours at 5% and 10% substitution is References feasible and advantageous, as these present characteristics that are indistinguishable from those of Aristizábal J; Henao S. 2004. Adaptación y validación wheat bread. de tecnología para utilización de harina de yuca en panificación. In: Informe de proyecto. CLAYUCA, Of the cassava varieties used to manufacture bread Palmira, Colombia. from wheat-cassava composite flour, M Col 1505 performed best in the specific volume tests, had the Henao S; Aristizábal J. 2009. Influencia de la variedad de highest water absorption values, and did not present yuca y nivel de sustitución de harinas compuestas differences of acceptability to consumers in terms of sobre el comportamiento reológico en panificación. aroma, flavor, crumb texture, and overall acceptability. Revista Ingeniería o Investigación 29(1):39–46. Glues from Dry-Extracted Cassava Starch for Use with Corrugated Cardboard Ana Milena Bonilla and Lisímaco Alonso To identify new products and options for marketing another source of raw material for their products, thus cassava, and as part of CLAYUCA’s research and helping them to reduce costs of importing raw development activities, research was developed to materials. In particular, the “dry” process would help analyze the technical and economic viability of strengthen the role of the cassava crop as a source of producing glues from refined cassava flour and thus employment, foreign exchange, and income for the replace certain starches used in the glue industry. country’s cassava-producing sector. Cassava starch is traditionally extracted by means This feasibility study handled issues such as of a “wet” process (Chuzel 1991), where polluting extraction of refined flour and production of ultra- effluents are generated that are mostly discharged into refined flour, which is known as “dry” starch (testing rivers and other sources of water for the rural areas five selected cassava varieties). Several formulas for where starch-extraction agribusinesses are located. making two types of glues were also evaluated and Moreover, in most of these regions, water is limited and compared with commercial glues (Bonilla and Alonso does not have the quality needed for preparing a quality 2002). product. Preselecting cassava varieties A “dry” process needs to be found for obtaining cassava starch without generating polluting effluents To produce ultra-refined flour (with <100-μm diameter (Garcia 2006; Garcia et al. 2006; Herrera et al. 2007; particles), five cassava varieties were preselected from Barona and Isaza 2003) while producing a quality the elite clones group in the germplasm bank held at product that is competitive in price for use in glue CIAT (Improved Cassava Project). Criteria were amylose manufacture. Such a process would help reduce content, viscosity, high field production, and high negative environmental effects; and give industries starch yield. The varieties were HMC-1 (ICA P-13), 455 Cassava in the Third Millennium: … Table 23-11. Proximal analyses of ultra-refined cassava flours, CM 6740-7 (Reina), M Per 183 (Peruana), CM 523-7, types 1 and 2, and maize pearl starch. and M Col 1522 (Venezolana). Table 23-9 provides the values of these varieties’ principal characteristics. Identification Protein Crude Fat Ash Moisture Starch (%) fiber (%) (%) (%) (%) (%) High amylose content generates an effective glue Flour type 1 as an end product. As the glue dries, the amylose HMC-1 4.6 4.5 0.7 3.3 10 78 aligns, forming a rigid layer. Furthermore, it permits CM 6740-7 3.6 4.1 0.8 2.4 9 83 rapid evaporation of water on union, thus producing M Per 183 3.7 3.2 0.6 3.1 11 83 faster drying, that is, the amylose molecules tend to reassociate. Fast drying is an important characteristic Flour type 2 for glues used to seal cardboard boxes. HMC-1 3.9 2.7 0.7 2.5 9 85 CM 6740-7 3.1 2.6 0.7 2.2 10 85 Amylose also fulfills a very important task in the M Per 183 2.3 2.2 0.9 2.7 10 86 glue’s penetration into the paper or cardboard (Skeist 1977). Amylose is a polymer, able to recrystallize the Maize pearl 0.6 0.3 0.7 0.1 12 87 starcha starch after gelatinization, a process known as retrogradation. This is significant for the end product’s a. Sample provided by Cartón de Colombia. stability and conservation. Table 23-10 records data from amylographs of maize pearl starch in terms of percentages of protein, native or raw starches extracted from the previously crude fiber, fat, ash, moisture content, and starch. selected varieties. The ultra-refined cassava flours were obtained by As this project began, Cartón de Colombia showed classifying wholemeal flour, using meshes with 100-μm interest and offered a sample of maize pearl starch, a openings. In this study, two types of ultra-refined flours raw material used to make glues for different were handled: type 1, which came from either the total applications. This starch was characterized in terms of disintegration or grating of roots before drying in a its proximal composition and was compared with continuous artificial system; and type 2, which was different cassava flour samples. Table 23-11 lists the obtained by milling chips that were dehydrated in a compositions of the different ultra-refined flours and batch or fixed-bed dryer. This study also compared the rheological patterns Table 23-9. Characteristics of cassava varieties preselected for of maize pearl starch with those of the ultra-refined the production of “dry” cassava starch. flours of the three cassava varieties that were finally selected. The patterns for refined cassava flours were Variety Yield Dry matter Amylose (t/ha) (%) (%) significantly different to those of the native starches of these same three cassava varieties. HMC-1 20–22 34 24 CM 6740-7 20–28 36 15 The refined flour samples, without taking into M Per 183 25–40 32 22 account variety, presented a slight increase in viscosity CM 523-7 18–26 36 21 during cooling, in contrast to the native or pure M Col 1522 10–25 29 23 cassava starches, thus showing higher product stability Table 23-10. Characteristics ascertained by amylographsa of native starches extracted from previously selected cassava varieties. Variety Tgel Vmax V 90 V 90/20 V 50 tcook Gel instability Gel index (ºC) (BU) (BU) (BU) (BU) (min) (BU) (BU) HMC-1 25 507 420 280 380 13 227 40 CM 6740-7 26 420 400 241 380 15 179 20 M Per 183 25 420 400 250 320 13 170 80 CM 523-7 23 410 340 218 350 11.5 192 20 M Col 1522 20 500 420 260 345 15 240 75 a. Abbreviations Tgel refers to gelatinization temperature; Vmax, maximum viscosity; V 90, viscosity at 90 ºC; V 90/20, viscosity at 90 ºC after 20 minutes; V 50, viscosity at 50 ºC; tcook, cooking time; Gel index, gelation index. 456 Production and Uses of Refined Cassava Flour over time. Stability is higher in maize pearl starch Refined cassava flour 25% (possibly a modified starch but information not Water 75% supplied by the company). When the varieties were Calcium chloride 0.1% compared for viscosity (Table 23-12), the performance alpha-amylose 0.027% (temperature found to most resemble that of pearl starch was that of between 70 and 80 °C) variety HMC-1 for both types 1 and 2 of ultra-refined Hydrochloric acid 0.47% flour. Gelatinization temperatures were between 65 and Anti-foam 0.47% 82 °C, and maximum peak viscosity was between Sodium hydroxide 0.70% 100 and 120 BU. Talcum 5.88% Formol 4.7% Gelatinization temperature is a very important factor in starch used as raw material for glues. It varies The second formula, using chemicals, involved the with different starches, and is indispensable for application of magnetic and manual agitation in the applying the enzyme, enabling it to act effectively in laboratory. This conditioned the cassava flour with 10% starch hydrolysis. Furthermore, the lower the solids. Borax may be added to stop the sodium gelatinization temperature, the less energy is hydroxide reaction, and the anti-foam prevents froth consumed in manufacturing glues. from forming through agitation. The formula for this glue was as follows: The viscosity curve of maize pearl starch showed great stability over time to temperature changes and Refined cassava flour 10% also resistance to shearing stress over time. Similar Water 90% characteristics also appeared in samples of ultra- Anti-foam 1.5% refined flour (types 1 and 2) from variety HMC-1. Sodium hydroxide 1.5% Stability is important in most products containing starch, as it helps their conservation and good A general conclusion of this part of the study was appearance. that the ultra-refined flours (with <100-μm-diameter particles) from the three cassava varieties selected were Adjusting two selected formulas for glues suitable as raw materials for glue manufacture, using either the chemical or enzymatic method. The glues Initially, to select the glue formulas for this study, obtained were suitable for sealing cardboard boxes and several adjustment tests were carried out, taking into had characteristics that complied with the account solid contents, additives in the formula, effects requirements set by the standard sample. of different reagents used, temperature, and agitation times. The first formulation for glue, using enzymes, With the enzymatic formula, glues achieved short was as follows: fixing times because of the high solid contents, which Table 23-12. Data from amylographsa of ultra-refined flours from three selected cassava varieties and maize pearl starch. Identification Tgel Vmax V 90 V 90/20 V 50 tcook Gel instability Gel. index (ºC) (BU) (BU) (BU) (BU) (min) (BU) (BU) Flour type 1 HMC-1 82 100 90 95 100 9 5 5 CM 6740-7 80.5 95 60 90 100 11 5 10 M Per 183 67 140 140 110 140 15 30 30 Flour type 2 HMC-1 65.5 120 120 100 120 27 20 20 CM 6740-7 58 160 160 160 180 15 0 20 M Per 183 70 200 175 145 210 16 55 65 Maize pearl 79 120 110 125 120 11 5 -5 starchb a. Abbreviations Tgel refers to gelatinization temperature; Vmax, maximum viscosity; V 90, viscosity at 90 ºC; V 90/20, viscosity at 90 ºC after 20 minutes; V 50, viscosity at 50 ºC; tcook, cooking time; Gel index, gelation index. b. Sample provided by Cartón de Colombia. 457 Cassava in the Third Millennium: … Table 23-14. Relative sale prices compared for different glues generated certain advantages. These glues could used to seal cardboard boxes, Colombia, May therefore be used for boxes with a heavy carrying 2002. capacity (10–20 kg). In contrast, the chemical formula, Glue Sale price involving low solid contents, created a glue with longer (US$a/kg) fixing times (1 hour) and which was more suitable for Enzymatic formula (CLAYUCA) 0.06 boxes with a light carrying capacity (7 kg) and not Chemical formula (CLAYUCA) 0.02 requiring immediate shipping. Polyvinyl acetate (PVA) 0.28 Hot-melt adhesive (HMA) 0.69 Table 23-13 summarizes the principal Pegol 015b 0.09 characteristics of the two formulas (enzymatic and chemical), and compares them with the standard glue, a. US$1.00 = Col$1800 in 2010. b. Supplied by Industrias del Maíz S.A. that is, glue 002 made by Almidones Nacionales. Table 23-14 records the relative sale prices of several glues found on the market and used in the industry to seal cardboard boxes, and compares them with the Traditionally, the glue was based on phenol glues made from refined cassava flour. The value of the formaldehyde, a formulation that involves a high enzymatic glue was US$0.06 per kilogram. The percentage of wheat flour to help adhesion by estimated sale price of glues in this phase of the increasing the quantity of solids in the formula. project showed that incorporating cassava flour in the formula was advantageous. Laboratory tests showed that 50% of wheat flour could be replaced by cassava flour. A 100% substitution Additional activities were carried out informally to was not possible as cassava flour reduces viscosity by strengthen the potential of cassava flour for use in the 20%, compared with wheat flour. Nevertheless, cassava glue industry, and consider related possible research flour is a new alternative for reducing the costs of glue topics. However, a glue manufacturer evaluated the in the manufacture of plywoods. At the time of writing, glues and found that, overall, apparent stability was cassava flour cost US$0.31 per kilogram, while wheat good and the glue was moderately dark in color. Fixing flour cost US$0.56 per kilogram. tests were carried out for paper on paper, kraft paper on kraft paper, and kraft paper on cardboard and on References glass. Results showed excellent adhesion. A glue with such characteristics could be used to manufacture Barona SM; Isaza LE. 2003. Estudios para el desarrollo kraft paper bags and seal cardboard boxes. de un proceso de extracción de almidón a partir de trozos secos de yuca (Manihot esculenta Crantz) con In addition to manufacturing glues for sealing mínima utilización de agua. BSc thesis in Agricultural cardboard boxes, the possibility of entering the Engineering. Universidad del Valle, Cali, Colombia. agglomerate wood market (plywoods), replacing wheat (Also available in: CLAYUCA. Informe anual de flour, was proposed. In this industrial application, glues actividades. Palmira, Colombia.) must unite two faces of timber to form an agglomerate. Table 23-13. Characteristics of glues made from refined cassava flour compared with those of a standard glue (glue 002, Almidones Nacionales, Colombia). Variable Enzymatic Chemical Standarda glue glue glue Solid contents (%) 25% 10% 23% Viscosity (cP) 8000–12000 10000–18000 6000–12000 pH 7–9 10 8–9 Adhesion Good Good Good (% of scraped area) (100 s) (3600 s) (100 s) Adhesive tack Excellent Good Excellent Stability (days) 30 days 15 days 30 days a. Glue 002, made by Almidones Nacionales S.A., Yumbo, Colombia. 458 Production and Uses of Refined Cassava Flour Bonilla AM; Alonso L. 2002. Estudio de la viabilidad García JA; Gallego S; Alonso L. 2006. Establecimiento técnica, económica y comercial de la obtención de una planta piloto para la producción continúa de de adhesivos para uso en la industria de cartón harina refinada de yuca. In: Informe de proyecto. corrugado, a partir de almidón de yuca extraído por CLAYUCA, Palmira, Colombia. vía seca. In: CLAYUCA. Informe anual de actividades. Palmira, Colombia. Herrera CA; Rosillo ME; García JA. 2007. Cassava flour separation using inverse cyclone. Rev Bras Eng Agríc Chuzel G. 1991. Almidón de yuca, uso actual y potencial. Ambient 11(5):515–520. In: Yuca: Boletín Informativo. CIAT, Palmira, Colombia. 15(1):9–11. Skeist I. 1977. Handbook of adhesives. 2ed. Van Nostrand Reinhold, New York. p 192–211. García JA. 2006. Evaluación de ciclones en la clasificación de partículas refinadas de yuca. BSc thesis in Mechanical Engineering. Universidad del Valle, Cali, Colombia. Cassava Leaf Flour for Human Consumption Johanna A. Aristizábal and Andrés Giraldo Introduction Table 23-15. Nutritional value of cassava leaves, beef, and cow’s milk in accordance for a person’s Daily Reference Values (DRV). Leaves of cassava (Manihot esculenta Crantz) contain, Nutrient DRVs Cassava Beef Cow’s on a wet basis, 77% water, 8.2% crude protein, 13.3% leaves (100 g) milk soluble carbohydrates, 1.2% fat, and 2.2% crude fiber. (100 g) (100 g) Cassava leaves are regarded as a green vegetable with Calories (%) 2000 cal 4.0 7.0 3.0 a high protein concentration. They also contain Protein (%) 50.0 g 13.0 41.0 6.0 minerals such as iron, calcium, potassium, Iron (mg) 18.0 mg 42.0 18.0 0.6 phosphorus, magnesium, copper, and zinc, which are Calcium (mg) 1000.0 mg 67.0 3.0 25.0 significant in human nutrition. Cassava leaves also have Niacin (mg) 20.0 mg 17.0 36.0 1.0 high contents of vitamins, particularly beta-carotenes Vitamin A (mg) 750.0 mg 261.0 0.5 5.0 and vitamins A, B1, B2, B6, B12, and C; and of other Vitamin B (mg) 10.9 mg 28.0 10.0 4.0 vitamins, including niacin, which is a depurative and Vitamin C (mg) 60.0 mg 1036.0 0.0 0.0 powerful detoxicant; folic acid, which is a powerful anti-anemic vitamin; and pantothenic acid, which prevents deterioration in skin tissues (Guillén 2004). protein content would be reduced to 18% to 21%. An Table 23-15 shows that beef surpasses cassava inverse relationship occurs for fiber content, which leaves for protein content. However, for many other tends to be about 9% for leaf blades, but increases to nutrients such as calcium and certain vitamins, cassava 20% to 25% when the entire upper part of the plant is leaves surpass both beef and cow’s milk by large incorporated (Domínguez [1983]). Some authors margins. therefore consider that cassava leaves to have high potential as animal feed and human food. Petioles and, The nutritional composition of cassava foliage consequently, leaves, from the nutritional viewpoint, varies in quality and quantity, according to cultivar, are valuable. time of cutting, planting density, and the proportion of leaves (leaf blades + petioles) and stems. The part of Most research on the use of cassava leaves for the plant used also determines nutritional composition, human consumption has been conducted in Brazil. for example, if only leaf blades are used, protein Much of the research evaluated this product content would be 23% to 28% (dry basis). But, if incorporated into dietary mixtures that were consumed petioles and apical green branches are also included, by people with nutritional deficiencies or with health 459 Cassava in the Third Millennium: … problems because of low levels of vitamins and re-sprout for a future harvest. minerals (Brandão and Brandão 1991). The harvested plants comprised leaves (i.e., leaf Although the principal disadvantage of cassava blades and petioles) and stems. However, only leaf leaves is their HCN content, these levels can be blades were needed for the process. During selection, reduced by efficient flour preparation. In countries such only those leaves that presented the characteristic as Indonesia and Tanzania, cassava leaves are green color of the cassava leaf were taken. Those consumed fresh, like any other vegetable, after first leaves that had yellow or coffee-colored leaf blades, or cooking. In Peru, cassava leaves are consumed in showed spots were rejected. In preparing the raw capsules or tablets as nutritional supplements. material, both stems and petioles were removed manually, so to obtain only leaf blades. The use of cassava leaf flour for human consumption is not promoted or commercially Washing and disinfection. Cleaning ensured that supported in the way it should be. Not only could it be the end product presented adequate microbiological as a dietary alternative, providing nutritional benefits, and commercially acceptable characteristics according but it could also, as a byproduct, be an option for to Colombian Technical Standard NTC no. 267. This adding aggregate value to the cassava crop. The standard is used to obtain flour suitable for human inclusion of cassava leaf flour for human consumption consumption. Adequate washing reduced the microbial is a food alternative. Hence, methods and processes for population present in the raw material, thus obtaining producing high-quality flour should be established for an aseptic product. its use as a raw material in the preparation of foodstuffs such as soups, pies, and extruded products. Giraldo To wash, drinking water in a container was used. and Aristizábal (2006) therefore studied the process of The leaves were submerged for 15 min, thus removing obtaining cassava leaf flour for human consumption. impurities such as earth, insects, and larvae, and They proposed alternative uses according to end- residues of insecticides or pesticides. The leaves were product quality and determined the technical and then removed from the water and disinfected with an economic indicators for the flour’s production. aqueous solution of sodium hypochlorite at a concentration of 20 ppm. The leaves remained in the Preparing flour from cassava leaves solution for 10 min, the maximum time possible before leaf color was affected. The equipment had also been In preparing cassava leaf flour, the various stages of previously washed and disinfected with a hypochlorite operation were evaluated for the most suitable solution at 50 ppm. conditions for obtaining a quality product. Similarly, evaluations and analyses were conducted to calculate Reducing leaf size. Leaf blades were obtained in how to eliminate HCN during flour production. their entirety, which meant that they had to be treated to help eliminate HCN contents. Leaf blades were Selecting varieties. Cassava varieties HMC-1 and therefore chopped into smaller pieces, using an M Col 1505 were selected on the following criteria: industrial mill that possessed appropriate cutting blades. The chopping broke up the leaf tissues, • Availability, whereby typical cassava varieties releasing HCN, and thus ensuring that HCN levels in planted near CIAT were chosen, and the end product were lower than in the initial raw material. Different types of cuts were evaluated; the • Variety. To guarantee low HCN contents in the more finely the leaf blades were cut, the more efficient end product, sweet varieties with HCN contents was the release of HCN. of about 180 ppm and planted in inter-Andean valleys were chosen. Drying. Drying was carried out in two ways—solar and artificial drying (in a tray dryer)—to determine Harvesting, selecting, and adapting the raw which was the better method. Solar drying was carried material. Two harvests of cassava leaves were carried out on inclined trays, placing an average of 2 kg of leaf out, one at 3 months and the other at 5 months, to blades per tray. The blades remained exposed to the compare the composition (e.g., protein, fiber, and sun for 24 hours or more, depending on climatic HCN) of cassava leaves at harvest. Harvest was carried conditions. Solar drying was considered to be out by cutting the plant at a height of 30 to 40 cm inefficient and, microbiologically, the product could not above ground level to guarantee that the plant would be guaranteed to be aseptic. Artificial drying was 460 Production and Uses of Refined Cassava Flour carried out in a tray dryer with air circulation, using casein, a protein that has an almost 89% absorption rate temperatures of 40, 50, and 60 ºC. in the human organism. After leaf blades were dried by the two methods, All the diets were formulated as isoproteic and samples were collected from each test for HCN isoenergetic. The control diet was prepared with 12% analysis to determine the temperature at which the protein (casein), 10% sugar, 6% oil, 60% maize starch, enzyme linamarase acted most efficiently on 6% fibers, and 6% of a premixture of vitamins and cyanogenic glucosides (linamarin and lotaustralin) to minerals. For the diets with cassava leaves, the casein release HCN. was replaced with cassava leaf flour at the established percentages of 10% and 20%. To determine HCN contents, a protocol was established that included NaCl and activated carbon Tests were carried out with laboratory mice that during extraction to ensure that the were distributed at random in metabolic cages that were spectrophotometer readings were clear, as leaf designed especially to provide food to the animals and chlorophyll colors samples. Results indicated that collect their excreta. The animals were fed the diets over artificial drying at 60 ºC eliminates most of the HCN an experimental period of 15 days. For the first 7 days, (Figure 23-14). the mice were habituated to the diets. Over the next 8 days, samples were collected. Milling. The dried leaf blades were milled into small pieces, comparing three types of mills: blade During the experiment, three treatments were mill, hammer mill, and mill sieve. For each, evaluated: 10% cassava leaf flour, 20% cassava leaf flour, efficiency was evaluated according to the amount of and the control, each having three replications. The flour and granulometry obtained. three diets were analyzed for contents of dry matter, protein, neutral detergent fiber, and ash; and for energy. Granulometry of cassava leaf flour was The excreta were tested for digestibility of dry matter, determined, using sieves of different mesh numbers: protein, and neutral detergent fiber; and for energy. 50 (300-μm openings), 70 (212 μm), 100 (150 μm), 140 (106 μm), 270 (53 μm), and bottom. The best Habituation was necessary to ensure that the granulometry was obtained with the mill sieve, for animals’ digestive tracts were cleaned out and which almost 95% of flour passed through the no. accustomed to the treatment or diet that would be fed to 70 mesh (212 μm). them. During habituation, the animals received the food but neither the residues nor the excreta were weighed. Analyzing cassava leaf flours From the eighth day onwards, excreta from each mouse were taken, and the quantities of food provided and the Once cassava leaf flour was obtained, tests were amount left by each mouse were calculated. carried out to evaluate the digestibility of protein, dry matter, and fiber in diets. That is, for the tests, diets The excreta, collected after habituation, were were prepared, based on cassava leaf flour. For sampled and cleaned to remove hairs and food particles. comparative purposes, the control diet was based on They were then weighed and the data recorded. The excreta were kept in a freezer, in bottles that were duly marked with the corresponding mouse’s number and 25 diet. After the samples were collected, each bottle of 20 excreta was lyophilized to obtain dry and solid samples for analyses on the digestibility of each diet supplied to 15 the mice. 10 Data on the digestibility of dry matter and protein 5 (Figure 23-15) suggested that the diet with 10% leaf flour 0 is the most suitable for incorporation into a product for 30 40 50 60 70 human consumption. The level of digestibility could be Temperature (ºC) improved by mixing the leaves with food rich in Figure 23-14. Final total cyanide of dried cassava leaves at three methionine, which, in this case, is the limiting amino drying temperatures. acid (Lancaster and Brooks 1983). 461 Total cyanide (ppm) Cassava in the Third Millennium: … 100 From the nutritional viewpoint, the recommended 95 rate of including cassava leaf flour is 10%, as being the 90 most digestible. 85 80 To guarantee cassava leaf flour for human 75 70 consumption that is competitive on the market, 65 artificial drying systems must be used. Good 60 manufacturing practices must also be implemented 55 throughout production to minimize risks of 50 contamination and ensure high levels of safety and Control CLF 10% + CLF 20% + control control quality for the end product. Treatment References Figure 23-15. Dry matter ( ) and protein ( ) digestibility of diets evaluated in mice (CLF n% refers to cassava leaf flour at the percentage of substitution). Brandão CT; Brandão RF. 1991. Alimentação alternativa. Pastoral da Criança, CNBB (Conferência Nacional de Bispos do Brasil), Brasília, Brazil. Conclusions Domínguez CE, Ed. [1983]. Yuca: Investigación, Any cassava variety, either sweet or bitter, can be used producción y utilización. Centro Internacional de to obtain cassava leaf flour because the stages of Agricultura Tropical (CIAT). United Development chopping and drying guarantee an efficient elimination Programme (UNDP), Cali, Colombia. 656 p. of HCN, the contents of which are low in the end product. Giraldo A; Aristizábal JA. 2006. Estudio de la obtención de harina de hojas de yuca (Manihot esculenta Efficient washing of leaves and their later Crantz) para consumo humano. BSc thesis in immersion in sodium hypochlorite solution, together Agroindustrial Engineering. Universidad del Cauca, with a prior washing and disinfection of equipment Popayán, Colombia. used in the process, will ensure that the flour obtained from cassava leaves is of acceptable microbiological Guillén V. 2004. Maravillas curativas de las hojas de yuca. quality. Revista Interamericana Ambiente y Saneamiento A&S. Lima, Peru. p 32–36. The release of HCN is favored by the leaves being finely chopped and exposed to long drying times at a Lancaster PA; Brooks JE. 1983. Cassava leaves as human temperature of 60 °C in a dryer with forced hot-air food. Econ Bot 37(3):341–348. circulation. 462 Protein digestibility (%) CHAPTER 24 Producing Hydrated Bioethanol from Cassava Bernardo Ospina1, Sonia Gallego2, Harold Patiño3, and Jorge Luis Gil4 Introduction in developing countries, suffer severe increases in food prices that put them at risk of reduced food security Bioenergy, and biofuels in particular, have become and increased poverty. priority topics on the research and development agenda of world agriculture. Their significance lies in A major reason for giving priority to the generation their enormous potential towards overcoming problems of bioenergy and the use of biofuels on the global related to using the world’s oil reserves such as agricultural development agenda is the possibility that shrinking volumes, growing use, price increases, and these technologies can become strategies for reducing increasing emissions of greenhouse gases with poverty and overcoming the social inequalities that resultant climate change. Bioenergy can also help exist in many developing countries. More than answer the growing urgency to promote sustainable 2000 million people around the world are estimated to socioeconomic development. In particular, it can lack access to any modern energy source (UNDP provide farmers with additional employment and 2004). Hence, production technologies, and the use incomes opportunities. and marketing of biofuels, must be designed and implemented to help rural communities of few The world is demanding economic and social resources minimize their dependence on fossil energy, sustainability from the various biofuel production and permit a more equitable distribution of the benefits systems currently operating. Although the technology available along the entire agricultural production chain for producing bioethanol has partially met these for biofuels. expectations, the same cannot be said of other components of biofuel production systems. Most Rural Social Biorefineries: An Approach ethanol-producing systems are characteristically based to Small-Scale Biofuel Production on monocultures (e.g., sugarcane and maize), which create serious environmental problems in terms of Since 2006, CLAYUCA has been implementing a biodiversity loss, excessive use of water, and generation research and development project to establish a of considerable quantities of effluents with high technological platform for processing hydrated ethanol potential for contamination. Furthermore, to at the level of small rural communities. The raw implement these systems, large investments are materials used were cass ava (Manihot esculenta required, thus preventing rural communities of few Crantz), sweet potato (Ipomoea batatas (L.) Lam.), and resources from participating and benefiting from these sweet sorghum (Sorghum bicolor (L.) Moench). technologies. Indeed, such communities, usually found This initiative, called Rural Social Biorefineries (RUSBI)5, seeks to promote the development of rural 1. Executive Director, CLAYUCA, Cali, Colombia. communities of few resources and located in the E-mail: b.ospina@cgiar.org marginal regions of Latin America and the Caribbean 2. Chemical Engineer and Specialist in Postharvest Management Systems, CLAYUCA. E-mail: s.gallego@cgiar.org (LAC). The idea is to produce and use a biofuel— 3. Zootechnologist, Lecturer in Postgraduate Program in Zootechnics, Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, Brazil. E-mail: harold.patino@ufrgs.br 5. For an explanation of this and other abbreviations and acronyms, 4. Zootechnologist and Specialist in the Use of Cassava in Animal see Appendix 1: Acronyms, Abbreviations, and Technical Feed, CLAYUCA. E-mail: j.l.gil@cgiar.org Terminology, this volume. 463 Cassava in the Third Millennium: … hydrated ethanol—as the starting point for establishing Several private- and public-sector groups showed a level of agroindustrial development that will have a interest in bioethanol production from cassava, social impact on these regions. That is, it will help including farmers, businesses, universities, and farmers stimulate the economies of their regions, research centers, both national and international. They create productive employment and opportunities for were given firsthand access to the technologies income, increase security of energy, food, agriculture, developed (Ospina et al. 2008). and improve their families’ quality of life (CIAT 2011). Based on preliminary results, a small biorefinery The local production and use of hydrated ethanol is was established in 2009 at CIAT’s facilities in Palmira, the principal focus of the RUSBI approach. It involves Colombia. Technological support was received from five technological components (Figure 24-1), and Usinas Sociais Inteligentes (USI, a Brazilian private integrates modern concepts of agronomic enterprise) and the Universidade Federal do Rio Grande management, processing engineering, and effluent do Sul (UFRGS, Brazil) (Patino et al. 2009). Figure 24-2 management. The strategy is to promote, in marginal shows the equipment used in the rural social regions, self-sufficiency in energy, agricultural biorefinery, including (1) a plant to dry and refine the development, and food security (Figure 24-1). flours of cassava and sweet potato, and a plant to mill sweet sorghum; (2) a pilot plant to produce hydrated The CLAYUCA research on bioethanol ethanol (96%) at a capacity of 10 to 20 L/h; and (3) a production from cassava began in 2006 with a project plant to treat effluents. Other equipment used in the financed by the Ministry of Agriculture and Rural biorefinery included a stationary plant to generate Development (MADR, its Spanish acronym) of bioelectricity from hydrated ethanol and an ethanol- Colombia. The MADR’s support enabled the fueled stove for cooking (Figure 24-3). construction and operation of a prototype processing plant for hydrated ethanol. In this project, evaluations The small-scale operational prototype for processing were also carried out to assess the potential of different hydrated ethanol was inexpensive to construct, operate, cassava varieties as raw materials for ethanol and maintain. It is based on the use of saccharine (e.g., processing. sweet sorghum) and/or amylaceous (e.g., cassava and 1. Sustainable and competitive cassava production 2. Evaluation of processing technologies for obtaining fermentable biomasses Self-sufficiency in energy 3. Development of a model pilot plant to produce bioethanol Agricultural development 4. Evaluation of local uses for hydrated ethanol Food security 5. Sustainable management of wastes and effluents generated during processing Figure 24-1. Technological components of the Rural Social Biorefinery (RUSBI) approach. Figure 24-2. Equipment used in the Rural Social Biorefinery (RUSBI) established at CLAYUCA. 464 Producing Hydrated Bioethanol from Cassava “Clean-cook” stove Energy generator Flex tek kit Vehicle powered by ethanol from cassava Figure 24-3. Validated uses of hydrated ethanol biofuel. sweet potato) bioenergy crops as sources of substrata. Producing Bioethanol During 2009–2011, the prototype was evaluated, its operation validated, and adjustments made to perfect Figure 24-5 illustrates how hydrated ethanol is produced the process. from cassava, using the RUSBI methodology. The cassava crop is among the richest sources of fermentable CLAYUCA is now attempting to disseminate the substrata for ethanol production, having high starch model to rural communities that have limited access to content (between 70% and 85%, dry basis). electrical power, are highly dependent on fossil fuels, and, usually, depend entirely on agriculture for To produce bioethanol, cassava roots are first subsistence and income. The pilot plant’s installations converted into flour, after which, during biomass can be used for demonstrations and training activities pretreatment, water is added. The resulting liquid for groups of farmers and technicians from Colombia biomass is known as starch milk. At this stage, incubation and other countries in LAC, as well as other regions in environmental conditions (pH and temperature) must be the world facing similar problems. adjusted for the next stages: hydrolysis and fermentation. This stage can also be carried out with fresh cassava The RUSBI approach (Figure 24-4) could have high roots, which are very finely grated to facilitate the later impact on LAC’s marginal regions. Biofuel production stages of hydrolysis and fermentation. When fresh cassava from energy crops would provide access to electrical roots are used, less water is needed, as root water content power and thus open up opportunities for establishing is used. However, the mash obtained after fermentation value-added processing of crops such as flour and must be filtered, as it has high fiber content. Also, when starch products for human and animal consumption or cassava flour is used instead of fresh roots, drying leads industrial use, and organo-mineral fertilizers for to two byproducts that can be sold for use in animal feed, restoring soils and improving crop yields. thus helping to reduce the additional costs for the energy needed to convert roots into flour. 465 Cassava in the Third Millennium: … Conditioning the raw material Water Washing → Chipping → Drying → Milling Flours Cassava/ sweet potato Preparing the mash Washing → Grating Pulp Crude mash Sweet Milling Juices sorghum Enzymes Hydrolysis Sweet mash Organo-mineral fertilizers Animal feed Yeasts Fermentation CO2 Clarified Solid Fermented effluents residues mash Vinasse Treatment of vinasse Distillation Stationary motors Biopolymers Hydrated bioethanol Stoves (96%) Automobiles Figure 24-4. Schematic concept of the RUSBI approach, showing procedures, inputs, and products. Enzymes Yeast Conditioning Water CO the raw material 2 Cassava Flours Crude mash Drying and Preparing must Fermented milling Simultaneous hydrolysis and mash fermentation (SHF) Vapor Water Generation of energy Water Domestic uses Distillation Ethanol H y drated bioethanol Industrial uses (96%) Vehicular biofuel Vapor Vapor Treatment of Water vinasse Management of residues Water Solid residues Animal feed Vinasse Organo-mineral fertilizers Biopolymers Cassava roots and Clarified foliage effluents Figure 24-5. Flow chart for the production of hydrated ethanol from cassava. 