ldl::J) t::I f7861 dlJ , .11od~H 1~nuuy Cover: An Asian farmer begins the production cycle by carefuUy planting her potato seed . Women play important roles in the food systems of developing countries. • --- International Potato Center Annual Report 1984 INTERNATIONAL POTATO CENTER P.O. Box 5969, Lima, Peru 1985 The International Potato Center (CIP) is a nonprofit, autonomous scientific institution established in 1972 by agreement with the Government of Peru for developing and disseminating knowledge for greater use of the potato as a basic food in the developing world. CIP is one of 13 nonprofit international research and training centers supported by the Consultative Group for International Agricultural Research (CGIAR). The CGIAR is sponsored by the Food and Agriculture Organization (FAQ) of the United Nations, the United Nations Development Programme (UNDP), and the International Bank for Reconstruction and Development (World Bank), and comprises more than 45 countries, international and regional organizations, and private foundations. CIP received funding in 1984, through the CGIAR, from the following donors: the governments of Australia, Belgium, Brazil, France, Germany, Ireland, Italy, Japan, Mexico, Netherlands, Norway, People's Republic of China, Philippines, Spain, and Switzerland; the Canadian International Develop- ment Agency (CIDA); the Danish International Development Agency (DANIDA); the European Economic Community (EEC); the Inter-American Development Bank (IDB); the International Fund for Agricultural Development (IFAD); the Swedish Agency for Research Cooperation with Developing Countries (SAREC); the United Kingdom Overseas Development Administration (UKODA); the United States Agency for Inter- national Development (USAID); the OPEC Fund for International Development; and the German Foundation for International Development (DSE). The 1984 Annual Report is published in English and Spanish by the International Potato Center (CIP). This report covers the period from 1November1983 to 31 October 1984. Mention of specific products by trade name does not imply endorsement of or discrimination against such products by CIP. Citation: International Potato Center. 1985. Annual Report CIP 1984. Lima, Peru. 168 p. Printed by the International Potato Center, P.O. Box 5969, Lima, Peru, July 1985 . Copies printed: 2555 Contents Foreword Board of Trustees Staff List of Abbreviations and Acronyms Darwin and the Potato: A Commentary on Adaptability Summary of Research Agroecological Zones of Peru CIP Research Organization RESEARCH THRUSTS Maintenance and Utilization of Unexploited 5 7 8 12 15 19 29 31 Genetic Resources 35 II Production and Distribution of Advanced Breeding Material 41 III Bacterial and Fungal Diseases 51 IV Potato Virus Research 63 V Integrated Pest Management 75 VI Warm Climate Potato Production 83 VII Cool Climate Potato Production 91 VIII Postharvest Technology 97 IX Seed Technology 111 x Potatoes in Developing Country Food Systems 127 Regional Research, Training, and National Program Development 137 Publications 153 Research and Consultancy Contracts 155 Financial Statement 159 The CGIAR: A Global Agricultural Research System 167 Foreword 1984 has been a year of external reviews for all the CGIAR centers. Several man years of CIP staff time have been expended on the various exercises required by these reviews needed to justify the existence of the CGIAR centers, which are probably the most cost-effective investments in world agriculture today and in the foreseeable future. From this series of reviews , donor agencies and developing countries should have a better insight into the value of the CGIAR system. One result already emerging is the realization that the existing data base on developing country agriculture is inadequate for identifying priorities. It is hoped that the final review documents will give sufficient attention to the shortages of food, labor, and cash in the developing world today and to the role of the CGIAR in assisting with these problems. Already the farms of Asia are growing smaller. This means more intensive agriculture where vegetables such as the potato have a comparative advantage over cereals. Few of the investments in agriculture today seem to recognize this trend . The inadequate data base that presently exists for many food commodities is a major limitation for the CGIAR centers and others involved in helping developing countries develop effective long-term planning. This is particularly true for root and tuber crops, which do not enter into international trade channels; therefore, statistics on their production and consumption have not received the same attention as the cereals. Until the international data base for all food commodities is improved , any attempt to establish research priorities will be subject to this limitation. Moreover, simply because FAO statistics may be the only data base available across commodities , this does not justify the use of these statistics unless they can be improved upon to the point of being fairly representative. To help provide information for the many reviews within the CGIAR system and to correct the international data base on potatoes in the devel- oping world, CIP has produced its own impact study entitled Potatoes for the Developing World: A Collaborative Experience. The study relies heavily on information coming directly from developing countries worldwide who are rapidly expanding potato production with CIP's technical support. In Rwanda, a case study presented in CIP's report, the government has made a significant investment in the potato after this commodity provided 5 a major supply of food and diverted the country from starvation during a recent famine in the region. Rwanda's increased reliance on the potato as a staple food indicates a trend that is becoming common in many developing countries - this alone clearly justifies the CGIAR investment in this crop. One chapter in the impact study is devoted to the various strategies that CIP has developed and used to comply with its mandate , many of which are now being adopted by other institutions. At a recent CGIAR "think tank" on African food production and the role of the international centers, CIP's strategy for collaborative pooling of national resources was mentioned many times as the only cost-effective solution for many countries. A major donor to the CGIAR system stated that technical assistance agencies could no longer take a country-by-country approach to problems and that CIP's networking approach was essential for effective use of funding. During 1984, the two oldest networks-PRECODEPA , now six years old , and SAPPRAD, in its third year - were thoroughly reviewed , and the advantages of these collaborative systems have been documented for the benefit of others. At CIP, the cost-effective strategies already in place for the potato will permit the center to address other similar commodities at little additional cost. Several donors and agencies in the CGIAR system have mentioned the possibility of adding the sweet potato to CIP's research program. CIP's Board of Trustees and staff have been considering this proposal carefully. A position paper and budget on sweet potato research have been produced, which complement the ongoing research programs of other international organizations. CIP is prepared to use its considerable expertise in virus iden- tification and elimination, advanced tissue culture techniques, and collection , maintenance, and distribution of genetic material through its global research and transfer network to strengthen research on another major food crop. When the CGIAR Technical Advisory Committee finishes its present priorities study in 1985 , CIP, the only single-crop center in the system, may become a two-crop center. We are ready for this additional challenge. 6 12JaJ l f!awyw Richard L. Sawyer Director General Board of Trustees Executive Committee DR. JACK MEAGHER, Chairman Chief, Division of Plant Research Department of Agriculture , Victoria P.O. Box 4041 G.P.O. DR. FLAVIO COUTO, Secretary Director Melbourne , Vic. 3001 , Australia Centro Nacional de Pesquisa de Hortalips - EMBRAP A P.O. Box (11) 1316 70.000 Brasilia D.F., Brazil DR. RICHARD L. SA WYER Director General International Potato Center P.O. Box 5969 Lima, Peru Program Committee DR. MAGNHILD UMAERUS, Chairman Professor of Plant Breeding Swedish University of Agricultural Sciences Department of Plant Breeding P.O. Box 7003 S-750 07 Uppsala, Sweden DR. DAVID CALL Dean College of Agriculture and Life Sciences Cornell University Ithaca, New York 14853 U.S.A. DR. ERNST R. KELLER Professor of Crop Science Swiss Federal Institute of Technology Crop Science Department CH-8092 Zurich, Switzerland DR. VICTOR PALMA VALDERRAMA Director Investigaci6n Agropecuaria - INIP A Av. Guzman Blanco 309 Lima, Peru DR. KLAUS RAVEN General Coordinator Regional Institutes for Rural Development National Agrarian University P.O . Box 456 La Molina, Lima, Peru DR. MAX RIVES Senior Breeder Geneticist INRA 289 rue Lecourbe 75015 Paris, France DR. NOBORU TAKASE Technical Consultant Sugar Crop Development Fund Dairy Farming Center Bldg. 1, West 7 Ave., North 3 St. Chuo-ku Sapporo, Japan 7 Staff SENIOR MANAGEMENT Richard L. Sawyer, Ph.D ., Director General Jose Valle Riestra, Ph.D., Deputy Director General William A. Hamann, B.S., Assistant to the Director General Orville T. Page, Ph.D., Director of Research Kenneth J. Brown, Ph.D., Director of Regional Research Primo Accatino, Ph.D., Coordinator, Research Transfer Adrian Fajardo, M.S., Executive Officer Leonardo Hussey, Controller RESEARCH THRUSTS (Coordinators) I. Maintenance and Utilization of Unexploited Genetic Resources (C. Ochoa) II. Production and Distribution of Advanced Breeding Material (H. Mendoza) III. Research on Bacterial and Fungal Diseases (C. Martin) IV. Potato Virus Research (L. Salazar) V. Integrated Pest Management (S. Raymundo) VI. Warm Climate Potato Production (D. Midmore) VII. Cool Climate Potato Production (J . Landeo) VIII. Postharvest Technology (R. Booth) IX. Seed Technology (P. Malagamba) X. Potatoes in Developing Country Food Systems (D . Horton) 8 RESEARCH DEPARTMENTS Breeding and Genetics Humberto Mendoza, Ph.D. , Head of Department Gary Atlin, M.S. , Breeder* + Charles Brown , Ph.D., Geneticist* Ali M. Golmirzaie , Ph.D. , Breeder Zosimo Huaman , Ph.D., Geneticist Masaru Iwanaga , Ph.D., Cytogeneticist Juan Landeo , Ph.D., Breeder Peter Schmiediche, Ph.D., Breeder Maria Scurrah, Ph.D., Breeder Nematology and Entomology Parviz Jatala , Ph.D., Head of Department Javier Franco, Ph.D., Nematologist K. V. Raman , Ph.D., Entomologist Severino A. Raymundo , Ph.D., Plant Protection Specialist Luis Valencia, M.S., Entomologist (Reg. I) Pathology Edward R. French, Ph.D., Head of Department Jan Henfling , Ph .D., Mycologist (Reg. I) Upali Jayasinghe , Ph.D. , Virologist Carlos Martin, Ph.D. , Patho logist Luis Salazar, Ph.D. , Virologist Physiology Patricio Malagamba, Ph.D., Head of Department Cornelia Almekinders, Ir. , Associate Expert + Robert H. Booth, Ph.D., Physiologist John H. Dodds, Ph.D. , Tissue Culture Peter Keane, B.S., Processing Specialist David J. Midmore, Ph.D. , Physiologist Noel Pallais, Ph.D. , Physiologist Siert Wiersema, Ph.D. , Physiologist Taxonomy Carlos Ochoa, M.S., Head of Department Social Science Douglas E. Horton , Ph.D ., Head of Department Peter T. Ewell, Ph.D., Economist Angelique Haugerud, Ph.D., Anthropologist (Reg. III) + Anibal Monares, Ph.D., Economist Gordon Prain , Ph.D., Anthropologist+ Robert E. Rhoades, Ph.D., Anthropologist Gregory J. Scott, Ph.D., Economist Research Support Fausto Cisneros, Ph.D., Head of Department Dennis Cunliffe, Ing. Agr., Field & Greenhouse Supervisor, Lima Enrique Grande, Field Supervisor, San Ramon Miguel Quevedo, Ing. Agr. , Field & Greenhouse Supervisor, Huancayo Pedro Ruiz , Ing. Agr., Field Supervisor, Yurimaguas Marco Soto, Ph.D., Superintendent, Huancayo REGIONAL RESEARCH AND TRAINING Headquarters James E. Bryan, M.S., Senior Seed Production Specialist Region I- Andean Latin America Apartado Aereo 92654 Bogota 8, D.E., Colombia Oscar Malamud, Ph.D., Regional Representative Fernando Ezeta, Ph.D., Co-leader Potato Program (Peru)+ Cesar Vittorelli, Ing . Agr., Agronomist, Seed Production Specialist , Team Leader, Seed Program , Peru+ Juan Aguilar, Ing. Agr., Seed Production Specialist+ Claude Auroi, Ph.D. , Economist+ Karin Luther, Agr. Eng. ETH, Virologist+ Urs Scheidegger, Ph.D., Agronomist, Seed Production Specialist+ Region II- Non-Andean Latin America c/o Centro Nacional de Pesquisa de Hortalir,;as Caixa Postal (11) 1316 70.000 Brasilia, D.F., Brazil Oscar Hidalgo, Ph.D., Regional Representative Region III - Tropical Africa P.O. Box 25171 Nairobi, Kenya Sylvester Nganga, Ph.D., Regional Representative Andre Devaux, Ir., Research Scientist (Rwanda)* Anton Haverkort, Ir., Research Scientist (Rwanda) George Hunt, CEI, Agr. Eng., Associate Expert-Storage+ Michael Potts, Ph.D., Research Scientist (Burundi)+ Region IV - Near and Middle East P.O. Box 2416 Cairo, Egypt Sidki Sadik, Ph.D., Regional Representative Cristoph Engels, Ph.D., Agronomist (Egypt)+ Region V - North and West Africa 11 Rue des Orangers Ariana, Tunis, Tunisia Roger Cortbaou°i, Ph.D., Regional Representative Jurgen Benz, Ir., Associate Expert+ Roland von Arx, Ph.D., Entomologist (Tunisia)+ Region VI - South Asia c/o NBPGR Indian Agricultural Research Institute New Delhi, 110012, India 9 Mahesh Upadhya, Ph.D., Regional Representative Bharat L. Karmacharya, Ph.D., Research Scientist (Bhutan)+ Lyle Sikka, M.S. (Seconded to IADS Bangladesh) + Region VII - Southeast Asia c/o IRRI P.O. Box 933 Manila, Philippines Peter Vander Zaag, Ph.D., Regional Representative J eroen Kloos, Ir., Associate