466 Producing Hydrated Bioethanol from Cassava Hydrolysis is a significant phase in the process. It 1. Liquefaction, saccharification, and transforms starches into fermentable sugars, which are conventional fermentation (LSF). The starch is then metabolized and assimilated by yeasts during first liquefied, then converted into glucose (i.e., fermentation, thus generating ethanol. Enzymatic saccharified), and, finally, fermented, using the hydrolysis, or saccharification, breaks up the large yeast Saccharomyces cerevisiae (Figure 24-6). starch molecules to obtain units of glucose. Glucose syrups or sweet mash are obtained from starch Heat-stable enzymes used for liquefaction and through the liquefaction and later saccharification of saccharification are, respectively, alpha-amylose starch. Two methods of hydrolyzing starch can be and glucoamylase. Table 24-1 describes the used: Thermostable alpha-amylose Glucoamylase Yeast Recovery of alcohol Liquefaction Saccharification Fermentation Distillation and dehydration Water JET COOKER >100 ºC 5-8 min Cassava Storage tank Starch Secondary liquefaction 85 ºC 60 ºC ~90 min 8–10 h Tank for optional starch milk Effluents Figure 24-6. Conventional process for producing bioethanol from cassava (from Genencor International, a Danisco company; see www.genencor.com). Table 24-1. Operating conditions for the hydrolysis and fermentation of organic biomass in conventional processing and simultaneous hydrolysis and fermentation (SHF) processing. Conventional processing: Condition Hydrolysis Fermentation (liquefaction, followed by saccharification) T (°C) 82–86 65–70 32 pH 5.7–6.0 4.3 4.5 SHF processing: Condition Hydrolysis Fermentation (liquefaction + saccharification) T (°C) 30–33 30–33 pH 4.0–4.5 4.5 467 Cassava in the Third Millennium: … operating conditions conventionally used with evaluated as a biofuel in suitably adapted equipment, this method. selected for being commonly used by rural communities such as kitchen stoves, electrical power 2. Simultaneous hydrolysis and fermentation generators, and other motors (Figure 24-3). (SHF). A mixture of enzymes allows the saccharification and liquefaction processes to The validated uses of hydrated ethanol as a biofuel occur simultaneously (Figure 24-7). produced from the cassava crop will help rural communities have access to electrical power, enabling This method uses STARGEN enzymes (which them to establish processing enterprises to add value enable hydrolysis at low temperatures) and to their crops, and thus link with markets that will combines saccharification and fermentation afford them higher incomes and improved food security within a single stage, because the enzymes and quality of life. function under the same conditions of temperature and pH as does the yeast (i.e., Bioethanol Production Trials S. cerevisiae). Table 24-1 indicates the operating conditions used with this method. The preliminary results obtained by CLAYUCA for cassava variety evaluation in ethanol production In the RUSBI methodology to produce bioethanol, showed that enormous potential exists to exploit the CLAYUCA used the SHF method to reduce processing crop’s genetic diversity and improve the processing of time, energy consumption, and installation costs (i.e., no cassava biomass into ethanol. Considering the average need to install a heating system for the mash). The end value of starch found in the varieties analyzed, we could product of the SHF process—fermented mash—was estimate a theoretical value of 220 L/t and determine distilled at 78 °C, and its steam—ethanol—captured and an experimental value of 118 L/t to convert biomass condensed. The distillation products were therefore into ethanol. This means that real processing efficiency ethanol at 96% purity and an organic liquid byproduct represented only 54% of the theoretical potential known as vinasse. Finally, the hydrated ethanol was (Table 24-2; Arriaga 2008). Recovery of alcohol Hydrolysis and fermentation Distillation and dehydration Water Cassava Storage tank Starch Tank for starch milk STARGEN™ + yeasts Effluents Figure 24-7. Simultaneous hydrolysis and fermentation (SHF) (from Genencor International, a Danisco company; see www.genencor. com). 468 Producing Hydrated Bioethanol from Cassava Table 24-2. Comparing cassava varieties for ethanol production. Variety Production Starch Theoretical Real Efficiency Ethanol (t/ha) (%) conversion conversion (%) production (L/t) (L/t) (L/ha) CM 4574-7 25 32.3 230.6 118 .0 51 2950 CM 6438-14 26 33.3 237.8 129.8 55 3374 M TAI 8 29 31.6 225.6 129.1 57 3743 Verónica 29 29. 0 207.1 99.9 48 2897 Ginés 27 27.9 199.2 114. 7 58 3096 Average 27 ± 1. 8 31 ± 2. 3 220 ± 16. 3 118 ± 12.2 54 ± 4.2 3212 ± 350 More recent work carried out on the CLAYUCA et al. 1990). A relatively low value (61%) was also biorefinery model aimed to optimize the enzymatic obtained for the efficiency of the process in terms of hydrolysis of the starch present in cassava (Cajamarca real ethanol production versus the theoretical 2009). The efficiency of bioethanol production from conversion. This implies the presence of polluting cassava flour was also estimated at a pilot scale by agents, especially during fermentation, which either calculating the balances of materials and energy in the reduced or limited the fermentative glycolysis of process (Martínez 2009). Table 24-3 presents trials ethanol. carried out with cassava flour in the pilot plant, using the SHF method at room temperature. Table 24-4 shows the results of two trials with fresh cassava roots, using the same conditions of According to the results shown Table 24-3, the simultaneous hydrolysis and fermentation at room best results were for Trial 3. Yields were 372.5 L of temperature. ethanol per ton of flour, and 106.4 L per ton of fresh roots. These values are slightly lower than those Initially, in the real results of hydrated ethanol reported in the literature (Vinh 2003; Atthasampunna production from fresh cassava roots, no notable Table 24-3. Results of three trials for producing hydrated bioethanol from cassava flour at the CLAYUCA pilot plan. Trial 1 2 3 Raw materials Refined flour (kg) 75 86 120 Enzymes (STARGEN™) (kg) 0.375 0.428 0.600 Yeast (Ethanol Red®) (kg) 0.250 0.286 0.400 Urea (kg) 0.175 0.200 0.300 Water (kg) 400 400 400 Generated product Hydrated ethanol at 96%, v/v (L) 21.8 27.3 44.7 Quantitative analysesa Total production (liters of ETOH) 21.8 27.3 44.7 Yield (L ETOH per ton of flour) 290.7 317.4 372.5 Yield (L ETOH per ton of roots)b 83.1 90.7 106.4 Yield (L ETOH per hectare)c 2076.4 2267.4 2660.0 Efficiency in production of ETOHd 48% 52% 61% Ratio of vinasse to ethanol (v/v) 25.3 19.81 14.1 a. ETOH refers to hydrated ethanol at 96% (v/v). b. Conversion factor for fresh cassava roots to refined flour is 3.5:1. c. Average yield of cassava roots is 25 t/ha. d. Calculated as the ratio of real production to theoretical conversion. 469 Cassava in the Third Millennium: … Table 24-4. Results of two trials on hydrated bioethanol production from fresh cassava roots at the the amount of water used to produce ethanol and CLAYUCA pilot plant. effluents. Six fermentation tanks, each having a Trial 1 Trial 2 capacity of 1000 L, were used in a randomized complete block experiment design replicated over time, Raw materials with four replications per treatment. Results showed a Fresh cassava roots (kg) 300 300 37.5% reduction in the amount of water used (i.e., from Enzymes (STARGEN™) (kg) 0.380 0.380 800 to 500 L), a 107% increase of ethanol production Yeast (Ethanol Red®) (kg) 0.500 0.500 (i.e., from 21.75 to 44.94 L), and a 33% increase in Urea (kg) 0.300 0.300 processing yield (i.e., from 268.8 to Water (kg) 300 450 357.5 L/t) (Table 24-5). Generated product Hydrated ethanol at 96%, v/v (L) 48 48 Results for processing yield, using less water in the fermentation tanks, were 62% higher than the Quantitative analysesa theoretical value estimated for the evaluation of cassava Total production (liters of ETOH) 48 48 varieties (357 versus 220 L/t). They were very close to Yield (L ETOH per ton of roots) 160 160 the values used internationally to evaluate ethanol Yield (L ETOH per hectare)b 4000 4000 production from cereal grains (400 L/t) (Jansson et al. Efficiency in production of ETOHc 89% 89% 2009). Ratio of vinasse to ethanol (v/v) 13.6 16.7 a. ETOH refers to hydrated ethanol at 96% (v/v). The 37.5% drop in the amount of water used b. Average yield of cassava roots is 25 t/ha. reduced the ratio of vinasse to ethanol by 44% c. Calculated as the ratio of real production to theoretical (25.34 versus 14.09 L/L) (P < 0.05) (Table 24-5). conversion. These results are highly significant as the competitiveness of the biofuel chain in small variation is observed for the treatments tested, resulting agribusinesses is highly sensitive to the management of in a production of 160 L for 1 t of fresh roots. For Trial generated effluents, as additional resources must be 1, 13.6 L of vinasse were obtained per liter of ethanol, used to manage them according to the environmental indicating that the quantity of effluents produced per standards in force. liter of ethanol was reduced. This aspect is of utmost importance, as the disposal or management of these Analyses of the hydrated bioethanol produced effluents is critical in ethanol production. (Table 24-6) demonstrated that this is a crude redistilled alcohol of industrial use. It can be easily converted into Furthermore, Del Ré et al. (2010) conducted an a neutral rectified alcohol that meets technical experiment at CLAYUCA/CIAT to evaluate the effect of standards for pharmaceutical and potable use. Table 24-5. Production of ethanol (L), yield of ethanol (L/t of dry matter), and quantity of vinasse generated per liter of produced bioethanol. Treatmenta 1 2 3 Raw materials Refined flour (kg) 150 150 150 Enzymes (STARGEN™) (kg) 0.714 0.714 0.714 Yeast (Ethanol Red®) (kg) 0.500 0.500 0.500 Urea (kg) 0.350 0.350 0.350 Water (kg) 800 700 500 Generated product Hydrated ethanol at 96%, v/v (L) 21.75 b 27. 28 b 44.94 a Quantitative analysesb Total production (liters of ETOH) 21.75 b 27.28 b 44.94 a Yield (L ETOH per ton of flour) 268.80 b 306.60 ab 357.50 a Ratio of vinasse to ethanol (v/v) 25.34 b 19.81 ab 14.09 a a. Values in the same row with different letters are significantly different, Tukey’s at 5%. b. ETOH refers to hydrated ethanol at 96% (v/v). 470 Producing Hydrated Bioethanol from Cassava Table 24-6. Characteristics of hydrated bioethanol produced in the CLAYUCA pilot plant. Characteristic Unit Specification ANPa Result Aspect — Clearb Clear Color — Colorless to yellow Colorless Total acidity (e.g., acetic acid), max. mg/L 30.0 17.0 Alcoholic percentage % (v/v) 93.2 ± 0.4 91.3 pH — 6.0 to 8.0 Aldehydes (e.g., acetaldehyde), max. mg/L 60 29 Esters (e.g., ethyl acetate), max. mg/L 100 47.3 Methanol, max. mg/L 500 No data Higher alcohols, max. mg/L 500 163.8 a. National Petroleum Agency (ANP, its Portuguese acronym). b. Clear in color and free of water or materials in suspension. Energy Balance Total energy consumption indicates that the consumption of electrical power was 95.3 kWh or Figure 24-8 shows the energy balance for producing 342.9 MJ (1 kWh = 3,600,000 joules = 3.6 MJ), while 250 L of hydrated ethanol. The electrical power thermal energy consumption, as according to the wood consumed by equipment is recorded according to consumed, was 3932.5 MJ. In short, total energy operating time for producing cassava flour and ethanol, consumption (electrical + thermal) to produce and the thermal energy required for the boiler to 250 L of hydrated ethanol was 4275.4 MJ. generate steam. Consequently, energy consumption for processing 1 L of ethanol at the biorefinery is 17.1 MJ/L. Reception of cassava roots Washing and chipping 7.2 kWh Natural drying Feeder Mill 1 and 2 2.6 kWh 13.0 kWh Fan 1 Milling and refining Fan 2 10.4 kWh 10.4 kWh Gate tap 1 Gate tap 1 0.7 kWh 0.7 kWh Shakers Thermal boiler (wood) Power (kW) 0.25 Hydrolysis and Heating power (MJ/kg) 18.48 Time (h) 72 fermentation (SHF) Wood consumption (kg/h) 11.2 Energy (kWh) 18 Time (h) 19 Energy (MJ) 3932.5 Pump for feeding mash Water pump for boiler Power (kW) 0.37 Power (kW) 0.37 Time (h) 18 Time (h) 3 Energy (kWh) 6.66 Energy (kWh) 1.11 Water-cooling tower Reflux pump Power (kW) 0.56 Distillation Power (kW) 0.37 Time (h) 18 Time (h) 18 Energy (kWh) 10.08 Energy (kWh) 6.66 Pump for cooling water Pump for vinasse Power (kW) 0.37 Power (kW) 0.37 Time (h) 18 Time (h) 3 Energy (kWh) 6.66 Energy (kWh) 1.11 Figure 24-8. Energy balance for producing 250 liters of hydrated bioethanol at the CLAYUCA biorefinery. 471 Cassava in the Third Millennium: … If we assume a value of 1.54 MJ/L for the principal could indeed be viable, depending on the cost of agronomic operations to produce 1 L of ethanol from gasoline and the possibility of tax exemption cassava (Assis 2008), a total value (i.e., agronomic + (Table 24-8). Moreover, the study concluded that if a industrial consumption) of 18.64 MJ/L is reached. biorefinery were implemented in La Macarena, it would This indicates that if we obtain 23.375 MJ from 1 L provide 0.5% of the rural population with access to of ethanol, then the rate of return for energy is positive electrical power and that 7.3% of the volume of at 1.25. gasoline currently sold in the rural area could be mixed at 30% with ethanol. Costs of Producing Hydrated Bioethanol The study also recommended that, to improve the Based on the data obtained for the CLAYUCA project’s efficiency, improved cassava varieties must be biorefinery model (500 L/day), total production costs introduced and technological improvements in for hydrated ethanol (96%, v/v) was US$1.34/L. This converting cassava into ethanol must be identified. includes the costs of raw materials, processing, Also, farmers should receive training and support, and depreciation, and maintenance, as well as the possible their associations or small groups should be promoted. profits derived from the sale of byproducts (Table 24-7). Managing Effluents Finally, Gomes (2010) evaluated the technical and When hydrated ethanol is being produced as a biofuel economic viability of implementing a biorefinery from cassava, one aspect of considerable (500 L/day) in three rural areas of Colombia with environmental and energy sensitivity is the huge problems of self-sufficiency and/or high energy costs: quantity of effluents resulting from the process. On Puerto Carreño, La Macarena, and Leticia. The study average, for every liter of ethanol obtained, 10 to concluded that the project was not viable in Puerto 15 L are generated of an effluent, known as vinasse. As Carreño and Leticia, as production costs of ethanol described previously, vinasse is the organic liquid were not competitive with the prices of local fuels byproducts resulting from the fermentation of brought in at low cost from Venezuela and Brazil, carbohydrates (e.g., sugarcane juice and molasses or respectively. In contrast, in La Macarena, the project cassava starch milk) and later distillation of the fermented mash. The composition of vinasse is variable and depends on the characteristics of the raw materials (e.g., cassava flour or fresh cassava roots) used to produce the alcohol, and on the type and Table 24-7. Estimate of the costs of producing hydrated bioethanol from cassava at the CLAYUCA pilot plant. efficiency of fermentation and distillation (CIAT 2011). Item Cost (US$)a Vinasse is usually made up of water, mineral salts, (per liter) (%) organic matter, residual yeast, and non-fermentable Raw materials constituents. Table 24-9 presents the bromatological Cassava roots (US$0.055/g) 0.51 38.0 composition, in vitro dry matter digestibility, organic Flour production matter content, and starch content of vinasse obtained Electricity 0.02 1.5 from fermenting fresh cassava roots. Table 24-10 Labor 0.06 4.5 indicates the mineral concentration (dry basis). Ethanol production Water 0.01 0.7 Electricity 0.02 1.5 Table 24-8. Data for current gasoline prices, potential market, Wood 0.04 3.0 and costs of biofuel for each of three regions in Reagents 0.41 30.6 Colombia. Labor 0.06 4.5 Site Potential Current Cost of Subtotal for process 1.13 market gasoline price ethanol Sale of byproductsb -0.08 (L/year) (US$/L) (US$/L) Depreciation, maintenancec 0.29 15.7 Total production costs 1.34 100.0 Puerto Carreño 1,364,000 0.92 1.14 a. US$1.00 = Col$ 1800 in 2010. La Macarena 4,548,000 1.41 1.19 b. Cost recovery through sale of byproducts (375 kg at US$0.11/kg). Leticia 6,503,640 1.17 1.21 c. Depreciation: 5 years at 250 days/year; maintenance: annual at 4. 472 Producing Hydrated Bioethanol from Cassava Table 24-9. Bromatological composition (%) of vinasse produced during the processing of cassava into bioethanol. Crude protein Ash Ether extract Crude fiber Moisture IVDMDa OMb Starch 11.60 5.23 4.86 60.35 8.49 64.70 93.52 0.74 a. IVDMD refers to in vitro dry matter digestibility. b. OM refers to organic matter. Table 24-10. Mineral contents present in vinasse produced during the processing of cassava into bioethanol. P K Ca Mg S Zn B Mn Fe Cu Al Na (%) (ppm) 1.42 1.49 5.38 0.40 0.48 40.4 15.5 104.5 3305.1 14.2 3120.6 38,398.2 Mineral concentrations in vinasse from cassava Because of its high production, storing this byproduct processing are low except for Ca (5.38%), limiting their is not easy. Hence, in many places, the effluents are use as an individual product. García and Rojas (2006) poured directly on to the soil and/or into water sources reported that these effluents are deficient in elements, without treatment, polluting large extents of surface implying low fertilizer power. To supply crop needs, and ground water and heavily affecting the large quantities must therefore be applied. However, environment. they are extremely acid and have a high electrolytic concentration, which may favor their use over other With the growth in the production and use of byproducts. biofuels, the search for methods to treat and use vinasse has increased. This means that technologies Most of the chemical components of vinasse are for their use are available, such as fertilizer applications; chelants, enabling the formation of organic complexes production of biogas, compost, unicellular protein (i.e., with nitrogen and other minerals of greater SCP), and animal feed; energy generation; brick bioavailability for animal nutrition. However, vinasse production; concrete reinforcement; and production of also contain typical chemical components, including chemical compounds. Technologies for managing soluble inorganic substances (particularly ions of K, Ca, vinasse include recirculation to reduce volumes to 2 L and SO4), dead yeast cells, organic substances resulting of effluents per liter of ethanol, with 60% total solids from the metabolic processes of yeasts and polluting content, thus facilitating transport, storage, and use. microorganisms, alcohol and residual sugars, insoluble organic substances, and volatile organic substances. Concentrating vinasse by evaporation has high energy cost and requires chemical compounds to Vinasse is one of the most polluting organic wastes periodically wash the system to eliminate deposits of for the planet’s flora and fauna, as they present high non soluble salts in the evaporation tubes. Another organic matter contents, which are measured in terms technology for treating vinasse is methanization or of chemical oxygen demand (COD) and biological anaerobic degradation, which not only removes more oxygen demand (BOD). Values range from 24,635 to than 90% of the BOD and 70% of the COD, but also 65,457 and 26,500 to 33,600 mg of O2 per liter, generates methane gas, which can be used as fuel. A respectively. Effluents also contain high concentrations further alternative is composting for use as fertilizer. of fixed soluble solids (1400 to 2000 mg/L), low This use, despite being more environmentally friendly, electrical conductivity (2.6 to 4.2 mS/cm), very low pH demands high levels of capital, area, and time to (3.6 to 3.8), high concentrations of phenols (478 to operate. 541 mg gallic acid equivalents/L), absence of a buffer capacity because of low pH, and contents of To treat and use effluents generated in ethanol phosphates and sulfates that range between 290 and production, no simple techniques of bioremediation 1705 mg/L, and 308 and 946 mg/L, respectively (filtration) are available that comply with environmental (Robles and Villalobos n.d.). standards, as the particle sizes of most of the solids found in solution are extremely fine. In the RUSBI The principal problems are that, for each hectoliter methodology, vinasse is treated with biopolymers. (hL) of ethanol produced, about 15 hL of vinasse are These electrically charged chemical compounds are obtained as residues (Lezcano and Mora 2008). prepared from starch, and are used to guarantee the 473 Cassava in the Third Millennium: … controlled release of nutrients from fertilizers, reduce generated new ecological alternatives for managing erosion, increase the penetration of water into soil, and wastes generated by alcohol distilleries at the national improve the germination rate of seeds. level. One was to process cassava products (i.e., roots and foliage) on an industrial level, together with When biopolymers come into contact with vinasse. That is, they are incorporated into protein and solutions carrying high loads of ionic solids and basic energy supplements for ruminants, or are prepared pH, they foster flocculation and later coagulation of fertilizers from agroindustrial residues of cassava these loads. After the organic matter in the effluents production. The effluents and substrate wastes can flocculates and coagulates and the resulting sludge is therefore be used for irrigation and soil fertilizer removed, the clarified liquids may be used for other applications, and the production of compost, biogas, activities in the distillery or irrigation. yeasts, and animal feed (Figure 24-10). To flocculate and coagulate vinasse, the The first efforts were directed towards preparing biopolymers used are prepared to a concentration of solid organo-mineral fertilizers (Tables 24-12 and 24-13 1000 ppm and added to the effluents, generating and Figure 24-11). Table 24-13 shows the values, clarification. The products obtained are called clarified obtained in laboratory, for the chemical composition of vinasse and clarified sludge. Figure 24-9 illustrates the organo-mineral fertilizers prepared from vinasse decanting of solids from the effluents, and Table 24-11 produced during cassava processing, plus the addition lists the nutrient contents present in each clarified of minerals, cassava wastes, and polymers. Because product, from sugarcane biofuel processing (Patino et al. 2007). Table 24-12. Experimental formula of an organo–mineral fertilizer based on vinasse produced during the CLAYUCA in collaboration with Soil Net–Polymer processing of cassava into bioethanol. Solutions (a private U.S. company in Madison, WI, Raw material Inclusion (%) Contribution (%) of: USA; www.soilnetllc.com) and the Universidade Federal do Rio Grande do Sul (UFRGS, Porto Alegre, Brazil), N P2O5 K2O Vinasse 15.80 0.27 0.51 0.80 Cassava wastes 25.00 0.10 — — Vinasse Urea 20.00 9.20 — — Elevated pH KCl 19.00 — — 9.50 (6–7) Triple Agitation (100 rpm) superphosphate 20.00 — 9.20 — for 2 min Polymer 0.20 — — — Biopolymer Total 100.00 9.57 9.71 10.30 (concentration 1000 ppm) Agitation (100 rpm Table 24-13. Chemical composition (%) of an organo–mineral for 2 min fertilizer, based on crop wastes and vinasse produced during the processing of cassava into Clarified sludge Clarified vinasse bioethanol. Moisture Ash C N P K Ca Mg Total S Figure 24-9. Sequence of clarification of vinasse, using biopolymers. 9.22 28.58 30.10 6.48 6.04 1.26 6.55 0.33 0.40 Table 24-11. Nutrient contents present in vinasse and clarified byproducts formed during the processing of sugarcane into bioethanol. Description Total Total Total Total S Fe Cu Na Zn Protein OMa P K Ca Mg (%) (%) (%) (mg/kg) Sugar cane vinasse 2.97 10.24 0.88 1.14 1.23 986.0 6.0 3066.0 54.0 6.95 56.83 Clarified sugar cane vinasse 0.00 1.06 0.48 0.12 0.14 32.0 0.0 366.0 3.0 0.81 6.79 Sugar cane clarified sludge 2.75 2.99 14.26 0.20 9.30 525.0 47.0 467.0 19.0 5.15 27.51 a. OM refers to organic matter. 474 Producing Hydrated Bioethanol from Cassava Flocculation and coagulation Clarified vinasse Vinasse Clarified Biopolymers sludge Nutritional supplements Animal feed Cassava roots and foliage Organo-mineral materials Mixed Pressed Organo-mineral fertilizers Crops Figure 24-10. Management of wastes and effluents in the RUSBI methodology, established at CLAYUCA. Figure 24-11. Final appearance of the organo-mineral fertilizer produced from crop wastes and vinasse produced during the processing of cassava into bioethanol. the mineral contents of the vinasse are low, minerals extent, pigs and poultry. For cattle, the vinasse is used must be added to the end product. as a raw material to prepare nutritional supplements, which may have various presentations according to the Animal feed prepared from vinasse has been type of production. Organic matter is sourced from mostly directed towards ruminants and, to a lesser vinasse, other byproducts, derivatives, and leaves, 475 Cassava in the Third Millennium: … Table 24-14. Bromatological composition (%) of supplements for stems, and bagasse from sweet potato, cassava, and ruminants and prepared from byproducts, sweet sorghum. These, together with urea, minerals, derivatives, and effluents of ethanol production. and additives, are incorporated into supplement Nutrient Protein Energy preparations for ruminants (Figure 24-12). Block Salt Block Salt Table 24-14 presents the results of bromatological Dry matter 78.01 93.44 78.99 94.15 analyses of the prepared supplements (protein-mineral Organic matter 67.59 59.43 67.67 65.04 and energy-mineral), using the strategy described Protein 33.07 39.51 9.61 17.20 above. Fat 0.82 2.20 1.30 1.59 TDNa 65.54 64.26 69.91 65.54 Nutritional blocks prepared from vinasse and a. TDN refers to total digestible nutrients. wastes of ethanol production are highly palatable to animals (Torres 2010). They also present high levels of in vitro dry matter digestibility (ranging between Conclusions 71 and 78%), which is very attractive to the national market. When levels of crude protein increase in The goal of a Rural Social Biorefinery (RUSBI) is to use vinasse, this may be attributed to the presence of yeast several types of biomass (e.g., cassava, sweet potato, wastes. These enrich the product, enhancing its value and sweet sorghum) to produce ethanol for energy (Loaiza 2008). generation and, at the same time, use the various derivatives and wastes generated to obtain a range of The microbiological quality of prepared byproducts, thus maximizing the added value of the supplements made from vinasse is adequate, according raw materials. to Loaiza (2008) and Torres (2010). Their observations of the products under different storage conditions Partial results from studies conducted by suggested that their microbiological quality complied CLAYUCA in Colombia to evaluate cassava in the with the guidelines established by the Colombian production of hydrated ethanol suggested that Institute of Agriculture (ICA, its Spanish acronym, and enormous potential exists. The cassava crop’s genetic entity that governs the standardization of animal feed in diversity must be explored and the processing of the Colombia; see www.ica.gov.co). That is, the products, biomass into ethanol in the pilot plant optimized. stored under conditions established by the Good Further, more detailed, studies are needed on the Manufacturing Practices for Animal Feed (BPFA, its balance of mass and energy and on bioeconomic Spanish acronym), maintained acceptable efficiency to define energy expenditure and the cassava microbiological status for 40 days. crop’s economic viability as a raw material for ethanol production. Adding protein-mineral supplements in feed for calves (Gil et al. 2007) and young bulls (Campos et al. The economic and environmental sustainability of 2007) consuming poor quality feed led to liveweight the RUSBI will depend on the correct use of gains of between 350 and 550 g/day. This is similar to byproducts and wastes generated by the process. gains obtained with the more costly commercial Hence, more studies are needed to characterize these supplements found on the market. materials and propose alternative uses. Nutritional blocks Pellets Meal Figure 24-12. Animal feed products manufactured from crop wastes, byproducts, and vinasse produced during the processing of cassava into bioethanol. 476 Producing Hydrated Bioethanol from Cassava The incorporation of the biorefinery concept into CIAT (International Center for Tropical Agriculture). 2011. biofuel production has high potential to revitalize Linking the poor to global markets: Pro-poor social-inclusion programs, adding value to products, development of biofuel supply chains. In: Final report. and fostering the socioeconomic development of family CLAYUCA, Palmira, Colombia. agriculture. Hence, the RUSBI approach obviously implies the inclusion of sustainability of the Del Ré D; Patino H; Ospina B; Gallego S; Cajamarca environment and the socioeconomic development of JA. 2010. Efeito da diminuição na utilização de rural communities where such biorefineries are água sobre o rendimento na produção de etanol a established. partir de mandioca (Manihot esculenta Crantz) em micro-usinas. Department of Zootechnics of the Rural social biorefineries can, in the future, Universidade Federal do Rio Grande do Sul (UFRGS), become key components for the development of Porto Alegre, RS, Brazil. (Also presented as a poster integrated production models for food, raw materials, at the Simposio Estadual de Agroenergia—Reuniões feed and fuels, especially at the level of small rural Técnicas de Agroenergia (3°), da Mandioca (10°) e communities located in marginal areas and with little Batata-doce (2°) held in Pelotas, RS, Brazil.) access to conventional energy sources. García A; Rojas C. 2006. Posibilidades de uso de la vinaza References en la agricultura de acuerdo con su modo de acción en los suelos. Nota técnica. Tecnicaña 16:3–13. Arriaga HA. 2008. Análisis estadístico y producción en laboratorio de etanol de yuca (Manihot esculenta Gomes AR. 2010. Avaliação de implementação de Crantz) fresca y seca de diferentes variedades biorefinarias rurais e sociais na Colômbia. MSc thesis de Colombia. MSc thesis in Environmental in Food Engineering. Universidade Técnica de Lisboa Sciences. Wageningen University, Wageningen, the (UTL), Lisboa, Portugal. Netherlands. Gil JL; Campos R; Giraldo L; Patino H; Perilla S. Assis D. 2008. Análise energética de sistemas de 2007. Desarrollo y evaluación de un suplemento produção de etanol de mandioca, cana-de-açúcar utilizando la planta integral de yuca y subproductos e milho. Universidade Estadual Paulista “Júlio de de la agroindustria de la caña de azúcar. Revista Mesquita Filho” (UNESP), Botucatú, SP, Brazil. Colombiana de Ciencias Pecuarias 20(4):623. (Also presented as a paper at the IX Encuentro Atthasampunna P; Liamsakul W; Artjariyasripong S; Nacional and the II Internacional de Investigadores Somchai P; Eur-aree A. 1990. Cassava ethanol de las Ciencias Pecuarias [ENICIP] held in Medellín, pilot plant: a demonstration project for upgrading Colombia.) of cassava wastes and surpluses by appropriate biotechnology. Doc. 7924 e. Microbiological Jansson C; Westerbergh A; Zhang J; Hu X; Sun C. 2009. Resources Centre (MIRCEN) of the Thailand Institute Cassava: a potential biofuel crop in China. Appl of Scientific and Technological Research (TISTR), Energy 86:S95–S99. Bangkok, Thailand. Lezcano P; Mora L. 2008. Las vinazas de destilería de Cajamarca JA. 2009. Optimización de la hidrólisis alcohol contaminación ambiental o tratamiento para enzimática para la producción de bioetanol a partir evitarlo. In: Proc Encuentro de nutrición y producción de yuca. BSc thesis in Agroindustrial Engineering. de animales monogástricos held in La Habana, Cuba. Universidad Nacional de Colombia, Palmira, Instituto de Ciencia Animal (ICA), San José de las Colombia. Lajas, Cuba. p 48–52. Campos R; Castrillón MI; Giraldo L; Patino H; Ocampo ID. Loaiza JK. 2008. Usos de los subproductos de la caña 2007. Comparación del uso de suplemento proteico en la elaboración de dos suplementos nutricionales de yuca en un sistema de bovinos en el Valle del para rumiantes en el Valle del Cauca. BSc thesis in Cauca, Colombia. Revista Colombiana de Ciencias Food Engineering. Universidad de Caldas, Manizales, Pecuarias 20(4):617–618. (Also presented as a paper Colombia. at the IX Encuentro Nacional and the II Internacional de Investigadores de las Ciencias Pecuarias [ENICIP] held in Medellín, Colombia.) 477 Cassava in the Third Millennium: … Martínez GM. 2009. Determinación de la eficiencia en la Robles V; Villalobos F. n.d. Vinazas mezcaleras: producción de bioetanol a partir de yuca mediante un problema de contaminación ambiental. (Available balances de materia y energía. BSc thesis in at www.utm.mx/~mtello/Extensos/extenso Agroindustrial Engineering. Universidad Nacional de 080109.pdf; accessed 27 January 2011.) Colombia, Palmira, Colombia. Torres LA. 2010. Elaboración de bloques nutricionales a Ospina B; Gallego S; García JA. 2008. Diseño, partir de residuos de la agroindustria de la caña de construcción y puesta en operación de una planta azúcar. BSc thesis in Food Engineering. Universidad prototipo para la producción de alcohol carburante a de Caldas, Manizales, Colombia. partir de yuca y otras materias primas. In: Informe de proyecto. CLAYUCA, Palmira, Colombia. UNDP (United Nations Development Programme). 2004. Energy for sustainable development in Asia and Patino H; Gil JL; Espinosa JD; Loaiza JK. 2007. Protocolo the Pacific Region: challenges and lessons from para el desarrollo y la evaluación de suplementos UNDP projects. New York, USA. (Available at nutricionales para rumiantes elaborados a partir http://www.undp.org/energy/esdasiapac.htm; de subproductos de la agroindustria de la caña de accessed 21 March 2008.) azúcar. In: Informe de proyecto. CLAYUCA, Palmira, Colombia. Vinh NT. 2003. Ethanol production from cassava. In: Jacques KA; Lyons TP; Kelsall DR, eds. The alcohol Patino H; Ospina B; Gallego S; Payán JS. 2009. BIRUS- textbook, 4th edn. Nottingham University Press, Biorefinarias rurais sociais: Uma proposta para o Nottingham, UK. p 59–64. etanol social. In: Proc First Simpósio Brasileiro de Agropecuária Sustentável, Agricultura, Pecuária e Cooperativismo held in Viçosa, MG, Brazil. Departments of Zootechnics and Rural Economics of the Universidade Federal de Viçosa, Viçosa, Brazil. p 283–298. 478 CHAPTER 25 Conserving and Treating Fresh Cassava Roots Teresa Sánchez1 and Lisímaco Alonso2 Cassava (Manihot esculenta Crantz) is an important • Polyphenols—the most important—are and economic food source of calories, especially for involved in the postharvest physiological the low-income population of the tropics. Scientists deterioration described above. have accordingly made major efforts to develop higher • Tannins, which are found in low concentrations yielding varieties and design appropriate low-input in fresh parenchyma, but in larger quantities in technologies that improve crop production. The the peel. on-farm application of these technologies has triggered significant production increases. • Dry matter (DM), which accounts for 30%–45% of the parenchyma. Carbohydrates (the non- Because cassava is increasingly used as human nitrogen fraction) account for 90%–95% of the food and in other fields, special attention should be DM (Table 25-1). given to the development and transfer of different postharvest technologies to solve the problem of the • Cyanide (CN-), a radical that generates toxic fast deterioration of cassava roots once harvested. compounds at certain levels, which is found in Postharvest deterioration not only increases production variable amounts in cassava roots. It is found costs and risks, but also causes considerable losses to mainly as a cyanogenic glucoside known as wholesale dealers and retailers. As a result, high linamarin (90%), with the rest being free marketing margins are created for this crop to cyanide. compensate the appreciable volume of roots lost. To help solve this problem and increase the demand and marketing options for cassava, the Centro Table 25-1. Chemical composition of cassava roots. Internacional de Agricultura Tropical (CIAT)3 and other Root component Contents research entities have developed ways of conserving harvested cassava roots that are low cost and allow Energy 1460 calories/kg long-term storage. Water 66.00% Carbohydrates 35% Physicochemical Composition of Roots Protein 1.2% Fat 0.2% Cassava roots are rich in calories, but deficient in Fiber 3.1% proteins, fats, minerals, and vitamins. Root tissues also Ash 1.9% contain several secondary compounds: Calcium 330 mg/kg Iron 7 mg/kg Phosphorus 440 mg/kg 1. Chemist, Head of the Quality Control Laboratory, Cassava Improvement Project, CIAT, Cali, Colombia. Vitamin A 0.21 mg/kg E-mail: t.sanchez@cgiar.org Thiamine 0.6 mg/kg 2. Agricultural Engineer, Postharvest Management Systems, Riboflavin 0.8 mg/kg CLAYUCA, Cali, Colombia. E-mail: l.alonso@cgiar.org 3. For an explanation of this and other acronyms and abbreviations, Niacin 6 mg/kg see Appendix 1: Acronyms, Abbreviations, and Technical Vitamin C 360 mg/kg Terminology, this volume. 479 Cassava in the Third Millennium: … The characteristics described above vary according Storage in an atmosphere of nitrogen or vacuum to variety and factors such as plant age, soil type, eliminates environmental oxygen. This isolation can also fertilizer applications, and harvest time. be achieved by covering cassava roots with thin layers of paraffin that act as an artificial barrier to oxygen. Root Deterioration Roots may also be stored at low temperatures to After harvest, cassava roots may undergo two types of inhibit enzymatic processes. At 2 ºC, polyphenoloxidase deterioration: one physiological and the other and other related enzymes forming the typical pigments microbial. of physiological deterioration are inhibited. Physiological deterioration Microbial deterioration Physiological deterioration appears first with different Microbial decomposition begins on days 5 to 7 after root tissues acquiring a blackish-blue color, especially harvest. It initially manifests as a vascular streak, similar near the xylem (Figure 25-1). This is caused by a to that observed in physiological deterioration, and then postharvest accumulation of certain phenolic becomes a moist rot, with fermentation and maceration compounds that, when polymerized, form the blackish- of tissues (Figure 25-2). blue pigment. Microbial deterioration is related to the activity of Visible signs of physiological deterioration appear several pathogenic microorganisms and is therefore from 24 to 48 h after harvest. Before these signs accelerated in an environment with high relative humidity appear, roots show brilliant blue fluorescence under and temperatures, especially in physically damaged roots. ultraviolet light because of the accumulation of a Etiological studies have isolated, from affected tissues, phenol known as scopoletin. This fluorescence is a fungi of the genera Penicillium, Aspergillus, Rhizopus, sure indication that deterioration has started. and Fusarium, as well as several species of bacteria of the Physiological deterioration starts rapidly in wounds, genera Bacillus, Pseudomonas, and Corynebacterium. which almost always occur in the root’s distal and proximal extremes during harvest. Root Quality Physiological deterioration involves enzymatic Quality comprises all the conditions and characteristics reactions that need oxygen to develop. Therefore it can of a product, including its internal composition—enforced be prevented by impeding the access of oxygen to through legal provisions—and meeting consumer parenchymatous tissues or by inhibiting enzymatic preferences or acceptability. Even if a product complies reactions. Knowledge of these mechanisms led to the with legal provisions, it may, nevertheless, be rejected by design of storage systems in which factors favoring the consumer because of its color, smell, or flavor. Roots deterioration in roots are eliminated. For example: must therefore undergo adequate treatment to meet the requirements of the markets in which they are to be A B offered. A B Figure 25-1. Physiological deterioration gives tissues close to the xylem a dark blue color (arrows): cross-sectional Figure 25-2. Microbial deterioration first appears as vascular cut (A) and longitudinal cut (B) of a cassava root. streaking (A) and then as moist rot (B). 480 Conserving and Treating Fresh Cassava Roots Quality criteria for roots as demanded by the fresh Morphological quality market are rigorous even though they vary considerably from region to region. Good root quality is usually Morphological quality has to do with certain associated with the following aspects: low cyanide characteristics of the shape of the root that, depending content, intermediate DM and starch contents, on the variety, determine its suitability for conservation. acceptable culinary quality, and resistance to The principal aspects affecting morphological quality deterioration. Total cyanide content of pulp for fresh- include: root consumption should not exceed 60 ppm. Cooking the roots eliminates the cyanide from the pulp tissue. • Shape of roots. Cylindrical or conic roots, with well-developed peduncles, are highly desirable Culinary quality because they suffer less physical damage during harvest and storage. Round roots are Culinary quality refers to the time required to cook or also preferable because roots with imperfect prepare the roots as well as their acceptance by shapes may suffer damage to the peel during consumers. To determine the culinary quality of a given transportation and storage. cassava variety, several plants are selected at random from the plot, their roots harvested, and then various • Length of peduncles. Long peduncles are roots selected at random for cooking. better than short ones because it is difficult to separate the latter from the stump and, once For cassava, good cooking quality depends on: separated, the peel almost always breaks and the parenchyma is damaged. • Cooking time: after 30 min of cooking, its consistency is between hard and very soft. • Length of roots. Rather long roots are undesirable as long roots break easily during • Flavor: neither bitter nor sweet. Bitterness harvest (Figure 25-3). indicates that the roots have high hydrocyanic acid (HCN) content, whereas sweetness indicates The previous criteria indicate that the most high sugar content. appropriate cassava varieties for conservation are those with medium-sized roots and well-developed peduncles • Fibers: no fibers should be present nor should the parenchymatous tissues be lignified. Peduncle development Capacity for Notes • Consistency: cooked pulp should be firm, conservation without hard parts or a glassy appearance; the Well √ starch should be white or yellowish in color, formed never transparent. Hard to detach Poorly X from stem These factors are mostly detected during without formed damaging it consumption of the cooked cassava and cannot be distinguished by observing the roots’ external appearance. Root shape √ In brief, quality factors and conditions of cooked Cylindric cassava should be as follows: Quality factor Conditions Conic √ Cooking time <30 min (parenchyma) Flavor Neither bitter nor sweet Consistency Firm Round Fibrousness Absent X Tends to crack Starch color White or yellow Figure 25-3. Characteristics of the cassava root peduncle and shape that make roots apt for conservation (X = not suitable). 481 Cassava in the Third Millennium: … (Figure 25-4). These roots suffer less physical damage refined techniques have limitations, some because of during harvest, selection, and storage. their high costs. Furthermore, the simplest techniques have not been disseminated in agricultural practice, Sanitary quality despite satisfactory results obtained at experimental levels. Depending on duration, there are three types of Healthy roots do not present external or internal rot. To root storage: short-, medium-, and long-term. ensure quality, any root presenting rot must be discarded, as only one, even with an incipient disorder, Short-term storage (7 to 10 days) overcomes some may cause the complete loss of an entire root lot. of the obstacles currently hindering cassava marketing and can reduce losses by deterioration that tend to Such rots are not always easy to detect. Internal rot occur before the product is sold. This is a feasible due to cassava root smallpox is transmitted through a system that should meet the following requirements: subterranean burrower bug (Cyrtomenus bergi). The rot is not visible on the outside, and roots must be • Be low-cost peeled to evidence the rot (Figure 25-5). Some stem • Be easy to apply and readily adaptable to the diseases can infect roots through the lignified current marketing system peduncle. Therefore roots must be carefully selected • Prevent physiological and microbial deterioration after harvesting. of roots by favoring the healing of wounds • Be easy to transport Storing Fresh Cassava • Conserve the roots’ culinary quality and appearance To date there is no universal technique to conserve cassava roots for commercial use. Even the most Medium-term storage (2 to 3 weeks) tends to be more expensive and complex than short-term storage. Its principal objective is to provide conditions so that root wounds are healed, stopping the advance of physiological and microbial deterioration. Roots should still be easy to transport and root quality should remain unchanged. Examples of this type of storage are systems involving the application of paraffin, wax, and the use of boxes containing wet sawdust. Long-term storage can conserve roots for more than 3 weeks. It is unlikely that this system will be used because of the difficulty of maintaining root quality over prolonged time periods, as the roots usually acquire a sweet flavor due to starch hydrolysis. Furthermore, the Figure 25-4. Medium-sized roots with a well developed peduncle probability of loss due to microbial deterioration conserve better. increases. Freezing is a good example of a long-term storage system that avoids these effects; however, it is expensive and only economical when roots are destined for export or supermarkets, in which case costs are not a significant factor. Traditional methods Traditional storage techniques are simple. For example, small quantities of roots are buried, covered with mud, or stored in water. These methods are successful because storage conditions are propitious for healing any wounds that the roots may have. They are inappropriate, however, for storing large amounts of cassava and much less if the storage period is Figure 25-5. Root affected by the cassava smallpox disease. prolonged. 482 Conserving and Treating Fresh Cassava Roots Field silos. The earthen and straw silos used to Palmira. Cassava roots are packed in wooden boxes preserve potato have been tested for storing cassava measuring 50 cm long, 29 cm wide, and 30 cm high, roots. The silo is built on dry and leveled land. Inside containing sawdust to one-third the depth. Humidity the silo, fresh roots are conically piled on a circular bed in the box should be 50% to favor the healing of root made of straw or dry cane or grass leaves, then covered wounds and to prevent excessive moisture loss first with straw, similar to that used at the base, followed (Figure 25-7). The moisture in the sawdust should be by earth. A drainage ditch is then dug around the silo carefully controlled: if too dry, then the wounds are (Figure 25-6; Booth 1977). not healed and the physiological deterioration of the roots occurs rapidly. If too moist, there is excessive The silo maintains high environmental humidity. development of secondary roots and roots present Under suitable conditions, root wounds caused during severe rot. harvest and transportation are healed by the formation of a waxy substance called suberin. Roots conserve well The box is sealed with a wooden top, placed in for 4 to 6 weeks, time after which starch content drops the shade or in the field, and covered with a slightly and sugar content increases proportionately. waterproof cloth. Under CIAT conditions, the internal These changes, however, do not affect the final quality temperature varies between 24 and 28 ºC when the of the roots. The healing and storage period may vary roots are placed in the shade, or between 26 and with silo design and prevailing conditions in the region. 34 ºC when they remain in the open field. The results of storing cassava roots in silos under In experiments conducted with this storage environmental conditions different from those of system, the quality of about 75% of the roots was still CIAT–Palmira (mean temperature, 26 ºC and 70% acceptable after 4 weeks of storage. However, if there relative humidity) may vary greatly. In some cases, 80% is a delay of even 1 day between harvest and of the roots were healthy after 1 month of storage, but packaging, this percentage is reduced by as much as in others, all roots presented symptoms of 49%. Sawdust is the major drawback of this storage deterioration. This variation is related to the system because it contains insects and fungi and temperature and relative humidity of the storage period. increases transportation costs. In practice, this In cool humid periods, storage results can be method has been little used. satisfactory, but in dry hot periods when temperatures may rise rapidly and remain at more than 40 ºC, almost Modern methods all the silage could be lost. Better results are obtained with silos that have openings to allow the entry and exit Polyethylene bags. This new method of storing of air. cassava roots addressed important issues such as time between harvest and packaging, effect of the Silos were first used to store cassava roots in 1974. sun on root quality, and required activity This method had proven efficient at the experimental coordination. level, but has not yet been applied in the field. Wooden boxes. This method has proven to be very effective under the environmental conditions of CIAT– Earth 25 cm Straw 25 cm Cassava Drainage control √ 2 cm 9 50 cm 12.50 m Figure 25-6. Cross-section of a pyramidal silo for storing cassava in the field. Figure 25-7. System of storing cassava roots in wooden boxes. 483 30 cm Cassava in the Third Millennium: … The latter is decisive: harvesting, packaging, and roots. Figure 25-9 shows different levels of damage treatment should all be done rapidly and efficiently. To and how they affect cassava’s suitability for achieve this, workers are divided into groups, with each conservation. group being assigned a task (or stage), for example, harvesting, selection, packaging, treatment, sealing, Roots are harvested manually, separating the root and transportation. As a result of this coordinated from the stem (or stump) using a machete or effort, there is: secateurs. The latter tool is more adequate, as a more precise and careful cut causes less damage to the root. • A continuous, more efficient flow of work, with A small piece of peduncle is left on the root so that the safer results. The opposite would occur if all the parenchyma is not exposed to air (Figure 25-10). workers worked simultaneously on one stage of the process. Selection of roots. Harvested cassava is classified into three categories (A, B, and C) according to root • No accumulation of cassava roots from stage type (commercial or noncommercial) and magnitude to stage. of physical damage received (Table 25-2). • Minimal damage of harvested roots when Overall, for category A, from 80% to 90% of the activities must be suspended because of rain or roots are commercial and show little or no physical other causes, due to the short time that elapses damage, making them suitable for treatment and between harvest, packaging, and treatment. conservation. Figure 25-8 shows the stages of this method. For category B, a smaller volume of roots is classified as commercial but the severe damage they Harvesting of roots. Roots are harvested when plants are between 8 and 12 months old, that is, when yields are the highest. Care should be taken during Capacity for harvest to avoid breaking or physically damaging the conservation Absence of peel √ Harvest Bark √ Selection √ Pulp X Packaging X Application of treatment X Transportation of bags and X marketing Longitudinal wound Figure 25-8. Flow of activities involved in the conservation of Figure 25-9. Conservation capacity of roots taking into account cassava in polyethylene bags. damage suffered during harvest (X = not suitable). 484 Conserving and Treating Fresh Cassava Roots at the harvest site during the early morning, late afternoon, or under shade. Materials and equipment for treatment. A minimum amount of equipment and additional materials must be available at the operations site, including: • A high-pressure pump or back sprayer, with a maximum capacity of 20 L. • A fungicide, usually Mertect 450 FW, to apply to roots. Figure 25-10. A good harvest practice is to leave a piece of peduncle adhered to the root. • Polyethylene bags. Two types are generally used: 4-kg bags, 0.4 mm thick, measuring 21 × Table 25-2. Categories in which cassava roots are classified 12 cm, and 12-kg bags, 0.6 mm thick, according to use. measuring 21 × 48 cm. The bag size used will depend on market needs. Category Use of root Physical damage Frequency to root in lot • Labels that provide the following information: A Commercial Slight or none 80%–90% name of company distributing the cassava, B Commercial Severe 5%–10% harvest and packaging dates, weight of content, C Noncommercial Present or absent 5%–10% guaranteed shelf life, and instructions for proper handling of product. This information can also be printed directly on the polyethylene bags. present renders them non-apt for conservation. The frequency of roots falling into this category probably • An easy-to-handle scale, in good conditions. increases during summer months when harvesting is more difficult. Category B cassava has several potential • Staplers adequate for the type of packaging uses: for sale in the fresh-root market for human used, with sufficient replacement staples or consumption, as ensilage, as raw material for animal fasteners. feed companies, or in starch production. Procedure. The following steps are involved: Noncommercial roots (category C) can be used for packaging of selected cassava roots, treatment with some of the above-mentioned uses, thus taking fungicide, and preparation of bags for transportation to advantage of the entire harvest. marketing sites. Packaging and treatment. Several aspects • Only package undamaged, previously selected, should be considered during this stage, as follows: commercial-sized roots (Table 25-2). Place roots in the bags in vertical position, with the peduncle Time between harvest and packaging. Results of facing upwards. Package roots of different sizes experimental tests as well as past experiences indicate in the same bag to avoid filling the last bags with that packaging and treatment should be carried out as smaller roots. soon as possible after harvest. A delay of more than 4 h may cause the complete loss of the entire produce Adjust the weight of the bags according to their due to physiological deterioration. The time elapsed capacity. If a 4-kg bag weighs less than the between harvest and packaging should be less than designated amount, then it is not fair to the 3 h. This requires that pertinent tasks be performed at consumer and, if the bag weighs more, then the the harvest site itself or somewhere close by. farmer loses. Effect of the sun. The direct exposure of roots to • Apply the fungicide, which consists of a solution the sun over a prolonged period will increase the risk based on Mertect 450 FW at 0.4% of losing the harvest to physiological deterioration. concentration, once the roots have already been Loss can be prevented by harvesting and packing roots placed in the bags. To prepare the solution, first 485 Cassava in the Third Millennium: … fill the fumigation tank (in this case, of 20 L) with water and then add 80 mL (0.08 L) Mertect (0.4% of 20,000 mL). Thoroughly mix the solution with a stick or with the pump lance. Replace pump filter and tank top. The fungicide solution is now ready for application. Introduce the lance of the pump into each bag and bathe roots with the solution, in particular root tips (Figure 25-11). It is important to eliminate any excess fungicide solution from the bag because excess internal moisture favors the development of fungi. Figure 25-12. A diagonal cut at the bottom of the bag helps Turning the bags upside down to drain the drains excess fungicide. excess liquid is not only impractical because roots could fall out but also represents additional labor. The recommendation is to make diagonal cuts on the corners of the bottoms of the bags before beginning to pack the roots. These cuts prove highly practical, allowing the excess liquid to drain (Figure 25-12) while also helping to regulate the interior moisture of the bags, especially when roots have been harvested during the rainy season when moisture is excessive. This practice greatly favors root conservation. Approximately 100 mL solution are needed to Figure 25-13. The last step is to staple on the information label. treat one 4-kg bag so 1 L Mertect 450 FW is enough to treat 10 t of cassava. • Close the bags by folding the opened end of the Transporting the bags. The polyethylene bags bag 2 or 3 times and then staple the bag shut, containing treated roots are transported in the same using as many staples as necessary. Finally, type of vehicles used to transport fresh cassava. staple the information label to the bag However, because this first stage of the conservation (Figure 25-13). process creates conditions that favor the healing of wounds or damage caused to the roots, which is very important for successful storage, prevailing climatic conditions should be closely monitored during transportation to ensure that the healing process continues unaltered. The internal temperature of bags during transportation should be approximately 30 °C. When the climate is warm, it is not advisable to keep bags inside the vehicle for long periods of time since their internal temperature should not surpass the maximum level allowed (40 °C). On the other hand, in temperate or cold climates, it is sometimes necessary to cover bags with a canvas to protect them from the cold. In Figure 25-11. To treat with fungicide, introduce the spray lance extremely cold climates, for example in the Andean into the bag and completely drench the roots. region, bags traveling long distances should be 486 Conserving and Treating Fresh Cassava Roots previously placed in a warm environment (30 to 40 °C) harvested, decompose 2 or 3 days later. This for 24 h to make sure that the wound healing process deterioration increases with increasing distance from occurs prior to transportation. the cultivation site to consumption centers and when the marketing of agricultural cops is deficient in the It is also necessary to know the conditions of the region. This is not an easy problem to solve. roads. If roads are in poor conditions and the distances to travel are great, roots will undoubtedly suffer physical Because cassava deteriorates so quickly (CIAT, damage, which will in turn affect their conservation. It is 1976; 1987), it must be sold as soon as possible. therefore advisable to place the bags within the vehicle Market prices vary significantly, affecting both in such a way that there is no contact between them producers and consumers. Much cassava is never sold during the trip. Groups of bags can also be placed in because sales intermediaries discard it before it plastic or wooden containers. Finally, the vehicle should reaches the market. be driven carefully. The former Technological Research Institute (IIT, When poor transportation conditions cause physical its Spanish acronym) in Colombia conducted several damage to the roots, guaranteed shelf life (usually 15 studies on how to best conserve fresh cassava roots. days) is almost always reduced, possibly to 10 or 7 days. Results highlighted the application of paraffin and IIT The distributor could request that the shelf life indicated presented this method as an alternative to delay on the label be modified accordingly. deterioration and reduce cassava marketing losses (IIT, 1972; 1973). The temperature maintained during transportation should be maintained at the storage site upon arrival. Effectiveness Once it has been confirmed that root wounds have healed, bag temperature can be lower than 30 °C. This method guarantees root conservation because it: However, under no circumstances should temperatures above 40 °C be accepted. • Partially inactivates the enzymes present in cassava tissues Marketing. Marketing surveys carried out in • Notably reduces permeability to oxygen and Bucaramanga, Colombia (CIAT, 1991), indicate that 4-kg indirectly controls the action of peroxidases bags are most appropriate for local consumers. This • Reduces water loss amount of cassava is sufficient to satisfy the needs of an • Reduces contamination by microorganisms average-sized family (5 members) for one week and the due to the high temperatures used in bag adequately conserves the cassava as it is treatment consumed. In places where cassava consumption is • Controls fermentation because of reduced lower, the distributor could retail the cassava in the yeast count 12-kg bags. This way the retail distributor benefits from the storage method and the consumer from the The application of paraffin therefore ensures guaranteed quality of the product and the more good-quality fresh cassava, without notable changes favorable price. in organoleptic characteristics, with a shelf life of 20 to 30 days (IIT, 1972). Consumer acceptance studies have also been conducted in Bucaramanga (CIAT, 1991), involving bags Stages containing cassava conserved for 1 or 2 weeks postharvest. Based on the data gathered, it was Basic stages of the paraffin treatment process are concluded that consumers did not detect changes in the indicated in Figure 25-14. Because the application of culinary quality of roots and that 90% preferred to paraffin does not improve cassava quality, only its purchase cassava conserved in the polyethylene bags conservation, it should only be used with roots described herein. presenting very good culinary quality (IIT, 1973). Applying paraffin to fresh cassava roots Paraffin should be applied within 4 h postharvest. Therefore the facility where the paraffin is applied A little less than one fourth of the fresh cassava destined should be located close to cultivation sites or for human consumption is lost because the roots, once collection sites of fresh roots. 487 Cassava in the Third Millennium: … Harvest and collection Transportation Selection Classification Washing Second quality control Figure 25-15. Cassava roots harvested with care. Leaving sufficient peduncle helps protect the roots from bacteria attacking that tip of the root while Disinfection facilitating their handling during the paraffin treatment process. In cassava-growing regions where paraffin is applied to roots, between 15% and 30% of the roots Drying of roots harvested prove suitable for paraffin treatment (A Martínez 2010, pers. comm.). The remaining roots are sold on the fresh market or used as raw material to prepare frozen chips, sticks, or croquettes. Application of paraffin Transportation to the paraffin treatment facility. Transport roots in wooden or plastic boxes, as is the case of most delicate crops. Maximum capacity of each box is 20 to 25 kg (Figure 25-16). Cooling Selection and classification. Once the roots arrive at the paraffin treatment facility, discard roots that are broken, damaged, or have an unacceptable size. Supermarkets usually define desired root Packaging dimensions depending on consumer preferences. During this first quality control check, also discard roots showing signs of physiological and microbial Figure 25-14. Flow chart indicating the main stages of paraffin treatment to fresh cassava roots. deterioration. Washing. Use good quality water, preferably Harvesting. Roots should be harvested with potable water, to wash the roots. Remove superficial extreme care to avoid damaging their surface earth by scrubbing the root with a sponge or using a (Figure 25-15). The process practically begins with the brush with soft plastic bristles to avoid damaging the careful harvest of roots, which will ensure that a high peel (Figure 25-17). percentage will be suitable for paraffin treatment. 488 Conserving and Treating Fresh Cassava Roots Figure 25-16. Packaging of fresh cassava roots in plastic boxes for transportation to paraffin treatment facility. Then immerse the roots in a tank adapted with a bottom grid and a collector of solid residues to facilitate their precipitation, subsequent removal, and change of water. This system avoids dirty water mixing with clean water, while allowing the use of low-pressure water jets for sprinkling or spraying. Washing should completely eliminate any earth from the root surface so that the paraffin can adhere well to the root peel. Submit washed roots to a second quality control check to discard any roots found unsuitable that may have been missed during the first quality control Figure 25-17. Tank for washing fresh cassava roots. check. Check roots for signs of deterioration, adjust stumps or peduncles, and remove parts of the epidermis that have become detached. Drying of root surface. Cassava roots are left to air dry under shade by some companies. Others place Disinfection. After washing, spray roots with roots in a hot-air oven or tunnel at 40 or 45 °C. Paraffin ‘Lonlife’, a new product based on citrus seed oil that treatment requires that the root surface be completely protects roots from the attack of fungi and bacteria dry. (Figure 25-18), mixed with water as follows: 1 g of Lonlife in 1 L of water for a concentration of 250 ppm Paraffin treatment. A mixture of paraffin from active ingredient. China and locally obtained paraffin is generally used. Because of its rough consistency, the local paraffin Roots can also be disinfected with Mertect does not adhere perfectly to the root peel. On the other 450 FW (thiabendazole) prepared by adding 1 mL hand, the finer Chinese paraffin adheres better to the product to 1 L water. Submerge the roots in the peel and improves the appearance of the root; however, solution for 3 min. it is consumed in greater amounts during the process. 489 Cassava in the Third Millennium: … Figure 25-18. Lonlife is a product obtained from citrus seeds used to counteract fungi and bacteria attacking cassava roots. In Colombia’s coffee-growing region, some businessmen say that a 50%-50% mixture is perfect, processing some 4000 kg of fresh cassava (J Botero Figure 25-19. Manual application of paraffin to fresh cassava 2000, pers. comm.) with only 50 kg of paraffin. Others roots. only use Chinese paraffin. Temperature and inmersion time must be perfectly controlled. The poor, excess, or insufficient application of paraffin due to timing or temperature issues not only voids the process, but could accelerate root deterioration. Submerge dry roots in a container with paraffin at a temperature ranging between 140 and 160 °C. If the temperature is below 140 °C, the root is covered with a very thick layer of dull-looking paraffin. Above 160 °C, paraffin evaporates hence its consumption would increase and roots could be even boiled. Have a thermometer on hand to permanently check the temperature of the container and turn the equipment on and off as necessary (J Botero, 2000, pers. comm.). Paraffin is usually applied manually (Figure 25-19). First introduce half of the root into the container, wait until the paraffin film cools, then introduce the other half and wait until that paraffin film cools. Place the treated roots on a table next to the container until cooled completely. A stainless steel basket was developed in Armenia, Colombia (SENA, 2001) that allows batches of 2 or 3 kg of roots to be treated at once (J Botero 2000, pers. comm.). The process only takes a few seconds— the time it takes to lower the basket to the bottom of Figure 25-20. Steel rod basket that holds from 2 to 3 kg of fresh the container and then lift it out (Figure 25-20). Roots cassava roots, used during paraffin treatment. 490 Conserving and Treating Fresh Cassava Roots should not remain in the paraffin more than 3 s to avoid risk of the pulp becoming contaminated or acquiring a subsequent cooking problems. paraffin-like taste. Normal shelf life of intact roots ranges between 20 to 25 days (IIT, 1972; 1973). Cooling and packaging. Pack cooled roots in plastic boxes, when shipping to supermarkets, or Freezing of Cassava Chips or Sticks wooden boxes (Figure 25-21). Boxes usually have a capacity to store 20–25 kg of roots. If you need to Refrigeration, one of the techniques used to store fresh accelerate the cooling of the treated roots to avoid cassava, consists of storing roots in a cold storage delays in shipping, submerge treated roots in cold room (temperature: 0–2 °C; relative humidity: water. 85%–95%). Low temperatures inhibit enzymatic processes causing physiological deterioration of roots. Based on April 2010 estimates, the cost of applying If, in addition, roots are kept in plastic bags under good paraffin was COP460/kg fresh roots, distributed as storage conditions, their shelf life is further extended. follows: $130 for labor, $200 for paraffin, and $130 for Refrigerate cassava immediately after harvest. Storing packaging (A Martínez 2010, pers. comm.) roots in a normal household refrigerator will keep them in good conditions for 5 or 6 days (ITT, 1978). Roots should be free from wounds and cuts. Some However, before refrigeration, select and wash roots. supermarkets, however, request that the tip of treated Scrub the roots with a soft bristle brush to eliminate roots be cut off so buyers can appreciate the quality of earth and mud; then apply a disinfectant. the parenchyma (Figure 25-22). This practice not only shortens shelf life to just 8 or 10 days, but increases the The sale of frozen, peeled cassava chips or sticks has increased in recent years. Some companies precook them before freezing to reduce the preparation time for the final buyer. The production of fresh cassava chips or sticks for freeze-conservation involves several stages (Figure 25-23). For complementary information, consult the guide distributed by CONGELAGRO, a Colombian company specializing in frozen foods, to its dealers (CONGELAGRO, 2000). Harvest and selection When a company markets fresh cassava for the production of frozen chips or sticks, it must first select the roots for paraffin treatment. Those that do not classify because of their lower quality are distributed to Figure 25-21. Cooling the paraffin-coated roots in the basket used to submerge roots. the local food markets or plazas as well as to the frozen chip market. Time of harvest is determined depending on cooking quality of roots. Reception of raw material Upon reception of raw material, a first quality control check is performed to verify variety, size range, organoleptic quality, and degree of healthiness (absence of deterioration, physical damage, fungi, viruses, and bacteria). Organoleptic quality is assessed by cooking a sample of each material. Cooking time of 1 kg roots should take no longer than 20 min. In addition, the pulp should have a soft texture, good flavor, and preferably white in color. If not, then the quality of the Figure 25-22. Applying paraffin to part of the root. raw material should be reevaluated. 491 Cassava in the Third Millennium: … Harvest and selection Reception Control of root size, variety, texture, and flavor. Cook 1 kg of cassava. If it takes longer than 20 minutes to cook, then reevaluate the quality of the batch. Use pressurized potable water and a First washing brush. Change the water after washing every 200 kg of roots, outside the processing area. Removal of tips and chopping roots to form cylinder-shaped pieces Peeling Wash with potable water and then immerse in a disinfectant solution of active chlorine (Cl2) at 10 ppm from Second washing and first 5 to 10 min. Prepare the solution with disinfection 1 mL sodium hypochlorite (commercial bleach) at 2.5% in 1250 mL water. Change water every 200 to 500 kg, depending on the container. Confirm if pulp color has been affected Deveining and after submerging roots in disinfectant chopping into sticks solution. If washed in a container with jets of potable water, change water after washing every 100 kg of roots. Then Third washing and second immerse roots in a solution of 30 ppm disinfection Cl2 and 50 ppm quaternary ammonium [N(CH3)4] for a maximum of 7 min. Change the solution every 500 kg of Wash baskets with soap and water. roots. Disinfect by spraying with a solution Conservation treatment containing 50 ppm Cl2 and 200 ppm N(CH3)4. 30-kg bags. Disinfect table with a Wash hands and forearms with potable solution containing 25 ppm Cl2 and Draining and packaging water and scent-free soap. Disinfect the 25 ppm N(CH3)4. Do not rinse off. container and dispenser with a solution of 15 ppm Cl2 and 200 ppm N(CH3)4. Fast freeze at –30 °C Important note: The dose of sodium Maximum temperature of product on hypochlorite (commercial bleach) should loading the van: –5 °C. Freeze storage be proportional to the recommended value (in ppm) of Cl2. Figure 25-23. Stages of the production process of frozen fresh cassava sticks or chips. 492 Conserving and Treating Fresh Cassava Roots Total cyanide (CN-) content of pulp should be less than 60 ppm, usually, moist base . This parameter could vary depending on the variety. The cassava should not have a bitter taste, neither in the initial taste test upon reception of raw material nor in second taste test of end product. Calibration and washing Separate fresh roots according to length and diameter (commonly between 4 and 8 cm). Pressure-wash roots with potable water and, if necessary, use a brush to remove difficult earth or mud. If washing is performed outside the paraffin treatment facility, then change the water for each batch of 200 kg of roots when these are washed in 55-gallon containers. Blunting, chopping, and peeling. Remove Figure 25-25. Peeling the cylinder-shaped cassava roots. extremes (stump and tip) of roots and cut into cylinder- shaped pieces, 5 to 6 cm long (Figure 25-24). Then remove the cortex or thick peel from each cylinder active chlorine (Cl2) during 5 to 10 min. Prepare the (Figure 25-25). solution with 1 mL sodium hypochlorite (commercial product, at 2.5%) in 1200 mL water. During Second washing and first disinfection. Wash disinfection, permanently check the root pulp for the cylinders with potable water for the second time and appearance of brownish-gray spots. Change the water then submerge in a disinfectant solution of 10 ppm used for washing as well as the disinfectant solution after each batch of 200 or 500 kg of cylinders, depending on the size of the container used for this operation. Elimination of fiber and formation of cassava sticks. Cut cylinders lengthwise to obtain four uniformly sized pieces that meet production company requirements. Carefully remove fibrous tissue or central vein from each piece (Figure 25-26). Third washing and second disinfection. Wash sticks with potable water. If a container is used, then change water after each batch of 100 kg of sticks. Subsequently submerge sticks in a solution of 30 ppm active chlorine (Cl2) and 50 ppm quaternary ammonium [N(CH3)4] for a maximum of 7 min. Change the solution after each batch of 500 kg of sticks. Conservation treatment. To avoid subsequent contamination of cassava sticks and thus guarantee their quality to the end-consumer, submerge sticks in an aqueous solution containing preservatives such as Sorbate (200 ppm) and potassium erythorbate Figure 25-24. Removal of tips and chopping roots into cylinders. (25 g/100 kg of cassava) for 20 min. 493 Cassava in the Third Millennium: … Fast freezing Packaged cassava sticks freeze quickly at –30 °C. Sometimes sticks (or chips) are first placed in ample containers and, once frozen, packaged and stored. Storage Store packaged cassava sticks in cold rooms at –18 °C (Figure 25-27). After each operation, clean the work area and all equipment and tools (baskets, walls, trash cans, and other work elements) very well. Quality control Microbiological quality. The parameters established by CONGELAGRO, 2000, for suppliers of raw material (cassava roots) regarding the final microbiological status of the processed product (sticks) are as follows: Aerobic mesophyl count: <100,000 colony Figure 25-26. Deveining of roots by cutting cylinder-shaped forming units (cfu)/g pieces into four. Total coliform count: <500 cfu/g Fecal Escherichia coli: <10 cfu/g Draining and packaging Fungi and yeasts: <3,000 cfu/g Psychrophils: <1,000 cfu/g Drain the sticks (or cylinders) and package in low- density polyethylene bags of predetermined capacity. Make sure the area used for packaging is completely clean and disinfected to avoid recontamination of the end product. • First wash the plastic baskets used to transport the product with soap and water and then disinfect by spraying them with a solution of 50 ppm Cl2 and 200 ppm N(CH3)4. • Make sure all workers wash their hands and forearms with scent-free soap and potable water and then rinse with a solution of 15 ppm Cl2 and 200 ppm N(CH3)4 to avoid possible contamination of the product during this delicate stage of the process. • Disinfect tables where operations are carried out on with a solution of 25 ppm Cl2 and 25 ppm N(CH3)4. There is no need to rinse off the surfaces. • Keep all cleaning solutions in containers with dispensers. Figure 25-27. Cassava sticks packed and stored at freezing temperature. 494 Conserving and Treating Fresh Cassava Roots Each company purchasing or processing frozen CIAT (Centro Internacional de Agricultura Tropical). 1976. cassava sticks establishes their own thresholds for Almacenamiento de raíces de yuca. In: CIAT. Causas these microorganisms, depending on their own de deterioro que se presentan después de la cosecha standards of quality and the conditions in which the de raíces frescas. Cali, Colombia. p 27–28. product is handled. CIAT (Centro Internacional de Agricultura Tropical). 1987. Organoleptic quality. The organoleptic quality of Almacenamiento de raíces frescas de yuca—Guía cassava sticks is evaluated based on the following de estudio para ser usada como complemento de parameters: la unidad audiotutorial del mismo tema. Scientific contents: C Wheatley. Cali, Colombia. 34 p. • Taste. After harvest, cassava should not have a bitter or unusual taste. CIAT (Centro Internacional de Agricultura Tropical). 