Expert+ Ponciano Batugal, Ph.D., Coordinator- SAPPRAD + TRAINING AND COMMUNICATIONS DEPARTMENT Manuel Pifia, Jr. , Ph.D. , Head of Department Linda Peterson, B.F.A., Senior Editor Carmen Podesta, M.A., Librarian Hernan Rincon, Ph.D., Spanish Editor Garry Robertson, M.A., Senior Training Specialist Helen Salazar, Foreign Language Translator Carmen Siri, Ph.D., Training Materials Specialist+ Rainer Zachmann, Ph.D., Training Materials Specialist ADMINISTRATION Office of the Executive Officer Carlos Bohl, Transportation Supervisor Gustavo Echecopar, Ing. Agr. , Plant & Equipment Supervisor Ana Dumett, B.S. Asist. Soc., Social Worker Juan Iladoy, Recreation Supervisor Lucas Reano , C.P.C., Administrative Supervisor German Rossani, M.D., Medical Officer Jacques Vandernotte, Pilot Office of the Controller Oscar Gil, C.P.C., Assistant Controller Blanca Joo , C.P.C., Accountant Edgardo de los Rios, C.P.C., Accountant Guillermo Romero, Head Accountant 10 SCIENTIFIC ASSOCIATES Manuel Canto, Ph.D. (Peru) Nelson Estrada, Ph.D. (Colombia) Enrique Fernandez-Northcote, Ph.D . (Peru) Cesar Fribourg, M.S. (Peru) Alfredo Garcia, M.E. S. (Peru) Vera Nifiez , M.A. (Peru) L. V. Turkensteen, Ph.D. (Netherlands) Sven Villagarcia, Ph.D . (Peru) VISITING SCIENTISTS Yoshihiro Eguchi, B.S. (Japan) Franz Frey, Ph.D. (West Germany) Reinhold Mankau, Ph.D. (U.S.A. ) Sarojam Mankau , Ph.D. (U.S.A.) Frarn;:oise Bourgeois Rousselle , M.S. (France) Patrick Rousselle, Ph.D. (France) Andrea Sonnino, M.S. (Italy) Norio Yamamoto, Ph.D. (Japan) SCIENTIFIC AND OTHER ASSISTANTS (By Department or Region) Walter Amoros, M.S. , Breeding & Genetics Luis Calua, M.S., Breeding & Genetics Jorge Espinoza, Ing. Agr., Breeding & Genetics Rosario Galvez, M. S. , Breeding & Genetics Luis Manrique , Ing. Agr. , Breeding & Genetics Jose Luis Marca , Ing. Agr., Breeding & Genetics Rodomiro Ortiz, Biol., Breeding & Genetics Roger Vallejo, M.S., Breeding & Genetics Ricardo Wissar, M.S., Breeding & Genetics* Jesus Alcazar, Ing. Agr., Nematology & Entomology Marcia Bocangel, B.S. , Nematology & Entomology* Rosa Canicoba, Nematology & Entomology Arelis Carmen Garzon, B.S., Nematology & Entomology Alberto Gonzales, M.S., Nematology & Entomology Renate Kaltenbach , B.B.A., Nematology & Entomology* Angela Matos, Ing. Agr., Nematology & Entomology Raul Salas, Ing. Agr., Nematology & Entomology Maria Villa, Biol., Nematology & Entomology Jorge Abad, M.S., Pathology Ilse Balbo, Biol., Pathology Carlos Chuquillanqui, B.S., Pathology Wilman Galindez, Ing. Agr., Pathology Liliam G. Lindo, Ing. Agr., Pathology Charlotte Lizarraga, B.S., Pathology Josefina Nakashima, Biol., Pathology Ursula Nydegger, Tech. Dip ., Pathology Hans Pinedo, Ing. Agr., Pathology Herbert Torres, M.S., Pathology Ernesto Velit, Biol., Pathology Nilda Beltran, Ing. Ind., Physiology Donald Berrios, Ing. Agr., Physiology Fausto Buitron, Ing. Agr., Physiology Rolando Cabello, Ing. Agr., Physiology Nelson Espinoza, Biol., Physiology Rolando Estrada, Biol., Physiology* Nelly Fong, M.S., Physiology Rolando Lizarraga, Ing. Agr., Physiology Norma de Mazza, Q.F., Physiology Jorge Roca, B.S., Physiology Pilar Tovar, Biol., Physiology Alberto Tupac Yupanqui, M.S., Physiology Jesus Amaya, Tech. Dip. , Taxonomy Matilde Orrillo, Biol., Taxonomy Alberto Salas, Ing. Agr., Taxonomy Adolfo Achata, Ing. Agr., Social Science Maria Isabel Benavides, B.S., Social Science* Pierre Bidegaray, B.S., Social Science Hugo Fano, B.S., Social Science Rosa Antunez, B.S., Research Support Lauro Gomez, Research Support Nelson Melendez, Tech. Dip., Research Support L. Zapata, Ing. Agr. (Reg. I) J. Queiroz, Ing. Agr. (Reg. II) S. Kasule, B. S. (Reg. III) J. Kimano, B.S. (Reg. III) M. Shahata, B.S. (Reg. IV) M. Sharkani, B.S. (Reg. IV) M. Kadian (Reg. VI) K. C. Thacur (Reg. VI) R. Acasio, M.S. (Reg. VII)* A. Demagante, M.S. (Reg. VII) V. Escobar, M.S. (Reg. VII) B. Fernandez, M.S. (Reg. VII) C. Montierro, M.S. (Reg. VII) B. Susana, B.S. (Reg. VII) Jesus Chang, M.S. Ed., Training & Communications Martha Crosby, B.A., Training & Communications Jorge Palacios, Dip., Training & Communications Luis Cabanillas, B.S., Executive Office Jorge Bautista, B.S., Controller's Office Jose Belli, B. S., Controller's Office Vilma Escudero, B.S., Controller's Office Alfredo Gonzalez, B.S., Controller's Office Alberto Monteblanco, C.P.C., Controller's Office Djordje Velickovich, Copilot, General Operations Rocio Jimenez, B. S., Auxiliary Services Staff as of December 31, 1984 are listed by Department or Region. * Left during the year. + These positions are separately funded as Special Projects by the following donor agencies : Australian Development Assistance Agency Canadian Interna"tional Development Agency (CIDA) Food and Agriculture Organization of the United Nations (FAQ) General Administration for Cooperation and Development (AGCD), Belgium German Society of Technical Cooperation (GTZ), Fed. Rep. Germany Ministry of Foreign Affairs, Netherlands Overseas Development Administration (ODA), United Kingdom Rockefeller Foundation Swiss Development Cooperation and Humanitarian Agency W. K. Kellogg Foundation World Bank 11 List of Abbreviations and Acronyms AARD AMY andigena APLV APMV ASAR avg AVRDC BARI BW CGIAR CIAT CIP cm cm2 CNPH CPE CPRI CV CV. d DLS DNA EBN ELISA EMBRAPA FAO FDR FON Al AP GA GCA h ha IADS ICA IDIAP 12 Agency for Agricultural Research and Development (Indonesia) alfalfa mosaic virus when not italicized in text refers to breeding materials with characteristics of Solanum tuberosum ssp. andigena Andean potato latent virus Andean potato mottle virus Asociaci6n de Servicios Artesanales y Rurales (Bolivia) average Asian Vegetable Research & Development Center (Taiwan) Bangladesh Agricultural Research Institute bacterial wilt Consultative Group on International Agricultural Research Centro Internacional de Agricultura Tropical (Colombia) Centro Internacional de la Papa (Peru) centimeter square centimeter Centro Nacional de Pesquisa de Hortali9as (Brazil) centrally planned economy Central Potato Research Institute (India) coefficient of variation cultivar day diffused-light stores deoxyribonucleic acid endosperm balance number enzyme-linked immunosorbent assay Empresa Brasileira de Pesquisa Agropecuaria (Brazil) Food and Agriculture Organization of the United Nations first division restitution Fondo Nacional de lnvestigaciones Agropecuarias (Venezuela) gibberellic acid general combining ability hour hectare International Agricultural Development Service Instituto Colombiano Agropecuario (Colombia) lnstituto de Investigaci6n Agropecuaria de Panama (Panama) IDRC INIA INIAP INIPA INPT INRA INRAT INTA IPO ISABU L lat. LB LDC LER long. LSD LUE min MJ ml mm mm ho mo NASH ND ns NS OP PCARRD Pf/Pi PLRV PNAP ppm PRACIPA PRAPAC PRECODEPA PROCIPA PSTV PTM PVS PVX PVY International Development Research Centre (Canada) Instituto de Investigaciones Agropecuarias (Chile) Instituto Nacional de Investigaciones Agropecuarias (Ecuador) Instituto Nacional de Investigaci6n y Promoci6n Agropecuaria (Peru) Institut National de la Pomme de Terre (Togo) Institut National de la Recherche Agricole (Senegal) Institut National de la Recherche Agronomique de la Tunisie Instituto Nacional de Tecnologia Agropecuaria (Argentina) Research Institute for Plant Protection (Netherlands) Institut des Sciences Agronomiques du Burundi liter latitude late blight less developed country land equivalent ratio longitude least significant difference light use efficiency minute megajoule milliliter millimeter millimho month nucleic acid spot hybridization test not determined not significant not studied open-pollinated Philippine Council for Agriculture and Resources Research and Development final population density /initial population density potato leafroll virus Programme National de !'Amelioration de Ia Pomme de Terre (Rwanda) parts per million Programa Andino Cooperativo de Investigaci6n en Papa (Andean region) Programme Regional d'Amelioration de la Culture de Pomme de Terre en Afrique Centrale (Central Africa) Programa Regional Cooperativo de Papa (Central America-Caribbean) Programa Cooperativo de Investigaciones en Papa (southeast region of South America) potato spindle tuber viroid potato tuber moth potato virus S potato virus X potato virus Y 13 RH RNA SAPPRAD SD sec TCA TPS tuberosum UNA UNDP var. vol vs. w wk WP wt yr 14 relative humidity ribonucleic acid Southeast Asian Program for Potato Research and Development standard deviation second tissue combining ability true potato seed when not italicized in text refers to breeding materials with characteristics of Solanum tuberosum ssp . tuberosum Universidad Nacional Agraria (Peru) United Nations Development Programme variety volume versus watts week wettable powder weight year DARWIN AND THE POTATO: A COMMENTARY ON ADAPTABILITY During his explorations and voyage aboard the H.M.S. Beagle in 1836, Charles Darwin's attention was drawn to an amazing South American plant that exhibited an adaptability which seemed to defy the very laws of nature. In his log, the great naturalist wrote: It is remarkable that the same plant should be found on the sterile moun- tains of Central Chile, where a drop of rain does not fall for more than six months, and within the damp forests of the southern islands. 1 The remarkable plant that Darwin observed was the potato, today the fourth most important food crop in the world and by far the world's most important vegetable. The potato is found growing in 130 countries - more than any other crop except for maize - and production is increasing faster in developing countries than that for any other food crop . A major reason for this upward trend is the potato's great adaptability to diverse climatic con- ditions. It can be produced readily in over a dozen distinct climates in developing countries, ranging from an altitude of 4000 meters in high tropi- cal mountains down to sea level in 1Darwin , Charles. Journal of Natural History of the Various Countries Visited by the H.MS. Beagle. London: Henry Colburn, 1840. xiv+ 615 pp. tropical Sri Lanka. Despite this great versatility , a misconception has devel- oped among the public and among many scientists concerned with food production that potatoes can only be produced in cool climates, located mainly in northern latitudes or high- land tropical areas. The facts and figures of European or North American potato production are often used - by those not familiar with this crop-as indices to judge the potato's production potential in developing countries. For example, in northern climates, an average of at least 150 days is often required for the potato to attain maximum yield. However this is not true for tropical conditions, where farmers begin har- vesting potatoes as early as 50 days after planting. In the Peruvian jungle at an altitude of 800 meters, farmers regularly obtain yields of 20 to 25 tons per hectare under rainfed condi- tions in less than 90 days; while in the Philippine lowlands, farmers obtain 20 tons per hectare in 90 days. Myths or beliefs about important food crops often grow from a lack of accurate information. For this reason, the International Potato Center (CIP) set out several years ago to collect data on precisely where and under what climatic conditions the potato is being produced in the developing world. 15 16 --~--------------------- • Potato Production Zones in Developing Countries 17 18 As the data was being compiled, CIP's Social Science Department established the International Potato Reference Files, which contain detailed informa- tion on 95 developing countries. Analysis of these country files shows that, in addition to cool climates, the potato in its spread around the world has also become well adapted to the arid, hot zones, and lowland and mid- elevation tropical and mesothermal areas. Today, the potato serves as an important staple vegetable for the large populations of rural and urban low- income families who live in these areas. From the map presented in this sec- tion, one can see the great extent of potato production zones in the devel- oping world. An important key to understanding the potato's adaptability is the process of tuberization. Whether or not the potato produces tubers depends large- ly on minimum night temperatures and not mean daily temperatures. This explains how the potato can be grown successfully in the hot desert areas of North Africa or in the semi-arid tropics such as the Peruvian coastal desert. Potato crops can also be produced in extremely warm tropical areas if night temperatures drop or if agronomic practices are used to modify the environment. The Asian potato-rice food system , which stretches from the Punjab of India throughout Southeast Asia into China (see map) , produces over 40°/o of all potatoes in the developing world . The rapid expansion of the potato in this lowland, densely popu- lated Asian belt is due not only to better adapted varieties, but also to the ability of the potato to rotate well with cereals, especially rice and wheat. Indications are that the potato will continue to spread in these Asian zones as farmers attempt to diversify their crops. The hot, dry lowlands of Asia , Africa, and South America, where average daily mean tempera- tures may reach as high as 30° C, account for approximately 10°/o of production, while about 5°/o occurs in the warm, humid lowlands and mid-elevation zones of developing countries. The potato has a comparative ad- vantage over most crops at high eleva- tions. Of the total production in developing countries, almost 25°/o comes from the highland areas in 25 countries, and an additional 20°/o comes from climates properly classi- fied as high latitude, temperate zones, mainly those of China and Turkey. Charles Darwin made his