1991. Conservación de raíces de yuca en bolsas de • Texture. At time of purchase, the stick or chip polietileno—Guía de estudio para ser usada como should be frozen and rigid; at time of complemento de la unidad audiotutorial del mismo consumption, it should be fiber-free, with a tema. Scientific contents: C Wheatley. Cali, Colombia. soft, not hard, farinaceous consistency. Hard, 34 p. peeled cassava is rejected by consumers. CONGELAGRO S.A. (Compañía Congeladora de • Cooking time. It should not take longer than Productos Agrícolas). 2000. Descripción del 20 minutes to cook cassava using a traditional procesamiento de yuca en los centros de acopio: pot. Proveedores, norma y materia prima. Línea de croquetas de yuca. Manual. Bogotá D.C., Colombia. Conclusions 4 p. The conservation and treatment methods or practices IIT (Instituto de Investigaciones Tecnológicas). 1972. La described herein, such as applying paraffin to cassava yuca parafinada. Tecnología 14(78):47–51. roots and preparing frozen cassava chips, have been successfully used by CIAT and others and are gaining IIT (Instituto de Investigaciones Tecnológicas). 1973. importance in both national and export markets, Proceso de parafinar yuca: Ventajas y economía. mainly to USA and Europe. Bogotá, Colombia. Tecnología 14(86):33–51. Central American countries such as Costa Rica, IIT (Instituto de Investigaciones Tecnológicas). 1978. which traditionally have not been cassava-growing Preservación del método de parafinado. Tecnología countries, now export significant amounts of paraffin- 15(36):1–15. treated cassava and frozen chips to the USA and European markets. If the markets for these products SENA (Servicio Nacional de Aprendizaje). 2001. La yuca: continue to grow, Colombia could become a major Producción, cosecha y poscosecha en la cadena supplier. agroindustrial. Programa Nacional de Capacitación en Manejo de Poscosecha de Frutas y Hortalizas. References Centro Agroindustrial Vereda San Juan, Armenia, Colombia. 36 p. Booth RH. 1977. Storage of fresh cassava (Manihot esculenta Crantz); II: simple storage techniques. Exp Agric 13(2):119–128. 495 Cassava in the Third Millennium: … CHAPTER 26 Sour Cassava Starch in Colombia* Freddy Alarcón M.1 and Dominique Dufour2 Introduction Sour cassava processing principles are applied across all extraction plants, although the technology Sour cassava starch is a fermented product used in the used varies significantly. For example, some of them food industry. It was initially produced by rural families process everything completely by hand, others have for domestic use, and they employed homemade, implemented mechanization yet they are still very manual tools for its extraction. It has been used as an traditional, and then there are those with very high ingredient in different foods, especially those of technological processes but remain at a small-scale regional or traditional origin where the breadmaking industrial level (Zakhia et al. 1996). potential of cassava starch is needed. Furthermore, there are plants that are large-scale As an agroindustrial activity in Colombia, cassava producers of native or natural (unfermented) cassava starch extraction began in the 1950’s. The demand for starch in the departments of Atlántico and Sucre the starch increased over the following years, and its (Alarcón 1993a, 1993b); this process uses a higher extraction became a completely handmade agro- degree of technology. Native starch (also known as industry. From then on, mechanical innovations for sweet cassava starch) is used in different industrial certain processing steps were introduced, thereby sectors (mainly glue and paper manufacturing), the boosting the production capacity of these small textile industry (warp sizing), and prepared food factories that began to call themselves “rallanderías” or industry as well as in oil well drilling and dynamite “ralladeros”; in this text, they will be referred to as manufacturing. cassava starch extraction plants or simply extraction plants. This activity had a positive impact on the In 1989, the French Agricultural Research Centre socio-economic level of poor smallholders living in the for International Development (CIRAD)3 and the Centro northern zone of the Colombian department of Cauca Internacional de Agricultura Tropical (CIAT) launched (CECORA 1988; Gottret et al. 1997a; Gottret and the Cassava Development Project in Latin America, Ospina 2004). which aimed to improve traditional technology used in small-scale cassava starch processing by developing More than 200 of these extraction plants involved technologies that would increase starch extraction in producing cassava starch for bakery goods (such as profitability and product quality and could be pandebono, pandeyuca, etc.) have been set up in transferred to rural producers (Chuzel and Muchnik, Colombia, and they are harnessing that product’s 1993; Alarcon, 1996). special breadmaking properties. Most of the project activities, including an important survey of producers in 1995, were undertaken in the department of Cauca, where cassava * Taken from the work of the same name, written by Freddy Alarcón starch extraction plants are found on both sides of the M. and Dominique Dufour. 1998. 1. Plant Products Chemist, formerly of CIAT. Currently Director, Pan-American Highway along the section between Starch Technology, Inc., USA. E-mail: falarcon@starchtechnology.org 2. Food Science Specialist, CIRAD-UMR QUALISUD, Montpellier, 3. For an explanation of this and other acronyms and abbreviations, France; CIAT, Cali, Colombia. E-mails: dominique.dufour@cirad.fr see Appendix 1: Acronyms, Abbreviations, and Technical and d.dufour@cgiar.org Terminology, this volume. 496 Sour cassava starch in Colombia Pasto-Popayán-Cali. These plants are basically dry matter/ha); however, average global yield in actual dedicated to producing sour cassava starch. Only a few conditions (marginal soil, severe climate, and produce natural starch. association with other crops) is 9.8 t/ha (12.4 t/ha in Latin America). One ton (1000 kg) of fresh cassava This collaborative project aimed to technologically yields 280 kg of flour, 230 kg of starch, 350 kg of dry improve cassava processing for obtaining the natural chunks, or 170 L of alcohol (CIAT 1996). and sour starch from this root. Its results can be applied to most of the Latin American, Asian, and While cassava is a hardy plant, it is susceptible to African cassava-growing regions that have an adequate three significant diseases: bacterial blight (on leaves water supply. CIAT and CIRAD objective is to spread and stems), root rot, and the African mosaic virus (just these technological innovations among tropical in Africa). Several sap-sucking insects (green aphid, smallholder farmers, whereby they can take advantage mealybug, whitefly) and some phytophagous pests of an agricultural product that so far has served them (hornworms) attack the leaves. The roots are only as a means of subsistence in order to improve sometimes damaged by burrower bugs. their socio-economic level. Cassava can withstand drought (without affecting Since 1991, these two institutions have transferred production) because it possesses three particular sour cassava extraction technology (herein described) characteristics: (1) stomata close when air is dry, to different Colombian regions. In 1993 and 1994, this (2) roots extract water from deep soils (up to transfer work was continued in Ecuador. In 1997 and 2.5 m), and (3) its photosynthesis system captures 1998 introduced the technology for improved sour atmospheric carbon even when it has limited water starch processing to some cassava-producing regions (under prolonged hydric stress). of Nicaragua, and it is currently conducting a feasibility study for transferring it to other Latin American This crop survives in low-phosphorus soil because countries and other continents. it creates associations with fungi (mycorrhizae) that provide this element. It also grows in acid soils (with Cassava cultivation aluminum). Cassava does not tolerate waterlogging. Roots can be harvested 7 months after planting and Cassava (Manihot esculenta Crantz) is a starchy root can remain in the ground for up to 3 years. Once they crop grown in the tropics and subtropics. Although it is are harvested, they deteriorate within 3 to 4 days. As a one of the most important food crops in tropical result, they must be consumed or processed without countries, it is not well known elsewhere. delay. It originated in tropical America. Even before the Cassava should not be simply regarded as a crop turn of the 17th century, Portuguese explorers were for human consumption since a considerable amount taking it with them to Africa and Asia. It is now of production is processed and sold as starch and other cultivated in 92 countries, where it feeds more than derived products. Although the virtues of this crop are 500 million people. beginning to spread out, it is often feared that its expansion can damage soil fertility and cause erosion, Plant and cultivation particularly those seen as marginal agricultural lands. At the present, there are more than 6500 cassava In fact, cassava extracts an amount of nutrients varieties, each one with its own peculiar characteristics. that is similar to the level extracted by other plants. Moreover, under proper agronomic management, its Its flowers (male and female) are small and cross- production is sustainable. Furthermore, cassava has pollination is a frequent occurrence. Its fruits are the ability to grow in depleted soils, an extraordinary dehiscent, and seeds are small and oval-shaped. The advantage that, when coupled with its huge production root is conical, with an external and an internal bark potential, presages this crop will have an important (white or pink in color). The mature stalks are cut into future as a basic energy source for marginal regions of 7–30 cm stakes or cuttings, which are subsequently the tropics (Cock 1989). used for propagation purposes. Despite it prefers hot and humid climates, cassava Under experimental conditions and in a monocrop adapts to a large range of climatic conditions. It grows system, cassava yields up to 90 t of roots/ha (25–30 t very well between latitudes 30º N and 30º S. 497 Cassava in the Third Millennium: … Root analysis Cultivated varieties with industrial uses should have high starch content (Wheatley 1991; Sánchez Cassava roots (Figure 26-1) are composed of three et al. 2009). tissues: periderm (bark), cortical parenchyma (peel), and parenchyma (Figure 26-2). Cyanogenic compounds. Cassava contains a cyanogenic glycoside called linamarin that • Approximately 80% of the fresh root weight hydrolyzes and releases doses of cyanhydric acid comes from the parenchyma or pulp, the tissue (HCN) that range from innocuous to toxic and lethal in which the plant stores the starch. when in the presence of enzymes (mainly linamarase) in an acid environment. This reaction normally occurs • Root dry matter content fluctuates between 30% in decomposed plant tissues or in animal digestive and 40%. tracts. • Parenchyma dry matter is primarily (90%–95%) While botany and agronomy previously classified composed of the non-nitrogenous portion, i.e. cassava varieties as “sweet” and “bitter” in relation to by carbohydrates (starches and sugars). the amount of HCN they could generate, this classification is no longer used because there is no • The remainder of the dry matter is fiber stability in the “content” of acid or its originator, (1%–2%), fats (0.5%–1.0%), ash or minerals linamarin, in either category. “Sweet” varieties (1.5%–2.5%), and protein (2.0%). generally produce below than 60 mg of acid per kilogram of fresh root (a rather small amount), while • Starch represents the largest portion of the the “bitter” can generate more than 1000 mg/kg. To carbohydrates (96%) and is, hence, the main date, science has not discovered a non-cyanogenic component of the root dry matter. variety. Environmental conditions may affect cassava’s “content” of cyanogenic compounds such that a “sweet” cultivar grown in one region may become “bitter” in another region. The root bark contains higher concentrations of cyanogenic compounds, and these are likewise found in leaves and other plant organs, although in lesser quantities. Conventional cooking methods are effective in reducing cyanogenic contents of cassava to harmless levels. However, when roots from a “bitter” variety are consumed, without proper previous CASSAVA (Manihot esculenta Crantz) cooking and when diets lack protein and iodine Figure 26-1. Harvested cassava roots. See how the bark is (conditions that are generated during war and partially peeled. famine), then people may suffer from cyanide poisoning, a situation that would seriously affect their health. Periderm or bark Processing the roots of a “bitter” variety is quite demanding. However, there are two reasons why some farmers prefer to plant them: (1) the cyanogenic compounds seemingly help to protect the plants from Cortical pests (current and potential) and (2) food products parenchyma made with their starch have better texture. When high cyanogenic content cassava varieties are processed, the final product (starch) does not Parenchyma contain any residual acid whatsoever, and the reason for that is HCN dissolves completely in the large volume of water required for processing and is thus Figure 26-2. Cassava root transverse section. removed from the starch. 498 Sour cassava starch in Colombia Varieties Zaire 18 Each cassava variety behaves differently, and the optimal harvesting time is different for all of them. While Thailand these characteristics depend upon two conditions 18.5 inherent to the place where they are grown, namely climate and altitude, they also depend upon the variety’s Brazil genetic traits and management practices (Alarcón 23 1994a). Indonesia When cassava’s optimal harvesting period is over, 16.4 the water and fiber content increase, and the percentage of starch notably decreases. Therefore, in the process of obtaining the starch, a large amount of black starch called “mancha” in Colombia (scum skimmed off the Nigeria surface of sedimented starch), a byproduct that contains 32.7 poor quality starch, is produced. Figure 26-3. Cassava root production (millions of tons) in main producing countries worldwide (FAO 1999). • Pest- and disease-resistant cassava varieties that can adapt to different climatic and soil conditions have been developed. These are Human consumption 60% high-yield varieties that contain elevated concentrations of starch; many of them reach the harvesting stage in a short growing period (Domínguez [1983]). • When inadequate growing practices are used, the variety’s yield declines, diseases that attack the plant occur, and the soil loses its minerals and nutrients (Domínguez [1983]). Production and yield Starch and others Animal fodder 7% In the world. Cassava cultivation has been a major 33 % traditional activity for rural communities across many Figure 26-4. Distribution of cassava production allocated for countries. It is one of the main components of the food local use (85%) in the world. diet of people living in developing nations, who also use SOURCE: FAO 1999. it as animal feed, and when there is a surplus, it is sold in the market. Close to 85% of global production (Figure 26-4) is Global cassava production in 1999 yielded more used in the place where it is grown (in situ), and from than 169 million metric tons, of which 54.4% that percentage, 60% is set aside for human (92.5 million) was grown in Africa, 27.6% (47 million) in consumption, nearly 33% for animal feed, and 7% for Asia, and the remaining 18% (29.3%) in Latin America starch production and biotransformation (Jones, 1983). and the Caribbean. The remaining 15% (around 30 million tons) is The main cassava-producing nations are Nigeria, exported each year to Europe and Japan as pellets or Brazil, Zaire, Thailand, and Indonesia. Figure 26-3 starch, and 75% of the product is exported from shows fresh root production figures (FAO 1999). Thailand, with the rest from Indonesia and China. The Annual per capita and per region consumption is higher European Union annually uses 5 million tons of pellets in Africa (more than 90 kg), and Zaire is the country to supplement animal fodder. with the highest level of cassava consumption: 391 kg/person per year, or the equivalent of In Colombia. Cassava production in Colombia 1123 calories a day. Global consumption is around increased in 1999 to 2 million metric tons, making it 18 kg/person per year. 499 Cassava in the Third Millennium: … the 16th largest producer in the world (FAO 1999). Producers and processors. It is estimated that 97% Average yield is 9.93 t/ha. The primary producing region of producers in Cauca use traditional farming practices is the Atlantic Coast, yet a sizeable amount of this for cassava cultivation, only 3% employ more technical product is grown in the Eastern Plains (Llanos methods, i.e., healthy cuttings are planted from Orientales). The department of Cauca accounts for improved varieties and farmers use a “package” of 4.6% of the total national production. efficient agronomic practices, such as the ones recommended by the National Agricultural Research On account of the seasonal rains, most of the Program. annual production takes place during certain times of the year. For the cassava agro-industry, this situation A 1995 survey found that there were 210 cassava creates a raw material shortage in some months of the starch extraction plants in the department of Cauca, year and a surplus in others as well as the loss of fresh and 51% of them were also cassava producers. Yet, the roots due to damage from extended storage, when the area that they cultivated represented just 8% of the offer is high, and price fluctuations in raw material and department’s entire cassava cultivation area (Gottret starch. et al. 1997a). In the department of Cauca. The department of Production and benefit. 3.6% of all departmental Cauca (IGAC 1993) is the main producing region of sour production is for direct human consumption or animal cassava starch in Colombia since it processes nearly feed on farms. From the remaining 96.4%, which is the 80% of the entire national supply. In 1994, there were marketable share, agro-industry uses 90% to produce some 6450 ha of cassava fields in this department from fermented (sour) starch and 10% is sold for direct which roughly 53,500 t of fresh roots were produced. human consumption in the department (Chacón and This production accounted for 3.2% of the national Mosquera 1992). total. The entire regional agro-industrial sour starch The average yield in this department, according to production is estimated to be 10,700 t/year, a figure Ministry of Agriculture and Rural Development (MADR) that represents 70%–80% of the country’s entire of Colombia figures, is 8.3 t/ha. Local production is production (Gottret 1996). Another 135 t/year of native insufficient to meet the current demand by cassava starch is also produced for industrial use (Gottret et al. starch extraction plants. When the department of Cauca 1997b; Henry and Gottret 1998). experiences a shortage of cassava, it needs to be purchased from other regions of the country. Cassava farming- and transformation-related activities in the northern sector of the department of In order to fully use the installed capacity of the Cauca occupy a major place in the regional economy. extraction plants, it is estimated that an area of They are also the main source of income for almost 19,700 ha would have to be cultivated. 4000 rural families that manage the above-mentioned 210 sour cassava starch extraction plants. The CIAT Cassava Program tested, with good results, some varieties that had been improved in CIAT Farmers located in areas near the plants supply for Cauca conditions and requirements, in other words, them with cassava. During periods of raw material for a determined time between planting and harvesting, shortage, processors organize themselves and high yield, and very high quality starch for breadmaking. purchase cassava from Ecuador and the Colombian Improved and tested varieties still recommended to departments of Antioquia (the Urabá zone) and farmers are the following: Quindío (Armenia). Roots, stored in trucks for the two or more days it takes to transport them, deteriorate • Catumare variety (CM 523-7). It is a good starch and lose their quality. producer and is destined for fresh consumption and for the frozen food industry. Cassava Processing • MBRA 12 variety. It is a high-yield product, a After cellulose, starch is the most abundant good percentage of starch can be extracted carbohydrate in nature. It is one of the main energy from it, it produces high-quality starch for reserves in plants and is found in sources as varied as breadmaking, and it is not stolen from the fields cereals (corn, wheat, barley, and rice), potatoes, since it is a bitter cassava. cassava (Figure 26-5), and many other crops. 500 Sour cassava starch in Colombia The extraction plants treat 1–10 t of cassava a day. The technology they used, described later on in this chapter, does not vary much from factory to factory and remains quite traditional. Some of these in the Colombian Andean region have been constructed according to the site topography (Figure 26-7) to harness energy derived from the gravity gradient. Root washing The purpose of this operation is to wash away the dirt and debris stuck to the cassava root bark and to remove the bark itself (external bark or periderm). Figure 26-5. Natural or native starch granules under an electron microscope. It can be observed the erosive action of the amylolytic bacteria in fermented or sour Washing methods. starch granules (right). Manual washing/peeling. This is done by hand, Starch is the most important carbohydrate for yet it is also done with the feet in some areas of the human activity due to its role in nutrition and its departments of Cauca (23 extraction factories) and multi-purpose character in industry and commerce. Caldas (Figure 26-8). The bark detaches itself from the friction caused from one root rubbing against As opposed to cereal starch, which requires very another during the washing. This operation uses a high-technology industrial processes to obtain, large number of rural family members and therefore extracting starch from roots and tubers (potato, sweet is a source of income for communities. potato, achira, and cassava) is very easy in rural settings since all that is needed is grating, sieving, Peeling. Roots are peeled manually (with knives) separation with water, sedimentation, and drying. in these extraction plants. This means that the peel (cortical parenchyma) is cut away, leaving the pulp The overall extraction process for cassava starch is cleaned and bare. illustrated in Figure 26-6. The washing, grating, and sieving operations have been mechanized, although Mechanical washing/peeling. Mechanical washing processors in some regions still do those operations and peeling are done in a cylindrical drum. Cassava manually. roots are washed as they rub against each other and the drum wall. Cassava roots The wall is slatted (rectangular) so the waste Water Washing Root peel products inside the drum are released through them. The water flow helps clean away the debris (dirt and Grating the remains of the peels) and strip off the root peel. Types of washers. Water Sieving Fiber residue Side loading half-shaft cylindrical washer/peeler Sedimentation Wastewater (Model 1). The drum is supported by a half-shaft coupled to a bearing housing on one of its ends. The Fermentation half-shaft propels the drum. This system is installed on a tank where the water and debris are captured. Drying Drying The drum (Figure 26-9) is made of a single sheet of galvanized steel and covered completely with Native starch Sour starch oval-shaped openings through which water and Figure 26-6. Overall flow of native and sour cassava starch debris are discharged. extraction. 501 Cassava in the Third Millennium: … Water Reception of fresh roots Washing Root peel Water Grating Sieving Fiber residue Channel sedimentation Wastewater Tank fermentation Sun drying Figure 26-7. Schematic distribution of starch production operations in a cassava starch extraction plant that is designed for sloped terrain to harness gravity. Cassava root loading and unloading Half- hopper Water access shaft Drive pulley Debris outlet Washed cassava container Figure 26-8. The roots are peeled by the feet during the washing operation in some cassava starch extraction plants. Characteristics: Friction causes the bark to come off. Capacity: 1000 kg of roots per hour Water: 100 L/100 kg of roots Rotational speed: 30 rpm Figure 26-9. Side loading half-shaft cylindrical (drum) cassava root washer/peeler. 502 Sour cassava starch in Colombia This washer is loaded and unloaded through a (A) Root access semi-circular opening in the center of one of the drum Water sides (or bases). There is a hopper (or similar apparatus) access on that side for loading and unloading, which is very practically and easily done by hand and does not require the machine to be turned. Therefore, washing/peeling with this machine is quick and practically continuous. Drive A perforated pipe for supplying the water enters pulley through the same side opening. The roots exit the washer/peeler and drop into a container underneath the Washed cassava container hopper. Characteristics: Front loading center shaft cylindrical washer/peeler Capacity: 1000 kg of roots per hour (Model 2). This has a single drum driven by a center Water: 100 L/100 kg of roots shaft that is supported on each end by a bearing Rotational speed: 21 rpm housing (Figure 26-10a). (B) Drum walls are made of galvanized steel and Water Root access access contain oval- or rectangular-shaped openings. There is a hatch that runs along the length of the drum for loading and unloading purposes. A perforated pipe, fixed above Washed and running parallel to the drum, sprays pressured water roots onto it. These washers/peelers are difficult to load and Drive unload as well as to start. It takes a considerable amount pulley of time to wash and peel the different loads. Debris outlet Semi-continuous cylindrical washer/peeler (Model 3). This has a single drum driven by a center shaft that Characteristics: spins on bearing housings. Capacity: 1500 kg of roots per hour Water: 130 L/100 kg of roots Drum walls are made of galvanized steel and Rotational speed: 30 rpm contain oval- or rectangular-shaped openings through Figure 26-10. (A) Front loading, (B) semi-continuous action which the water and debris are discharged. A hopper is center shaft cylindrical (drum) cassava root attached to one end for loading the roots into the drum washer/peeler. and an exit hatch is coupled to the other end. • The recently developed semi-continuous model To supply the water, a tube runs the entire length of 3 has greater capacity (1500 kg/hr) and the drum and enters it through special openings at reasonable water consumption (130 L/100 kg of either end in a suitable position so as not to hinder the roots). It is practical and easy to use. Each load drum’s spinning (Figure 26-10b). In some of these takes approximately 5 minutes to complete. models, the water is sprayed into the drum through a These can be attached to grating operations to perforated center shaft. provide more continuity and therefore streamline the process (CIAT 1995b). Washer/peeler capacity. Washer/peeler capacity depends on the type, whether a traditional (model 1 and Washing/peeling losses. Losses during the cassava 2) or semi-continuous (model 3). root washing and peeling operation depend upon three factors: (1) the cassava variety, (2) the condition of the • Traditional models have a capacity of roots, and (3) the characteristics of the washer. 1000 kg/hr. Water consumption is less than 100 L for every 100 kg of roots. Each load takes • Loss of raw material and, hence, of starch from approximately 10 minutes to complete. the washer is mainly due to the length of the 503 Cassava in the Third Millennium: … washing process and the design of the drum Grating is usually done with dry roots. Only in holes. If these have a very large inner rim, they special cases is it performed with water, for example, might tear the root tissue and thus shred it into when the machinery can be installed on sloped terrain, tiny chips. Normal losses per washing load vary thereby taking advantage of gravity so that the water between 2% and 3% of the fresh root weight. used can easily flow to the next operation or to the waste water tank (where it is treated). • Front loading center shaft-driving washers also lose water because a portion of it splashes out of The percentage of starch extraction depends on the the drum. grater. If it does not sufficiently shred the root tissue to separate the starch granules from the fiber, then yield Grating the roots from the extraction process will be low, and plenty of starch in the fiber residue will be lost. Grating refers to the action of releasing the root starch through any method possible. The method’s efficiency The grater cannot be too fine because very small is called the grating effect (GE) and has been computed starch granules would be damaged physically and (Alarcón 1989) from this equation: afterward degrade enzymatically. Under these conditions, A sedimentation would be slower (fine granules lose GE = { 1 – A x F R } x 1 00 density), and greater quantities of black starch would AR x FA form (CIAT 1995a; 1995b). where: Appendix 1 (Photo 26A-2) shows a traditional grater A A = starch recovered in the fiber residue (%) used in cassava starch-extraction plants in the department of Cauca. The grating effect currently F = raw fiber in the fresh roots (%) reached in this department is close to 80%, which means R it is very efficient. A R = starch in the fresh roots (%) Sieving F = raw fiber in the fiber residue (%) A This operation can be done manually, with continuous As the grating is performed, starch granules mechanical sieves or with mechanical sieves that handle contained in the cells of the root are released individual loads. (Figure 26-5). The efficiency of this operation determines in large part the total starch yield in the Manual method. There are 23 small cassava starch extraction process. extraction plants in Cauca, in the northern section of Valle, and in Caldas that manually sieve grated cassava. The grater. This is comprised of a wooden drum mounted on a steel shaft. The drum is covered on the This is carried out using a piece of fabric attached to outside with a sheet of galvanized steel that has been a wooden frame. The frame is then placed overtop a manually punctured along its entirety with a nail (or container or tank where the starch milk from the grated punch). Generally, there is one to two holes per each cassava that has been sieved is sedimented out square centimeter. (Figure 26-12). The drum rotates between 1200 and 1300 rpm. The Yield from the manual sieving process is equal to machine yields on average 1500 kg of roots every hour. that of the mechanical sieves used in the Cauca When water is used, it consumes 90 L/100 kg of roots. department extraction plants. In fact, it depends upon the cassava variety, type of grater used, and the number The grating operation. The rough, cutting surface of people, and their skill level, involved in the operation of the drum, produced by the sharp edges of the (CIAT 1995b). numerous holes, establishes a cutting line (a rasp) with the inner side of a wooden plank that is placed in front Continuous mechanical method. In the of the drum. This grater produces a pile of grated department of Caldas, they use a wooden type of cassava, the size of the individual pieces being fine or continuous sieve, with a worm gear, the lower part of thick depending upon the space (“light”) between the which is supported by a piece of fabric equal in length to drum and the wooden plank (Figure 26-11). the gear (see Appendix 1, Photo 26A-3). The sieve is 504 Sour cassava starch in Colombia (A) Wooden plank (B) Cassava roots Hopper Hopper Wooden plank Drive pulley Grated cassava mass Grating drum (C) Cassava roots (D) Hopper Hopper Grating drum Wooden plank Drive pulley Grating drum Drive pulley Characteristics: Capacity: 1500 kg of roots per hour Water: 90 L/100 kg of roots Rotational speed: 1200–1300 rpm Figure 26-11. Traditional cassava root grater. There is a perforated sheet on the outside of the drum that, when spinning, grates the cassava against the flat wooden plank. (A) Upper view. (B) Side view. (C) Front view. (D) Blueprint. located below the grater to help with the flow of the Intermittent mechanical method. This grated cassava mass. mechanical sieve is made up of a drum connected to a half-shaft that is supported by a bearing housing. It The worm screw, 3.5–5 m long, extracts the starch rotates at 20 to 22 rpm and is loaded and unloaded at very easily and facilitates fiber residue expulsion and one end through a hopper (Figure 26-13). compression, hence speeding up the time it takes to dry this byproduct at a later date. Inside the drum are blades that mix the grated cassava mass with water. The interior sheet is covered Capacity of a sieve of this type is between 200 and with an 80-mesh fabric or nylon sieve in which the 250 kg of cassava per hour. They are currently being grated cassava aqueous mass is strained. This sieve used in Riosucio, department of Caldas. lets starch milk pass and retains the fiber. 505 Cassava in the Third Millennium: … Grated Water access cassava mass loading and unloading hopper Fiber residue container Drive pulley Starch milk outlet Characteristics: Figure 26-12. Manual sieving of the grated cassava mass, as Capacity: 250–300 kg of grated cassava mass per hour performed in the department of Cauca. Water: 500 L/100 kg of grated cassava mass Rotational speed: 20 rpm Sieve: 100 mesh Normal capacity of this mechanical sieve is Figure 26-14. Mechanical drum sieve supported on four 250–300 kg of wet grated cassava mass per hour. bearing housings. Starch quality, in terms of fiber and debris content, depends on the sieve. Using 120-mesh or finer sieves Sieving characteristics. Sieving is the slowest will produce better quality starch. operation in the starch extraction process and is therefore its main constraint. Another model of this type uses four rollers. The transmission (drive pulley and shaft) spins on two Fiber residue (byproduct). The byproduct generated rollers which turn the drum that is also supported by by the sieving process is called fiber residue. After it has the other two rollers (Figure 26-14). The drum spins dried in the sun, it is used as feed supplements or as counter clockwise to the spin of the bearings. Except direct animal feed (Buitrago, 1990). A chemical analysis for this, this model is the same or very similar to the of this material indicates that dry fiber residue has a dry above-described model. matter content of 80% to 85%, of which 60%–70% is Grated cassava mass loading Water access and unloading Half- hopper shaft Sieve Hopper Drive pulley Fiber residue container Starch milk outlet Characteristics: Capacity: 250–300 kg of grated cassava mass per hour Water: 500 L/100 kg of grated cassava mass Rotational speed: 20 rpm Sieve: 100 mesh Figure 26-13. Intermittent, half-shaft cylindrical mechanical siever for grated cassava mass. 506 Sour cassava starch in Colombia starch and 12%–14% is fiber. For instance, these figures Tanks have two other disadvantages. First, they are related to those obtained in the mass balance from allow the starch to mix with the black starch and Figure 26-21 for 1000 kg of fresh cassava roots. Thus, second they lose up to 2% of the sedimented starch in the box titled “Fiber residue”, there is a starch when it is separated from that byproduct (a process content of 56.0 kg, which falls within the above- called “desmanchar” in Spanish). In order to separate mentioned percentage: the two substances, the top layer of the sedimented starch must be cleaned using water and long handled 56.0/90.1 kg x 100 = 62.2% squeegee (Appendix 1, Photo 26A-4). Fiber residue production in the department of Sedimentation channels. There are 100 cassava Cauca is figured to be 4500 t/year. This information starch extraction plants in the department of Cauca was obtained by Gottret (1996) and through the cited that use sedimentation channel systems. These are survey. covered with tiles or similar materials so the starch milk can flow. Channel length varies from 100 to 200 m, Second sieving. In many cassava starch extraction and it should be absolutely level to the floor. While the plants, the starch milk is passed through small sieves starch gradually settles, it forms a slight slope that after the main sieving process. The back and forth helps the remaining starch milk to flow. motion of these devices captures the fine fibers that might have been left over from the main sieving. The recommended number of channels in a system is seven, each one measuring 25 to 30 m in Starch sedimentation length (Figure 26-15). These systems can be designed so as to adapt to the land topography (Appendix 1, Once the starch milk has passed through the sieve, it page 516). contains starch, fine fiber, and proteins in suspension. It is then directed into tanks or channels where the There should also be a grit chamber at the front of starch is sedimented out. It is from this starch milk, the channels where sand and other solids in the starch either flowing in channels or stagnating in tanks, that milk can accumulate. the densest component, the starch, whose different sized granules accumulate on the bottom, is separated. The tiles make it so the starch milk flows evenly and without interruption, which will keep the black In a channel system, this process can last up to starch, sand (when there is no grit chamber), and other 3 hours, yet in sedimentation tanks, it takes 6 to debris (fiber) in the starch from settling. If there are 8 hours. When this step is completed, there is a layer of relatively large spaces between tiles, this will cause compacted starch on the bottom (of the channel or these starch contaminants to sediment. tank). The supernatant water is discarded (read farther ahead). When the sedimentation process has ended, there will be three layers in the channels and two different Sedimentation tanks. There are 106 cassava types of starch: starch extraction plants in the department of Cauca that use sedimentation tanks, which are made of brick • The lower layer is the starch. and covered with tiles. The volume of water that passes through them per ton of fresh roots is 4.8 m3. • The middle layer, called black starch, is a mixture of starch with proteins. Its thickness This amount of water, 5 m3 (500 L/100 kg of will vary. cassava), is also used to screen and sediment out 1000 kg of fresh roots (Figure 26-18). • The top layer is the supernatant water or wastewater. The tanks are a rather large constraint to the process given the labor they require. Extraction plants Wastewater. Wastewater is eliminated in the do not actually have the proper number of tanks to following manner: handle their grated cassava production capacity. Moreover, the wait time for starch sedimentation on the • For tank elimination, pull out the plug from the bottom of the tank is 8 hours. drain pipe located near the base of the tank, a little higher than the level where the sedimented 507 Cassava in the Third Millennium: … Figure 26-15. System of 7 channels for starch sedimentation of starch milk. starch layer usually ends (as the water flows out, • To settle on the bottom, one starch grain it will carry away a little of the starch with it). If must move 0.80 m in a tank and just 0.10 m the plug is on the inside, it will have a string in a channel. This difference explains, in attached to help pull it out. large part, the above-mentioned advantage, specifically the speed of sedimentation. • For channel elimination, removing, one by one (from top to bottom), the four or five thin planks When sedimentation is done in tanks, 2% of the or hatches at the end of the last channel. As the starch is lost during the black starch separation level of starch milk rises during the stage. When sedimentation is done in channels, sedimentation process, these planks, each almost all the black starch exits with the wastewater measuring 60 x 8–10 cm (channel height is such that very little of it accumulates as sediment on 40 cm), are placed one on top of the other. the layer of starch. During the black starch separation stage in the channel using the squeegee, With the removal of one large plank (60 cm x there is no 2% loss of starch as there is in the tanks. 40 cm) after the sedimentation process has been completed, the wastewater will exit the channel system, Black starch (byproduct). It is a byproduct of carrying with it a large part of the black starch and a the starch production process, and it is obtained in decent percentage of the starch. Total wastewater this stage. The starch it contains is of low density, volume of a channel system is around 50,000 L. poor quality, and high protein content. It is used as pig feed and in glues (Alarcón 1994b). The channel system has the following advantages: Black starch production estimates for the • Sedimentation in channels does not stop the department of Cauca are 750 t/year, as reported by benefit process, i.e. when the starch milk Gottret (1996) and based on the above-mentioned completes its flow through the system, the survey. sedimentation is deemed complete and the next stage begins. 508 Sour cassava starch in Colombia Wastewater is left to sediment again in a tank (to separate the remaining black starch) and is later routed to rivers and streams. It may also be recycled for use in the washing process if water is a constraint and conserving it is convenient. It should be treated before disposal or recycling (see Appendix 4). The starch that has settled on the bottom of the tanks or channels is subsequently directed to two places: • The drying area, where it becomes natural or native starch for industrial and feeding purposes. • Fermentation tanks, where it becomes sour starch for breadmaking after 20 to 30 days. Wooden interior Cement exterior Starch fermentation Supernatant water Brick construction Fermentation is a natural process produced by Dampened starch amylolytic lactobacillus in anaerobic conditions (without oxygen in the environment). Cassava, a Figure 26-16. Sour cassava starch fermentation tank. highly perishable agricultural product, it can be used best when conserved as fermented starch. This substance acquires special flavor, texture, odor, and The supernatant water (3–4 cm higher than the leavening characteristics when baked that are starch) is left in the tanks to maintain the anaerobic desirable qualities for breadmaking and that cannot state. Filled tanks are protected from the sun by damp be found in native or unfermented starch (Figueroa residual fiber or wet polypropylene bags, thereby 1991). preventing the water from evaporating (see Appendix 1, Photo 26A-5). In very hot zones, the fermentation tanks Sour starch is used in baking such breads as should be buried. pandebono, pandeyuca, snacks, and others that have recently appeared in the markets and that are much Fermentation time is variable and depends on the sought after by populations living in different regions ambient temperature. of the country (Pinto 1977). One method of checking the fermentation is Fermentation process. Sedimented starch is through its pH level, but this type of control is not placed in fermentation tanks, and a thin layer of water practiced in the cassava starch extraction plants. The pH is poured on top. There it is left for 20 to 30 days, a at the end of the process will be between 3.5 and 4.0. period that will vary depending on the region’s climatic conditions. The tanks vary in size, according Starch drying to the extraction plant’s capacity (Figure 26-16), and are generally covered with wood on the inside. Starch needs to be dried before it can be used. Native starch can be sun-dried or oven-dried, but sour starch Small tanks should be used for two reasons: can only be sun-dried. After fermentation, the starch is (1) they are easy to fill and (2) they simplify the daily removed from the tanks or channels in compacted drying operation. blocks and then transported to the drying patios where it is exposed to sunlight. The necessary inoculant for fermentation can be the water that has been used in the fermentation The blocks are milled to help the drying process, process for several days or a piece of already this being done by hand or with a drum grater that is fermented starch or even some dampened residual covered on the inside with screws or nails and that fiber spread over the top layer of starch in the tank. “pulverizes” the starch blocks before drying. 509 Cassava in the Third Millennium: … It is then spread out in 1- 2 kg/m2 layers on black Yield polyethylene bags since they absorb large amounts of sunlight and thus contribute to rapid and uniform Figure 26-18 shows a flow chart summarizing the sour drying. In these conditions, 1 t of starch will need starch extraction process as it is carried out in La approximately 1000 m2 of drying space. That area is, Agustina extraction plant located in the department of consequently, another constraint that clearly affects Cauca. The final quantity of starch in the flow chart is several of the cassava starch extraction plants based on what 1000 kg of fresh MVen 25 cassava considering they are located in regions whose variety would produce. Another study was conducted topography is very rugged. recently to compare efficiency of Vietnamese and Colombian technologies for cassava starch production Starch can be dried on trays or sliding trays at low rural level (Da et al. 2012). (Figure 26-17) built into the factories’ roofs or above their floors (see Appendix 1, Photo 26A-6). Quality Starch drying requires roughly 6 hours in the sun Breadmaking potential (BP) is the main criterion in in Colombia. The product is removed very gently 2 to sour starch quality. BP is defined as the capacity of the 3 times during that period with rakes made from a starch to leaven during baking. It is not possible to pliable material so as not to damage the plastic. During reach uniform quality with artisanal sour starch the operation, winds will carry off starch dust, which production, and this fact, consequently, hinders its leads to losses (0.7% in dry base) that are extremely access to market. difficult to avoid. BP primarily depends on the variety of cassava and Final treatment of the starch the fermentation and sun-drying processes of the starch. The choice of suitable varieties and proper When the moisture content of the starch is between management (and control) of both production 12% and 14%, it is collected from the drying area. processes would greatly improve sour starch quality While it dries, the starch again forms relatively (Dufour et al. 1996). hardened lumps that must be milled and sieved. Studies have been conducted on the relationship The lumps are milled using the drum graters between fermentation inoculant microflora and described above in the drying process. Sieving, on the starch quality. Some starch producers use, as the other hand, is done with a mesh (100–120 mesh), inoculant in their fermentation tanks, water from a whose caliber will depend on the desired results. different tank in which high quality starch was produced. Also compared were results from sun-drying After being sieved, the starch is loaded in woven and oven-drying at different temperatures and under polypropylene sacks. UV light (Brabet et al. 1996). Sour starch quality improves when the layer of water in the fermentation tank (3–5 cm) guarantees anaerobic fermentation, lactic acid production (specific amylolytic bacteria strains), and a drop in pH to 3.5. In an oven that controls starch moisture and that bathes the starch in UV light, its quality could be improved to greater levels because starch extraction plants could uniformly dry their product. Unfortunately, it is not possible to achieve the same BP as with sun-dried starch. Further studies have been performed that examined the influence of cassava type and root storage time on sour starch quality as well as the effect Figure 26-17. Sour cassava starch drying system in some of the produced by the overall climate and water used in the extraction plants in the department of Cauca. production process (Brabet et al. 1996). 510 Sour cassava starch in Colombia Cassava Fresh roots: 1000 kg 295 kg of starch Washing Washing debris: 32 kg Water Washed roots: 968 kg 9 kg of starch 120 L/100 kg 286 kg of starch 3.1% of initial starch Grating Water Grated cassava mass: 968 kg 90 L/100 kg 286 kg of starch Sieving Fiber residue 90.1 kg Water Starch milk production 56.0 kg of starch 500 L/100 kg 230 kg of starch 18.6% of initial starch Water Black starch 3.6 kg Sedimentation Supernatant 2 kg of starch 228 kg of starch 0.7% of initial starch Fermentation 228 kg of starch Water required for the process 710 L/100 kg of cassava (dried) Loss during drying 31 L/kg of starch Drying (in the sun) 2 kg of starch 228 kg of starch Relation (roots/starch): 4.4:1 0.7% of initial starch Process yield: 22.6% Starch recovery rate: 76.7% Sour starch 226 kg of starch Figure 26-18. Example of the sour cassava starch (MVen 25 variety with 35% of dry matter) extraction process of La Agustina extraction plant located in the department of Cauca and starch yield figures. The initial quantity of starch in this example is represented in the 295 kg contained in the initial 1000 kg of fresh cassava. From that quantity, 226 kg of sour starch, or 76.6%, is recovered. Marketing Truck drivers deliver the starch to major cities in the region (Cali, Buga, Cartago, and Tuluá), and in the Sour and native (sweet) starches are sold mainly country (Bogotá, Pereira, Ibagué, Medellín, Cartagena, through agents. In Cauca, these agents transport the Armenia, Monteria, among others). product to Santander de Quilichao, a town in the northern sector of the department. Once there, they General recommendations sell it to other agents, who then transport it to Colombia’s major cities. Of the 210 cassava starch For cassava starch extraction plants. Several extraction plants in the Cauca department, 35 directly years of research on cassava starch extraction plants in sell their product to bakeries, 8 to the snack food the department of Cauca, provides enough experience industry, 20 sell it through the Cooperative Association to recommend certain machinery, methods, and of Extraction of Cauca (COAPRACAUCA), and the rest designs (Chuzel et al. 1995a). Nevertheless, each plant deal with agents. is a specific case, and any recommendation should be 511 Cassava in the Third Millennium: … tailored to fit their infrastructure and their owners’ that they have to be absolutely level to the economic limitations. ground and designed with ends that are curved or rounded so the starch milk does not strike the Traditional extraction plants. These are labeled channel walls, thereby creating turbulence from Type 1 processing plants (see above description), the counterflow in which the black starch and the whose capacity ranges between 800 and starch mix together. 1000 kg of roots every hour. 4. Plant owners should carefully think about making the 1. The washer/peeler used in this extraction plant change from a system built on flat terrain to one that operates on a cycle-by-cycle (models 1 and 2), uses gravity to move the product. The change is so and operators lose time during each loading/ costly that it would mean making over the entire unloading pass. These machines should be starch extraction plant. changed to a semi-continuous washer/peeler (see Figure 26-10B, model 3) because it simplifies the 5. If there are frequent power outages in the region operation and also increases plant’s capacity to where the extraction plant operates and if the 800 to 1500 kg of roots per hour. cassava is not processed for hours or days, then a gas powered engine should be installed besides an 2. Mechanical graters that feature four bearing electric backup plant. housings (Figure 26-14) have certain drawbacks: 6. The belts that drive the engines (transmission) are • Overloading the machine is not a good idea very dangerous. It is recommended installing them since it will shut down or detach itself from the on just one side of the processing plant and to use drive pulley. protective shields around them to reduce risks. • Starch can become contaminated with rust or 7. For more industrial safety, then install several gear bearing grease because the starch milk can motors (one for each machine that may need it) come in contact with the rollers. These should, instead of running all the equipment off just one therefore, be substituted for “hanging” or engine alone (electric or gas powered). The cost of half-shaft sieves (Figure 26-13) since these do this improvement is high. not present that problem. Additionally, the fabric or mesh that is outside the sieves should For a Type 1 cassava starch extraction plant to be finer (120-mesh) to be able to retain the increase its production, the following measures should fiber that passes through the sieves. This fiber be taken: affects starch quality. • Install an additional sieve. 3. Starch milk sedimentation capacity is the largest constraint to any starch extraction plant, and it • Increase the number of sedimentation tanks or depends upon the system used for sedimenting build a channel system. the daily production. • Increase the number of fermentation tanks in • If sedimentation tanks are used, the capacity relation to daily production. is limited by the number of tanks the plant has available. Likewise, the black strach and the • Increase the drying area. starch mix together in the tanks, thus lowering starch quality to average. Improved cassava starch extraction plant. These are called Type 2 (see process description above). They use • If sedimentation channels are used, then the a channel system and have streamlined their operations operation is non-stop. Also, the water carries by harnessing the terrain’s slope (Chuzel et al. 1995b). off the less dense material (black strach) and leaves cleaner the starch on the bottom since 1. These starch extraction plants can improve their the black starch does not mix with it. drying operation through installing a pulverizing mill to crumble or “break apart” the compacted starch. • Channels can be of different length. An After being crumbled, the starch can be spread important recommendation to keep in mind is easily, quickly, and uniformly. 512 Sour cassava starch in Colombia 2. The water that runs through the channels can be Comparative yield. The following table compares recycled to wash cassava roots, thereby making the processing capacity of the three models (in tons more water available in the plant which will increase of fresh roots per month) and the extraction efficiency, the speed and efficiency of the washing operation which is the relation (in weight) between the processed and the overall process. Figure 26-19 shows the roots and the starch extracted from them. ideal blueprint of a Type 2 starch extraction plant. “Rallanderia” Plant Capacity Ratio (by weight) New cassava starch extraction plant. When (t/month) roots: traditional planning to build a new extraction plant model, called a starch Type 3, the following should be kept in mind: Traditional 20 5.5:1 • Must use good quality and abundant water Improved 30 5.0:1 throughout the process: close to 30 m3 per day. New 50 4.5:1 • Water temperature must be below 25 ºC (fresh water). Thus, building a plant with greater capacity means improving its starch extraction capabilities. Moreover, • It is recommended that the effluents from the profitability of the extraction process noticeably sour starch production process be treated so depends upon the level of starch extraction. they do not contaminate nearby streams. If the wastewater cannot be treated, then it should be For input management. directed to an area far from the extraction plant that would, therefore, be at a lower level on the Water. 10,700 t of starch is produced in the terrain. department of Cauca each year. Processing each kilogram of starch requires 31 L of water, or an annual • The plant should be built at a site where gravity, amount of 332,000 m3, which is equivalent to the due to its topography, can be harnessed for the amount of contaminated water a town of process. The difference between the plant’s 10,000 inhabitants would generate yearly. highest and lowest points should be 3.5 m, making it possible to conduct the starch The water used in the starch extraction process production process with the help of gravity. The comes from a variety of sources and has the following system will facilitate a semicontinuous flow of characteristics: operations at a lower cost. • Lake, river, gully, or surface well water is usually • Fermentation tanks should be buried so that contaminated with organic matter and the top is at the same height as the upper part microorganisms. of the channels. • Spring water normally has low mineral content • Water from the last channel can be directed to and is very good for this process. flow around the tanks to keep their external temperature constant. • Deep well water, compared with water from surface wells, is free of organic matter and • If the chosen site is on flat terrain, it is still microorganisms because it is purified as it possible to raise the grating operation to the filters through the different soil layers. proper height (building a metal structure and using a conveyor belt) to create a system by However, an underground well can become gravity artificially. contaminated by abandoned septic tanks, gutters, and sewers. Contaminated water has been known to travel The drawing of a new, Type 3 plant with all the great distances through veins of limestone and other above described starch extraction processes can be porous materials to end up polluting streams. seen in Figure 26-19. 513 Cassava in the Third Millennium: … 514 Columns Receiving Washing Grating Sieving Sedimentation Fermentation Residual water (outlet) Black starch (recovery channels) Figure 26-19. Descriptive plan of an ideal, well established extraction plant that graphically shows the sour cassava starch extraction process. The above figure shows the roofed version of this plant. Part of this design is currently being used in some plants in the department of Cauca (for example, the CETEC Totoyuca plant in Siberia, Caldono). Sour cassava starch in Colombia Therefore, a natural filter should be built for Raw material. The quality of the cassava is water used in the extraction process and designed essential for extracting an important percentage of high with layers of thick gravel, fine gravel, and clay, which quality starch that has elevated breadmaking potential will reduce the minerals and solids suspended in (dough rising while baking). It is therefore vital to select stream, river, and well water (Rojas et al. 1996) (see the cassava variety to be grown wisely for the roots that Appendix 4). will be processed. Water that has been used in sedimentation Machinery. All machines in the plant should be channels is usually directed into tanks close to the placed in such a way so that the product moves with factory for its subsequent transport to a water the help of gravity. This layout will improve production treatment plant. When the water is not dumped into a capacity, use less work area, and allow all machines to natural stream, it can be used again for the cassava run on just one engine, thereby making the process washing process, which translates into a savings of very economical. nearly 17% in water consumption for the entire extraction process (Colin et al. 2007). 515 Cassava in the Third Millennium: … Appendix 1: Graphic Description of the Starch Extraction Process The photographs show the methods used in different regions (such as Cauca and Caldas). Please note the development of the process, from the traditional to the mechanized system. Photo 26A-1. Washing cassava Photo 26A-2. Grating washed Photo 26A-3. Continuous roots with the feet. cassava roots. sieving of the grated cassava using a worm screw. Photo 26A-4. Sedimented starch in tanks Photo 26A-5. Starch fermentation in tanks. (the worker is separating the black starch). Photo 26A-6. Fermented starch drying in the sun. Figure 26-20A. Traditional system (type 1) to extract cassava starch. 516 Sour cassava starch in Colombia Photo 26A-7. Sacks of cassava arrive at the Photo 26A-8. Semi-continuous mechanical root extraction plant. washing. Photo 26A-9. Grating the washed roots. Photo 26A-10. Sieving the grated cassava mass. Photo 26A-11. Starch sedimentation channels. Photo 26A-12. Starch fermentation in tanks. Photo 26A-13. Fermented starch drying in the sun. Figure 26-21A. Mechanized system (types 2 and 3) to extract cassava starch. 517 Cassava in the Third Millennium: … Appendix 2: Industrial Use of Cassava Starch Starch production is a major world agroindustry, with a as a thickener in white sauce and a stabilizer and volume of around 33 million tons per year, of which just emulsifier in salad dressings, nutritious gelatins, 3.8 million (11.4%) comes from cassava. The rest is instant dessert mixes, ice creams, pudding, and from corn (21.2 million), potato (1.96 million), wheat baby food. Depending on how it is changed, it can (2.01 million), rice (0.05 million), and sweet potato be used in the paper, adhesive, and other (4.17 million) (Ostertag, 1996). industries (Balagopalan et al. 1988). Food industry Paper industry Natural starch (also known as native, sweet, or Native starch used in the paper industry is called industrial) is used, by itself or in a blend, to make unmodified starch (UM starch). There are three macaroni and different flours. These are subsequently operations in its treatment process: (1) refining (or used to make puddings, baked goods, cookies, wafers, screening), (2) purifying (strictly industrial operation), sponge cake, creams, ice creams, soups, salads, and (3) drying. sausages, and other food products. Fermented starch (sour) is used to make traditional Colombian food Paper and cardboard. Producing paper and products like pandebono and pandeyuca cardboard is a multi-step process and, in one (or more) (Figure 26-22A). of them, UM starch is added to the final product to give it certain properties and different grades of quality. • Native starch can be changed through physical means into pregelatinized starch (PG starch), • The paper industry requires three basic which has the property of being soluble in water characteristics from cassava-based UM starch: without first having to be cooked. (1) whiteness, (2) low fiber content, and (3) few impurities. The starch may have other physical or • It is used as a thickener, stabilizer, or glaze on fruit chemical characteristics that affect the pies, dry mixes, puddings, and milk cream. Adding papermaking or slurry production process. PG starch improves the texture and appearance of these and other, similar products. • UM starch helps the cellulose fibers bond and forms a top layer that reduces fuzz and increases • Native starch can also be changed through the individual sheet’s consistency, solidity, and chemical means into a food industry product used durability. This thin layer also improves cardboard’s strength of material. • UM starch is also used as an adhesive for laminating certain papers, corrugated cardboard boxes, wall paper, cardboard tubes, and other articles. It is also used in paper and cardboard recycling. Glues. UM starch is the raw material for making the basis of inexpensive glues or adhesive products. • These adhesives are used to make such disposable products as packing materials, stickers, wrapping paper, and label/envelope glue. • These inexpensive glues are very useful for high Figure 26-22A. Colombian food industry products made with speed packing machines and labelers for two sour cassava starch. reasons: relative low cost and high gluing speed. 518 Sour cassava starch in Colombia Organic decomposition. UM starch used in the would seriously disrupt the textile making process. paper industry lasts 3 to 4 days without decomposing, at which time it becomes fermented by different • Permanent sizing is used in fabric finishing and is microorganisms. relatively stable since it remains on the fabric at least until it is in the hands of the consumer. This fermentation produces gases (whose foul odor is not immediately smelled) and denaturalizes the UM • The fabric is impregnated with starch, which starch, thereby altering its properties, primarily losing improves its texture, increases the surface 25% of its adhesive capacity, reducing its viscosity, and brightness, gives it “body” and solidness to help in changing it acidity (pH). its handling, increases the “weight”, the print quality, and the overall appearance and feel of a Therefore, anti-bacterial substances should be good quality fabric. added to UM starch to keep the lactic acid-producing and coliform bacteria, as well as fungus (genera Pharmaceutical industry Penicillium and Aspergillus and yeasts), from growing. PG starch is used to dilute, to glutinate, to lubricate, or Textile industry to disintegrate different solid products. It also helps absorb, gives viscosity, and acts as a vehicle for pasty, UM starch is the most abundant and inexpensive liquid, or semisolid substances in dermatological ingredient, and thus the most important, in different creams and lotions. textile glues. It is furthermore used to make fine facial, compact, Warp sizing. The textile industry prefers (almost and nutritional powders, and as raw material in making exclusively) to use UM starch for two reasons: (1) it is wafers (Balagopalan et al. 1988). the only substance that can treat very white fabrics and (2) it degrades less than starches made from other Other uses sources. Fabrics can be sized temporarily or permanently. UM cassava starch is used in the chemical industry to make alcohol, glucose, acetone, explosives, colorants, • Temporary sizing is when starch is applied to warp dry batteries, and dental impressions as well as to yarns just before these are turned into fabric so coagulate rubber. that they are stronger, softer, smoother, and more flexible. The sizing agent is deposited as a film on, The mining industry uses it as a flocculating agent and totally covering, the warp threads. and a component in oil drilling solutions. • This process keeps the threads from unraveling, tangling, spotting, and breaking, any of which 519 Cassava in the Third Millennium: … Appendix 3: Cassava Starch Extraction Plant Costs Construction and set up Operating costs Table 26A-1 shows the infrastructure and equipment A cassava starch extraction plant with the equipment costs of a Type 3 starch extraction plant with a 30-t listed in the above table generally operates at 80% of its monthly production capacity (300 t/year for 10 months capacity, thereby producing annually 250 t of sour of operation). starch. Operating costs, however, are estimated on its basic capacity (30 t/month) and expressed in United State Dollars (US$1.00 = Col$1450; from September 1998). 1. Cost of producing 1 t of dry starch: Fixed costs Administration (US$351.00/month) US$11.75 Plant maintenance 3.55 Depreciation (Per unit produced. See below) 1.70 Subtotal (ST1) 17.00 Variable costs Labor (3 shifts, US$5.53/shift) 16.60 Electricity (2 kW/hour, US$0.20/kW) 0.40 Water (Natural streams, no cost) — Packaging (20, US$0.35/unit) 7.00 Miscellaneous costs 7.00 Freight cost 17.20 Subtotal (ST2) 48.20 Total (operating costs/t) = ST1 + ST2 US$65.20 2. Cost of producing 30 t (1 month of operating) US$65.20/t x 30 t/month = US$1956/month 3. Yearly depreciation: Equipment and machinery service life ≈ 10 years Salvage value (junk) ≈ US$300 Production over course of service life ≈ 250 t/year x 10 years = 2500 t Accounting period = 1 year Applying the formula: Dep./t = US$4500 – US$300 ≈ US$1.70 per ton produced 2,000 t Dep./Month = US$1.70 x 30 t ≈ US$51 per month in operation Dep./Year = US$1.70 x 250 t ≈ US$420 per year in operation These costs were updated in 2012 (Da et al. 2012). 520 Sour cassava starch in Colombia Table 26A-1. Cassava starch extraction plant costs (values from September 1998). Item Quantity Cost (US$) Machinery and equipment for the process a Cassava washer/peeler (2 t of roots/hour) 1,000 Cassava grater (2 t of roots/hour) 500 b (300 kg of grated cassava mass/hour) x 2 2,000 c Reciprocating screen 300 Motorized pulverizing mill (1.5 kg/hour) 700 Subtotal 4,500 Plant infrastructure d Sedimentation channels (each 30 m x 60 cm x 40 cm) x 7 15,000 Starch drying patio (2000 m2, 8 cm thick) 18,000 e Fermentation tanks (1.5 m3) x 20 15,000 f General civil engineering work (400 m2) 10,000 g Factory cover or roof 6,000 Starch warehouse (30 m3) 8,000 Black starch deposit tank (30 m3) 8,000 Fiber residue deposit tank (15 m3) 4,000 Power transmission 700 Subtotal 84,700 Total 89,200 a. Different washer/peeler models yield this amount. b. Model: Intermittent mechanical. c. For second sieving. d. Covered in tiles. e. Covered in tiles and wood. f. Columns, walls, floors, and drains. g. Bamboo and zinc, mainly. 521 Cassava in the Third Millennium: … Appendix 4: Wastewater Treatment System Ricardo Ruiz Cabrera4 The cassava starch extraction process consumes large Reactor evaluation quantities of water and produces effluents that have considerable negative impacts on biotic systems when In 1997, the Corporación para Estudios directed into surface streams. From an economic and Interdisciplinarios y Asesoría Técnica (CETEC) set up technical viewpoint, anaerobic systems and, in anaerobic treatment systems in three cassava starch particular, biodigesters are an important alternative for extraction plants in Santander de Quilichao, Cauca, treating these types of effluents. that dump their wastewater into the Mandiva River. This appendix will present and evaluate a normal The reactor constructed in these factories was a digester and a digester complemented by aquatic tank digester supplemented with an aquatic plant plants. system, and their performance evaluation was conducted by the Universidad del Valle Environmental Background Sanitation Department, the results of which were published in the thesis titled: “Evaluación del Wastewater from the sedimentation stage of starch desempeño de dos biodigestores en el tratamiento de extraction is the main environmental problem of that las aguas residuales del proceso de extracción de process. On average, a cassava starch extraction plant almidón de yuca” [Perfomance Evaluation of Two can produce somewhere between 20 and 30 m3 of Biodigesters for Treating Wastewater from the Cassava wastewater per day, depending on the level of Starch Extraction Process] and presented by Javier A. technology used and the hours in a work day. Manrique M. from the Chemical Engineering Department in June 1999. According to the studies conducted by Rojas in 1992, and reported in Rojas et al. (1996), this Study objectives were: wastewater has considerable pollution capacity because it carries large amounts of particulate organic matter, • Setting up and operating a pilot treatment system. possesses moderate acidity, and contains small quantities of the cyanogenic ion (CN–). • Evaluating system performance by measuring the percent of organic and solid matter removed. Several studies have found (Duque 1994) that this type of effluent biodegrades at 70% for an insoluble • Determining the necessary conditions for adapting sample and 92% for a soluble one. The 8% of the matter the biomass to the substrate and for guaranteeing resistant to biodegradation is probably inorganic. the system’s routine operation. Extraction process effluents show OCD5 values Its main conclusions were: between 3000 and 7000 mg/L. The Sanitary Engineering Department, Universidad del Valle, has • Under the conditions in which the reactor conducted different studies that show the feasibility of operated, the largest drop in OCD was 76.6% and purifying wastewater when using anaerobic digestion solid removal was 61%. These values were systems, examples being the two-phase reactor and the recorded for a 21 hour hydraulic retention period, upflow sludge blanket reactor. as illustrated in Table 26A-2. 4. Industrial Engineer, Rural Agro-industry, CETEC, Cali, Colombia. • It is not possible to assert that tank digesters are E-mail: todoyuca97@yahoo.com not a suitable alternative for treating wastewater 5. OCD = Oxygen Chemical Demand. The amount of oxygen a from the cassava starch extraction process. If the determined volume of effluent requires for chemical degradation of the organic matter it contains. OCD is the amount of oxygen operating parameters of the reactor were very for microbiologically degrading the organic matter in an effluent. strictly controlled, particularly pH (which should be 522 Sour cassava starch in Colombia Table 26A-2. Tank digester operating results from a 1999 evaluation conducted by the Universidad del Valle. and Quinimayo basins. Each digester is comprised of two dual layer polyethylene heavy duty polyethylene Parameter Value Value Removal (units) Affluent Effluent (%) tanks, 2.5 m in diameter, with additives to protect against acids and UV light. The tubes are buried in pH 6.7 6.9 different pits with a cross-sectional area of OCDt (mg/L) 3806.17 890.23 76 3 m2. Both ends of the tubes are connected and OCDs (mg/L) 3012.58 816.12 79 completely sealed to concrete boxes that are the TSS (g/L) 0.58 0.23 61.15 affluent inlet and effluent outlet. A sludge evacuation VSS (g/L) 0.52 0.21 60.34 system is attached to the bottom part and a biogas outlet at the top. a. OCDt = total oxygen chemical demand (includes algae in M.O. contents) OCDs = soluble oxygen chemical demand (excludes algae) Digester design parameters are: TSS = total suspended solids (in the effluent, for example) VSS = volatile suspended solids (in the effluent, for example) • Average affluent flow: 2.7 m3/hour between 6.7 and 7.4), then it would be possible to • Minimum hydraulic retention period: 21 hours achieve highly satisfactory results with it. • Required volume: 57 m3 • To maintain wastewater pH within the optimal range for anaerobic digestion, it is necessary to Given these parameters, digester construction have a system that allows an alkalizing solution to requires these elements: be continuously and proportionally introduced into the managed substrate flow. Calcium and sodium • 2 pits, 16 m long, with a net cross-sectional area hydroxide returned good results in that area. of 3 m2 and real cross-sectional area of substrate occupation of 2 m2. • If the alternatives sought out for treating wastewater have to be within reach of social • 2 dual layer, heavy duty polyethylene tanks, 2.5 m sectors with limited access to technology and in diameter and 20 m long. financial resources, then it is worth improving these types of reactors since the infrastructure • 2 brick inlet boxes, 1.0 m3 and 0.70 m high, with a costs are very low. 12” diameter concrete tube. Tank digester description and set up • 2 brick outlet boxes, 1.0 m3, with a 12” diameter concrete tube. This system was set up in two cassava starch extraction plants in the northern sector of the Department of • Sludge evacuation system and biogas routing and Cauca. 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Trop Sci 36:247–255. 525 Cassava in the Third Millennium: … CHAPTER 27 The Use of Cassava Products in Animal Feeding* Julián Buitrago A.1, Jorge Luis Gil2, and Bernardo Ospina3 Introduction moisture level of fresh roots and foliage, its use in poultry and swine diets was not recommended. Improved feeding technology and the introduction of high yielding varieties of cassava have open the The silage processing contributed to improve the possibility to increase its participation in commercial management practices since the roots and foliage could production of animal feeds. Although yields of cassava be chopped and preserved for long periods before they roots may be as high as 60 t of fresh roots per hectare, were supplied to animals. under conditions of commercial cultivation it is possible to obtain production levels of 25 to 40 t of In later stages, natural drying (sun drying) or fresh roots (9.5 to 15 t of dry roots) and around artificial drying (gas, diesel, coal, or steam) was 5 to 10 t of fresh foliage (1 to 2 t of dry foliage) per introduced as a practice for commercial production of hectare. This productivity levels are almost impossible cassava root meal (CRM)5 or cassava foliage meal, which to obtain in tropical environments with other opened the opportunities for large scale feeding agricultural crops of direct application in animal programs, including poultry, swine, and aquaculture feeding. production. The main value offered by cassava root as a Some feed management limitations (dustiness, feedstuff is its capacity to provide starch which is a palatability) with high levels of CRM were overcome with valuable source of useful energy for monogastric and the introduction of new pelleting or extruding techniques. ruminant animals. On the other hand, cassava foliage Through the inclusion of pelletized diets for poultry and provides a high level of protein which can be used for swine, high levels of CRM and cassava foliage meal were ruminants and to a limited extent (as a dried product) included, and the performance results were comparable in monogastric feeding. Table 27-14 illustrates the main to those with conventional cereal diets. nutrients present in fresh and dried samples of cassava products. The following revision shows some of the most relevant results with the inclusion of different products Most of the early studies with cassava products derived from cassava roots and foliage (fresh, ensiled, were based on the use of fresh roots in swine and cattle natural drying, artificial drying, and pelletized diets). The feeding as a day-to-day practice. Due to the high first part is directed to traditional feeding practices with fresh and ensiled products for swine and ruminants. The second part also presents traditional information with dried products for poultry, swine, and ruminants. The * This chapter contains an authorized adaptation of text presented in the publication “The Cassava Handbook”, edited by Reinhardt third part provides more recent developments, especially H. Howeler, 2012. related to the introduction of fullfat soybean (FFSB) as a 1. Medical Veterinary, consultant of CLAYUCA, Cali, Colombia. strategic complement to dried cassava diets in poultry E-mail: julianbuitrago@yahoo.com 2. Zootechnician, research assistant of CLAYUCA. and swine feeding. E-mail: j.l.gil@cgiar.org 3. Executive Director, CLAYUCA. E-mail: b.ospina@cgiar.org 4. To facilitate readability, all of the 70 tables referred to in this 5. For an explanation of this and other abbreviations and acronyms, chapter can be found at the end of this document before the see Appendix 1: Acronyms, Abbreviations, and Technical References section. Terminology, this volume. 