obser- vations on the great adaptability of the potato in its South American homeland more than 150 years ago. But as the potato began its migration outward - as early as the sixteenth century- to all continents and virtual- ly into most nations , its comparative fitness enabled it to adapt to diverse world climates. The potato still con- tinues its world migration into new zones each year, and in doing so relies on its same natural resistances that are centuries old . Summary of Research International Germplasm Distribution This year CIP published Potatoes for the Developing World, a study of CIP's progress through collaborative involvement with national potato programs and a documentation of potato pro- duction increases in the Third World. The study reports that 70 developing and 18 developed countries are using CIP's improved germplasm, while more than 30 countries have identified pro- mising clones and 22 have released new varieties from material received from CIP. In 1984, CIP distributed more than half a million units - clones, tuber families, in vitro plantlets, and true potato seed - to 51 countries. All export material was tested for freedom from 12 different viruses and a viroid as well as from other pathogens and pests. CIP's pathogen-free, in vitro collection has been increased to include 214 varieties, advanced clones, primitive cultivars, and wild species. Varieties from the Colombian national program sent to Vene- zuela and Bolivia compared well with the local varieties in on-farm trials. The Mexican-derived clone Cruza 148, selected for its bacterial wilt resistance in Costa Rica, has been recently named as a new variety in Burundi. A variety recently selected in Rwanda, as well as other introductions from Kenya and Rwanda have out- yielded standard varieties in field tests for late blight resistance in Burundi. Seedlings from crosses involving seven Solanum spp. were subjected to various selection pressures at the National Institute of Agricultural Technology (INTA) at Balcarce, Argentina, as part of CIP's international research collaboration. Sixty-four selections have been made from more than 34,000 different clones since 1978, and a comprehensive list of this material, including genotypes with combined virus resistance and good yield under long days, is available at INT A. Through a research contract with the Victoria Department of Agriculture, Australia, pathogen-tested germplasm is being produced and sent to 12 countries in Southeast Asia and Oceania. A computerized model to predict the yield performance of individual clones has been developed through a 19 contract with Agriculture Canada, and with few exceptions good correlation between observed and predicted yields has been ob- tained. In contract research at the University of Wisconsin in the United States, selected tuberosum haploids have been shown to be especially effective in producing hybrids that tuberize regardless of the species parent. TPS progenies from 4x- 2x hybrids were generally superior to open-pollinated 4x seed. Developments in Disease Research Studies were continued to further understand the process of infection and multiplication of potato leafroll virus (PLR V) within an infected host. Loss of resistance observed in the field in PLRV- resistant clones appears to be associated with concomitant infec- tion with potato viruses X and Y (PVX, PVY). Resistance to PLR V multiplication in clones was estimated by determining virus con- centration in graft-inoculated plants, which varied in maximum concentrations in the clones tested. The behavior of two resistant clones as a virus source of inoculum is now being evaluated in the field. Three broad groups of PLR V isolates were distinguished by their reaction on Physalis floridana. By means of monoclonal and polyclonal antibodies to PLR V, supplied through a Swiss research contract, a low level of serological variation was confirmed among the 129 PLRV isolates examined. For detecting PVY in potato, monoclonal antibodies have been found to be more suitable than polyclonal. Clones having immunity to PVX and PVY were not infected with resistance-breaking isolates of these two viruses under field conditions in Peru, indicating the stability of this type of resistance. A nucleic acid spot hybridization (NASH) test kit for the detec- tion of potato spindle tuber viroid (PSTV) has been developed, based on the principles used to produce ELISA kits for developing countries. With the NASH kit, potato scientists in the regions can spot up to 100 samples on a nitrocellulose membrane and mail them to CIP headquarters for PSTV identification. Forty-four ELISA kits, for detecting up to 600 samples each of PLR V and PVY, have been sent to several developing countries for evaluation; for the reuse of the PVY microtiter plates, a procedure has been developed and is included in the kit. Several new viruses have been identified in the potato, including alfalfa mosaic virus (AMV), identified in the highlands of Peru, 20 and a potexvirus, found during a field survey in Guatemala in potato plants showing severe mosaic symptoms. CIP is producing an antiserum to this virus, which seems to be one of the most disseminated viruses in Central America. A new population derived mainly from crosses between wild diploid species and tetraploid phureja sources has shown encour- aging levels of resistance to bacterial wilt (BW) (Pseudomonas solanacearum) in infested fields in Peru. The late maturity of this new material is being improved by crosses to early and heat- adapted tetraploids. Eight isolates of P. solanacearum were assayed against 15 antibiotics in continuing research to develop a method of characterizing various strains. An antiserum specific to P. solanacearum has been produced that reacts with three races of the bacterium, but not with healthy potato sap or other pathogenic bacteria. In the regions, a field method of artificial inoculation was developed in Kenya to screen CIP introductions for BW resistance; while in Sri Lanka, significant progress has been made through a contract with the Department of Agriculture in developing advanced clones with BW resistance. Contract research at the University of Wisconsin has confirmed the positive correlation between tuber calcium content and resist- ance to bacterial soft rot (Erwinia carotovora pv. atroseptica) and internal brown spot of tubers. Brown spot was shown to be negatively correlated with the calcium content of tubers; and in mist chamber assays of soft rot severity on tubers from different field plots, tubers from high-calcium plots were more resistant to soft rot than those from low-calcium plots. In cooperation with the Peruvian national potato program of INIPA, CIP has selected clones with outstanding resistance to late blight (LB) (Phytophtora infestans) for further field testing in the region. During 1984, over 4000 clones with LB resistance were distributed to nine countries for field evaluation. In Colombian field trials, diploids with LB resistance - produced at Lima and shipped as true seed to the national program of !CA-compared favorably with local LB-resistant varieties. In other studies on LB resistance in tubers, a positive correlation was established between tuber and foliage resistance to LB under controlled conditions at CIP's experimental site in Huancayo and in the field at Huanuco, Peru. Field studies on soil-borne diseases have resulted in the selec- tion of advanced clones and varieties in Peru with high levels of resistance to potato smut (Angiosorus solani). The yield of 21 healthy tubers increased 250°/o in on-farm trials in which a fun- gicide combination of Basamid and Ridomil was used to control pink rot (Phytophthora erythroseptica). Through a contract with the Research Institute for Plant Protection, Netherlands, a survey of bacterial and fungal diseases was carried out in Burundi, Rwanda, and Zaire; and in order of importance, the most preva- lent diseases were late blight, bacterial wilt, and soft rot . Pest Management An efficient technique has been devised to do mass seedling screening for resistance to potato cyst nematode ( Globodera pallida ). This technique makes use of a modified petri dish test that requires a vigorous single sprout treated with hormones. Clones with combined resistance to two important cyst nema- tode pathotypes have been selected by this test. A field trial in Ecuador to compare G. pallida multiplication rates, carried out in collaboration with the national program of INIAP, showed that CIP advanced clones significantly reduced multiplication of cyst nematodes over the local cultivar. Soil solarization in the greenhouse and in seedling nursery trials was as effective as chemical soil treatment in controlling root- knot nematodes (Meloidogyne incognita) on plants from seedling tubers and true seed. The combination of soil solarization and an application of the fungus Paecilomyces lilacinus, which is para- sitic on the eggs of root-knot nematodes, reduced root galling without further treatment during the second growing season. More than 1800 clones were screened in the laboratory and field for resistance to potato tuber moth (PTM) (Phthorimaea operculella); selected clones are now being intercrossed to increase the frequency of PTM resistance. A PTM sex pheromone applied as a microencapsulated spray had short-term activity when used under nonshaded field conditions . A less costly unpurified phero- mone mixture consisting of a 2:3 ratio of PTM pheromone 1 and 2 was as effective as a purified pheromone in trap capture of male moths. In Egypt, the effectiveness of insecticide application in controlling PTM was related to the population dynamics of PTM as determined by pheromone traps. In both Tunisia and Morocco, pheromone-baited water traps have been used to monitor PTM population density to predict the best time to h arvest. For the control and monitoring of leafminer fly (Liriomyza huidobrensis) populations in the field, sticky traps have proved highly effective. 22 Warm and Cool Climate Production Agronomic practices suited to warm climate production have remained a priority. In studies of planting position, tubers planted on the warm side of ridges in combination with mulch increased yields in San Ramon. Cropping systems in which potato was planted simultaneously with maize, in the ratio of 9:1, made effi- cient use of radiation and land occupancy. A cropping sequence involving rice, maize, or pasture reduced the BW incidence in Yurimaguas. Further improvement in heat tolerance and light interception is indicated for clones bred for heat stress conditions. Lowland variety trials were conducted in ten countries of South- east Asia using seed supplied through a CIP contract in Australia. In the Philippines, yields in excess of 25 tons per hectare were reported from a lowland site in Mindanao; and in separate trials, similar yields were reported at a coastal site in Kenya. In Vietnam, three CIP clones now occupy all of the cultivated area around Dalat in the central highlands. For cool climate production, two separate populations have been developed and are being improved to fit the Andean highland tropics and the non-Andean highland tropics and subtropics. Breeding is directed at combining frost resistance, early maturity, and tuberization response to the effects of long days, especially for subtropical latitudes. More than 9000 seedlings from crosses between frost-resistant and early maturing clones were screened, with 10°/o survival at -3° Cina growth chamber. Of another 12 ,000 seedlings screened, 15°/o survived at -4° C. Samples of clones from advanced stages of selection screened at Huancayo (3200 m) had two-thirds higher yield than those grown at a higher site in Usibamba (3800 m), reflecting the yield potential of this material under less severe climatic stress. Frost-resistant seedlings, prescreened for tuberization under a 15-hour artificially extended daylength by using a single leaf-node technique, had comparable or superior yields to varieties locally adapted to the long days prevailing at Osorno, Chile (lat. 40° S). Laboratory and field experiments on the use of potash (K2 0) to control frost damage indicated that enhanced levels of K+ ion accumulate in frost-resistant clones, suggesting that potassium may play an indirect role in reducing freezing injury to plants. The acid soils of the Andean highlands have been tested through a research contract at the National Agrarian University in Lima to determine the basic levels of fertilizer application necessary for 23 potato production. Preliminary results suggest that 8 tons per hectare of CaC0 3 , 160 kilograms per hectare of P2 0 5 , and 80 kilograms per hectare of K 2 0 are sufficient for production. Postharvest Developments Research concentrated on the control of tuber moth, virus vectors, and soft rot of tubers in stores. Insect-repellent weeds, layered on seed tubers, had various effects in reducing tuber and sprout damage depending on the species of tuber moth. In diffused- light stores, no damage from Phthorimaea operculella (PTM) was observed in tubers after six months of storage when a combina- tion of Phenthoate, sex pheromone traps, and a covering of dried Lantana leaves was used; Phenthoate and Lantana also provided good control of Symmetrischema moths in stores. In field obser- vation trials on the interaction between PTM damage and Erwinia soft rot, the application of soil calcium significantly reduced Erwinia blackleg and tuber rot in the varieties Desiree and Rosita. The effect of desprouting seed tubers on their subsequent field performance was influenced by cultivar, storage, and transporta- tion from storage to the field-yields were reduced when lengthy transportation to planting site was