526 The Use of Cassava Products in Animal Feeding Fresh and Ensiled Cassava Roots and Foliage for Swine and Ruminants The usual feeding practice in most traditional experiences with fresh cassava has been the daily supply of the whole chopped roots supplemented with a dry mixture of protein and micro ingredients (vitamins, minerals, and feed additives). As anticipated, this practice is mainly suitable for small-or medium-size swine and cattle enterprises where cassava production is usually a complement to the animal operations and where hand labor is not an important limitation. Figure 27-1. Fresh cassava chips. For larger and more technified operations, the heavy hand labor requirements, the perishability of the product, and the troublesome management of the daily feeding program limit the extensive use of fresh products. The use of dried mixtures in automatic feeding systems is the general trend in these cases, where cassava roots and/or foliage should be dried and, preferably, pelletized, to be included in commercial diets. Although the information with fresh and ensiled roots for swine and cattle feeding is quite lengthy, a summarized report of the most relevant studies is included, with special emphasis on the experimental work conducted at the Centro Internacional de Agricultura Tropical (CIAT), the Colombian Institute of Agriculture (ICA), and the Latin American and Figure 27-2. Cassava chipper. Caribbean Consortium to Support Cassava Research and Development (CLAYUCA). Performance Results with Fresh Cassava Roots in Swine Feeding Programs based on fresh cassava are suitable for feeding growing-finishing pigs and breeding sows. Due to the high moisture and low energy of roots, the animals have to be supplied with ample amounts of chopped cassava roots and a limited amount of a dry protein supplement (Figures 27-1, 27-22, and 27-3). Nevertheless, in most cases the animal is not able to consume the total energy requirements even though the product is offered at free choice. The maximum Figure 27-3. Chipping fresh cassava. consumption of fresh roots obtained in most studies is around 3 kg for growing pigs, 4 kg for finishing pigs, and 6 kg for lactating gilts, which is less than the In the day-to-day feeding management program, expected consumption of 3.5–4, 5–6, and 8–10 kg, cassava can either be supplied in a mixture together respectively. Based on these limitations, the with the nutritional supplement or separately. performance is partially affected although in most Nevertheless, free choice supply of the supplement cases the cost:benefit criteria is positive for the small often results in over-consumption of protein, minerals, producer. and vitamins, which generally raises the price and makes the feeding program inefficient. 527 Cassava in the Third Millennium: … The most recommended programs to fulfill the supplement without affecting the performance of pigs’ nutritional requirements and at minimal animals. production costs are based on nutritional supplement supply in a daily controlled scheme, according to age The information obtained from the performance and weight of the animals. results confirms most of the observations already mentioned and illustrates some new approaches to be Fresh cassava from sweet varieties can be considered for a more efficient use of fresh roots. supplied either at free choice to pigs or in controlled amounts to avoid waste, although consumption In general, performance results are a little lower than should not be restricted. Each day, the corresponding those obtained with commercial corn-soybean meal amount of fresh roots must be offered to the animals (SBM) diets. The main reason is associated with a lower (Figure 27-4). consumption of DM when cassava roots are fed fresh, due to the incapacity of the pig to consume larger levels of the fresh product. The high humidity, and probably the effect of low levels of hydrocyanic acid (HCN) still present in sweet varieties of cassava roots, may also have some influence in this situation. When the protein supplement is provided in a free choice arrangement, the animals will consume larger amounts as compensation to the reduced consumption of cassava roots. Therefore, an over-consumption of protein (approximately an extra 20%) will occur, which results in the higher cost of the total diet (Tables 27-3 and 27-5). The over-consumption of protein supplement is observed regardless of the ingredients used in the formulation, but the inclusion of intermediate levels of meat meal and blood meal seem to stimulate a further Figure 27-4. Pig feeders for fresh cassava. increase in the daily consumption (Table 27-5). As a mechanism to avoid the over-consumption of When pigs weight less than 50 kg, they consume the protein supplement, it should be offered every day in smaller amounts of fresh cassava (2.5–3.5 kg/day), but controlled amounts related with the body weight of the afterwards, during the final fattening stages, pig. Although the protein consumption is controlled, the consumption should increase up to 4.0–4.5 kg/day. total consumption of DM is still deficient due to the Since these quantities still do not provide the pig with lower cassava intake, which partially affects the animal’s the required dry matter (DM) or energy level to obtain performance (Table 27-3). maximum performance, the animal tries to compensate this deficit with a higher consumption of In Table 27-4 it can be observed that the addition of the nutritional supplement (in the case that it is offered sugarcane molasses or raw sugar to the cassava roots at free choice). resulted in a small increase in consumption of roots and DM, and a lower consumption of the protein In the following tables, results of different trials supplement, which improves the energy:protein ratio as with growing-finishing pigs and breeding females are well as the performance of the pigs. analyzed. Lowering the protein content of the supplements Fresh cassava roots for growing-finishing pigs also helps in reducing protein consumption in pigs, although the consumption of fresh roots is also reduced. Tables 27-2 to 27-7 illustrate different feeding The total DM intake from cassava roots are reduced, approaches which have been tested as viable while the supplement consumption and weight gains are alternatives to maximize the consumption of fresh improved by providing lower protein percentages, which roots and to avoid the over consumption of protein also results in a better feed conversion (Table 27-6). 528 The Use of Cassava Products in Animal Feeding When bitter varieties (i.e., CMC-84) of fresh cassava Performance Results with Ensiled roots are used, a decrease in its consumption is Cassava Roots in Swine Feeding observed with a parallel increase in the consumption of protein supplement when it is offered ad libitum A large proportion of the information obtained with (Table 27-7). However, when the protein supplement is fresh cassava in animal feeding also applies to the controlled to the required daily level, both the cassava preserved product obtained through the silage process and the protein supplement consumption are reduced, (Figures 27-5, 27-6, and 27-7). creating a larger deficit in the daily energy intake and a drastic reduction in animal performance. The principal nutritional differences are due to the starch fermentation and the reduction in moisture Fresh cassava roots for gestating and lactating gilts A small number of studies with fresh cassava roots have been conducted during gestation and lactation. While gestating females need small amounts of energy to fulfill their requirements, lactating females require two to four more intakes of energy as well as protein. Therefore, the reduced consumption of cassava roots should not be an important limiting factor in gestation, in contrast to the high demand during lactation. Table 27-8 summarizes the feed treatments and the performance results of gestating gilts kept on pasture or in confinement. Both cassava roots and the 40% protein supplement were offered in controlled amounts to supply the daily requirements. The feeding of gilts on pasture was adjusted so they received smaller amounts of cassava and protein supplementation since the pasture provided part of the requirements. The daily feed intake of cassava and protein Figure 27-5. Ensiled cassava chips. supplement corresponded to the predicted daily need of DM and protein during gestation. While cassava fed gilts gained more weight during gestation, the litters were smaller and lighter. Piglet weight and litter weight at birth were lower in case of the cassava treatments, especially in the confined gilts. On the other hand, the performance of sows and litters during lactation was not affected by the inclusion of cassava roots and protein supplement in a balanced proportion (Table 27-9). The mixture of cassava roots and protein supplement was equivalent to a 16% protein diet on a DM basis, which is similar to the control group given a corn-SBM diet. Daily consumption of DM in the cassava group was smaller (3.40 kg) than in the control group (4.32 kg). In spite of the reduced consumption of DM, total litter weight at weaning was not affected, even with the smaller litter size of the cassava fed sows. The sows from the control group gained a little more weight during lactation since their DM consumption was higher. Figure 27-6. Cassava roots silage in small polyethylene bags. 529 Cassava in the Third Millennium: … roots in a free choice supply and the controlled supply of protein supplement. Table 27-10 refers to growing-finishing pigs which were fed three possible cassava-based feeding schemes: fresh roots, ensiled roots, and ensiled roots plus foliage. In all cases, the cassava products were supplemented with a fixed amount of protein supplement (38% protein) to satisfy the daily requirements. From the performance results it may be concluded that the silage process of cassava roots is a valid alternative to be considered as a mechanism to preserve their nutritional value. The high perishability of the fresh roots may be overcome through the inexpensive practice of anaerobic silage production, which also facilitates the feeding management practices for the small- and medium-size producer. Table 27-10 shows a very similar response in weight Figure 27-7. Cassava silage in big bags. gains and feed efficiency when fresh roots are compared with ensiled roots on a DM basis. However, the inclusion of cassava foliage to the ensiled product during the silage production process. Again, negatively affected the consumption of the silage, monogastric animals, like swine and poultry, generally which is reflected in lower weight gains and poorer feed are not able to consume the total amount of DM from conversion ratios. The lower consumption of the the ensiled roots to satisfy the energy requirements combined roots and foliage silage may be related to the during the higher demanding phases. Their lower palatability of leaves and stems even at minimum performance is slightly affected in terms of weight levels (10%). gains, although feed efficiency and production costs will probably compensate for the slower weight gain. The information presented in Table 27-11 illustrates Growing-finishing pigs, gilts, and sows are suitable to the possibilities to include different ingredients as be included in feeding programs based on cassava protein supplements to cassava silage in growing- silage, once the performance limitations are finishing pigs. Excluding the high cottonseed meal considered. supplement, where the consumption was reduced, these alternatives compare favorably with pigs fed As was already mentioned with the fresh cassava commercial balanced diets. feeding practices, the ensiled product also has to be offered in a day to day scheme. Protein The addition of 2% common salt (Table 27-12) to supplementation can be offered at free choice or in the cassava root silage showed a beneficial effect on daily controlled amounts. However, the most feed conversion rate, without affecting the weight recommended feeding practice consists in ad libitum performance of pigs. The same experimental work supply of ensiled chopped roots plus a controlled demonstrated that silage stored for long periods (more quantity of protein supplement which has to be than 6 months) does not affect production periodically calculated to fix the precise amount to be performance of pigs. The ensiled product progressively offered. decreases in moisture content which resulted in better feed conversion ratios. Ensiled cassava roots for growing-finishing pigs Ensiled cassava roots for lactating sows The following information on the performance of pigs In a similar experimental comparison as the one included in different feeding demonstrations with described for fresh cassava roots, ensiled cassava roots ensiled cassava, considers the use of ensiled cassava were also included in diets for lactating sows. Protein 530 The Use of Cassava Products in Animal Feeding supplemented cassava silage diets were compared with based on conventional sources and the same green corn-SBM diets, either fed as mixed or separated forage (Table 27-14). products (Table 27-13). Confined milking cows also showed a slightly Performance of sows and litters was not affected by superior production of milk associated with the the use of cassava silage as total replacement of the consumption of cassava roots and protein supplement cereal grains normally used in the dry lactation feeds. in addition to star grass hay (Table 27-15). Even though the amount of cassava silage was more than twice the amount of dry feeds consumed by the Fresh cassava roots for beef cattle sows, a small shortage of DM and energy is still observed in their total daily consumption. However the The results of a feedlot study are shown in Table 27-16 performance of sows and their litters was not affected in which growing-finishing steers were supplemented up to weaning time. Litter size, individual weights, as with a fixed level of fresh grass (elephant grass) plus well as total litter weight were comparable among different dry supplements vs. the cassava group which treatments, which demonstrate the feasibility for the was fed a similar quantity of fresh grass plus fresh inclusion of cassava root silage as the main component cassava roots and a protein supplement with a high for lactating sows (Table 27-13). level of urea. One part of the protein supplement was mixed with 10 parts of cassava roots as a complement Performance Results with Fresh Cassava to the fresh grass in this last group. Roots in Ruminant Feeding The performance results demonstrated excellent Fresh cassava roots for dairy cattle growing rates and feed efficiency in the cassava fed group. The inclusion of a high level of urea in the Tables 27-14 and 27-15 show the effect on the cassava group provides an important advantage by performance of heifers and milking cows when the replacing a high percentage of other costly protein feeding treatments were mainly based on fresh cassava sources. roots and protein supplements. Performance Results with Fresh Cassava Heifers fed with cassava roots and protein Foliage in Ruminant Feeding supplement (Figure 27-8), in addition to green forage (sugarcane tops), showed a slightly superior daily weight The use of fresh cassava foliage is almost limited to gain than heifers receiving a commercial concentrate ruminant feeding, considering its high moisture (70%–72%) and fiber (4%–6%) levels. Due to its high quantity and quality of protein, the fresh product resembles conventional legumes and is suitable as a forage supplement for ruminants (Figure 27-9). The best quality foliage should contain a larger proportion of green leaves, petioles, or tender parts from branches, and a minimum of stems or woody Figure 27-8. Calves consuming fresh cassava. Figure 27-9. Chopped cassava fresh foliage. 531 Cassava in the Third Millennium: … parts of the plant. The age of the plant is also an important factor in defining the nutritional quality: when cuts are made from the early stage forage (i.e., less than 3 months) and thereafter harvested at frequent intervals (i.e., every 2–3 months), an excellent product can be obtained in terms of nutrient quality and quantity. Special care should be taken with fresh forage due to the higher level of HCN in leaves and petioles. The chopping or cutting procedure plus a wilting process during at least 6 hours is very effective in reducing the HCN concentration to safe levels in cattle feeding. Figure 27-11. Drying trays for cassava root chips. Tables 27-17 and 27-18 illustrate three examples with dairy and beef cattle where cassava foliage is included in a large proportion of the feeding program. In all cases there was an improvement in animal performance associated with the inclusion of cassava foliage. In one of the trials, cassava foliage was offered as a total replacement of alfalfa forage with superior performance results (Table 27-17). Dry Cassava Root and Foliage Meal for Poultry, Swine, and Ruminants The information concerning the use of dried cassava Figure 27-12. Industrial drying of cassava root chips. products for animal feeding is quite ample in all productive species, mainly swine, poultry, and ruminants. The dried products can be handled more easily and with higher accuracy than programs based on fresh or ensiled cassava (Figures 27-10 to 27-15). The roots and foliage are dehydrated in order to increase the total nutrient concentration and to facilitate the preservation of the finished feed. In addition, dehydration by heat eliminates most of the cyanogenic components which produce toxic and deleterious effects on animal performance. Figure 27-13. Dried cassava chips. CRM is essentially a carbohydrate product with a high concentration of starch (60%–65%). The metabolizable energy content of good quality meal for poultry and swine is around 3.20 and 3.40 Mcal/kg, respectively, while the total digestible nutrient (TDN) content is around 86%. Its main nutritional limitation is due to the low protein level, so that protein supplementation is required, with special emphasis on Figure 27-10. Solar drying of cassava root chips. the first limiting aminoacid: methionine. 532 The Use of Cassava Products in Animal Feeding to the elements of less importance on the root (protein, aminoacids). Based on the above classification, it is possible to recommend the use of CRM, according to more precise nutritional criteria, and better adapted to the different animal production stages, as follows: Grade 1: broilers, piglets, and aquaculture Grades 1 and 2: layers, growing-finishing pigs, and calves Grades 1, 2 and 3: pullets, gestating, and lactating pigs Grades 1, 2, 3, and 4: dairy, beef, goats, and horses. Conversely, cassava foliage meal is characterized by its high fiber and protein levels. Depending on the leaves:stems ratio and the age of the plant, crude fiber may range between 18% and 30%, while the protein content may vary from 16% to 28%. Under practical conditions, the green plant top or its third superior aerial part, should be considered as the recommended material to be processed. Figure 27-14. Cassava root flour. The plant top is a mixture of leaves, petioles, and primary and secondary stems. The proportion in which these elements participate in the final product will determine the nutritional quality of the foliage meal. Table 27-20 illustrates the differences in separate samples of the foliage components. Different alternatives may be considered when foliage tops are harvested for feeding purposes: a single cut may be obtained simultaneously with the root at harvesting time, or the top cuts may be obtained periodically (every 2–3 months) without root harvesting. Moreover, the cassava crop can be completely oriented for just foliage production. Figure 27-15. Dried cassava foliage flour. It is also important to note that foliage meal from early regrowth (less than 3 months) will provide better The quality of the roots being dehydrated to nutritional characteristics (more than 18% protein and produce CRM has a natural, direct influence on the final less than 20% fiber) in contrast with late regrowths quality of the product. Roots with fibrous impurities (less than 18% protein and more than 20% fiber) as is (stems, leaves, peels, waste material) or those illustrated in Table 27-21. contaminated with sand or soil affect the nutritional quality and reduce the energy concentration. Performance Results with Dried Cassava Roots in Poultry Feeding Although there is not an official method to grade the quality of CRM, Table 27-19 shows an approach, based The results of some selected experiences will be on the proposal of Muller et al. (1972), and presented in the following tables, where CRM is complemented by the authors of this chapter. This included in medium to high levels of the diet for initiative refers principally to the parameters of primary broilers and layers. Most of the early demonstrations importance for determining the energetic value (main were conducted with ground diets and free choice contribution of the roots), and giving a secondary value consumption. In the more recent experiences, pelletized 533 Cassava in the Third Millennium: … diets were introduced as an important mechanism to Once the nutrient adjustments are introduced in improve the performance of broilers and to reduce the diets with high levels of CRM, improvement on dusty conditions in diets with high cassava meal production parameters are generally obtained. The content. essential aminoacid methionine and the energy concentration are important factors in egg production The economic considerations when CRM replaces and egg size, while linoleic acid is mainly involved in corn or other cereal grains in commercial operations egg size. Tables 27-26 and 27-27 illustrate the effect of should consider the lower energy and protein values of high levels of CRM when the diets are correctly the cassava root. These limitations normally indicate balanced in energy and methionine. The results that CRM should have a cost not higher than 70% to obtained in egg production, egg size, and feed 80% of the price of corn. conversion ratio are generally comparable with corn- SBM diets. The use of FFSB (8% linoleic acid) shows a Dried CRM for broilers favorable effect in the size, pigmentation, and weight of eggs (Table 27-27). Table 27-22 illustrates an early, but conclusive study to measure the effect of diets where cassava meal Performance Results with Dried Cassava gradually replaced corn as the energy source for broiler Roots in Swine Feeding diets, without the adjustment of energy level. The results show a slight decrease in performance mainly Several experiments have been conducted with swine associated with higher levels of cassava meal due to in order to demonstrate the effect of different levels of the reduction in metabolizable energy. CRM in conventional feeding programs for piglets, growing, finishing, gestating, and lactating pigs. Partial The inclusion of vegetable oil in diets with high to total substitution of cereal grains, inclusion of cassava meal compensates the lower energy and different protein supplements, and comparisons provides an improvement in performance of broilers, between sweet and bitter varieties of cassava have been as is illustrated in Table 27-23, where the diets analyzed in a large number of feeding trials. contained different levels of cassava meal but similar protein and metabolizable energy concentrations. In As already mentioned in poultry feeding, with high addition, vegetable oil provides an increment in linoleic levels of cassava meal the dustiness of the diet may acid, which is an essential fatty acid for poultry. Total become one of the main limitations for an efficient use replacement of corn by cassava meal did not affect of the mixed diet. The addition of sugarcane molasses, body weight or feed conversion of broilers. animal fat, or vegetable oil helps in the prevention of the dusty presentation and to avoid feed waste. Pelletized diets provided an additional benefit to Whenever it becomes possible, pellet processing is the high cassava meal diets at the different levels of best practice when high levels of cassava meal have to cassava meal inclusion for broiler diets (Table 27-24). be included. Dried CRM for layers Similarly to poultry feeding, the cost of cassava meal compared to corn or other cereal grains is the key The inclusion of dried cassava roots in layer feeding factor in deciding the economics of its use. The lower has also been experimented in different comparisons energy and protein concentration in CRM generally where corn is gradually replaced. In several of the bears to an adjustment in the price of cassava meal, earlier studies there was not a precise adjustment in which, in general, should be equivalent to around some of the nutrients, mainly metabolizable energy, 70%–80% of the price of corn. methionine, and linoleic acid (Table 27-25), which lowers the production performance. Dried CRM for growing-finishing pigs Egg production and feed conversion ratio are Feeding practices with dried cassava roots have been affected in most cases when cassava meal replaces extensively studied during the growing-finishing stage corn without adjustments in the diet, especially at high of pigs. Some of the most representative feeding levels of substitution. Egg yolk pigmentation is also studies have been selected in the following tables, affected with high levels of CRM due to the absence of which summarize the performance results under xantophyl pigments in roots, in contrast with its high different environmental and management conditions. concentration in cassava leaves. 534 The Use of Cassava Products in Animal Feeding Table 27-28 compares sweet (less than 80 ppm controlled quantities during gestation and at free HCN) and bitter (150–200 ppm HCN) varieties of CRM choice during lactation. In general, there are no as the main source of energy in diets for growing pigs. detrimental effects in performance due to cassava Although the sun drying process partially reduced the usage, although the first trial (Table 27-32) shows a HCN content, there is still a negative effect in smaller litter size with no differences in the individual consumption and weight gains of the pigs. However, weight of piglets. Conversely, Table 27-33 shows no this effect is very marginal compared to the effect differences in litter size, individual piglet weight, or total observed when the roots are fresh, since all HCN litter weight. The weight differential between breeding remains in the tissue of the unprocessed product. time and weaning time of females was not affected when CRM totally replaced corn. In most studies the inclusion of low HCN cassava root varieties can replace cereal grains without Dried CRM for piglets detrimental effects in growing-finishing pigs, even though in some trials no adjustments were made in the Creep feed for lactating piglets with increasing levels of energy levels of high cassava diets (Table 27-29). Yields cassava meal has been offered from 10 days up to of lean meat cuts were not affected and no clear weaning time. The first trial results during a lactation differences were noticed on fat percentages, fat quality, period of 30 days are summarized in Table 27-34. No or saturation index (iodine number), although all differences were observed in performance of piglets animals showed a larger proportion of body fat proper with levels up to 20% of CRM in the diet. Weight gains, to the crossbred pigs available at the experimental feed consumption, and feed conversion were equivalent time. to piglets receiving diets with corn. In a second feeding trial (Table 27-35), creep feed diets with 0%, 20% and The addition of cane molasses, raw sugarcane, or 40% cassava meal were compared in order to measure animal fat to diets based on CRM as the only energy consumption of lactating piglets when fed at free source, did not contribute to the improvement of feed choice up to weaning time at 56 days. There was a consumption or performance in growing pigs, as positive effect in feed consumption associated with shown in Table 27-30. Animal fat addition decreased higher levels of cassava meal. Palatability of the diet feed consumption and improved the feed conversion and performance of piglets were clearly improved with ratio, due to the increment in energy density of the increasing amounts of CRM, even though dustiness diet. Unexpectedly, methionine supplementation did was greater in these diets. not improve the performance of growing pigs in this study. Nevertheless, in other experiments the beneficial Performance Results with Dried Cassava effect of methionine supplementation to diets Roots in Ruminant Feeding containing high levels of cassava has been observed. CRM diets have been used at different stages of Table 27-31 illustrates the positive response to ruminant nutrition. A selection of experimental diets methionine, compared to other sulfur sources in an and production performance obtained in calves, effort to explore the effect of sulfur in cassava based milking cows, and growing-finishing steers are diets with high levels of HCN. included in the following tables. Dried CRM for gestating and lactating sows Dried CRM for calves The continued use of high levels of CRM has also Tables 27-36 describes different feeding treatments been tried during gestation and lactation in order to with variable levels of CRM for early feeding of calves. evaluate its effects on the mothers and on their At low levels of cassava meal, performance was offspring. Tables 27-32 and 27-33 summarize the maintained close to those of the corn or sorghum- results observed in performance of Yorkshire and based diets but levels higher than 25% usually Duroc x Yorkshire females during gestation and produced a slight decrease in consumption and growth lactation, as well as in piglets during the lactating rate of calves. In this experiment calves were raised period. with cow milk until the sixth week, and from this moment until the fourth month the dry diet was In Tables 27-32 and 27-33 a corn-based diet was provided at free choice plus forages (alfalfa hay or compared with diets where the corn was completely ensiled sorghum) at free choice. replaced by CRM. The 16% protein diets were offered in 535 Cassava in the Third Millennium: … Dried CRM for dairy cows An important factor in cassava foliage, relevant to poultry feeding, is its high content in xanthophyll The results from two experiments with dairy cows are pigments (500-600 mg/kg), which improves the described in the following tables. Table 27-37 presents pigmentation of skin in broilers and egg yolk in layers results in milking cows where dried diets were supplied when used at levels between 5% and 8% of the diet. in addition to sorghum silage. The inclusion of CRM in substitution of 50% of the sorghum in the dried feed The best quality forage meal contains a larger did not affect milk production. Similar results were proportion of leaves and young stems which can be observed when cassava meal replaced oats as the main easily obtained from plants less than 3 months of age. energy source of the dried supplement (Table 27-38). The nutritional quality decreases as the plant gets older and the leaf:stem ratio changes to a lower proportion of Dried CRM for growing-finishing steers young leaves. Steers under intensive grazing or under total Though HCN levels in dehydrated foliage are confinement have also been included in experiments generally over 200 ppm, the low foliage percentage where CRM has been used as a component of the dried recommended for poultry and pigs usually does not feed supplements. present a danger of toxicity; however, in some cases, a HCN content can affect the palatability of the diet, and, Table 27-39 shows the results with growing- eventually, cause toxicity problems. finishing steers under intensive grazing (4.8 head/ha) conditions, supplemented with controlled quantities of It is suggested than no more than 6% of forage dry feed based on CRM, cane molasses, urea, and meal is included in broiler diets and no more than 10% blood meal. Animals with higher levels of cassava in layer diets. The addition of methionine and fat to consumption showed a slight increase in daily weight these diets is a recommended practice in order to gain. overcome the deficit in these nutrients. At this low level of usage, the cyanide content in dried forage does not Table 27-40 shows the results with feedlot steers constitute a limiting factor. consuming a controlled amount of sorghum silage plus a free choice of dry supplement based on cassava meal Dried cassava foliage meal for broilers or sorghum. Daily feed consumption of the supplement decreased with increasing levels of cassava meal. Low (less than 6%) levels of cassava foliage meal may Conversely, sorghum silage consumption was be used, mainly as a natural skin pigmenter, with a very increased to fulfill the energy deficit. Nevertheless, light negative effect on feed consumption and weight there was a negative effect on daily weight gains gain. When the inclusion of the foliage is higher than associated with lower supplement consumption as a 6%, the growth rate and feed consumption are result of increasing levels of CRM in the diet. negatively affected. When a high level (more than 15%) of cassava foliage is compared with alfalfa meal, the Performance Results with Dried Cassava performance results are negatively affected in both Foliage in Poultry Feeding treatments, but a larger effect is observed for cassava foliage (Table 27-41). In general, dried cassava foliage does not have a significant potential for poultry feeding due to its low Table 27-42 also shows the results of diets with energy level and poor palatability. As it happens with high levels (20%) of cassava foliage and the effect of other forage products, fiber is a limiting factor which methionine supplementation, since this aminoacid dilutes the concentration of the essential nutrients, becomes limiting in this type of diets. The growth rate mainly energy and protein. Although the protein level is negatively affected with high foliage content. in good quality dried cassava foliage is high However, up to 0.3% methionine addition improves the (18%–26%), the high fiber and low energy growth performance, although it does not reach the concentration limits its use to levels not higher than levels obtained by broilers consuming high energy 10%. The aminoacid profile is characterized by the high diets. lysine content (7.2 g/100 grams of crude protein) and the low methionine level (1.7 g/100 grams of crude protein). 536 The Use of Cassava Products in Animal Feeding Dried cassava foliage meal for layers adjustments may be obtained if the dried cassava foliage is included at levels not larger than 6%–8%. Little information is available in performance of layers fed cassava foliage diets, except in relation to its Recent Developments with Dried Cassava pigmenting effect on egg yolk. Table 27-43 shows the Roots and Foliage Meal for Poultry and effect of low levels (2.5% and 5.0%) of cassava foliage Swine meal when added to white corn diets in comparison with yellow corn diets. There is a linear response to higher Although cassava meal can be combined with several levels of cassava foliage, although the pigmenting effect ingredients in order to obtain balanced diets, the FFSB of yellow corn is still superior at this low level of foliage has become a strategic product considering its meal. In recent evaluations, cassava foliage meal at nutritional benefits which somehow complements levels around 8% show a pigmenting effect similar to some of the cassava limitations (Figures 27-16 and yellow corn, without affecting the performance of layers. 27-17). FFSB refer to the heat processed soybeans, through extrusion or toasting processes (Figures 27-18 Performance Results with Dried Cassava and 27-19), which will guarantee the needed Foliage in Swine Feeding temperature to eliminate the antinutritional factors (trypsin inhibitors, hemaglutinins, and lipoxygenase) Once again, since pigs are monogastric animals, the present in raw soybeans. inclusion of cassava foliage does not have an important role in commercial feeding programs, especially for high The inclusion of cassava meal and FFSB as the energy demanding growing-fattening pigs. Gestating main ingredients in diets for poultry and swine, and lactating females provide a larger space for the simplifies the feeding programs in most of their inclusion of a higher percentage of cassava foliage, productive stages, where there is a high need for considering the need for crude fiber during these stages. metabolizable energy, essential aminoacids, lecithin, The high fiber content, low energy, and poor palatability of dried cassava foliage are the main limiting factors for its inclusion in swine diets. As a general recommendation it is suggested that no more than 8% of cassava foliage meal may be included in the diets of growing-finishing pigs, no more than 15% in gestating females, and no more than 10% in lactating females. At this low level of usage, the cyanide content in dried foliage (200–500 ppm) does not constitute a potential danger of cyanide poisoning in pigs. Methionine and fat supplementation is a recommended practice whenever cassava foliage is included. Dried cassava foliage meal for growing-finishing Figure 27-16. Cassava root flour. pigs Some of the early studies (Tables 27-44 and 27-45) showed the effect of including more than 10% of dried cassava foliage in growing-finishing feeding programs. In every case there was a reduction in feed consumption and growth rate of pigs, even though the non-cassava foliage diets still did not have the needed energy concentration for modern genetic pig breeds. In the high demanding energy diets of modern lines, metabolizable energy and methionine supplementation are key factors to partially counteract the poor production performance with high cassava forage diets. These nutrient Figure 27-17. Fullfat soybeans. 