required. In contract research at the University of Glasgow, Scotland, the effect of diffused light on potato sprout growth during storage was investigated. Varietal responses to irradiance level, wavelength, and day/night temperature interactions were observed. High irradiation (about 330 mW m- 2 ), a high temperature regime, and a wavelength of 550 nm (blue light) were effective in sprout suppression. Various aspects of storage technology were evaluated in the regions: Rwanda-dormancy breaking by burying seed; Burundi- use of heat shock to induce sprouting; Tunisia - the effect of high temperatures on seed tubers stored during the summer; Egypt-improvements in low-cost nawalla seed stores; and Vietnam -how construction materials influence the efficiency of diffused-light stores. In Peru, simple processing-an important component of post- harvest technology-has been successfully demonstrated by the development and large-scale testing of CIP's M-6 mixture, consisting of 30°/o potato, 26°/o cereal-legume, and 2°/o salt. The product, which can be sold profitably in Peru for about US$1.00 per kilogram (or US$.02 per ration), has received good consumer acceptability in Peru. 24 Seed Tuber and True Seed Production Potatoes are traditionally propagated by planting seed tubers, a method which uses about 12°/o of the total potato crop in devel- oping countries. The use of true potato seed (TPS) as an alterna- tive method of propagation continues to stimulate the interest of national potato programs. Because of increased demand for TPS, especially hybrid TPS, CIP research has focused on methods of improving flowering, fruit development, and TPS quality. Under long-day conditions in southern Chile, and also through the use of growth regulators under short-day conditions in Peru, both the number of inflorescences and flowers per inflorescence have been increased. Large amounts of pollen have been stored successfully under low temperatures to provide pollen during the protracted flowering period of female parent plants. A simple screening test is being developed to identify superior lines capable of recovering from transplant shock through the rapid regenera- tion of roots. Early field establishment of seedlings by fluid drilling seed into the soil was superior to other methods of direct sowing. In field experiments on the coast of Peru, sufficient tubers to plant one hectare were produced by seedlings growing from only 8 grams of TPS. Small seedling tubers required a high plant density for optimum multiplication efficiency; per unit of planted tuber weight, the production efficiency of 5-gram tubers was found superior to 50-gram tubers. In the more traditional potato areas on the coast, farmers preferred seedling tubers produced in seedbeds or sown directly into field plots; while seedling trans- planting was more acceptable to farmers familiar with growing vegetables in intensive cropping systems. A mid-season survey of on-farm TPS trials in Rwanda reported that farmers were already familiar with seedbed preparation and had encountered no serious difficulties in growing TPS seed- lings. In Sri Lanka, the extension staff of the Department of Agriculture has distributed seed to 150 farmers, and methods of producing hybrid TPS in sufficient quantities are being investi- gated. Hybrid seed produced by DT0-33 x R-128.6 has been successful in farmers fields for both seedling tuber and consumer potato production in the Philippines. Similarly, progenies of two hybrids grown in Bangladesh gave yields comparable to the local cultivar Patrones with 7 5°/o marketable tubers. The best 4 of 16 TPS hybrid families tested in Colombia produced sufficient 25 seedling tubers per 1 OO-m 2 nursery to plant up to two hectares . In Egypt, an extensive TPS research program has been established to investigate agronomic practices suitable for local conditions. TPS nursery management practices, including suitable soil mix- tures, fertilizer regimes, control of damping-off, and seedling tuber storage in traditional nawallas, are under study. While CIP research during the year was strongly oriented toward the production and use of true seed, conventional seed tuber pro- duction was not neglected. Improved varieties selected from CIP introductions now constitute 50°/o of the seed produced by the national potato program in Rwanda, and seed output is expected to double in 1985 with the operation of a new seed farm. In 59 on-farm trials in Burundi and Rwanda, improved seed tubers gave an average yield increase of 50°/o. From original in-vitro, virus-free plantlets supplied by CIP, the National Institute for Agricultural Research in Ecuador produced 60 tons of registered seed in 1984 and also 50,000 cuttings for initial multiplication. As a result of recent regional training courses, tissue culture main- tenance laboratories have been established in Indonesia, Thailand, and the Philippines. The successful seed production program in Vietnam, based on in vitro sources of pathogen-free plantlets and rapid multiplication techniques, now supplies all seed tubers for the Dalat area. Potatoes in Food Systems Both biological and social scientists at CIP are involved in studies of potatoes in developing country food systems. The findings from a survey of 445 farms in Peru on how potato seed systems function indicated that, in general, Peru is self-sufficient in potato seed production and most farmers use their own seed. The varie- ties grown in the three major potato-producing zones, the practices relating to seed quality, the use of fertilizer, and seed movement within the country were documented by the survey. The technical level and economic efficiency of seed growers and farmer adoption of potato technology were evaluated by CIP anthropologists and economists assigned to the Peru- vian national potato program. Although it had been previously assumed that "improved" varieties were used for urban sale, the evaluation showed that "native" varieties had good market demand, while improved varieties were often grown for home consumption. 26 Salient findings of potato marketing studies conducted in Ban- gladesh, Central Africa, and Thailand revealed the following trends: Bangladesh's internal m arket will probably absorb all the potatoes the country can produce in the years ahead; the principal con- straint to demand in Burundi is the high price for potatoes relative to other foods; Rwanda's high population growth has required a steady acceleration in potato production; potatoes marketed in East Zaire, if not sold locally, are transported 2000 km to Kinshasa, thus improved marketing is crucial for the development of Zaire's national potato program; and in Thailand, a campaign to promote more potato consumption may be needed to improve potato marketing, since demand seems to be highly dependent on tourists in Bangkok and the changing tastes of young Thai. To follow world trends in potato production, CIP has recently completed a second and more expanded edition of the Potato Atlas. The statistics indicate that potato production in developing market economies has nearly doubled in the last 15 years and has increased more rapidly than for other food crops. The nutritious potato ranks first in energy production per day in developing countries, and among major food crops, it ranks high in protein production. A specially funded project conducted on household gardens, including rural subsistence and urban budget gardens, revealed that these small enterprises provide a food equivalent of about 1 O°jo of annual income for the low-income families surveyed in Peru during the project. A wide range of management practices, and a diversity of food crops combined with the use of both horizontal and vertical planting space, and the complementary activity of small, domestic animal production characterize the adaptive functions of these home gardens. 27 Arid _____ __. Highlands ______ ___, Mid-elevation tropics -----------' Low, humid tropics ___________ __. 28 Agroecological Zones of Peru The cultivated potato originated on the high plains (altiplano) in what are now parts of Peru and Bolivia. This center of diversity is not only for the potato but also for its major pests and diseases. CIP has four experimental stations located between latitudes 6° and 12° S that represent the four major agroecologi- cal zones of Peru : Lima-La Molina , arid ; Huancayo, highlands ; San Ramon, mid- elevation tropics ; and Yurimaguas, low, humid tropics. The small range of lati- tudes gives little variation in daylength, but the geographical location of CIP's sta- tions ensures wide variation in altitude , temperature , rainfall regimes, soil types, and incidences of pests and diseases. All major climatic characteristics of tropical zones found in the developing world are represented within Peru's four agroeco- logical zones. CJP research sites in Peru and potato-growing seasons, with meteorological data for 1984. Site : Lima-La Molina Huancayo San Ramon Yurimaguas Latitude: l 2°05'S l 2°07'S 11 °08'S 5°41'8 Altitude: 240m 3280 m 800 m 180 m Growing season: Jan-Mar May-Nov Oct-May Nov-Mar May-Aug May-Aug Air max (°C) 26.8 21.2 20.4 28 .1 28 .5 30.4 Air min (°C) 18.4 14.9 6.4 18.1 16.1 20.6 Evaporation (total mm) 547.0 771.9 no data 784.8 550.8 247.7 Rainfall (total mm) 3.5 5.4 663.4 1156.5 545.3 633.8 Radiation (daily MJ/m 2 ) 19.24 11.70 19.21 19.95 17 .32 14.01 29 30 CIP Research Organization C IP's mandate is to conduct research that will lead to improving the po-tato for use as a staple food or an important vegetable in the developing world. To fulfill this mandate, CIP has established a program of research and development at its headquarters in Peru where an extensive potato germplasm collection can be inexpensively maintained and used. At CIP headquarters in Lima, research has been organized simply and effec- tively into Departments, Thrusts , and Projects. This organizational structure is integrated with a regional research and training network, which serves as an efficient system for evaluating CIP technologies under a range of local con- ditions in collaboration with national programs. This collaborative effort en- ables both CIP and national scientists to evaluate a technology quickly and determine if it is applicable to the growing conditions in specific regions. The feedback from these evaluations plays an important role in guiding CIP's over- all research program at headquarters in Lima. Regional Headquarters Andean Latin America (I) Non-Andean Latin America (II) Tropical Africa (III) Near and Middle East (IV) North and West Africa (V) Sou th Asia (VI) Southeast Asia (VII) Location Bogota, Colombia Brasilia, Brazil Nairobi, Kenya Cairo, Egypt Tunis, Tunisia New Delhi , India Manila, Philippines Departments are administrative units, each headed by a senior scientist, to which all scientists are assigned according to their field of expertise. The bioscience departments are Taxonomy, Breeding and Genetics, Pathology, Nematology and Entomology, and Physiology. These units , together with a Support Department, are responsible to the Director of Research. The Social Science and Training and Communications Departments, as well as seven Re- gional Research Programs, are administered under the Director of Regional Research and Training. Thrusts are major areas of research concentration that provide maximum interaction among teams of experts in various scientific disciplines, as well as a comprehensive framework to accommodate research at headquarters and in the regions. Each thrust has a coordinator responsible for integrating the various re search activities within a thrust. The ten research thrusts for 1984 are shown in Figure l . 31 32 PROJECTS RESEARCH THRUSTS I Collect , Maintain, Use Gene Pool 11 Produce, Distribute Advanced Clones 111 Control Bacterial and Fungal Diseases IV Contro l Virus Diseases v Integrated Pest Management VI Warm Climate Potato Production VII Cool Climate Potato Production VI 11 Postharvest Technology IX Seed Technology x Potatoes in Food Systems Figure 1 . Cl P research and technology transfer organization . NATIONAL POTATO PROGRAMS Projects are clearly defined, operational units of research that contribute to a thrust's research objectives. Each project has a leader and one or more cooperators who provide the necessary interdisciplinary research input. The leader is responsible for the overall direction of a project and for annual pro- gress reports. Project funding, an administrative activity , is through a project leader's department. Projects at the regional locations are funded through the Office of the Director of Regional Research. A Coordinator for Research Transfer provides liaison between the research activities in Lima and the seven regions. In summary, CIP's research organization is analogous to a matrix of rows and columns of numbers. The horizontal rows are the research thrusts, the vertical columns are the administrative departments , and the numbers are the scientists involved in the various research projects. Thus, scientists from dif- ferent departments cooperate through projects to carry out the broad objec- tives of a research thrust (Fig. I) . Planning Conferences are held by CIP at three- to five-year intervals to review the research activities of a thrust and develop recommendations that will serve as guidelines for thrust research. During the past 13 years, 283 scientists from 43 countries have participated in 28 CIP Planning Conferences. Proceedings of each conference are published by CIP and distributed on re- quest. Through the planning conference strategy, CIP's research undergoes a process of peer review by outside experts from both developed and devel- oping countries. Research and Consultancy Contracts have proved to be a cost-effective method of augmenting CIP's research capacity. During each of the past five years, CIP has funded an average of 35 research contracts. In 1984, 21 con- tracts were active in ten developing countries and 13 in seven developed coun- tries . The guiding philosophy is to fund contracts for one to three years at institutions where special expertise and facilities exist to carry out defined areas of research. Funding from CIP normally covers supplies, assistantships, casual labor, and travel expenses. Country Networks are cooperative systems between several countries in a geographical region that improve self-reliance on national scientific capability. This self-help approach challenges developing countries to work together and use available expertise to solve common potato production problems in a com- munity of countries. Member countries in a network assume specific projects for which they have a comparative research advantage and communicate the results to other countries in the network. Since 1978, five country networks have been established (Table 1) , with CIP providing the administrative and technical support necessary for their development: Programa Regional Coope- rativo de Papa (PRECODEPA), Programa Andino Cooperativo de Investiga- ci6n en Papa (PRACIPA), Programa Cooperativo de Investigaciones en Papa (PROCIPA), Programme Regional d'Amelioration de la Culture de Pomme de Terre en Afrique Centrale (PRAPAC), and Southeast Asian Program for Potato Research and Development (SAPPRAD). Table 1. Country networks and members, 1984. Network Year initiated Member countries PRECODEPA 1978 Costa Rica, Cuba, Dominican Republic, El Salvador, Guatemala, Honduras, Mexico, Panama PRACIPA 1982-83 Bolivia, Colombia, Ecuador, Peru, Venezuela PROCIPA 1982 Argentina, Brazil, Chile, Uruguay PRAPAC 1982 Burundi, Rwanda, Zaire SAPP RAD 1982 Indonesia, Papua New Guinea, Philippines, Thailand The various interlinked components of CIP's research organization re- spond directly to the needs of individual national programs and country net- works. The built-in flexibility permits changes in priorities and staffing with- out major interruptions in research continuity. The comprehensive research coverage codified in thrusts ensures that all potential· production constraints receive adequate attention. 33 THRUST I Maintenance and Utilization of Unexploited Genetic Resources A s part of a monographic study of Solanum spp ., research on the cross-ability of species in five series of the genus has been critically examined. In addition to substantiating evolutionary relationships, the research has pro- vided information concerning crossability between species that are of interest to potato breeders. Salt-tolerant clones from beach areas on the islands of Chile's Archipelago de los Chonos have been added to CIP's world potato col- lection. A total of 267 native Andean cultivars were added to in vitro stor- age ; the pathogen-free in vitro collection was also increased. New sources of disease and pest resistance have been identified in wild species. A synthetic DNA sequence that codes for improved protein quality has been successfully constructed, cloned, and inserted into infective plasmids through contract re- search in the United States. At CIP, whole plants have been regenerated from cultured hairy roots induced by Agrobacterium rhizogenes on wounded and inoculated in-vitro potato plants. Weedy forms of S. tuberosum found growing on beaches of the Archipelago de los Chonos. 35 BIOSYSTEMATIC STUDIES Research continued in 1984 on the cross- ability of tuber-bearing Solanum species in the series Olmosiana, lngaefolia, Cir- caeifolia, Conicibaccata, and Tuberosa. Over 200,000 hybrid seeds were obtained from about 4000 pollinations. The results of various crosses among species belong- ing to different series are summarized in Figure l. In the series Ingaefolia , a fairly strong crossability barrier exists between Sola- num ingaefolium and S. rachialatum , al- though both species belong to the same series and have the same ploidy (2n = 2x = 24). On the other hand, in the series Olmosiana, S. olmosense is the only mem- ber that crosses easily with S. rachialatum when the latter is used as a female ; the reciprocal cross gives only a few seeds. S. jalcae, however, crosses easily with both species of series Ingaefolia when used as a male parent and functions well as a female parent in crosses with S. rachialatum. S. jalcae has therefore been put definitely into series Ingaefolia, whose close taxonomic relationship with series Olmosiana has also been established. Use- ful crosses have been made between S. jalcae as the female parent to incorporate its frost resistance with the leaf miner re- sistance of S. olmosense. Crosses among species of the two larg- est series of tuber-bearingSo/anums, Coni- cibaccata and Tuberosa (Fig. 1), showed that fairly strong, although not complete, crossability barriers exist between the two series. However, S. bukasovii, as female , crossed readily with S. santolallae, as did S. leptophyes with S. chomatophilum, permitting exchange between important sources of genetic variation within the tuber-bearing Solanums. Crossability studies on the behavior of various members of the series Conicibac- cata and Circaeifolia verified the biosys- 36 tematic separateness of these two series. Despite the existence of strong crossabil- ity barriers, S. chomatophilum crossed easily with S. circaeifolium when used as a female parent (Fig. 1 ) . The fact that two species from the same habitat with common morphological features and the same ploidy, S. santolallae (Conicibac- cata) and S. circaeifolium (Circaeifolia), will not cross with each other has led us to assume that different endosperm balance numbers (EBNs) are probably present in the two series. This will be investigated further. The frost and late blight resistances present in S. chomato- philum and the cyst nematode resistance found in both species of the series Cir- caeifolia are now available to breeding programs. GERMPLASM MAINTENANCE The Austral University of Chile , in collab- oration with CIP, sponsored a collecting expedition to the unpopulated islands of the Archipelago de los Chonos, located at latitude 45° S. A total of 27 weedy clones were collected on 12 different is- lands from beach areas watered by waves at high tides. These materials have been added to CIP's germplasm collection and could be a good source of tolerance to salinity. In the world potato collection, an addi- tional 365 duplicate accessions were iden- tified and converted to true seed for stor- age . In 1984, 267 cultivars (94 diploids, 5 0 triploids, 115 tetraploids, and 8 penta- ploids) were transferred to in-vitro stor- age media ( + 4°/o mannitol) and stored at 8° C. Pathogen-free native cultivars for in vitro distribution were increased from 62 to 81 in 1984, and 49 more have been add- ed and are being freed of viruses. These materials include different genotypes of all 8 tuber-bearing cultivated species. ING X OLM N igf rch igf ~ 0 rch () ~ olm 6. • jlc • • INGAEFOLIA igf = S. ingaefolium rch = S. rachialatum jlc = S. jalcae olm 0 ~ 0 OLMOSIANA olm = S. olmosense jlc 6. • • CON X TUB ~ chm san lgl buk chm ~ () • () san 6. ~ 6. 6. lgl 6. 6. ~ 6. buk () • 0 ~ lph • 6. 6. • spl 6. 6. 6. () CON X CIR ~ chm san lgl chm ~ () • san 6. ~ 6. lgl 6. 6. I~ ·~ lph spl - 6. 6. 6. 6. 6. • • I~ • • ~ ere cap • 6. 6. 6. 6. 6. CONICIBACCATA chm = S. chomatophilum san = S. santolallae lgl = S. lignicaule TUBE ROSA buk = S. bukasovii lph = S. leptophyes spl = S. sparsipilum CONICIBACCATA chm = S. chomatophilum san = S. santolal/ae lgl = S. lignicau/e CIRCAEIFOLIA ere 6. 6. () ~ • ere = S. circaeifolium cap = S. capsicibaccatum cap 6. 6. () • Easy cross, abundant viable seeds. 0 Difficult cross, usually 1-4 seeds per fruit. • I~ b,. Cross made, but no seeds obtained . () Difficult cross, usually 10-15 seeds per fruit. Figure 1. Representative crosses among Solanum species (2n=2x=24) of the series lngaefolia, Olmosiana, Conicibaccata, Tuberosa, and Circaeifolia. 37 UTILIZATION OF WILD AND PRIMITIVE CULTIVATED SPECIES During 1984 research concentrated on using new sources of resistance to Pseudo- monas solanacearnm, the causal agent of bacterial wilt. Three new specific sources, S. sparsipilum , S. chacoense, and S. micro- dontum, are now in usable form at the tet- raploid level. New genepools with resist- ance to cyst nematode , Globodera pallida, and the potato tuber moth , Phthorimaea operculella, have been made accessible through Ph.D. thesis research. In preliminary studies of nutrient-use efficiency, 12 native cultivars and 12 im- proved varieties were grown in four repli- cations with 200-200-200 and 0-0-0 NPK fertilization . Nutrient-use efficiency was measured by yield losses between fertil- ized and nonfertilized treatments of each genotype. With no fertilization, yield re- duction among improved varieties ranged from 28°1o (Mi Peru and Participaci6n) to 73°/o (Renacimiento , Antarqui, and Tica- huasi), and among native cultivars from 21 °lo (OCH 10771) to 61 °lo (OCH 7245 and OCH 5576). INNOVATIVE TISSUE CULTURE FOR POTATO IMPROVEMENT Early experiments on the use of Agro- bacterium rhizogenes as a vector for the insertion of synthetic DNA fragments into potato have been successful. In con- tract research at Louisiana State Universi- ty (U.S.), a synthetic DNA sequence that Figure 2. Regeneration of whole plants from hairy roots induced by Agrobacterium rhizogenes on wounded and inoculated in-vitro potato plants . 38 codes for the production of a novel pro- tein high in essential amino acids has been constructed, cloned, and successfully in- serted into the infective plasmid of A. rhizogenes. At CIP, in vitro potato plantlets were wounded in the stem and inoculated with wild type A. rhizogenes to induce forma- tion of hairy roots. These roots were then excised and cultured on a medium that in- duced regeneration of whole plants (Fig. 2). This experimental sequence is now being repeated using transformed bacteria (including the synthetic DNA sequence) in place of the wild type. 39 L' II I 11111111111111 I I II I 11111 I I - ·········································································" - -: m THE l~HERNATIONAL POTATO CENTER : ~ ~ PLANT TISSUE CULTURE ,.::§'i.~~1::-, ,~, J - - - - : - - - - - : : : - - - - -• - ·.:.~,,,_-~_.., Tell ~ZSJ.35'3!14 Lom•Peri.t : - - - TO . J) & ~ .. .. ~.~-~-~ -~!~ .... ~Y.~ .. ~ .#-.9.~ ..... -. --- - - - THIS SIDE UP ADDRESS- ·· .. .. . ill.ii\ ........................... ... ·-·· ···· ················ ---- - - - - - - - - - - - - -: .. . ~ A.t/T,iA'tQ .... ~'-·· -~- ~J~.~ .............. . ................... Cr.H.J 0 .Lt ............................................... . --- - - -NOTICE : To all CustOfll Offlclal\ Post Office, Altways and Plant Protection Servicrs: - --• PLEASE FORWARD THIS PARCEL WITH THE LEAST POSSIBLE DELAY I • : USE EXTREME CARE IF NECESSARY TO OPEN INNER • - -: CONTAINER TO AVO ID CONTAMINATION OF ENCLOSED MATERIAL E - - - -i AIR MAIL LIV ING MATE R I AL E - -i •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• f. THRUST II Production and Distribution of Advanced Breeding Material A total of 137,420 seedlings were evaluated in 20 experiments at Lima and San Ramon . In 4 experiments, heritability estimates of genetic variation were made, while 16 experiments were conducted to select parental material on the basis of progeny performance. In inbreeding studies, about 30°/o of" the clones produced from selfed and open-pollinated seed performed as well as hybrids. Progenies with resistance to early blight and bacterial wilt were identified in field and screenhouse studies. Embryos and plantlets were ob- tained from over 7000 anther cultures, and "tissue culture ability" studies are being carried out. During the year, CIP distributed more than 32,000 units as clones, tuber families , and test-tube plantlets, and 570,545 true potato seeds to 51 countries. Field tests in southern Chile, under long-day conditions, have confirmed the value of selecting for tuberization response under artificial long-day con- ditions at Lima. In selections for warm climate conditions in Brazil, about 25°/o of 7000 genotypes were retained for further evaluation and also for bac- terial wilt resistance . Four screenhouses to multiply CIP germplasm were built at Muguga, Kenya. Two CIP introductions have been named as varieties in Burundi, and one CIP introduction has been released as a variety in Senegal. Results of contract research collaboration with Argentina, Australia, Brazil, Canada, and the United States are presented. In-vitro potato germplasm ready for export to national programs. 