537 Cassava in the Third Millennium: … In consideration to the previous observations, the following sections of this chapter will present various animal feeding programs for broilers, layers, and pigs, based on different combinations of CRM and FFSB (extruded or toasted FFSB). Performance Results with CRM and FFSB in Broiler Feeding Since the balanced feed for broilers is generally prepared in the form of a pelletized or crombelized product, the recommendations for the levels of CRM that can be used may go as high as the total substitution of cereal grains in diets for starting and finishing broilers. The dusty feature of diets with high levels of cassava meal is totally overcome during the pelletization process, without the need of agglutinants Figure 27-18. Soybean toaster. or special additives. The high oil content of these diets, due to the inclusion of FFSB, is also an important factor to improve the pellet quality. Moreover, this type of diets allows the incorporation of maximum levels of CRM (45%–50%) as well as the needed quantity of cassava foliage meal (5%–6%) in order to guarantee the proper pigmentation of broiler skins. When the starting point is the mixture of CRM, cassava foliage meal, FFSB, and SBM, it is possible to formulate perfectly balanced diets for broilers, following the most recent National Research Council (NRC, 1998) nutritional requirements, in which these three ingredients can represent more than 95% of the total feed, as illustrated in Table 27-47. Table 27-48 provides more detailed information about the nutritional composition of the above mixtures. Performance results based on diets with low and medium levels of cassava meal in broilers Even though the results obtained with the total replacement of cereal grains by cassava meal in pelletized diets have demonstrated that this criterion Figure 27-19. Soybean extruder. may become a viable practice in commercial feeding programs for broilers, it is possible that in many occasions, it is more convenient to use a partial and fatty acids. Cassava is rich in starches and substitution of the traditional cereal grains. This last energy, but poor in essential aminoacids and fatty modality is even a must when the diets are prepared in acids. On the other hand, FFSB are poor in starches, meal or flour presentation, considering the dusty but rich in essential protein, lecithin, and essential characteristics of the CRM. Nevertheless, pelletization fatty acids. or extrusion is always a very useful practice whenever CRM or other dusty products are used in a considerable As Table 27-46 indicates, the low concentration of percentage of the diet. some essential nutrients observed in CRM can be satisfactorily compensated by their high Tables 27-49 and 27-50 illustrate the composition concentrations in FFSB. of the diets with intermediate levels of cassava meal 538 The Use of Cassava Products in Animal Feeding plus FFSB, in which the objective was the substitution long as FFSB is included to provide the deficit of of about 40%–50% of the corn or sorghum used in energy, fatty acids, and protein. pelletized diets for the starting (0–21 days) and finishing (21–42 days) phases. Table 27-55 shows the overall performance of broilers until 42 days when the trial was finished. All Based on previous laboratory trials conducted with groups consuming cassava products and FFSB a small number of animals, the above diets were then obtained similar or better weight gains and feed tested with a larger number of chickens on commercial conversion ratios when compared to the control group farms in two locations: diets from Table 27-49 were fed with corn and SBM. The consumption of the tested under mild environmental conditions in the balanced feed was not affected by the inclusion of high Cauca Valley of Colombia (24 oC, 78% humidity, levels of cassava meal during the starting and finishing 1050 masl) and diets from Table 27-50 were tested production phases. under a warmer environment (32 oC, 86% humidity, 40 masl) near the north coast of Colombia (Cereté, In the treatments that included CRM, the effect of Córdoba). A total of 15,350 birds were used in the first artificial drying was superior to the sun drying trial and 72,400 birds were used in the second trial. In procedure. Both steam and gas drying equipments both cases, the cassava diets were compared with were equally effective for the drying process. The high corn-SBM commercial diets with similar nutrient temperature obtained during the artificial drying composition. facilitates the gelatinization of starches and the control of pathogenic germs. These two factors have probably The results obtained with respect to the an important influence on the superior performance of performance of broilers are shown in Tables 27-51 and these groups when compared with the sun dried 27-52. In general, it can be concluded that broilers cassava group. consuming diets with a substitution of 50% of corn or sorghum by CRM had the same (or better) performance Although the diets with a high percentage of than those that consumed the conventional diets with cassava meal and FFSB contain high potassium levels cereal grains. In terms of weight increase, feed in their final composition, it was not observed to have conversion ratio, and carcass yield, there were no an adverse effect on the chicken manure and humid significant differences. Adverse effects, above the litters. Humidity of the manure was analyzed at weekly normal figures, were not observed in terms of mortality intervals and no significant differences were observed. or morbidity as a result of the inclusion of CRM as the Additionally, the measure of the moisture content of main energy source plus FFSB as the main protein the litter did not indicate differences among groups. source. Differences in humidity of the litter used in the different poultry houses were not appreciable either. Through external measurements of the skin and by checking the chicken carcasses after sacrifice, Performance results based on diets with pigmentation of legs, skin, and internal fat were maximum levels of cassava root and cassava analyzed. The groups with diets based on just cassava foliage meal in broilers roots showed a poor pigmentation, while the group with cassava roots and foliage showed a pigmentation Experimental work conducted at CIAT compared a grade similar to that of the control group fed with diets commercial pelletized broiler diet based on corn and based on yellow corn. The visual appreciation on a SBM with pelletized diets totally based on cassava root scale from 1 (pale) to 5 (optimum pigmentation), gave and cassava foliage meal supplemented with FFSB. both the control and the group fed with cassava roots The comparison between solar dehydration and plus foliage meal a grade of 4, while the other groups artificial dehydration of cassava roots was also included without cassava foliage obtained a grade of 2 on the in the same study. A detailed description of the pigmentation scale. experimental diets as well as its nutritional composition for the starting (0–21 days) and finishing (21–42 days) Performance Results with CRM and phases is presented in Tables 27-53 and 27-54. FFSB in Layer Feeding Performance results demonstrated the feasibility of Feeding programs for layers generally involve the use preparing broiler feeding programs totally based on of diets in meal presentation, which becomes an CRM as the main energy source and limited levels of important limitation for the inclusion of high levels of cassava foliage meal as a partial protein source, as CRM due to the dustiness of the final product. This 539 Cassava in the Third Millennium: … situation is no longer a problem when low or medium No important differences were observed in the levels of CRM are included. Unless the possibility of production parameters of all experiments. Laying using pelletized or crombelized diets is considered, it is percentage and feed conversion was similar in diets difficult to incorporate levels higher than 25% of with no CRM compared to diets with 10%, 15%, and cassava root flour. 20% CRM. A slight reduction in egg laying percentage and feed conversion was observed in brown layers fed In relation to cassava foliage meal, it is also with 10% or 20% CRM (Table 27-67). recommended that its use in diets should not exceed levels of 6% in order to minimize the negative effects Performance Results with CRM and on palatability or high HCN presence in the feed. When FFSB in Swine Feeding high quality foliage meal is included at levels between 5% and 6%, a satisfactory pigmentation of egg yolks is Nutritional considerations already analyzed in poultry obtained, due to the presence of natural xanthophylls. feeding based on cassava and FFSB have a close similarity with other monogastric animals, mainly Table 27-56 illustrates an example of diets for swine. CRM and cassava foliage meal can partially or replacement layer chickens and laying hens based on totally replace the conventional cereal grains in maximum levels of CRM combined with FFSB and 6% commercial diets. FFSB also provide key nutrients foliage meal, in which these ingredients can represent which will complement the nutritional weaknesses of up to 85% of the total feed. The corresponding cassava. nutritional components are shown in Table 27-57. Tables 27-58 and 27-59 show similar examples in When cassava root flour is included at levels above which CRM has been restricted to levels not higher 20%, the pelletization or extrudization processes are than 25% of the chicken and layer diets. always recommended, especially for starting piglet diets. In growing-finishing pigs and breeding animals, Performance results based on diets with pelletization is also recommended, although the medium levels of cassava meal for laying hens addition of molasses, fat, or FFSB can alleviate the dustiness of high cassava meal diets. As in broiler and Field experiments have been conducted in one of the layer feeding, it is possible to formulate balanced diets main poultry regions of Colombia (Cauca Valley). In all for the different production stages in pigs, based in the feeding trials the diets were prepared in meal or flour mixture of cassava roots and cassava foliage meal, form and the level of replacement of corn was not more FFSB, and SBM, in which these ingredients can than 50%. represent more than 95% of the total feed, as illustrated in Table 27-68. Tables 27-60, 27-62, 27-64, and 27-66 show the composition of the diets used in several experiments In recent studies, the inclusion of high levels of conducted in commercial layer farms, during different CRM has been successfully proven in finishing diets laying periods. CRM was included at levels from 10% to where FFSB has been also included. The total 20% of the total diet. FFSB, either extruded or toasted, replacement of cereal grains by CRM is possible once was used in all cases at levels not higher than 20%. the nutritional adjustments are introduced (Tables 27-69 and 27-70). Results in productivity of layers fed the experimental diets already described are presented in Tables 27-61, 27-63, 27-65, and 27-67. 540 The Use of Cassava Products in Animal Feeding Table 27-1. Main nutrients in cassava roots and foliage. Nutrients Fresh products Dry products Roots Foliage Roots Foliage Moisture, % 64–66 70–72 12–14 12–14 Starch, % 28.0 4.1 73.0 14.0 ME, Mcal/kga 1.20 0.34 3.0–3.1 1.38 Protein, % 1.10 6.5 2.80 21.0 Fiber, % 1.20 4.7 3.2 18.4 Fat, % 0.47 1.8 1.2 5.9 Ash, % 1.12 1.7 2.9 5.6 Methionine, % 0.01 0.07 0.03 0.28 Cystine, % 0.008 0.04 0.02 0.16 Lisine, % 0.02 0.37 0.06 1.6 Triptophane, % — 0.05 — 0.2 Threonin, % 0.01 0.27 0.03 1.17 Calcium, % 0.10 0.52 0.30 1.7 Phosphorus, % 0.15 0.09 0.40 0.26 Potasium, % 0.25 0.34 0.65 1.2 a. Megacalories of metabolizable energy (ME) per kilogram of product. SOURCE: Buitrago (1990). Table 27-2. The effect of using fresh cassava roots and protein supplements in free choice supply to Duroc x Landrace growing pigs (15–50 kg)a on their performance. Diet 1 Diet 2 Diet 3 Diet 4 Protein supplement (Ingredients %) Cottonseed meal 16.0 23.0 23.0 — Sesame meal 18.0 25.0 — 25.0 Peanut meal 14.0 — 25.0 23.0 Fish meal 36.0 36.0 36.0 36.0 Meat meal 14.2 14.2 14.2 14.2 Lysine 0.2 0.2 0.2 0.2 Vitamin premix 0.6 0.6 0.6 0.6 Nutritional composition Digestible energy, Mcal/kg 2.85 2.83 2.88 2.77 Protein, % 54.2 53.9 56.0 52.9 Methionine, % 1.20 1.27 1.07 1.23 Lysine, % 3.19 3.18 3.28 3.15 Performance of pigs Daily weight gain, kg 0.59 0.57 0.64 0.53 Daily feed consumption: Fresh cassava, kg 3.24 3.24 3.15 2.98 Protein supplement, kg 0.50 0.45 0.52 0.51 Feed conversion ratio (DM) 2.66 2.63 2.44 2.79 a. Chopped fresh cassava roots and protein supplement offered in different feeders for free-choice consumption. SOURCE: Contreras (1973). 541 Cassava in the Third Millennium: … Table 27-3. The effect of using fresh cassava roots and protein supplements in free choice vs. controlled supply for Duroc growing- finishing pigs (18–100 kg)a on their performance. Parameter Free choice fresh roots + protein supplementb Corn-SBM dietc Controlled Free choice supplement supplement Soybean meal, % 61.50 61.50 10.59 Cottonseed meal, % 20.50 20.50 3.53 Minerals and vitamins, % 18.00 18.00 4.55 Corn, % — — 81.33 Daily consumption Fresh roots, kg 3.89 4.05 — Protein supplement, kg 0.73 1.17 — DM consumption, kg 2.07 2.52 2.60 Protein consumption, kg 0.372 0.564 0.459 Performance of pigs Daily weight gain, kg 0.79 0.83 0.84 Feed conversion ratio (DM) 2.90 3.36 3.43 a. Chopped fresh cassava and protein supplement offered in different feeders for free-choice or controlled consumption. b. Protein supplement with 43% protein. c. Commercial concentrate with 16% protein. SOURCE: Buitrago (1964). Table 27-4. Fresh roots and protein supplement added with molasses or sugarcane for Yorkshire growing- finishing pigs (20–90 kg). Parameter Feeding regimea Only roots Roots + molasses Roots + sugar Daily consumption (kg) Fresh cassava roots 2.99 3.27 3.11 Protein supplement (40% protein)b 1.02 0.92 0.85 Total DM 2.03 2.27 2.17 Total protein 0.54 0.51 0.46 Pig performance Daily weight gain, kg 0.69 0.72 0.74 Feed conversion rate (DM) 2.97 3.16 2.93 a. Molasses and sugarcane were used in a proportion equivalent to 15% of the total diet. b. Protein supplement based on soybean meal (80.0%), corn (8.5%), and minerals and vitamins (11.5%). Free choice supply in feeders separated from the cassava treatments. SOURCE: CIAT (1975). 542 The Use of Cassava Products in Animal Feeding Table 27-5. Fresh roots and protein supplements prepared with different protein sources for Duroc x Landrace growing-finishing pigs (19–90 kg)a. Diet 1 Diet 2 Diet 3 Diet 4 Diet 5 Diet 6 Protein supplement (Ingredients, %) Soybean meal 78.10 — — — — — Cottonseed meal — — 78.10 — 30.00 30.00 Meat meal — 70.50 — 44.30 21.30 — Blood meal 20.00 20.00 — Fish meal — — — — — 36.70 Corn 11.20 26.80 11.20 33.00 25.00 29.60 Vitamins and minerals 10.70 2.70 10.70 2.70 10.70 10.70 Protein level (%) 43.0 39.4 37.7 48.5 44.7 40.2 Daily consumption (kg) Fresh roots 4.00 3.40 3.13 3.88 4.00 4.08 Protein supplement 0.80 0.78 0.79 0.94 0.90 0.79 Total protein 0.34 0.31 0.30 0.44 0.40 0.32 Pig performance Daily weight gain, kg 0.72 0.68 0.59 0.72 0.72 0.68 Feed conversion rate 3.25 3.07 3.38 3.32 3.38 3.47 a. Both cassava roots and protein supplements were supplied at free choice in separated feeders. SOURCE: Maner et al. (1978). Table 27-6. Fresh roots and protein supplements with different protein levels for Yorkshire growing-finishing pigs (19–90 kg). Diet 1 Diet 2 Diet 3 Protein supplement (Ingredients, %) Soybean meal 26.73 53.15 79.56 Corn 67.27 37.85 8.44 Minerals and vitamins 6.0 9.0 12.0 Protein level (%) 20.0 30.0 40.0 Daily consumption (kg) Fresh roots 1.79 2.74 3.37 Protein supplement 1.39 1.00 0.75 Total DM 1.92 1.94 1.97 Total protein 0.34 0.40 0.39 Pig performance Daily weight gain, kg 0.71 0.67 0.65 Feed conversion rate 2.71 2.90 3.02 SOURCE: CIAT (1974). 543 Cassava in the Third Millennium: … Table 27-7. Performance of Yorkshire pigs fed with sweet vs. bitter cassava roots plus a protein supplementa with different protein levels. Sweet roots Bitter rootsb Free choice Controlled Free choice Controlled supplement supplement supplement supplement Daily consumption (kg) Fresh roots 2.99 3.40 0.98 0.93 Protein supplement 0.81 0.82 1.21 0.22 Total DM 1.78 1.80 1.43 0.52 Pig performance Daily weight gain (kg) 0.66 0.77 0.56 — Feed conversion ratio 2.99 2.61 2.86 — a. 40% protein supplement in all treatments. b. CMC-84 variety with 200 ppm cyanhydric acid. SOURCE: CIAT (1973). Table 27-8. Fresh cassava roots and protein supplementation in Duroc x Landrace gestating gilts. Feed treatment Control Cassava + Cassava + pasturea supplement supplement pastureb confinedc Ingredients (%) Soybean meal 18.0 64.08 66.75 Cottonseed meal — 20.53 20.53 Corn 74.8 — — Minerals and vitamins 7.20 15.39 12.72 Protein level (%) 16.0 40.0 40.0 Performance of gilts Weight gain in gestation, kg 19.90 24.90 37.70 Piglets/litter, No. 10.4 10.0 7.7 Piglet weight, kg 1.28 1.12 1.18 Litter weight, kg 13.31 11.20 9.08 a. Daily consumption/gilt: 1 kg of a corn-soybean meal diet. b. Daily consumption/gilt: 1.7 kg of cassava roots and 0.4 kg of protein supplement. c. Daily consumption/gilt: 3.1 kg of cassava roots and 0.62 kg of protein supplement. SOURCE: Maner et al. (1978). 544 The Use of Cassava Products in Animal Feeding Table 27-9. Fresh cassava roots and protein supplementation as compared to a corn-soybean meal ration in Duroc x Landrace lactating sows. Corn-SBMa Fresh roots + protein supplementb Ingredients (%) Soybean meal 15.00 87.10 Corn 81.35 — Minerals and vitamins 3.65 12.90 Protein level (%) 16.0 40.0 Daily consumption (kg) Corn-soybean meal diet 4.82 — Fresh cassava — 6.50 Protein supplement — 1.21 Total DM intake 4.32 3.40 Performance of sows Weight at farrowing, kg 179.30 158.30 Weight at weaning, kg 190.30 165.80 Performance of litter at birth Piglets, No. 10.8 9.3 Individual weight, kg 1.18 1.36 Litter weight, kg 12.74 12.65 Performance of litter at weaning (35 days)c No. piglets 9.0 7.6 Individual weight, kg 6.03 7.63 Litter weight, kg 54.27 58.00 a. Control group with free choice consumption; SBM = soybean meal. b. Cassava roots and protein supplement in a mixture to provide the equivalent to a 16% protein diet. Free choice consumption. c. Piglets received the same creep feed at free choice. SOURCE: Maner et al. (1978). Table 27-10. The effect of using fresh cassava roots compared with ensiled cassava roots and foliage for Yorkshire x Landrace growing-finishing pigs (18–98 kg). Ensiled rootsa Ensiled roots+ Fresh roots foliageb Supplement ingredients (%) Corn 10.9 10.9 10.9 Cottonseed meal 78.1 78.1 78.1 Vitamins and minerals 11.0 11.0 11.0 Daily consumption (kg) Ensiled cassava roots (and foliage) 3.84 3.05 — Fresh cassava roots — — 4.04 Protein supplement (38%) 1.01 1.01 1.01 Total protein 0.38 0.38 0.38 Pig performance Daily weight gain (kg) 0.77 0.64 0.75 Feed conversion ratio (DM) 2.92 3.17 3.09 a. Only chopped roots. b. Chopped roots, leaves and stems. SOURCE: Buitrago et al. (1978). 545 Cassava in the Third Millennium: … Table 27-11. The effect of feeding ensiled cassava roots with different protein supplements to Yorkshire growing-finishing pigs (16–90 kg) on their performance. Ensiled roots plus protein supplement Corn-SBMa diet Diet 1 Diet 2 Diet 3 Diet 4 Diet 5 Supplement ingredients (%) Soybean meal 44.0 — 88.0 — 8.5 Cottonseed meal 44.0 48.5 — 97.0 8.5 Fish meal — 48.5 — — — Sorghum — — — 78.0 Minerals and vitamins 12.0 3.0 12.0 3.0 5.0 Protein level (%) 41.0 47.0 44.0 52.0 15.5 Daily consumption (kg) Cassava root silage 2.85 3.01 3.10 2.98 — Protein supplement 0.86 0.67 0.73 0.60 — Control diet — — — — 2.06 Performance of pigs Daily weight gain (kg) 0.59 0.55 0.59 0.50 0.56 Feed:weight ratio (DM) 3.27 3.31 3.24 3.50 3.31 a. SBM = soybean meal. SOURCE: Buitrago et al. (1978). Table 27-12. The effect of feeding ensiled cassava roots with different storage time and added salt to Yorkshire growing-finishing pigs (22–95 kg) on their performance. Age of silage Salt Silage Supplement ADGb FCRc addition consumption consumptiona > 6 months — 3.30 0.78 0.63 3.34 2% 2.87 0.78 0.62 3.10 < 6 months — 3.45 0.78 0.63 3.46 2% 3.20 0.78 0.63 3.27 a. 40% protein supplement with the following composition: 44% soybean meal, 44% cottonseed meal, 12% minerals and vitamins. b. ADG = Average daily weight gain. c. FCR = Feed conversion ratio. SOURCE: Buitrago et al. (1978). 546 The Use of Cassava Products in Animal Feeding Table 27-13. Ensiled cassava roots (ECR) and protein supplement for Yorkshire lactating sows. ECR + supplement Corn + supplement Mixed corn-SBMa Feed ingredients (%) Corn — — 78.1 Soybean meal 78.0 56.0 16.4 Minerals and vitamins 22.0 44.0 5.5 Protein level (%) 40 28 16 Daily feed consumption of sows (kg) Cassava silage 9.35 — — Corn — 4.27 — Protein supplement 1.11 0.66 — Complete diet (corn-SBM) — — 4.54 Performance of sows Weight at farrowing, kg 140.9 168.5 155.4 Weight at weaning (35 days), kg 151.2 182.3 179.7 Performance of litters at birth Piglets, No. 10.6 10.0 10.7 Individual weight, kg 1.09 1.16 1.12 Total litter weight, kg 11.50 11.60 12.04 Performance of litters at weaning (35 days)b Piglets, No. 8.22 7.00 8.11 Individual weight, kg 5.54 4.95 5.33 Total litter weight, kg 45.51 34.66 43.23 a. SBM= soybean meal. b. Piglets consumed the same creep feed at free choice. SOURCE: Buitrago et al. (1978). Table 27-14. Fresh cassava roots and protein supplementation in Holstein growing heifersa. Commercial Fresh cassava roots + concentrate protein supplement Ingredients for supplemental feeding (%)b Corn 59.00 — Sugarcane molasses 10.0 12.0 Wheat bran 14.0 16.3 Cottonseed meal 13.0 61.0 Urea 1.5 3.7 Minerals and vitamins 2.5 7.0 Daily consumption (kg) Commercial concentrate 2.64 — Protein supplement — 1.08 Cassava roots (DM)c — 1.56 Sugarcane tops (DM)c 4.82 4.17 Total DM intake (kg) 7.46 6.81 Performance of heifers Initial weight, kg 191.8 190.6 Final weight, kg 366.8 377.3 Daily weight gain, kg 0.78 0.83 a. Heifers on group confinement from 8 to 16 months. b. Heifers in the control group received 3 kg of commercial concentrate per day. Heifers in the cassava group received 4.5 kg of fresh cassava and 1.23 kg of protein supplement per day. Besides the supplemental feed all heifers received fresh sugarcane tops ad libitum. c. Daily consumption expressed as dry matter (DM). SOURCE: Pineda and Rubio (1972). 547 Cassava in the Third Millennium: … Table 27-15. Fresh cassava roots and protein supplementation in white Fulani milking cowsa. Commercial Fresh cassava roots + concentrate protein supplement Ingredients for supplemental feeding (%)b Corn 50.0 — Palm cake 40.0 50.0 Peanut cake 10.0 50.0 Nutrient content (%) DM 90.0 91.0 Protein 15.7 26.7 Fiber 5.3 6.6 Fat 4.9 9.7 Performance of heifers 4% fat corrected milk (kg) 6.8 7.2 a. Confined cows during an 84-days lactation period. b. Cows in the control group received 0.42 kg of concentrate per kg of milk produced. Cows in the cassava group received 0.75 kg of fresh cassava roots plus 0.20 kg of protein supplement per kg of milk produced. Besides the supplemental feed all cows received star grass hay. SOURCE: Olaloku et al. (1971). Table 27-16. Fresh cassava roots and protein supplementation in growing-finishing Gyr x Brown Swiss steersa. Cassava + commercial Protein supplement concentrates Diet 1 Diet 2 Diet 3 Diet 4 Ingredients (%) Corn — 34.0 — — Rice polishings — 53.0 — — Cottonseed meal 75.0 10.0 16.3 15.3 Corn husks — — 81.4 — Cottonseed husks — — — 82.4 Urea 12.0 — — — Minerals and vitamins 13.0 2.3 2.3 2.3 Nutrient content (%) Protein 64.65 13.95 9.58 9.09 TDN 45.0 63.0 50.0 48.0 Ca 4.1 0.93 0.74 0.82 P 1.02 0.98 0.93 0.94 Daily feed consumption (kg)b Elephant grass 9.8 9.8 9.8 9.8 Fresh cassava 15.8 — — — Protein supplement 1.6 — — — Commercial concentrate — 8.9 5.6 9.6 Total DM intake 8.4 9.3 6.4 9.9 Performance of steers Initial weight, kg 252 252 252 252 Final weight, kg 402 432 346 359 Daily weight gain, kg 1.39 1.66 0.87 0.99 Carcass yield, % 56.7 54.0 46.0 50.4 a. 22–24 month old steers. b. Cassava roots were supplied at free choice in a 10:1 ratio with the protein supplement. Commercial feeds were supplied at free choice. SOURCE: Terleira et al. (1975). 548 The Use of Cassava Products in Animal Feeding Table 27-17. Fresh cassava foliage as a complement to grazing Table 27-20. Nutritional composition of cassava foliage meal Holstein heifersa. with different proportions of leaves, petioles, and stemsa. Feeding program Diet 1 Diet 2 Nutrients, % Leaves Leaves Leaves, Daily consumption (kg/day) and petioles, Fresh cassava foliage 7.50 — petioles and stems Fresh alfalfa — 10.00 Protein 22.7 21.6 20.2 Cane molasses 0.50 0.50 Ash 10.9 9.8 8.5 Mineral salt Ad libitum Ad libitum Fat 6.3 6.3 5.3 Performance of heifers Fiber 11.0 11.6 15.2 Initial weight, kg 189.3 183.6 Calcium 1.68 1.70 1.68 Final weight, kg 256.3 241.3 Phosphorus 0.29 0.24 0.28 Daily weight gain, kg 0.68 0.59 Potassium 0.69 0.60 1.09 a. Growing heifers on star pangola grazing lots. a. Products with 8%-10% humidity. SOURCE: Zapata et al. (1985). SOURCE: Van Poppel (2001). Table 27-18. Fresh cassava foliage and elephant grass for Table 27-21. Nutritional composition of cassava foliage meal at crossbred Zebu finishing steers on group different harvesting times. confinementa. Main nutrients Cassava foliage meala Feeding program Diet 1 Diet 2 Diet 3 2–3 5–6 More than Elephant grass, % of mixtureb 100 75 50 months months 8 months Cassava foliage, % of mixture — 25 50 Protein, % of DM 22.0 18.0 16.0 Performance of steers Fiber, % 16.0 20.0 26.0 Initial weight, kg 265.5 276.3 270.0 Ash, % 5.5 5.8 5.8 Final weight, kg 342.5 392.7 379.0 Fat, % 5.2 5.6 5.6 Daily weight gain, kg 0.31 0.46 0.44 Calcium, % 1.6 1.7 1.7 Feed conversion rate 17.6 13.7 13.7 Phosphorus, % 0.26 0.28 0.28 a. Growing steers on group confinement. TDNb,% 68.0 66.0 58.0 b. Fresh mixture offered for free choice consumption. DEb, Mcal/kg 2.94 2.65 2.40 SOURCE: Moore (1976). a. Third superior top (including leaves, petioles, and young stems). b. TDN = total digestible nutrient; DE = digestible energy. SOURCE: Buitrago (1990). Table 27-19. Quality grading of cassava root meal based on energy concentration. Grade Raw Ash Fiber + Metabolizable fiber azsh energy (%) (%) (%) (Mcal/kg) 1 < 2.8 < 2.0 < 4.8 3.30 2 < 3.6 < 2.5 < 6.1 3.15 3 < 4.5 < 3.2 < 7.7 2.92 4 < 5.2 < 4.0 < 9.2 2.60 SOURCE: Buitrago (1990). 549 Cassava in the Third Millennium: … Table 27-22. Different levels of cassava root meal in diets for broilersa. Cassava content 0 15% 30% 45% Sb Fb S F S F S F Ingredients (%) Cassava root meal 0 0 15.0 15.0 30.0 30.0 45.0 45.0 Corn 59.9 64.0 42.9 47.4 26.3 30.7 9.7 14.1 Soybean meal 30.7 27.6 31.0 28.2 32.0 29.0 33.0 30.0 Fish meal 6.0 4.0 7.3 5.0 7.9 5.8 8.5 6.5 DL-methionine 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.17 Minerals and vitamins 3.6 3.6 3.6 3.6 3.6 3.6 3.6 3.6 Nutritional content ME, Mcal/kg 2.94 2.96 2.86 2.89 2.78 2.79 2.70 2.72 Protein, % 22.1 20.0 22.1 20.0 22.1 20.0 22.1 20.0 Methionine + cystine, % 0.87 0.80 0.87 0.79 0.86 0.80 0.86 0.79 Lysine, % 1.26 1.10 1.33 1.26 1.39 1.22 1.44 1.28 Performance of broilers Final weight, kg 1.47 1.50 1.45 1.39 Feed consumption, kg 3.33 3.39 3.48 3.29 Feed conversion ratioc 2.45 2.42 2.56 2.56 a. 0–8 weeks broilers. b. S: starting: 0–5 weeks. c. F: finishing: 5–8 weeks. SOURCE: Enríquez V et al. (1977). Table 27-23. Different levels of cassava root meal in iso-energetic diets for broilersa. Cassava meal level (%) 0 20 30 40 50 58 Ingredients (%) Cassava root meal 0 20.0 30.0 40.0 50.0 58.0 Corn 54.0 30.0 16.0 9.0 3.9 — Rice polishings 10.0 9.0 8.6 8.1 0 — Fish meal 6.0 6.0 6.0 6.0 10.0 11.0 Soybean meal 27.0 31.0 35.0 32.0 32.0 27.0 Vegetable oil — 1.0 1.4 1.9 2.0 2.0 Minerals and vitamins 3.0 3.0 3.0 3.0 2.1 2.0 Broiler performance Final weight, kg 2.04 2.05 2.04 2.03 2.04 2.04 Feed conversion ratio 2.61 2.59 2.64 2.61 2.56 2.53 Mortality, % 9.2 3.0 3.0 4.0 10.2 5.0 a. 0–6 week broilers. SOURCE: Chou et al. (1974). 550 The Use of Cassava Products in Animal Feeding Table 27-24. Different levels of cassava root meal in pelletized iso-energetic diets for broilersa. Cassava meal level (%) 0 10 20 30 40 50 Ingredients (%) Cassava root meal 0 10.0 20.0 30.0 40.0 50.0 Wheat 53.9 48.9 38.9 28.8 18.3 6.1 Corn 16.2 10.5 9.5 9.0 9.0 10.0 Soybean meal 16.3 14.8 13.8 12.8 11.6 11.1 Fish meal 5.0 6.8 8.9 10.5 11.4 12.5 Meat meal 3.0 3.0 3.0 3.1 4.3 5.0 Vegetable oil 3.1 3.9 3.9 3.9 3.6 3.5 DL-methionine 0.11 0.12 0.15 0.18 0.20 0.23 Minerals and vitamins 2.4 2.0 1.9 1.7 1.6 1.4 Nutritional composition ME, Megajoules/kg 13.7 13.5 13.8 13.9 13.9 13.8 Protein, % 19.3 19.7 20.0 19.4 19.4 19.8 Broiler performance Final weight, kg 2.31 2.39 2.30 2.31 2.31 2.30 Feed consumption, kg 4.45 4.49 4.39 4.59 4.38 4.62 Feed conversion ratio 1.92 1.88 1.91 1.99 1.90 2.01 a. 0–7 week broilers. SOURCE: Stevenson and Jackson (1983). Table 27-25. Performance of Leghorn layers with increasing levels of cassava root meala. Diet 1 Diet 2 Diet 3 Diet 4 Ingredients (%) Cassava root meal — 10.0 25.0 50.0 Corn 62.0 50.0 32.1 2.1 Soybean meal 9.20 11.20 14.1 19.1 Rice bran 5.0 5.0 5.0 5.0 Copra meal 7.5 7.5 7.5 7.5 Fish meal 5.0 5.0 5.0 5.0 Meat and bone meal 2.5 2.5 2.5 2.5 Leucaena meal 3.0 3.0 3.0 3.0 Vitamins and minerals 5.8 5.8 5.8 5.8 Performance of layers Egg production, % 63.9 62.8 58.7 62.8 Weight of eggs, g 58 57 57 57 Feed conversion ratio 2.01 2.10 2.22 2.12 Yolk pigmentationb 6.0 6.0 5.0 3.5 a. 20–48 week layers. b. Roche pigmentation scale. SOURCE: Enriquez and Ross (1972). 551 Cassava in the Third Millennium: … Table 27-26. Performance of Hisex layers with increasing levels of cassava root meala. Diet 1 Diet 2 Diet 3 Diet 4 Diet 5 Diet 6 Ingredients (%) Cassava root meal — 10.0 20.0 30.0 40.0 50.0 Wheat 50.0 50.0 46.1 30.8 15.5 — Corn 13.2 8.5 5.8 8.8 11.9 15.2 Barley 12.7 5.4 — — — — Fish meal 3.0 3.0 3.0 3.0 3.0 2.9 Soybean meal 7.9 9.9 11.9 14.2 16.5 18.8 Meat and bone meal 5.0 5.0 5.0 5.0 5.0 5.0 Animal fat 1.0 1.0 1.0 1.0 1.0 1.0 DL-methionine 0.05 0.06 0.07 0.08 0.09 0.09 Vitamins and minerals 7.2 7.1 7.1 7.0 7.0 6.9 Nutritional composition ME, Megajoules (MJ)/kg 11.0 11.0 11.0 11.0 11.5 11.1 Protein, % 15.9 15.7 15.9 15.8 15.9 16.0 Calcium, % 3.2 3.3 3.3 3.3 3.3 3.3 Phosphorus, % 0.64 0.63 0.63 0.60 0.58 0.57 Performance of layers No. eggs in 280 days 205 203 205 215 201 196 Weight of eggs, g 55 56 55 55 55 56 Daily feed consumption, g 119 119 111 113 112 109 kg of eggs/kg of feed 0.38 0.34 0.35 0.38 0.35 0.36 a. 27–67 week layers. SOURCE: Stevenson (1984). Table 27-27. Performance of Shaver layers with increasing levels of cassava root meala. Diet 1 Diet 2 Diet 3 Diet 4 Diet 5 Diet 6 Ingredients (%) Cassava root meal — 25.0 50.0 — 25.0 50.0 Sorghum 65.2 38.7 12.1 57.3 28.3 — Soybean meal 11.3 14.8 18.3 — — — Fullfat soybeans — — — 15.3 20.0 24.7 Fish meal 7.0 7.0 7.0 7.0 7.0 7.0 DL-methionine 0.13 0.16 0.18 0.14 0.17 0.19 L-lysine 0.17 0.10 0.04 0.15 0.08 -- Corn cobs 6.6 4.9 3.2 10.6 10.1 6.8 Vitamins and minerals 9.6 9.3 9.2 9.5 9.3 11.3 Nutritional composition ME, Mcal/kg 2.65 2.65 2.65 2.65 2.65 2.65 Protein, % 15.5 15.5 15.5 15.5 15.5 15.5 Methionine + cystine, % 0.66 0.66 0.66 0.66 0.66 0.66 Lysine, % 0.98 0.98 0.98 0.98 0.98 0.98 Linoleic acid, % 0.78 0.51 0.24 1.92 2.01 2.10 Performance of layers Egg production, % 72.3 77.9 78.0 72.6 72.0 74.5 Weight of eggs, g 69 67 67 70 71 69 Daily feed consumption, g 125 133 132 122 121 120 Yolk pigmentationb 5.1 4.9 4.7 6.4 6.5 6.3 a. 42–62 week layers. b. Roche pigmentation scale. SOURCE: Hennesey and Ayala (1986). 552 The Use of Cassava Products in Animal Feeding Table 27-28. Bitter vs. sweet varieties of cassava root meal for Table 27-29. Root meal of low-HCN cassava varieties in growing Yorkshire pigsa. substitution of corn for growing crossbred pigs and their effect on carcass characteristicsa,b. Bitterb Sweetc Ingredients (%) Diet 1 Diet 2 Diet 3 Diet 4 Cassava root meal 71.0 71.0 Ingredients (%) Soybean meal 25.0 25.0 Cassava root meal — 20.0 40.0 58.5 Vitamins and minerals 4.0 4.0 Corn 60.0 40.0 20.0 — Performance of pigs Meat meal 5.0 5.5 6.0 6.5 Daily weight gain, kg 0.56 0.62 Sesame meal 20.0 23.0 26.0 29.0 Feed consumption, kg 1.35 1.77 Rice polishings 9.0 5.5 2.0 — Feed conversion ratio 2.43 2.86 Cane molasses 5.0 5.0 5.0 5.0 Vitamins and minerals 1.0 1.0 1.0 1.0 a. 38–58 kg. b. CMC-84 variety with 150-200 ppm HCN. Performance of pigs c. 80 ppm HCN. Daily weight gain, kg 0.79 0.78 0.84 0.80 SOURCE: Gómez and Buitrago (1982). Feed conversion ratio 3.50 3.60 3.30 3.30 Carcass characteristics Carcass length, cm 74.0 72.1 73.0 74.0 Dorsal fat, cm 3.10 3.40 3.30 2.90 Iodine number 69.3 64.5 71.3 69.3 a. 40–82 growing-finishing pigs. b. 40 ppm HCN in fresh roots. SOURCE: Chicco et al. (1972). Table 27-30. Effect of adding cane molasses, raw sugar, or animal fat to diets based on cassava root meal for Landrace x Yorkshire pigsa. Diet 1 Diet 2 Diet 3 Diet 4 Diet 5 Ingredients (%) Cassava root meal 65.9 65.7 55.5 55.5 55.5 Soybean meal 29.4 29.4 29.8 29.8 29.8 Cane molasses — — 10.0 — — Raw sugar — — — 10.0 — Animal fat — — — — 10.0 DL-methionine — 0.2 — — — Vitamins and minerals 4.7 4.7 4.7 4.7 4.7 Performance of pigs Daily weight gain, kg 0.71 0.68 0.69 0.68 0.63 Daily feed consumption, kg 1.94 1.88 1.89 1.84 1.59 Feed conversion ratio 2.73 2.76 2.74 2.70 2.53 a. 20–50 kg growing pigs. Isoproteic (16 %) diets. SOURCE: Maner et al. (1978). Table 27-31. Effect of adding methionine and other sulfur sources to diets based on cassava root meal for Landrace x Yorkshire pigsa. Feed treatment Performance of pigs Daily weight Daily feed Feed conversion gain, kg consumption, ratio kg Control diet (CD)b 0.67 1.81 2.43 CD + 0.2% methionine 0.70 1.77 2.29 CD + 0.8% sodium thiosulphate 0.61 1.58 2.32 CD + 0.2% elemental sulfur 0.65 1.64 2.29 a. 20–50 kg growing pigs. b. 16% protein control diet based on cassava root meal (70%), soybean meal (25%), and vitamin-mineral mixture (5%). SOURCE: CIAT (1975). 553 Cassava in the Third Millennium: … Table 27-32. Cassava root meal vs. corn in diets for gestating Table 27-33. Cassava root meal vs. corn in diets for lactating and lactation sowsa. sowsa. Diet 1 Diet 2 Diet 1 Diet 2 Ingredients (%) Ingredients (%) Cassava root meal — 67.0 Cassava root meal — 59.1 Corn 76.4 — Corn 81.5 — Soybean meal 18.8 28.2 Cane molasses — 10.0 Vitamins and minerals 4.8 4.8 Soybean meal 15.0 27.4 Nutritional composition (%) Vitamins and minerals 3.5 3.5 Protein 16.0 16.0 Nutritional composition (%) Metionine + cystine 0.55 0.47 Protein 16.0 16.0 Lysine 0.77 0.92 Metionine + cystine 0.52 0.44 Performance of sows Lysine 0.71 0.89 Breeding weight, kg 127.6 118.5 Performance of sows Farrowing weight, kg 160.6 146.1 Farrowing weight, kg 179.3 170.6 Weaning weight, kg 153.9 159.6 Weaning weight, kg 190.3 183.0 Performance of litters at farrowing Performance of litters at farrowing Piglets, No. 10.0 8.4 Piglets, No. 10.8 10.1 Individual weight, kg 1.09 0.97 Individual weight, kg 1.18 1.22 Litter weight, kg 10.9 8.15 Litter weight, kg 12.74 12.32 Performance of litters at weaning Performance of litters at weaning No. of piglets 9.4 6.6 Piglets, No. 9.01 7.90 Individual weight, kg 15.87 15.70 Individual weight, kg 6.08 6.80 Litter weight, kg 149.18 103.62 Litter weight, kg 54.0 53.7 a. 56–day weaning time. a. 35-day weaning time. SOURCE: Maner et al. (1978). Table 27-34. Effect of partial substituting of corn by cassava root Table 27-35. Feed consumption in lactating piglets associated meal in lactating pigletsa. with increasing levels of dry cassava root meal in their feeda. Diet 1 Diet 2 Diet 3 Ingredients (%) Age of piglets Total feed consumption (days) per litter (kg)b Cassava root meal — 10.0 20.0 0% 20% 40% Corn 59.6 49.0 38.0 cassava cassava cassava Soybean meal 27.7 28.3 28.9 meal meal meal Dehydrated milk whey 10.0 10.0 10.0 14 – 42 1.8 3.0 12.4 Vitamins and minerals 2.7 2.7 2.7 42 – 56 14.7 26.2 39.1 Nutritional composition 14 – 52 (total) 16.5 29.2 51.5 Protein, % 18.5 18.1 17.8 a. 1–56 day piglets. Lysine, % 1.12 1.12 1.12 b. Free choice cassava-sorghum-soybean diets with 20% protein. Calcium, % 0.78 0.78 0.78 SOURCE: Gómez et al. (1981). Phosphorus, % 0.59 0.59 0.59 Performance of piglets Daily weight gain, kg 0.38 0.37 0.39 Daily feed consumption, kg 0.68 0.60 0.60 Feed conversion ratio 1.63 1.62 1.64 a. 7–18 kg piglets (30 days). SOURCE: Ravindran et al. (1983). 554 The Use of Cassava Products in Animal Feeding Table 27-36. Effect of partial substitution of corn by cassava Table 27-38. Effect of partial substitution of oats by cassava root meal in the feed of dairy calvesa. root meal in the feed of dairy cowsa. Energy source in dry feedb Energy source in dry feedb 50% 25% 50% Oats Oats + Cassava sorghum sorghum cassava cassava meal 25% meal meal cassava meal Ingredients (%) Performance of calves (kg) Cassava root meal — 12.5 25.0 Initial weight 35.15 34.10 34.26 Oats 25.0 12.5 25.0 Final weight 89.0 92.4 81.03 Peanut meal 20.0 25.0 25.0 Daily weight gain 0.48 0.52 0.42 Legumes hay 35.0 35.0 35.0 Total feed consumption in Wheat bran 20.0 20.0 20.0 112 days (kg) Nutritional composition (%) Dry feed 109.3 108.2 82.0 TDNc 69.0 67.0 65.0 Alfalfa hay 28.4 28.6 29.1 Protein 15.5 16.0 15.5 Milk 132.7 135.3 126.9 Daily milk production (kg) a. 1 to 112-day Holstein calves. Only milk during the first 42 days Non-corrected milk 6.97 7.20 7.84 and ad libitum dry feed plus alfalfa hay from 42 to 112 days. b. Dry feed also supplemented with protein, mineral, and vitamin 4% fat corrected milk 7.81 7.91 7.84 sources. a. 140–day lactation period. SOURCE: Peixoto (1973). b. Daily supply of 1 kg of dried feed per 3 kg of milk produced plus ad libitum Para grass hay. c. TDN = total digestible nutrients. SOURCE: Mathur et al. (1969). Table 27-37. Effect of partial substitution of sorghum by Table 27-39. Growing-finishing crossbred Zebu steers under cassava root meal in dairy cowsa. intensive grazing supplemented with two levels of cassava root meala. Diet 1 Diet 2 Ingredients in dry diets (%)b Dry supplement (kg/animal per day) Cassava root meal — 27.0 Ingredientes (%) Sorghum 54.0 27.0 Cassava root meal 0.65 1.10 Cottonseed meal 44.0 43.5 Cane molasses 4.5 4.5 Urea — 0.50 Urea 0.23 0.25 Salt 1.0 1.0 Blood meal 0.22 0.22 Minerals 1.0 1.0 Performance of steers (kg) Nutritional composition (%) Initial weight 336.0 336.0 NDTc 69.0 67.4 Final weight 403.0 411.0 Protein 15.7 15.7 Daily weight gain 0.71 0.77 Daily milk production (kg) Non-corrected milk 12.0 12.4 a. Steers on intensive grazing (4.8 head/ha) plus controlled dry supplement. 4% fat corrected milk 11.4 11.3 SOURCE: Lozada and Alderete (1979). a. 63–day lactation period. b. Daily supply of 0.42 kg of dried feed per kg of milk produced plus ad libitum sorghum silage. c. TDN = Total digestible nutrients. SOURCE: Ribeiro et al. (1976). 