41 GENETIC RESEARCH Twenty experiments were carried out to estimate the heritability of earliness, tu- ber uniformity , yield per plant , and select- ability. A total of 137 ,420 seedlings were tested at both Lima and San Ramon. In four of these experiments, a North Caro- lina Design I was used , and 15 males each were mated to a random sample of 4 dif- ferent females . The heritability estimates derived from these experiments indicated the presence of sufficient genetic variabil- ity in these populations , leaving enough room for significant genetic progress in further cycles of recurrent selection. In a set of 16 experiments, progeny evaluations were conducted to select su- perior parental materials for true potato seed (TPS) use and also to identify proge- nies with adequate characteristics to be used for commercial potato production (Table 1). Experiments to study the effects of inbreeding on yield were conducted with a sample of 50 andigena clones taken at random from CIP's world potato collec- tion at Huancayo. From each clone , four types of progenies were obtained: selfed ( S ), open-pollinated (OP), hybrid to a pollen bulk of 10 male clones (B 10) , and hybrid to a pollen bulk of 20 male clones (B 20) (Table 2). Although selfed and OP progenies were generally inferior in yield to hybrids , about 30°/o of them per- formed as well as the hybrids. Apparent- ly, variable levels of additive gene action are present in those clones that did not show any inbreeding depression either in the selfed or OP progenies. Wide crosses . Research on the use of wide crosses in potato breeding, using wild species like Solanum etuberosum , S. acaule, S. verrucosum, and the primitive cultivated diploid S. phureja was com- pleted. The crossability barriers that were previously insurmountable in this material 42 Table 1. High-performing CIP progenies with their main attributes, 1984. Progeny Attributesa (Serrana x DT0-28).4 x 378015.16 Y, E,U,S (LT-2 x 7XY.1).9 x 378015.16 Y, E,U,S 377830.8 x 377964.5 Y, E, U, S 379642 .1 x L T-7 Y, U, S 377887.25 x 377904 .10 Y,U,S 377904.10 x 377250.7 Y , E, S 377964 .3 x L T-7 Y, E, U, S 378011 .23 x (377887 .17 x L T-7).21 Y, E, U, S Serrana x 378015.13 Y,S 78 .8.26 F2 x DT0-28 E,S ay =yield; E =earliness; U =tuber uniformity; S = selectability. Table 2. Average yield (g /plant) of the proge- nies of several andigena clones. Progeny typea Clone s OP 810 820 OCH-8501 492 499 785 755 OCH-9144 452 491 763 647 CIP 701275 590 678 818 727 OCH-8331 607 604 832 804 OCH-5298 415 400 566 593 OCH-9335 733 738 677 717 CIP 702749 606 646 613 689 HUA-385 981 910 935 887 CIP 701992 1192 758 960 941 HJT-5486 746 640 712 707 HUA-404 751 764 813 756 as= selfed; OP= open-pollinated; 810 hybrid, bulk pollen from 10 male clones; B2o hybrid, bulk pollen from 20 male clones. have now been overcome. At times, up to three bridging species had to be used to gain access to the valuable potato leaf- roll virus (PLRV) resistance genes of S. etuberosum , a non-tuber-bearing species. Crossability barriers were overcome by using the traditional method of bridging species in combination with embryo cul- ture in ways never before attempted. Anther culture. During 1984, 7500 an- thers, obtained from eight different plant sources, were cultured using conventional techniques. Three plants came from ma- terial supplied by Dr. G. Wenzel of the In- stitute for Genetic Resistance Breeding in West Germany. This material is known to exhibit a positive response in anther cul- ture or to possess "tissue culture ability" (TCA). The other five plants were hybrids that had been obtained from crosses with material either having or lacking this char- acteristic. Embryos and plantlets were ob- tained from these cultures and are cur- rently undergoing electrophoretic analysis to assess if they are of androgenic origin. International collaborative research. Argentina. At the National Institute of Agricultural Technology (INT A) in Bal- carce , research on developing greater ge- netic variability for breeding programs has produced a series of inter-specific hybrid populations. About 200,000 seeds were obtained in 4x - 4x, 4x- 2x, and 2x- 2x crosses involving S. tuberosum ( tbr), S. phureja (phu), S. chacoense (chc), S. ste- notomum (stn), S. gourlayi (grl) , S. spe- gazzinii (spg), and S. microdontum (med). Separate populations were subjected to various selection procedures as follows: 1) selection for scab and Fusarium rot resist- ance in a tetraploid tbr population; 2) re- current selection for general adaptation in a tetraploid population made up of tbr x grl hybrids; and 3) recurrent selection for adaptation and production in a diploid hy- brid population whose parentage included tbr, phu, chc, and med species. Field se- lection in 1983 -1984 involved more than 34,000 different clones that had survived previous selection. A comprehensive list of materials avail- able at Balcarce includes 64 clones that were derived from crosses made in 1978 and earlier. In general, these clones com- bine virus resistance with yield, tuberiza- tion under long days, and adaptation to warm conditions. Canada. The objective of this contract with Agriculture Canada has been to de- velop a method for obtaining environ- mental indices that measure productivity of diverse potato-growing areas and to construct a prediction model for individ- ual genotypes based on these environmen- tal indices. Yield data were obtained from 12 experiments conducted during 1983 and 1984 in Bangladesh, Brazil, Canada, Peru, Philippines, Rwanda, Tunisia, and Turkey. Twenty-nine genotypes were the same in these and nine other experiments carried out in 1983. The yield data for these 29 genotypes were treated as varia- bles in a principal component analysis. Genotypes with incomplete data from both sets of experiments were not in- cluded in this analysis. Yields in the nine sites ranged from 10.9 t/ha at San Ramon, Peru, to 33.0 t/ha for Turkey. Yield data of 20 geno- types in three of the 1984 experiments were used to verify the effectiveness of the prediction models to screen out po- tentially unfit genotypes. With few excep- tions , reasonable correspondence between observed and predicted yields was ob- tained for those genotypes judged as pre- dictable, demonstrating the effectiveness of the model. United States. In contract research at the University of Wisconsin, crosse_s among 40 S. tuberosum Group Tuber- osum haploids (2n = 2x = 24) and eight 2x wild species resulted in 111 hybrid fami- lies. Some haploids were especially effec- tive in producing hybrids that tuberized regardless of the species parent. Hybrids with S. berthaultii (ber), S. tarijense (tar), and S. microdontum produced the 43 largest tubers. Male fertility was strongly influenced by the species parent. All hy- brid families with ber and tar were fer- tile; haploid S. canasense families segre- gated in a 1: 1 ratio of fertile to sterile progeny. TPS progenies from 4x -2x hybrids had superior seedling vigor, seedling tuber pro- duction, and plant uniformity when com- pared to OP 4x seed. The high cost of producing hybrid seed could limit its use; however, OP seed could be an economic alternative in developing countries, since farmers could harvest their own seed at very low cost. POPULATION DEVELOPMENT In the development of disease-resistant populations, a sample of 10,500 seedlings from 120 progenies combining early ma- turity, good agronomical characteristics, and immunity to potato virus Y (PVY) was inoculated with PVY. A total of 5000 seedlings survived this screening and were transplanted to the field in Lima (summer) to select further for yield , earliness , heat tolerance, and tuber characteristics. A population of 300 progenies com- bining early maturity, high yield, and re- sistance to early blight (Altemaria solani) has been bred. Seedling screening tech- niques developed by CIP pathologists are being used to select resistant genotypes for distribution to developing countries . As part of the development of new ge- netic populations, studies on field plot techniques were conducted to determine the optimum plot size for evaluating seed- ling progenies. Plot sizes of 4 , 20, 60, 120, 360, and 720 plants were set up . When the magnitude of variances for the various plot sizes was analyzed and the variances and costs combined, a plot size of 40 seedlings per 12.6 m2 was found to be optimum. 44 Research on diploid and 4x -2x popula- tions. The successful development of 2x populations with specific attributes and first division restitution (FDR) 2n pollen was reported in 1983 . Some of these dip- loids were crossed with 4x female parents and the resulting 4x progenies evaluated for the following two attributes. Resistance to root-knot nematodes. A bulk pollen from some resistant diploids was crossed with six tetraploid females , and the resulting six families were evalu- ated for resistance along with two suscep- tible families. The means for resistance of the six 4x -2x families were significant- ly higher than those of the two suscepti- ble families. None of the 110 progenies of the susceptible families had a root gall- ing index below 3, whereas 17°/o of the progenies from resistant FDR diploids had a root galling index of 1 or 2 (see Ta- ble 3, Thrust V) . This shows clearly that the resistant diploids transmit their resist- ance to the 4x progenies and that highly resistant progenies can be selected from such a 4x -2x population. Resistance to bacteria/ wilt. The dip- loid clone MI49-10 was selected for resist- ance to bacterial wilt (BW) (isolate 204 of race 3 and 064 of race 1) and for pro- duction of a high frequency of 2n pollen. The parental value of this clone for pro- ducing progenies with BW resistance and desirable agronomic traits was compared with the parental value of the FDR clone W5295 .7. This clone was a parent of CIP's successful DTO clones and is known to produce progenies with good agronom- ic characters but with susceptibility to the most important diseases. The two clones were crossed with the same female parent and the resulting progenies were grown in Huancayo for agronomic evaluation . Progenies from MI 49-10 were as productive as those from W5295 .7, but were smaller in tuber size. Harvest of progenies from 4x-2x crosses for testing the combining ability of FDR dip- loids, Lima (winter) . The two families were then compared for their resistance to BW (isolate 204, race 3) by evaluating more than 40 clones per family with four replications. The family from the resistant FDR clone had a sig- nificantly higher level of resistance than the other family. Thus, it appears that MI 49-10 produces agronomically acceptable 4x progenies with some level of resistance to bacterial wilt. Combining ability test of FDR dip- loids. Any potentially useful diploids with FDR- 2n pollen production need to be evaluated for their combining ability (par- ental value) with tetraploid female par- ents . This type of evaluation is necessary, as the objective of this project is not the production of FDR diploids but the devel- opment of progenies from 4x-2x crosses. Nine FDR diploids were therefore crossed with five tetraploid females , giving 45 families. These families were planted in an experimental design with three replica- tions and 40 seedlings per plot and har- vested 14 7 days after transplanting. Al- though the results revealed no significant difference for marketable tuber yield per plant, highly significant general combin- ing ability (GCA) effects for such charac- ters as earliness and yield per plant, even among half-sib clones, were observed in this experiment. These results demon- strate the importance of selecting FDR diploids for combining ability. GERMPLASM DISTRIBUTION CIP's list of pathogen-tested cultivars was increased during 1984 and now comprises 150 varieties and advanced clones and 64 primitive cultivars and wild species. Dur- ing 1984, all of the material listed in Ta- ble 3 were tested by the following : indi- cator hosts, and latex or enzyme-linked 45 Table 3. Distribution of germplasm by CIP, 1984. CIP Countries Clones Tuber family In vitro True seed region (no.) Acces. Units Acces. Units Acces. Units Units 4 168 885 165 4,191 42 184 106,000 II 15 688 14,706 115 4,350 90 494 96,902 Ill 3 74 364 256 1,873 23 46 0 IV 4 0 0 59 1,491 45 90 247,851 v 3 44 463 99 559 0 0 13,000 VI 6 76 881 38 195 42 90 25,550 VII 6 46 230 319 579 102 206 22,800 Othersa 10 166 553 0 0 116 319 58,442 Total 51 1,262 18,082 1,051 13,238 460 1,429 570,545 a Developed market economies and centrally planned economies . immunosorbent assay (ELISA) serology for freedom from potato viruses A, M, S, T, V, X, Y, PLRV, Andean potato latent , Andean potato mottle, tomato black ring, and tobacco ring spot. By the end of the year, the nucleic acid spot hybridization test (NASH) was being used to diagnose potato spindle tuber viroid (PSTV), thus replacing the use of electrophoresis. Through a contract in Australia with the Department of Agriculture, Victoria , pathogen-tested potato germplasm is being produced for distribution to Southeast Asian and Pacific countries. During 1984, sets of 45 tubers of each of 11 CIP clones and three varieties were sent to the Cook Islands, Fiji, New Caledonia, Papua New Guinea, the Solomon Islands, Tahiti, and Vanuatu. Larger shipments of selected material were also sent to the Philippines, Bhutan, Burma, and Tonga. In-vitro plant- let cultures of 31 clones were sent to Papua New Guinea, 19 to the Philippines, and 8 to Peru. Heat treatment, virus in- dexing, and production of first genera- tion small tu be rs were completed for 13 clones, while an additional 13 pathogen- tested lines from CIP were indexed and multiplied to produce small tubers. About 46 15,000 small tubers of 37 pathogen-tested clones were produced for the 1984-1985 field plantings and for planting in insect- proof cages. Regional evaluation with national pro- grams. One aspect of CIP's regional programs is to promote the transfer of breeding material, selected by national programs, to other countries in the region. South America. During the year, the Colombian national program of ICA sent 31 segregating families to Venezuela. A number of Colombian varieties, tested in farmers' fields in Bolivia , performed well compared to local varieties; the three best are shown in Table 4. In Colombia, a joint CIP-ICA program for testing CIP Table 4. Yield of Colombian varieties tested by ASAR, Cocipata Alto, Bolivia, 1984. Yie ld (t/ha) Variety Site 1 Site 2 ICA - Purace 40.5 34 .3 ICA - Tequendama 37.5 26.7 Parda Pastu sa 26 .2 23.6 Alpha (control) 20.7 lmilla Blanca (control) 14.9 germplasm has continued over the past four years. Selection of clones with late blight resistance, good yield and tuber quality is well advanced, particularly in the Province of Antioquia (Table 5). CIP's collaborative contract with the national program of INIA, Chile , to test CIP genetic material for long-day adapta- tion has been completed successfully. A close correlation was established between selection for tuberization response under artificial long-day conditions at CIP, Lima (lat. 9° S) , and natural long-day conditions at Osorno, Chile (lat. 40° S). With this confirmation, CIP scientists in Lima can now select and distribute adapted geno- types for higher latitudes , with the assur- ance that these selections will tuberize. In Brazil , germplasm with heat toler- ance was field-tested at Brasilia and Espi- ritu Santo State under a joint CIP-CNPH project . Fifty-seven tuber families , prev- iously multiplied in the greenhouse , were planted in the field at both sites. In Bra- zilia, 7000 genotypes from these families were tested and 25°/o were selected as being adapted to warm conditions. Bac- terial wilt incidence was another impor- tant consideration for selection, with four of the tested families showing some meas- ure of disease resistance. In Espiritu Santo State, 1347 genotypes were tested and more than 70°/o were harvested. Some of these families also showed resistance to early blight, caused by Alternaria solani. In contract research with CNPH/ Brasilia, 24 CIP clones were field-tested for early blight resistance and compared with control varieties. Only 1 of the 24 clones was significantly better than Aracy, a local cultivar considered fairly resistant. Several of the 24 clones tested, however, were better than Delta and Bintje , two other control varieties used commercially. East Africa. CIP now has four screen- houses in operation at the Plant Quaran- tine Station Muguga , Kenya, for multi- plying CIP germplasm after it has passed quarantine inspection . In vitro propaga- tion , production of tuber families, and production of TPS are now routine . CIP germplasm was planted during the rainy season (1983-84) at Mau Narok, a high altitude site (3000 m) in Kenya. At harvest , the best clones yielded the equiv- alent of 60 t/ha, while three local control varieties averaged 40 t/ha. The highest yielding CIP clone matured 20 days later than the local varieties; however, several clones had acceptable early maturity and yielded in excess of 50 t/ha. Because of the severe drought in East Africa during 1984, the same highland evaluation of germplasm had to be discontinued since Table 5. Performance of the best introduced germplasm tested in Antioquia Province, Colombia. Late blight Specific CIP clone reaction° gravity 378508 .6 3.0 1.070 378508.13 3 .0 1.079 378508.17 2.5 1.086 378508.18 3 .1 1.073 Capiro (control) 4 .8 1.079 a Late blight scale: 1 =no late blight; 9 =death of plant. Yield (t/ha) La Selva experimental station 41.6 37.0 45.5 21.8 19.3 Regional trials in Antioquia 54.7 33.7 50.5 34.9 20.6 47 there was rain only during the planting season. When compared with the yields of the previous season, the 1984 yields were as low as 10 and 20 t/ha. In Rwanda, nearly 4000 tuber fami- lies and a group of 23 clones or varieties were introduced from CIP, Lima. The germplasm was evaluated by the national potato program (PNAP) according to the following testing sequence: 1) introduc- tion plots (tuber families) , 16°/o of clones were selected; 2) observation plots of 5 plants, 29°/o selected; 3) micro trials, 2 replications of 10 plants, 42°/o selected; 4) macro trials, 5 replication of 20 plants, 50°/o selected for further testing. In Burundi, two CIP introductions have been named as varieties by the national program of ISABU and were released in 1984. One (378711.5, Muziranzara) was selected from a CIP tuber family , while 720118 (Cruza 148 ,Ndinamagara) , a Mex- ican clone, was originally selected for BW resistance by CIP in Costa Rica. Cruza 148 is proving to be the most wilt resist- ant clone in East Africa. Two other ex- tremely promising clones will be included in the next season's regional trials. ISABU has initiated a long-term systematic eval- uation of germplasm with resistance to LB and BW to provide improved varieties for farmers. A total of 182 tuber families, comprising 1792 tubers, were received from various sources in East Africa . Ini- tially, 155 families have been selected for yield , LB resistance , and storability. From a further introduction of 476 tubers re- ceived from CIP, 22 selections were made. In another experiment conducted by ISABU, 89 selections were made from 497 genotypes received from CIP in 1983. These selections were replanted in March 1984 in BW-infested soil, and only four clones showing wilt tolerance were re- tained. Samples of the 89 selections are now being evaluated for LB resistance. 48 The 1984 East African drought limit- ed the potato program's multilocational yield trials in Burundi. But in spite of the drought, the new Burundese varieties mentioned earlier, as well as the Rwan- dese variety Kinigi and several other in- troductions from Rwanda and Kenya, all outyielded standard varieties such as Sangema and Kenya Baraka. Thus, the ISABU potato program is confident that the momentum of improved varieties can be maintained to overcome the past de- cline in areas planted to potato , which is due to the extreme susceptibility of older varieties to late blight. West Africa. In trials conducted by the National Institute of Agricultural Re- search (INRA) in Senegal, four of the clones received from CIP yielded in ex- cess of 500 g/plant in 99 days. DT0-33 , now named as Naatangue in Senegal and one of the top-yielding clones, is being multiplied on a large scale for distribution to farmers. In Togo , the National Potato Insti- tute (INPT) has only recently started test- ing CIP germplasm. Nineteen clones were planted in May and harvested in August, 78 days later. These will be evaluated fur- ther , after which time all clones yielding less than 10 t/ha will be discarded . South Asia. In Bhutan, the Ministry of Agriculture is testing 17 advanced clones in coordinated variety trials, and another 12 clones with BW resistance are under evaluation. The national potato program hopes to develop a Bhutanese variety that will stabilize potato production under lo- cal conditions, which are typical of the Himalayas where both BW and LB cause severe crop damage. The national potato program of Ban- gladesh (BARI) tested 86 genotypes, and in a series of advanced trials, 15 clones were finally selected . This group includes several that are being widely adopted in East Africa and other parts of Asia, for example, CIP clone 720088 from Argen- tina and clone 800224 from the Uni- versity of Wisconsin. Further selections made from material developed in Scot- land, India , and at A VRDC in Taiwan all gave consistently high yields over four seasons and will be grown in on-farm trials during the 1984-1985 season. TRAINING The first germplasm management course in Africa was held at Saida, Tunisia, and organized in collaboration with the na- tional potato program. It was attended by seven scientists from French-speaking North, West, and Central African coun- tries that are receiving advanced breeding materials for evaluation. Tissue culture and rapid multiplication methods, used by national programs to handle imported germplasm and multiply cultivars for basic seed tuber production, were the subjects of two courses held in South America. At Cali, Colombia, CIAT organized a course on tissue culture tech- niques for cassava and potato as a joint CIAT-CIP activity . The course was fund- ed from the UNDP project on Technology Transfer on Root and Tuber Crops. The national potato program in Ecuador also used UNDP funds to support their course, organized in collaboration with CIP, for 15 scientists from Sou th and Central America. Individualized training in tissue culture and rapid multiplication was given at CIP headquarters to nine visiting scien- tists from Latin America and Asia. 49 THRUST Ill Bacterial and Fungal Diseases A new tetraploid population from tetraploid/diploid crosses, which com-bined four specific sources of resistance to bacterial wilt (Pseudomonas solanacearum), was field-tested for the first time in Peru. Selected clones will be available for regional tests in 1985. A new group (VI) has been developed in the tetraploid program on the basis of the traditional Solanum phureja re- sistance; crosses for another group (VII) with more emphasis on late blight resistance have also been made . An antiserum specific to P. solanacearum did not react with healthy sap or other pathogenic bacteria and was able to detect P. solanacearum from tissue extracts of potato stems and tubers. In contract research at the University of Wisconsin, tubers inoculated with an avirulent mutant had 53°/o reduction in bacterial wilt infection when planted in an infested field. Also at Wisconsin, studies on the control of bacterial soft rot have confirmed the positive correlation between tuber calcium content and resistance to bacterial soft rot and internal brown spot of potato tubers. Research to increase gene frequency for late blight resistance by using the criteria of infection rate was continued. Eighty-five of 369 clones tested for late blight resistance were selected by using infection rate criteria. A selection of late blight-resistant clones was made under long-day conditions at Osorno , Chile. In Peru , preliminary field observations suggested that rapid advances in developing clones resistant to early blight can be achieved under dry season conditions at San Ramon. Field screening for potato smut (Angiosorus so Zani) has continued at Huancayo and clones with high levels of resistance have been selected. A survey of bacterial and fungal diseases in Burundi, Rwanda, and Zaire substantiated the importance of late blight , bacterial wilt , and soft rot dis- eases of potato. In Rwanda, a nonhost crop alternated with potato markedly reduced bacterial wilt infection . Conidia of Alternaria solani, causal agent of early blight. 51 BACTERIAL DISEASES Breeding for resistance to bacterial wilt (Pseudomonas solanacearum). Major em- phasis in breeding for resistance to bacte- rial wilt (BW) was placed on using new sources of resistance to P solanacearum. Although Solanum phureja is still an im- portant source of resistance , a new tet- raploid population has been developed that combines four specific sources of re- sistance. The BW resistance incorporated into this new population came mainly from wild diploid species as well as from a tetraploid population. The resistance in the tetraploid parents came from S. phu- reja . In spite of the strong input from wild diploid germplasm, the first 4x- 2x tetraploid generation had highly uniform tuberosum-type tubers with good agro- nomic quality (Fig. 1). Part of this new population was tested in BW-infested fields in Peru with encouraging results : several seedlings yielded more than 5 kg ; and high dry matter content was also ob- served in tubers of the selected plants. The high dry matter of the 4x hybrids was contributed by diploid clones with high dry matter, which are used in the breeding program at the diploid level. The late maturity of this new material (more than 120 days) is being improved by a series of crosses to advanced, early, and heat-adapted tetraploids. Because the expression of BW resistance is apparently linked closely to heat tolerance , some of this new genetic material is now being tested under heat stress conditions at San Ramon. Some of this new material , which will have widespread use in areas where heat stress and wilt are problems, is al- ready available for export. Jn the tetraploid breeding program, an additional group (VI) has been developed on the basis of traditional S. phureja lj-fll 3S . J; D c. Q.u. O,.o...j 52 , r Figure 1. Tuberosum-like tubers of a 4x bacterial-wilt-resistant population two generations removed from wild 2x species . Table 1. Variation in antibiotic resistance, salt tolerance, and phosphatase reactions among potato isolates of Pseudomonas solanacearum from low and high elevation sites in Peru . Antibiotic resistancea Isolate Altitude Biovar no. (m) Tetracycline 042 3350 L 015 1600 L 077 170 L 141 170 L II 017 2700 I II 102 3500 II 107 170 II 142 170 a L =low; I= intermediate; H =high. resistance. In crosses for a further group (VII), increased emphasis was placed on late blight (LB) resistance. Some material from both of these groups has been dis- tributed to CIP regional programs for testing in 1985 . Studies on P. solanacearum isolates. Fifteen antibiotics were tested for growth inhibition on eight isolates of P. solana- cearum from low and high elevation sites in Peru (Table 1). Also , salt tolerance was studied in vitro at 0.1, 0.5, 0.8, and 1°/o NaCl concentrations. Two of the antibi- otics studied gave results that may be use- ful for differentiating groups of P solana- cearum isolates. Biovar I isolates (race 1) had low resistance to tetracycline , where- as biovar II isolates had intermediate re- sistance. Resistance to oleandomycin was present in the three isolates from higher elevation sites; however, the same three isolates were inhibited by 0.8°/o NaCl and were negative for phosphatase. Antiserum production. An antiserum specific to P solanacearum has been pro- duced in a joint effort with Thrust IV. Although a race 3 isolate was used as the antigen , the antiserum reacted with iso- lates of races 1, 2, and 3 as well; however, it did not react with healthy sap or other Tolerance to Phosphatase Oleandomycin 0 .8°/o NaCl reaction H No Yes + Yes + I Yes + H No H No Yes + Yes + pathogenic bacteria (Table 2) . The anti- serum was more sensitive in detecting P solanacearum in extracts of potato stems and tu be rs than by the method of in vi- tro plating (Kelman's medium). The