555 Cassava in the Third Millennium: … Table 27-40. Feedlot crossbred Zebu steers under total confinement with free choice consumption of sorghum-cassava meal supplement and controlled sorghum silagea. Diet 1 Diet 2 Diet 3 Diet 4 Diet 5 Ingredients in dry supplement (%) Cassava root meal — 20.5 41.0 61.5 82.0 Sorghum 88.5 66.4 44.3 22.2 — Cottonseed meal 7.8 9.2 10.5 11.9 13.3 Urea 1.7 1.9 2.2 2.4 2.7 Vitamins and minerals 2.0 2.0 2.0 2.0 2.0 Performance of steers Initial weight, kg 302.7 306.2 317.2 305.8 315.4 Final weight, kg 424.4 425.1 427.2 412.4 404.3 Daily weight gain, kg 1.16 1.13 1.05 1.01 0.85 Dry supplement consumption, kg 10.2 9.3 8.6 8.1 6.9 Silage consumption, kg 3.1 5.0 5.5 5.2 5.2 Dry feed/weight gain 8.79 8.23 8.18 8.08 8.18 a. Free choice supplement and controlled sorghum silage (1.5 kg/100 kg body weight). SOURCE: Delgado et al. (1975). Table 27-41. Effect of including high levels of cassava foliage Table 27-42. Effect of including a high level of cassava foliage meal or alfalfa meal for Leghorn broilersa. meal and different levels of methionine in the feed of Leghorn broilersa. Diet 1 Diet 2 Diet 3 Diet 4 Diet 1 Diet 2 Ingredients (%) Cassava foliage meal 15.0 — 20.0 — Ingredients (%) Alfalfa meal — 15.0 — 20.0 Cassava foliage meal — 20.0 Corn 53.6 53.6 51.9 51.9 Corn 66.5 51.9 Soybean meal 19.9 19.9 16.6 16.6 Soybean meal 22.0 16.6 Tuna fish meal 5.0 5.0 5.0 5.0 Tuna fish meal 5.0 5.0 Meat and bone meal 5.0 5.0 5.0 5.0 Meat and bone meal 5.0 5.0 Vitamins and minerals 1.5 1.5 1.5 1.5 Vitamins and minerals 1.5 1.5 Performance of broilers Body weight at 21 days Weight at 3 weeks, g 191 212 186 203 (grams) Daily feed consumption, g 21.8 21.5 22.5 21.6 Methionine addition (%) Feed conversion ratio 2.40 2.13 2.54 2.24 0 208 114 a. 1–21 day old broilers. 0.2 220 185 SOURCE: Ross and Enriquez (1969). 0.3 — 211 0.4 — 205 0.5 — 202 Feed conversion rate Methionine addition (%) 0 2.10 2.73 0.2 1.99 2.32 0.3 — 2.18 0.4 — 2.35 0.5 — 2.18 a. 1–21 day old broilers. SOURCE: Ross and Enriquez (1969). 556 The Use of Cassava Products in Animal Feeding Table 27-43. Effect of including low levels of cassava foliage Table 27-44. Effect of including high levels of dried cassava meal on egg yolk pigmentation of Leghorn layers. foliage meal in Landrace x Yorkshire growing pigsa. Diet 1 Diet 2 Diet 3 Diet 4 Diet 1 Diet 2 Diet 3 Diet 4 Ingredients (%) Ingredients (%) Cassava foliage meal — 2.5 5.0 — Cassava foliage meal — 10.0 20.0 20.0 White corn 68.5 66.0 63.5 — Corn 74.40 66.85 59.85 59.65 Yellow corn — — — 68.5 Fish meal 8.0 7.0 7.0 7.0 Wheat bran 2.5 19.9 16.6 16.6 Meat and bone meal 7.0 7.0 5.0 5.0 Dextrose 0.5 0.5 0.5 0.5 Soybean meal 7.95 6.50 5.50 5.50 Fish meal 2.5 2.5 2.5 2.5 DL-methionine — — — 0.20 Peanut meal 5.0 5.0 5.0 5.0 Vitamins and minerals 2.65 2.65 2.65 2.65 Soybean meal 13.0 13.0 13.0 13.0 Performance of pigs Vitamins and minerals 8.0 8.0 8.0 8.0 Daily weight gain, kg 0.35 0.31 0.29 0.32 Egg yolk pigmentation Daily feed consumption, kg 1.21 1.10 1.08 1.13 Grade on Roche scale 1.0 4.9 5.4 9.5 Feed conversion ratio 3.42 3.52 3.79 3.50 SOURCE: Agudu (1972). a. Growing pigs with initial weight of 13.6 kg, consuming isoproteic (18%) diets. SOURCE: Choo and Hutagalung (1972). Table 27-45. Effect of including high levels of dried cassava foliage meal in landrace x yorshire growing pigsa. Diet 1 Diet 2 Diet 3 Diet 4 Diet 5 Ingredients (%) Cassava foliage meal — 20.0 20.0 20.0 20.0 Corn 77.6 57.1 52.1 54.1 51.9 Soybean meal 14.8 10.3 10.3 10.3 10.3 Fish meal 2.5 2.5 2.5 2.5 2.5 Meat and bone meal 2.5 2.5 2.5 2.5 2.5 Molasses — 5.0 10.0 5.0 10.0 Palm oil — — — 3.0 — DL-methionine — — — — 0.20 Vitamins and minerals 2.6 2.6 2.6 2.6 2.6 Performance of pigs Daily weight gain, kg 0.53 0.43 0.46 0.44 0.50 Daily feed consumption, kg 1.90 1.66 1.71 1.68 1.84 Feed conversion rate 3.60 3.90 3.74 3.80 3.68 a. Growing pigs with initial weight of 31 kg, consuming isoproteic (18%) diets. SOURCE: Choo and Hutagalung (1972). 557 Cassava in the Third Millennium: … Table 27-46. Main nutritional differences between cassava root Table 27-48. Nutritional composition of broiler diets totally meal (CRM) and fullfat soybeans (FFSB). based on cassava root meal, cassava foliage meal, fullfat soybeans, and soybean meal. Nutrients Unit CRM FFSB Protein % 2.8 38.0 Nutrients Starter Finisher Finisher (0-3 weeks) (3-6 weeks) (6-8 weeks) Fat % 1.2 19 ME, Mcal/kg 3.20 3.20 3.20 Starch % 70 9 Protein, % 23.0 20.0 18.0 ME, poultry Mcal/kg 3.1–3.2 3.6–3.8 Lisine, % 1.30 1.15 1.00 ME, swine Mcal/kg 3.2–3.4 3.7–3.8 Methionine, % 0.55 0.43 0.34 Linoleic acid % 0.2 8.9 Methionine + cystine 0.90 0.72 0.60 Fiber % 2.6 4.9 Threonine, % 0.85 0.78 0.69 Ash % 3.2 5.2 Tryptophane, % 0.30 0.25 0.20 Methionine % 0.03 0.51 Fiber, % 4.3 5.0 4.8 Cystine % 0.02 0.60 Fat, % 8.8 8.9 8.3 Lisine % 0.05 2.31 Ash, % 7.2 6.6 6.1 Threonine % 0.05 1.43 Calcium, % 1.00 0.90 0.80 Thryptophane % 0.02 0.52 Available phosphorus, % 0.45 0.36 0.30 Lecithin % 0.1 2.1 Linoleic acid, % 3.5 3.8 3.5 SOURCE: Buitrago (1990). Table 27-47. Broiler diets totally based on cassava root meal, Table 27-49. Composition of broiler diets with intermediate cassava foliage meal, and fullfat soybeans. levels of cassava meal and fullfat soybeansa. Ingredients (%) Starter Finisher Finisher Starting Finishing (0-3 weeks) (3-6 weeks) (6-8 weeks) Ingredients (%) Cassava root meal 41.05 44.70 50.50 Corn 25.34 30.79 Cassava foliage meal — 6.0 6.0 Cassava roots meal 25.0 25.0 Fullfat soybeans 44.50 44.74 40.80 Fullfat soybeans (toasted) 31.4 33.8 Soybean meal 10.60 1.40 — Soybean meal 12.1 4.8 DL-methionine 0.25 0.16 0.10 Chicken viscera meal 3.00 3.00 L-lysine — — — Dicalcium phosphate 1.30 1.00 Dicalcium phosphate 1.70 1.30 1.00 Calcium carbonate 1.00 0.90 Calcium carbonate 1.20 1.00 0.90 DL-methionine 0.23 0.10 Salt 0.30 0.30 0.30 Salt 0.35 0.30 Vitamins, minerals, Vitamins and minerals 0.12 0.10 additives 0.40 0.40 0.40 Anticoccidial 0.05 0.10 Fungicide 0.10 0.10 Nutritional composition ME, Mcal/kg 3.10 3.20 Protein, % 22.0 17.0 Methionine, % 0.56 0.40 Met + cystine, % 0.90 0.72 Lysine, % 1.24 1.10 Threonine, % 0.80 0.75 Linoleic acid, % 3.25 3.48 Calcium, % 0.90 0.82 Available phosphorus, % 0.42 0.39 a. Commercial Farm El Recreo–Carioca. Buga, Colombia. SOURCE: Buitrago et al. (2002). 558 The Use of Cassava Products in Animal Feeding Table 27-50. Composition of broiler diets with intermediate levels of cassava meal and FFSBa. Starting Finishing Ingredients (%) Cassava roots meal 20.0 25.0 FFSB (toasted) 32.0 34.0 Soybean meal 8.20 2.80 Fish meal 3.50 4.00 Palm oil — 0.10 Dicalcium phosphate 0.90 0.70 Calcium carbonate 0.80 0.90 DL-methionine 0.27 0.22 Salt 0.25 0.25 Chline chloride 0.12 0.10 Vitamins and minerals 0.12 0.10 Anticoccidial 0.05 0.10 Fungicide 0.10 0.10 Nutritional composition ME, Mcal/kg 3.15 3.20 Protein, % 21.0 19.0 Methionine, % 0.58 0.51 Met + cystine, % 0.88 0.77 Lysine, % 1.23 1.10 Threonine, % 0.60 0.59 Linoleic acid, % 3.08 3.10 Calcium, % 0.90 0.91 Available phosphorus, % 0.43 0.42 a. Commercial Farms: Avités – Nutrilisto. Cereté, Colombia. SOURCE: Buitrago et al. (2002). Table 27-51. Results on the performance of broilers with intermediate levels of cassava root meal in the dieta. Control Cassava-FFSBc (corn-SBM)b Number of birds at starting 7.680 7.673 Number of birds at finishing 7.415 7.108 Number of days 42 42 Mortality, % 3.2 5.7 Final weight, g 1.976 1.942 Feed consumption, g 3.754 3.781 Conversion efficiency 1.90 1.94 European conversion efficiency 239 218 a. El Recreo Farm. Buga, Cauca Valley, Colombia. b. Control commercial diet based on corn and soybean meal. c. Experimental diet based on cassava root meal and fullfat soybeans. SOURCE: Buitrago et al. (2002). 559 Cassava in the Third Millennium: … Table 27-52. Results on the performance of broilers with intermediate levels of cassava root meal in the dieta. Control Cassava-FFSBc (sorghum-SBM)b Number of birds at starting 48.441 24.000 Number of birds at finishing 46.199 22.392 Number of days 42 42 Mortality, % 4.6 6.7 Final weight, g 1.934 1.915 Feed consumption, g 3.559 3.152 Feed conversion ratio 1.84 1.69 European conversion efficiency 239 218 a. Avites Farm. Cereté, Córdoba, Colombia. b. Control commercial diet based on sorghum and soybean meal. c. Experimental diet based on cassava root meal and fullfat soybeans. SOURCE: Buitrago et al. (2002). Table 27-53. Composition of broiler diets with maximum levels of cassava meal and FFSB in the starting phase. Control CRM + FFSBa CRM + CFM + (corn-SBM) Solar drying Artificial drying FFSBd Ab Bc Ingredients (%) Corn 59.37 — — — — CRM — 45.75 45.75 45.75 40.45 CFM — — — — 6.00 FFSB 12.8 30.0 30.0 30.0 30.0 Soybean meal 21.0 18.7 18.7 18.7 18.7 Palm oil 3.0 2.9 2.9 2.9 4.5 DL-methionine 0.16 0.29 0.29 0.29 0.29 L-lysine 0.07 — — — — Bone meal 1.70 1.90 1.90 1.90 1.90 Ca carbonate 1.50 — — — — Salt 0.30 0.30 0.30 0.30 0.30 Vitamin Premix 0.10 0.10 0.10 0.10 0.10 Nutritional composition ME, Mcal/kg 3.20 3.20 3.20 3.20 3.20 Protein, % 22.0 22.0 22.0 22.0 22.0 Methionine, % 0.59 0.59 0.59 0.59 0.59 Met + cystine, % 0.90 0.90 0.90 0.90 0.90 Lysine, % 1.26 1.26 1.26 1.26 1.27 Linoleic acid, % 2.62 3.42 3.42 3.42 3.56 Ca, % 0.91 0.91 0.91 0.91 0.91 Available P, % 0.42 0.42 0.42 0.42 0.42 a. Cassava root meal + fullfat soybeans. b. Equipment with steam heating. c. Equipment with propane gas heating. d. Cassava root meal + cassava foliage meal + fullfat soybeans. SOURCE: Gil et al. (2001). 560 The Use of Cassava Products in Animal Feeding Table 27-54. Composition of broiler diets with maximum levels of cassava meal and FFSB in the finishing phase. Control CRM + FFSBa CRM + CFM (corn-SBM) Solar drying Artificial drying + FFSBd Ab Bc Ingredients (%) Corn 66.85 — — — — CRM — 49.8 49.8 49.8 46.1 CFM — — — — 6.00 FFSB 6.1 41.6 41.6 41.6 45.1 Soybean meal 20.7 5.2 5.2 5.2 — DL-methionine 0.13 0.23 0.23 0.23 0.23 Lysine 0.19 — — — — Bone meal 1.60 1.90 1.90 1.90 1.90 Ca carbonate 1.10 — — — — Salt 0.30 0.30 0.30 0.30 0.30 Vitamin Premix 0.10 0.10 0.10 0.10 0.10 Nutritional composition ME, Mcal/kg 3.20 3.20 3.20 3.20 3.20 Protein, % 20.0 20.0 20.0 20.0 20.0 Methionine, % 0.49 0.49 0.49 0.49 0.49 Met + cystine, % 0.78 0.78 0.78 0.78 0.78 Lysine, % 1.12 1.12 1.12 1.12 1.12 Linoleic acid, % 2.20 3.60 3.60 3.60 3.85 Ca, % 0.90 0.90 0.90 0.90 0.90 Available P, % 0.40 0.40 0.40 0.40 0.40 a. Cassava root meal + fullfat soybeans. b. Equipment with steam heating. c. Equipment with propane gas heating. d. Cassava root meal – cassava foliage meal + fullfat soybeans. SOURCE: Gil et al. (2001). Table 27-55. Results on the performance of broilers with maximum levels of cassava root meal and FFSB in the diet during the starting and finishing phases. Control CRM + FFSBa CRM + CFM (corn-SBM) Solar drying Artificial drying + FFSBd Ab Bc Initial weight, g 39.8 39,5 39.4 39.5 39.7 Final weight, g 2,139 2,279 2,237 2,387 2,113 Feed consumption 4.73 4.88 4.65 4.68 4.72 Feed conversion rate 2.21 2.14 2.08 1.96 2.24 a. Cassava root meal + fullfat soybeans. b. Equipment with steam heating. c. Equipment with propane gas heating. d. Cassava root meal + cassava foliage meal + fullfat soybeans. SOURCE: Gil et al. (2001). 561 Cassava in the Third Millennium: … Table 27-56. Example of layer diets with maximum levels of cassava root meal fullfat soybeans and cassava foliage meal. Ingredients (%) Replacement chickens Laying hens 0-6 weeks 7-15 weeks Phase 1 Phase 2 Cassava root meal 59.3 61.4 41.6 51.9 FFSBa 9.6 9.2 38.9 28.0 Cassava foliage meal — 6.0 6.0 6.0 Soybean meal 26.9 19.6 1.9 3.6 Calcium phosphate 1.4 1.2 1.2 1.2 Calcium carbonate 1.9 1.8 9.5 8.4 DL-methionine 0.21 0.10 0.23 0.23 Salt 0.30 0.30 0.30 0.30 Vitamins and minerals 0.40 0.40 0.40 0.40 a. Fullfat soybean. Table 27-57. Nutritional composition of layer diets with maximum levels of cassava root meal, fullfat soybeans, and cassava foliage meala. Nutritional composition Replacement chickens Laying hens 0-6 weeks 7-15 weeks Phase 1 Phase 2 Metabolizable energy, Mcal/kg 2.80 2.75 2.90 2.80 Protein, % 18.0 15.5 18.0 15.0 Lisine 0.98 0.68 0.86 0.75 Methionine 0.42 0.30 0.38 0.36 Met + cystine 0.72 0.54 0.73 0.64 Threonine 0.65 0.60 0.66 0.50 Calcium 0.90 1.10 4.00 3.60 Available phosphorus 0.38 0.35 0.32 0.32 Fiber 3.8 4.6 4.6 4.4 Fat 2.0 2.9 7.8 6.0 Linoleic acid 1.0 1.0 2.5 2.4 Ash 6.6 7.2 14.2 13.0 a. Nutrient requirements based on NRC (1998). Table 27-58. Example of layer diets with medium levels of cassava root meal, fullfat soybeans, and cassava foliage meal. Ingredients (%) Replacement chickens Laying hens 0-6 weeks 7-15 weeks Phase 1 Phase 2 Corn 39.0 42.9 19.7 31.0 Cassava root meal 25.0 25.0 25.0 25.0 FFSB 10.0 9.84 34.6 19.1 Cassava foliage meal — 6.0 6.0 6.0 Soybean meal 21.6 12.2 2.8 7.2 Calcium phosphate 1.3 1.2 1.1 1.1 Calcium carbonate 2.20 2.10 9.9 9.7 DL-methionine 0.14 0.06 0.20 0.17 Salt 0.30 0.30 0.30 0.30 Vitamins and minerals 0.40 0.40 0.40 0.40 562 The Use of Cassava Products in Animal Feeding Table 27-59. Nutritional composition of layer diets with medium levels of cassava root meal, fullfat soybeans, and cassava foliage meala. Replacement chickens Laying hens 0-6 weeks 7-15 weeks Phase 1 Phase 2 Metabolizable energy, Mcal/kg 2.80 2.75 2.90 2.80 Protein, % 18.0 15.5 18.0 15.0 Lisine, % 0.98 0.68 0.86 0.75 Methionine 0.42 0.30 0.38 0.36 Met + cystine 0.72 0.54 0.73 0.64 Threonine 0.65 0.60 0.66 0.50 Calcium 0.90 1.10 4.00 3.60 Available phosphorus 0.38 0.35 0.32 0.32 Fiber 3.8 4.6 4.6 4.4 Fat 2.0 2.9 7.8 6.0 Linoleic acid 1.0 1.0 2.5 2.4 Ash 6.6 7.2 14.2 13.0 a. Nutrient requirements based on NRC (1998). Table 27-60. Diets for commercial layers with 10% cassava root Table 27-61. Performance of commercial layers fed with 10% meal and fullfat soybeans. cassava root meal and fullfat soybeansa. Control 10% cassava Control 10% cassava (corn) root meal (corn) root meal Ingredients (%) Daily feed consumption, g 102.6 103.2 Corn 57.8 45.3 Laying, % 89.2 89.5 Cassava root meal — 10.0 Feed conversion (per dozen eggs) 1.4 1.4 FFSB (toasted) 5.3 9.1 a. 48 to 55-week laying period. La Esperanza Poultry Farm. Buga, Soybean meal 16.2 15.0 Valle. 1,010 masl. 26 oC. Fish meal (65 % protein) 5.0 5.0 SOURCE: Gutiérrez and Martínez (1998). Wheat bran 3.5 3.5 DL-methionine 0.18 0.20 Table 27-62. Diets for commercial layers with 15% cassava root Calcium carbonate 9.71 9.64 meal and fullfat soybeans. Calcium phosphate 0.95 0.91 Control 15% cassava Salt 0.30 0.30 (corn) root meal Vitamins and minerals 0.60 0.60 Ingredients (%) Nutritional composition Corn 41.1 34.1 Metabolizable energy, Mcal/kg 2.75 2.75 Cassava root meal — 15.0 Protein, % 17.5 17.5 Fullfat soybeans (extruded) 20.0 20.00 Methionine, % 0.44 0.44 Soybean meal 8.1 11.60 Met + cystine, % 0.75 0.75 Rice polishings 10.0 — Lysine, % 0.91 0.91 Wheat bran 9.1 7.60 Calcium, % 3.90 3.90 DL-methionine 0.18 0.19 Available phosphorus, % 0.45 0.45 Calcium carbonate 9.60 9.30 Linoleic acid, % 1.36 1.39 Calcinated bone meal 1.30 1.50 Salt 0.35 0.35 Vitamins and minerals 0.30 0.30 Nutritional composition Metabolizable energy, Mcal/kg 2.75 2.75 Protein, % 17.0 17.0 Methionine, % 0.45 0.45 Met + cystine, % 0.70 0.70 Lysine, % 0.85 0.85 Calcium, % 3.90 3.90 Available phosphorus, % 0.42 0.42 Linoleic acid, % 1.74 1.37 563 Cassava in the Third Millennium: … Table 27-63. Performance of commercial layers fed with 15% Table 27-66. Diets for commercial white and brown layers with cassava root and fullfat soybeansa. 10% and 20% cassava root meal and fullfat soybean. Control 15% cassava (corn) root meal Control 10% cassava 20% cassava Layers, No. 15,000 5,000 (corn) root meal root meal Daily feed consumption, g 114.0 115.0 Ingredients (%) Laying, % 78.3 79.0 Corn 41.1 34.1 23.0 Feed conversion (dozen eggs) 1.37 1.37 Cassava root meal — 10.0 20.0 Fullfat soybean a. 55 to 61-week laying period. Santa Anita Poultry Farm. Pradera, (extruded) 20.0 20.0 20.0 Valle. 1.010 masl. 26 oC. American Soybean Association (ASA), 2000. Soybean meal 8.1 10.4 11.8 SOURCE: Buitrago et al. (2002). Rice polishings 10.0 10.0 10.0 Wheat bran 9.1 4.3 3.6 DL-methionine 0.18 0.19 0.21 Calcium carbonate 9.60 9.50 9.40 Table 27-64. Diets for commercial layers with 20% cassava root Calcinated phosphate 1.30 1.40 1.40 meal and fullfat soybeans. Salt 0.35 0.35 0.35 Control 20% cassava Vitamins and minerals 0.30 0.30 0.30 (corn) root meal Nutritional composition Ingredients (%) ME, Mcal/kg 2.70 2.70 2.70 Corn 20.0 — Protein, % 17.0 17.0 17.0 Sorghum 30.6 36.2 Methionine, % 0.45 0.45 0.45 Cassava root meal — 20.0 Met + cystine, % 0.70 0.70 0.70 Fullfat soybean (toasted) 15.0 15.0 Lisine, % 0.85 0.85 0.85 Soybean meal 12.3 16.5 Calcium, % 3.90 3.90 3.90 Wheat bran 10.3 0.20 Available phosphorus, % 0.42 0.42 0.42 DL-methionine 0.23 0.23 Linoleic acid, % 1.74 1.49 1.37 Calcium carbonate 9.20 9.30 Calcium phosphate 1.40 1.60 Salt 0.35 0.35 Vitamins and minerals 0.60 0.60 Nutritional composition Table 27-67. Performance of commercial brown layers fed with 10% and 20% cassava root meal and fullfat Metabolizable energy, Mcal/kg 2.70 2.70 soybeansa. Protein, % 17.0 17.0 Control 10% cassava 20% cassava Methionine, % 0.45 0.45 (corn) root meal root meal Met + cystine, % 0.70 0.70 Layers, No. 3,840 10,956 5,160 Lisine, % 0.81 0.81 Daily feed consumption, g 115.1 115.8 114.8 Calcium, % 3.90 3.90 Laying, % 69.3 65.7 65.1 Available phosphorus, % 0.42 0.42 Feed conversion Linoleic acid, % 1.54 1.25 (per dozen eggs) 2.00 2.12 2.11 a. 78 to 88-week laying period. Lohmann Brown layers. Avicauca Poultry Farm. Jamundí, Valle. 1,005 masl. 25 oC. American Soybean Association (ASA), 1999. SOURCE: Buitrago et al. (2002). Table 27-65. Performance of commercial layers fed with 20% cassava root meal and fullfat soybeansa. Control 20% cassava corn root meal Daily feed consumption, g 111.6 111.1 Laying, % 92.4 91.0 Feed conversion (per dozen eggs) 1.50 1.46 a. 39 to 46-week laying period. Avícola Montegrande Poultry Farm. Tuluá, Valle. 1,025 masl. 25 oC. SOURCE: Gutiérrez and Martínez (1998). 564 The Use of Cassava Products in Animal Feeding Table 27-68. Swine diets totally based on cassava root meal, cassava foliage meal and fullfat soybean. Starting Growing Final Gestation Lactation Ingredientes (%) Cassava root meal 45.2 50.5 53.4 57.1 51.7 Cassava foliage meal — 4.0 8.0 8.0 8.0 Fullfat soybean 45.8 42.8 33.8 29.5 35.2 Soybean meal 6.0 — — — — Vegetable oil — 0.4 2.8 3.0 2.8 Methionine 0.06 0.05 0.03 — 0.04 Dicalcium phosphate 1.2 0.8 0.5 1.1 1.0 Calcium carbonate 1.2 0.9 0.9 0.7 0.7 Salt 0.35 0.35 0.35 0.35 0.35 Vitamins and minerals 0.20 0.20 0.20 0.20 0.20 Nutritional composition Metabolizable energy, Mcal/kg 3.35 3.35 3.35 3.32 3.35 Protein, % 21.00 18.00 15.50 14.00 16.00 Lisine, % 1.20 0.95 0.75 0.58 0.95 Met + cystine, % 0.65 0.54 0.44 0.37 0.48 Calcium, % 0.90 0.90 0.88 0.90 0.86 Available phosphorus, % 0.40 0.32 0.25 0.35 0.35 Table 27-69. High levels of cassava root meal and fullfat soybeans in diets for growing-finishing pigs. Control diet Cassava root meal + FFSBa Growing Finishing Growing Finishing Ingredients (%) Corn 36.70 33.80 — — Cassava root meal — — 44.93 48.10 Fullfat soybean 20.00 18.60 20.00 20.00 Sorghum 16.00 16.00 — — Fish meal — 0.50 — — Corn bran 8.00 12.00 — — Soybean meal 7.60 3.40 16.71 10.90 Wheat bran 8.00 12.00 12.00 15.00 Vegetable oil — — 3.70 3.30 Salt 0.39 0.39 0.39 0.39 Vitamins and minerals 3.31 3.31 2.27 2.31 Main nutrients ME, Mcal/kg 3.31 3.32 3.36 3.34 Protein, % 18.3 17.3 16.3 16.3 a. Fullfat soybean. Table 27-70. Performance of finishing pigs with high inclusion of cassava root meal and fullfat soybean dietsa. Control diet Cassava root meal + FFSBb Initial weight, kg 48.10 49.29 Final weight, kg 96.00 96.41 Daily weight gain, kg 0.75 0.74 Daily consumption, kg 2.22 2.12 Feed conversion ratio 2.96 2.89 a. Granjas Paraíso – CLAYUCA – Nutribal. Palmira, Valle. 2002. b. Fullfat soybean. 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Latinoamericano y del Caribe de Apoyo a la Investigación y al Desarrollo de la Yuca (CLAYUCA), Gómez G; Buitrago JA. 1982. Effect of processing on Federación Nacional de Avicultores de Colombia nutritional content of feeds: root crops. In: Rechcigl (FENAVI), Fondo Nacional Avicola (FONAV), Cali, M, ed. Handbook of nutritive value of processed Colombia. (Also available at www.clayuca.org/PDF/ foods. Vol II, p. 221–237. CRC Press, Boca Raton, FL, cassava_poultry_nutrition.pdf.) USA. 439 p. CIAT. 1973. Annual Report. Swine Production Systems. Gómez G; Santos J; Valdivieso M. 1981. Utilización de la Cali, Colombia. p 119–144. yuca en alimentación porcina. In: VII Curso Intensivo de Adiestramiento Posgrado en Investigación para la CIAT. 1974. Informe Anual. Sistemas de Producción de Producción de Yuca. CIAT, Cali, Colombia. 31 p. Ganado Porcino. Cali, Colombia. p 163–212. Gutiérrez G; Martínez L. 1998. Efecto de utilizar harina de CIAT. 1975. Annual Report. Swine Production Systems. yuca y soya integral en dietas para aves ponedoras. Cali, Colombia. p D1–D20. Thesis. Universidad Nacional de Colombia, Palmira, Colombia. Chicco CF; Garbati ST; Muller-Haye B; Vecchionacce H. 1972. La harina de yuca en el engorde de cerdos. Hennesey S; Ayala JC. 1986. Evaluación de soya integral Agron Trop (Maracay, Venez.) 22(6):599–603. cocida y harina de yuca en la alimentación de aves de postura. Thesis. Universidad Nacional de Colombia, Choo TL; Hutagalung RI. 1972. Nutritional value of Palmira, Colombia. tapioca leaf (Manihot utilissima) for swine. Malays Agric Res 1:38–47. Lozada H; Alderete R. 1979. Efecto de la harina de raiz de yuca y nivel de urea sobre el comportamiento de becerros en pastos de baja calidad con libre acceso a melaza. Producción Animal Tropical 4:46–48. 566 The Use of Cassava Products in Animal Feeding Maner JH; Buitrago JA; Portela R; Jiménez I. 1978. La Pineda J; Rubio R. 1972. Un concepto nuevo en el levante yuca en la alimentación de cerdos. Instituto de novillas para ganadería de leche. Revista ICA Colombiano Agropecuario (ICA) and CIAT, Cali, (Colombia) 17(4):405–413. Colombia. 113 p. (Mimeo.) Ravindran V; Kornegay ET; Cherry JA. 1983. Feeding Mathur ML; Sampath SR; Gosh SN. 1969. Studies on values of cassava tuber and leaf meals. Nutr Rep Int tapioca: effect of 50 and 100 percent replacement of 28(1):189–196. vats by tapioca in the concentrate mixture of dairy cows. Indian J Dairy Sci 22:193–199. Ribeiro PJ; Moreira HA; Vitela H; Silva T. 1976. Melazo deshidrato e raspa de mandioca como sustitutos Méndez A; Zaragoza L. 1980. Sustitución del sorgo por parciais do milho para producto de leite. Arq Esc Vet harina de yuca en la alimentación de cerdos. Agric Univ Fed de Minas Gerais 28(2):193–200. Tec Mex 6(2):83–91. Ross E; Enriquez FQ. 1969. The nutritive value of cassava Moore CP. 1976. El uso del follaje de yuca en alimentación leaf meal. Poul Sci 48(3):846–853. de rumiantes. In: Proc International seminar on tropical livestock. Acapulco, Mexico. p 47–62. Stevenson M. 1984. The nutritional value of cassava root meal in laying hen diets. J Sci Food Agric 35:36–40. Muller Z; Chou KC; Nash K; Tan TK. 1972. Study of nutritive value of tapioca in economic rations for Stevenson M; Jackson N. 1983. The nutritional value of growing-finishing pigs in the tropics. United Nations dried cassava root meal in broiler diets. J Sci Food Development Programme, UNDP/SF Project Sin Agric 34:1361–1367. 67/505. Pig and Poultry Research and Training Institute, Singapore. 35 p. Terleira HG; Ten Brinke HW; López W; Santisteban D. 1975. Uso de raíces de yuca, coronta de maíz y NRC (National Research Council). 1994. Nutrient cáscara de algodón en el engorde de novillos en requirements of poultry. 9th edition. Washington, Tarapoto-San Martín. Ministerio de Alimentación. USA. Dirección General de Investigación. Lima, Peru. 13 p. (Mimeo.) 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Cornell University, Ithaca, NY, USA. 567 APPENDIX 1 Acronyms, Abbreviations, and Technical Terminology Entities CENICAFE Centro Nacional de Investigaciones del Café, Colombia ABNT Associação Brasileira de Normas [National Coffee Research Center] Técnicas CGIAR* Consultative Group on International [Brazilian Association for Technical Agricultural Research Standards] CGP Cassava Genome Project ACCB Asociación Colombiana de Ciencias Biológicas CIAT Centro Internacional de Agricultura [Colombian Association of Biological Tropical, Colombia Sciences] [International Center for Tropical Agriculture] ACOGRANOS Asociación Colombiana Postcosecha de Granos CIMMYT Centro Internacional de Mejoramiento de [Colombian Association for the Maíz y Trigo Postharvesting of Grains] [International Maize and Wheat Improvement Center] ACOPOR Asociación Colombiana de Porcicultores [Colombian Association of Pig CIP Centro Internacional de la Papa Producers] [International Potato Center] AMCA Air Movement and Control Association CITA Centro Nacional de Ciencia y Tecnología International, Inc., USA de Alimentos, Costa Rica [National Center for Food Science and ARS Agricultural Research Service (of the Technology] USDA) CLAYUCA Consorcio Latinoamericano y del Caribe ASOMUDEPAS Asociación Municipal para el Desarrollo de Apoyo a la Investigación y al Sostenible de los Pequeños Agricultores Desarrollo de la Yuca de San Jacinto [Latin American and Caribbean [San Jacinto Small Farmers’ Municipal Consortium to Support Cassava Association for Sustainable Research and Development] Development] CNIA Centro Nacional de Investigaciones ASOPROSA Asociación de Mujeres Productoras de Agropecuarias (of CORPOICA) Santa Ana, Colombia [National Center for Agricultural [Women Farmers’ Association of Research] Santa Ana] CNPMF Centro Nacional de Pesquisa de BioEuroLatina Asociación para la Promoción de la Mandioca e Fruticultura (of EMBRAPA) Biotecnología en Latinoamérica en also Embrapa Mandioca e Fruticultura Cooperación con Europa [National Cassava & Fruits Research [Association for the Promotion of Center] Biotechnology in Latin America in Cooperation with Europe] CNRS Centre national de la recherche scientifique, France Biotecol Biotecnología de Colombia [National Center for Scientific Research] [Biotechnology of Colombia] CONGELAGRO Congelados Agrícolas S.A., Colombia CATIE Centro Agronómico Tropical de [Frozen Agricultural Products, p/c] Investigación y Enseñanza CBN Cassava Biotechnology Network CECORA Central de Cooperativas de la Reforma Agraria, Colombia * ‘CGIAR’ was originally the acronym for the ‘Consultative Group on [Federation of Agrarian Reform International Agricultural Research’. In 2008, CGIAR redefined Cooperative Associations] itself as a global partnership. To reflect this transformation, and yet retain its roots, ‘CGIAR’ was retained as a name. CGIAR is now a global research partnership for a food secure future. 569 Cassava in the Third Millennium: … CORPOICA Corporación Colombiana de Investigación IFAD International Fund for Agricultural Agropecuaria Development (of the International [Colombian Corporation of Agricultural Monetary Fund) Research] IIT Instituto de Investigaciones CUNY The City University of New York, USA Tecnológicas, Colombia DGIS Directoraat-Generaal Internationale [Technological Research Institute] Samenwerking, Netherlands IITA International Institute of Tropical [Directorate-General for International Agriculture Cooperation] IPGRI International Plant Genetic Resources DOE-JGI U.S. Department of Energy-Joint Institute (now Bioversity International) Genome Institute IPM Unit Integrated Pest Management Unit (of DRI Fondo de Desarrollo Rural Integrado (of CIAT) MADR) IRD Institut de recherche pour le [Fund for Integrated Rural Development] développement, France EMBRAPA Empresa Brasileira de Pesquisa [Institute of Research for Development] Agropecuária ISAAA International Service for the Acquisition [Brazilian Agricultural Research of Agri-biotech Applications Corporation] LABIOTSA Laboratorios de Biotecnología y ETH–Zurich Eidgenössische Technische Hochschule Servicios Anexos, Ecuador Zürich [Laboratories for Biotechnology and [Swiss Federal Institute of Technology Annexed Services] Zurich] LANUR Laboratório de Nutrição de Ruminantes EU European Union (of UFRGS) FAO Food and Agriculture Organization of the [Ruminant Nutrition Laboratory] United Nations MADR Ministerio de Agricultura y Desarrollo FEDEARROZ Federación Nacional de Arroceros, Rural, Colombia Colombia [Ministry of Agriculture and Rural [National Federation of Rice Growers] Development] FEDEYUCA Federación Nacional de Productores, OECD Organisation for Economic Co-operation Procesadores y Comercializadores de and Development Yuca, Colombia PRGA CGIAR Systemwide Program on [National Federation of Cassava Participatory Research and Gender Producers, Processors, and Traders] Analysis FENAVI Federación Nacional de Avicultores de RAD Project Rural Agroenterprise Development Colombia Project (of CIAT) [National Federation of Poultry Producers] SOCOLEN Sociedad Colombiana de Entomología [Colombian Entomology Society] FIDAR Fundación para la Investigación y Desarrollo Agrícola, Colombia UF University of Florida, USA [Foundation for Agricultural Research UFRGS Universidade Federal do Rio Grande do and Development] Sul, Brazil IBPGR International Board for Plant Genetic UN Universidad Nacional de Colombia Resources (now Bioversity International) [National University of Colombia] ICA Instituto Colombiano Agropecuario UNDP United Nations Development Programme [Colombian Institute of Agriculture] UNIANDES Universidad de los Andes, Colombia ICONTEC Instituto Colombiano de Normas Técnicas y Certificación UNIVALLE Universidad del Valle, Colombia [Colombian Institute for Technical and USDA United States Department of Agriculture Certification Standards] USI Usinas Sociais Inteligentes, Brazil 570 Acronyms, Abbreviations, and Technical Terminology Other abbreviations and acronyms c.f. conversion factor (for quantity of dried chips from a given batch of fresh cassava AAI alpha-amylose index roots) ABA abscisic acid CFM cassava foliage meal AD artificial drying (of cassava chips) cfu colony-forming unit (of microorganisms) ADP adenosine diphosphate (a nucleotide) Chl chlorophyll AFLP amplified fragment length polymorphism CM controlled pollination (used for coding cassava lines developed at CIAT) AGPase ADP-glucose pyrophosphorylase (an enzyme) cmg centimilligram (10–2 of a gram) AHAS acetohydroxy acid synthase CN group cyano group a.i. active ingredient CNP cyanogenetic potential (of a cassava variety) AN available nitrogen (i.e., usable by plants) COD chemical oxygen demand ANA α-naphthaleneacetic acid (used in plant tissue culture media) cP centipoise (a measure of viscosity) ATIS automated immersion systems CP commercial product BAC bacterial artificial chromosome CRM cassava root meal BamHI restriction enzyme derived from Bacillus cv., cvs cultivar, cultivars amyloliquefaciens CW controlled wild (refers to controlled BAP benzylamino purine (hormone used in pollination in wild × cassava crosses) plant tissue culture media) Da dalton (measure of atomic mass) BIRUS biorefinerias rurales sociales DAP days after planting (rural social biorefineries) DAP diammonium phosphate BOD biological oxygen demand db dry basis BSA bulk segregant analysis DC dried cassava chips Bt Bacillus thuringiensis (used for biological control) DDT dichlorodiphenyltrichloroethane (pesticide) BU Brabender units (these measure viscosity of a liquid) DE digestible energy 14C also carbon-14 or radiocarbon, a dm decameter (10 meters) radioactive isotope of carbon DM dry matter C3 pathway for capturing carbon dioxide DNA deoxyribonucleic acid during photosynthesis, involving a DNCP degree of nutrient element in the 3-carbon molecule, typical of cool- commercial product season plants DS dry soil C4 pathway for capturing carbon dioxide during photosynthesis, involving a dS/m deciSiemens per meter (used to measure 4-carbon molecule, typical of warm- salinity) season plants dw dry weight Ci/Ca ratio of intercellular CO2 to atmospheric E efficiency of fertilizer application CO2 E egg (insect) CAM also CAM photosynthesis, crassulacean acid metabolism, which is a carbon EC electrical conductivity fixation pathway that occurs at night ECR ensiled cassava root cDNA complementary DNA (synthesized from a ECZ edaphoclimatic zone mature mRNA template in a reaction catalyzed by the enzyme reverse EDTA ethylene diamine tetraacetic acid transcriptase and the enzyme DNA ELISA enzyme-linked immunosorbent assay polymerase) EM effect as mulch (of green manures) CEC cation exchange capacity ESTs expressed sequence tags 571 Cassava in the Third Millennium: … F and V fixed and variable costs LA low adaptation index to low soil K F1, F2, etc. first filial generation, second filial LAC Latin America and the Caribbean generation, etc. LAI leaf area index FC fresh cassava chips LAR local area report FEC friable embryogenic callus LSF liquefaction, saccharification, and FFSB fullfat soybean fermentation FN fixed nitrogen (in humus) L/T cassava chip load per sloping tray FOB free on board (a shipping term) MAP months after planting FRWA fresh root weight in air masl meters above sea level FRWW fresh root weight in water Mcal megacalories FRY fresh root yield (of cassava) MCP maximum capacity for processing (of FU farinograph units cassava chips) fw fresh weight mdh malate dehydrogenase maize probe GA gibberellic acid (hormone used in plant me malic enzyme maize probe tissue culture media) ME metabolizable energy GBSS granule-bound starch synthase (an MHD maximum level of humidity accepted enzyme) MLO mycoplasma-like organism GDC glycine decarboxylase (a photorespiratory MPa megapascal (a measure of force per unit enzyme) area) gfw grams (fresh weight) mRNA messenger RNA (an RNA molecule GM green matter encoding a chemical “blueprint” for a HA high adaptation index to low soil K protein product) HCN hydrocyanic acid (content indicates mS millisiemens cyanogenic potential of cassava roots) MS Murashige and Skoog culture medium HI harvest index MVAG micro-viscoamylograph hL hectoliter NAD-ME a C4 photosynthetic pathway, subtype HMA hot-melt adhesive nicotinamide adenine dinucleotide malic enzyme hp horsepower NADH nicotinamide adenine dinucleotide HPR host-plant resistance (reduced form) HQ headquarters NADP-ME a C4 photosynthetic pathway, subtype IA intermediate adaptation index to low nicotinamide adenine dinucleotide soil K phosphate malic enzyme IPDM integrated pest-and-disease management NBR normas brasileiras (usually followed by corresponding numbers, as established IPM integrated pest management by the ABNT) ISA measured in percentage, refers to (Brazilian standards) physicochemical characteristic of flour ND natural drying (of cassava chips) IVAG in vitro active genebank NE State of Nebraska, USA IVBG in vitro base genebank NF need for fertilizer application IVDMD in vitro dry matter digestibility NP not planted kPa kilopascal (a measure of force per unit NTC Norma Técnica Colombiana area) [Colombian Technical Standard] kVA kilovolt-ampere (a unit of electrical power OA osmotic adjustment equal to 1000 volt-amperes) OCD oxygen chemical demand L larva (insect) OM organic matter L liter 572 Acronyms, Abbreviations, and Technical Terminology OW open wild (refers to open pollination in RT-PCR real-time polymerase chain reaction wild × cassava crosses) (see also PCR) P pupa (insect) rubisco ribulose biphosphate carboxylase Pn photosynthetic rate (measured as µmol (enzyme found in chloroplasts) CO2 per m2/s) RVA units Rapid Visco Analyzer units (for flour P-protein phloem protein quality) PAR photosynthetically active radiation sat. saturation (referring to solar radiation for plants) SBE starch-branching enzyme p.c. paste concentrate SBM soybean meal PCR polymerase chain reaction (see also SCARs sequence characterized amplified regions RT-PCR) SCP single-cell protein, also known as PDA potato dextrose agar unicellular protein PEPC also PEP carboxylase, SE standard error phosphoenolpyruvate carboxylase (an SG specific gravity important enzyme in photosynthesis) SHF simultaneous hydrolysis and pH pouvoir hydrogène [hydrogen power] fermentation (unit to express the degree of acidity or alkalinity of a solution) SLA specific leaf area PIB post-illumination burst of CO SN nutrient in the soil 2 ppc phosphoenolpyruvate carboxylase maize SSRs simple sequence repeats probe STET compound of sucrose, Triton X-100, PPD postharvest physiological deterioration EDTA, and tris-HCl (of harvested cassava roots) SW self-pollinated cross between cassava PTO power takeoff (a drive shaft found on a and a wild Manihot species tractor) TDN total digestible nutrients pv. pathovar (bacterial strain) Tgel gelatinization temperature PVA polyvinyl acetate TILLING® targeting induced local lesions in PW polycross of cassava with a wild Manihot genomes species TN total nitrogen QPM quality-protein maize tris-HCl tris(hydroxymethyl)aminomethane- QR quantitative resistance hydrochloride QRLs quantitative resistance loci tRNA transfer RNA (a small RNA molecule that transfers a specific active amino acid to a QTLs quantitative trait loci growing polypeptide chain at the RDA recommended dietary allowance, ribosomal site of protein synthesis during now RDI or reference daily intake, translation) also recommended daily intake (USA) TTSS type III secretion system RFLP restriction fragment length polymorphism UE use efficiency (referring to plant use of RGAs resistance gene analogs water or nutrients) r.h. relative humidity USLE universal soil loss equation RITA® récipient à immersion temporaire VPD vapor pressure deficit(s) automatique Vs volume of soil [automatic temporary immersion device] W watts RN recommended nutrient wb wet basis RNA ribonucleic acid WFR whitefly resistance RNAi RNA interference technology WRC weighted requirement of crop rpm revolutions per minute Ws weight of soil 573 Cassava in the Third Millennium: … WUE water-use efficiency C carbon w/w weight by weight Ca calcium Cl chlorine Cassava diseases and pests Cu copper Fe iron ACMD, ACMV African cassava mosaic disease, African cassava mosaic virus K potassium CBB cassava bacterial blight, also vascular Mg magnesium bacteriosis of cassava Mn manganese CCMV cassava common mosaic disease Mo molybdenum CCSpV cassava Colombian symptomless virus N nitrogen CFSD cassava frogskin disease Na sodium CGM cassava green mite (see also Mt) O oxygen CMD cassava Caribbean mosaic disease P phosphorus CsCMD, CsCMV cassava common mosaic disease, S sulfur cassava common mosaic virus Zn zinc CsXV cassava X virus CVMD, CVMV cassava vein mosaic disease, Compounds cassava vein mosaic virus CaCO3 calcium carbonate EPNs entomopathogenic nematodes CN– cyanide radical (also cyanide anion) Mc Mononychellus caribbeanae CaO calcium oxide Mt Mononychellus tanajoa (cassava green mite; also CGM) CO2 carbon dioxide Tu Tetranychus urticae (green spotted mite) ETOH hydrated ethanol (at 96%, v/v) H2BO – VAM vesicular arbuscular mycorrhizae 3 boric acid ion Xam Xanthomonas axonopodis pv. manihotis H2O water vapor H2PO – 4 dihydrogen phosphate ion Soil textures Hg(NO3) mercury (II) nitrate (also mercuric nitrate or mercury dinitrate) C clay KCl potassium chloride CL clay loam K2O potassium oxide L loam MgCO3 magnesium carbonate S sandy MgO magnesium oxide (also magnesia) SC sandy clay MoO 2– 4 molybdenum oxoanion SCL sandy clay loam N2O nitrous oxide (also laughing gas) Si silt NaCl sodium chloride SiC silty clay NaClO sodium hypochlorite SiCL silty clay loam NH – 2 amine SiL silt loam NH3 ammonia SL sandy loam NH + 4 ammonium cation NO3 nitrate Chemical elements and compounds P2O5 phosphorus pentoxide SeO 2– 4 selenate ion Elements SO 2– 4 sulfate ion Al aluminum B boron 574 CIAT Publication No. 377 Corporate Communications, CIAT and Latin American and Caribbean Consortium to Support Cassava Research and Development (CLAYUCA) Translation: Elizabeth L. McAdam Lynn Menéndez Damian & Bibi Hager Editing: Elizabeth L. McAdam Production editing: Gladys Rodríguez Claudia Marcela Calderón Production: Oscar Idárraga (layout) Julio César Martínez (cover design) Printing: Impresora Feriva S.A., Cali, Colombia