anti- serum reacted with a wide range of races and strains of P solanacearum, although reactions showed a significant difference in absorbance values (ELISA A405). The latex test , although less specific, is highly sensitive and more easily used than the Table 2. Serological reactions of Pseudomonas and Erwinias spp . (106 colony-forming units/ml) with antiserum specific for P. solanacearum. Species P. solanacearum (race 1) P. solanacearum (race 2) P. solanacearum (race 3) P. solanacearum (race 3) P. /achrymans P. f/uorescens P. tabaci P. cariophy//i E. carotovora pv. carotovora E. carotovora pv. atroseptica PBS buffer (control) Latex reaction + + + + ELISA A4o5 (nm) 0.42 0.45 >2.0 0.55 0 .22 0.25 0.23 0.26 0.22 0.24 0.25 53 ELISA, therefore latex kits have been dis- tributed to the CIP regions for testing un- der field conditions where well-equipped laboratories do not exist (Fig. 2). Biological control of bacterial wilt. Contract research has continued at the University of Wisconsin (U.S.) on biologi- cal control of bacterial wilt by means of inoculating tubers with avirulent mutants of P. solanacearum. Under growth room conditions (28° C), the best results were obtained with paired plant tests in which the inoculum was provided by bacteria released from the inoculated , untreated source plant. The source plant was inocu- lated with the virulent strain 276. The test plant in each pot was grown from a tuber soaked for six hours in a suspension of the avirulent mutant (strain B82). The results indicated that plants grown from • . .. .. tubers treated with the avirulent mutant had consistent protection against bacterial wilt. There was a significant reduction in both disease incidence and disease sever- ity, confirming previous results with other assay methods. A subsequent field trial was conducted in Florida during 1984 in which tubers of cvs. Ontario (resistant) and Atlantic (susceptible) were treated as indicated above and planted in ridged rows in soil naturally infested with P. solanacearum. There were four treatments, replicated ten times. Significant differences were ob- tained in all parameters between treated and untreated plots of cv. Atlantic : bac- terial wilt incidence was reduced 37°/o and brown rot 53°/o. With Ontario, dis- ease incidence was very low in the control and, therefore , there was no measurable Figure 2. Serological diagnosis of P. solanacearum by the latex test. In each square a drop of antiserum-sensitized latex and a drop of antigen are mixed by rotary agitation for 30 minutes. Antigens are (A) sap extracts from plants infected with P. solanacearum; (B) sap extracts from healthy plants; (C) first two squares, a suspension of P. so/anacea- rum from a pure culture; last two squares, a suspension of£. chrysanthemi from a pure culture . 54 effect of tuber treatment. Yields of both cultivars were not affected significantly by the treatment with strain B82. Under the same contract at Wisconsin, studies have continued on the agglutina- tion of P. solanacearum by extracts from potato tubers and on serological speci- ficity in strains of P. solanacearum. Last year it was reported that bacterial cell walls contained a strong proteinaceous in- hibitor of bacterial agglutination caused by hydroxyproline glycoproteins extract- ed from potato. This bacterial protein has been extracted from P. solanacearum non pathogenic strain B 1 and consists of bacterial fimbriae , which are long, pro- teinaceous appendages of bacterial cells and are thought to be involved in bind- ing to specific surfaces. Because the fim- briae precipitated plant cell-wall material, and this precipitation was inhibited by bacterial extracellular polysaccharide, the results suggested that attachment of Bl cells is mediated by fimbriae. A patho- genic strain of P. solanacearum did not attach to cell wall material, which may be because the strain produces extracellular · polysaccharide . Screening for bacterial wilt resistance. In a research contract with the National Agricultural Laboratories of Kenya to screen CIP introductions for BW resist- ance, preliminary results have shown that in field tests of 53 clones, only 17°/o wilt- ed in a random pattern. An artificial in- oculation technique was used for uniform screening in which an aqueous solution of bacteria containing 107 to 108 viable cells/ml was poured around the base of the plants. This concentration increased the probability to infect, but was well within the natural population levels found in the soil and did not interfere with in- herent plant resistance. A contract project with the Depart- ment of Agriculture in Sri Lanka has made significant progress toward developing va- rieties resistant to bacterial wilt. Several new clones were evaluated, old ones were retested, and those that showed promise were evaluated in farmers' fields during 1984. In the highland testing site at Sita Eliya ( 1900 m) where race 3 is present, nine selections, previously resistant, were retested: clones 800226 and 800935, and tuber family entries 377847.1, 377847.4, and 377852.2 were again resistant to bacterial wilt. At a lower elevation site at Rahangala (1350 m), 46 previous se- lections were retested and 5 continued as resistant: 379669.67/27, 379687.77/ 16, 379695 .85 /7 , 379696.86/20, and 379696.86/21. On-farm trials of another group of 15 earlier selections were con- ducted in a paddy field . Bacterial wilt in- cidence in the control var. Vekaro was low (25°1o); the test clones were nearly all free of the disease, with seven outyielding Vekaro(125-171 g/plantvs.105 g). Field control of bacterial wilt. In Rwanda, rotation trials to control bacte- rial wilt, conducted in collaboration with the national potato program (PNAP), have ended after seven seasons. One non- host crop planted between two potato crops reduced wilt infection levels consid- erably. The effect of the normal dry sea- son (July-August) also reduced infection spread. Latent infection in tubers from plants adjacent to infected plants was high, and the development of wilt in the subsequent crops was very rapid. Plants two hills removed from the source of in- fection had much less latent tuber infec- tion. While adjacent plants are eliminated in PNAP seed multiplication plots, this is not a feasible practice for small farm- ers who maintain their own seed. Conse- quently, PNAP is introducing-through the on-farm trial program - the practice of positive selection of those plants dis- tant from the source of infection. 55 Bacterial soft rot and internal brown spot. Studies condu cted at the Universit y o f Wisco nsin on the control o f bacterial soft ro t. cau sed by Ehvinia caroto1·ora pv. atroseptica . have confirmed previous re- port s on the positive corre latio n be twe en tuber calcium content and res istance to bac terial so ft rot and int ern al h rown spo t (or heat necrosis) o f tubers. Pot at oes that had bee n harve sted fr om fact or ial ex- perimental plo ts with different le vels of ca lc iu m ( 16 treatments x 4 rep li ca tio ns) we re examined (40-80 tu be rs pe r trea t- ment) for th e prese nce of int ern al brown spo t. Brown spot was nega tive ly corre- lat ed (-0.75 4) with cal c ium content of tubers. The mean percentage o f brown spo t in cidence range d fr om 42.5 °/o a t the lowest cakium level to 5°/o at the highest. Mist chamber assa ys of bac terial so ft ro t seve rity on tu be rs from fie ld pl ots at three locatio ns in Wisconsin prov ided confirma- tion of result s obtained in previous sea- so ns: tube rs from high-calcium plot s were m ore resistant to soft ro t than tubers from low- calcium plots. FUNGAL DISEASES Testing for late blight (Phytophthora in- festans) resistance. During the year, 355 clones were tested for late blight (LB) re- sistan ce in Huanuco , Peru (2200 m), in cooperation with the na tional po tato pro- gram of INIPA . One hundred of these clones were evaluated in a sim ple 10 x I 0 latti ce and the o ther 255 in ten-hill ob- se rva ti on pl ots w ith a plant densit y o f 33,333 plants/ ha . The results , based on the di sease infection rate (r) and the area below the disease progre ss curve ( ADPC) , indica ted that 85 clo nes had some infec- tion within the range of re sistance , 144 showed no infection , and 120 were su s- ceptible. The perfo rmance of the eight best clones fr om th e lattice design is shown in Table 3. Of all clones evalu ated , 36 were se lected by the natio nal program for further testing in regional trials . Work has continued o n the collabo ra- tive project with the nati onal program of INIA. Chile , to extend the adaptability of LB-resistant material to longer days in subt ro pical latitudes. Seventeen families Table 3 . Yield performance and late blight reaction of the eight best clones under late blight exposure in the field, Huanuco, Peru, 1984. Yield Late blight reaction Cultivar (kg / p lant) Rate ADPC" (O/o) 380391 .1 1.597 a* .000 0 379954 .7 1.543 ab .036 0.6 380493.24 1.500 abc .107 1.5 380475.4 1.489 abed .000 0 380431 .2 1.455 abed .086 2.7 380474.6 1.393 abed .000 0 380493.18 1.380 abed .086 5.7 380431 .7 1.375 abed .179 9.0 Revoluc i6n (control ) 0 .576 .136 70.4 Mariva (control) 0 .279 .086 85.7 CV = 37 .60/o. a Area under disease progress curve. * Means fol lowed by the same letter are not significantly different at the 5°/o level. 56 that combine LB-resistance with earliness were planted under natural , long-day con- ditions at Osorno (lat. 40° S) , at a plant density of 4 7 ,619 plants/ha . This sample belongs to a subpopulation that is being adapted to nontropical highlands and sub- tropica l cool environments. The yields of selected clones were outstanding over yie lds of the local controls adapted to long days (Table 4). During 1984, nine developing cou ntries received late blight-resistant material from CIP : 504 tuber families ( 4641 clones) and 4200 true potato seeds. Also, 120 proge- nies were sen t to Rio Negro , Colombia, to be tested for LB resistance as part of the parental line se lection program ; the results of the evalua tions are being analyzed. Apparent infection rate (r) .10 .08 .06 .04 .02 Chitaga Capiro Tequendama Monserrate Table 4 . Yield of the eight best clones with re- sistance to late blight, planted in five-hill plots under long days at Osorno, Chile. Marketable Total yield yield Cultivar (kg/ plant) (kg/plant) FT381112 .18 2.883 2.900 FT 381079.41 2.370 2.430 FT 381112 .37 2.200 2.275 FT381104.18 2.070 2.150 FT 381097 .2 1.900 2 .120 FT 381110.48 1.900 2.050 FT 381081 .21 1.860 1.900 FT 381081 .62 1.810 1.890 Yagana (control)a 1.382 1.507 Ultimus (control)a 1.173 1.333 a Controls were replicated six times in five-hill plots. • .OD~~~~~~~~~~~~~~~~~~~~~~~~~~~ 0 10 20 30 40 50 Plant density/ha (x1000) Figure 3. Relation between the apparent late blight infection rate in four potato varieties and five planting densities. 57 Infection rate in relation to plant den- sity. Four varieties (Chitaga, Capiro , Te- quendama, and Monserrate) were planted at five densities ( 10, 20, 30, 40, and 50 x 1000 plants/ha) in plots of 6 x 6 m at Rio Negro. Ten LB evaluations, beginning at the time of flowering , were made at seven- day intervals. The apparent infection rate (r) for each row was determined and val- ues were averaged for each plot. Results indicated that , in all cases, the r value in- creased with plant density above 30,000 plants/ha (Fig. 3). At lower plant densi- ties , this factor appeared to be relatively unimportant. Late blight resistance in potato dip- loids. Diploids produced at CIP, Lima, were shipped as true potato seed (TPS) to Colombia, where 193 clones were pro- duced under greenhouse conditions by the national potato program of ICA. For field testing at ICA's La Selva Station in Rio Negro, each clone was planted in a two-hill plot , and six weekly blight evalu- ations were made beginning 60 days after planting. Data were transformed into ap- parent infection rate (r) and compared with the reaction of standard control va- rieties (Tables 5 and 6). Among the clones in the resistant group , some were not in- fected beyond a scale value of 2 (CIP late blight scale 1- 9), or they became infected very late in the season. Preferably, gener- al resistance should be sought among the clones of the moderately resistant group. After flowering, pollen was collected from each plant to study the production of FDR-2n pollen. Screening for late blight resistance in tubers. A total of 141 clones from CIP's germ plasm collection were tested in Huan- cayo for LB tuber resistance. The first group of 71 clones was retested after being reported as resistant in 1983 trials: 6 were resistant, 27 moderately resistant, and 38 susceptible. The second group of 58 Table 5. Number of late blight resistant (R), moderately resistant (MR), moderately suscep- tible (MS), and susceptible (S) clones in a test diploid population of Atzimba-derived clones. ICA, Rio Negro, Colombia. No. clones/ Range of r Resistance group values classification 80 .;;;0.100 R 57 0.101 - 0 .145 MR 24 0 .147 - 0.175 MS 32 ;;. 0 .176 s Table 6. Late blight resistance of selected ICA varieties, Rio Negro, Colomb ia. Resistance Infection rate Variety classification (r) Monserrate R 0 .060 Chitaga R 0.100 Tequendama MR 0 .103 Picacho MS 0.150 Capiro MS 0 .157 San Jorge MS 0.166 Guantiva s 0.250 70 clones was tested for the first time, with 35 resistant, 21 moderately resistant, and 14 susceptible. Late blight foliage readings were taken during the growing period of these clones and compared to tuber resistance. A positive correlation (r = .346) was established between tuber and foliage resistance to late blight. SOIL-BORNE DISEASES Potato smut (Angiosorus so/ani). Two field trials to evaluate advanced clones and varieties for their resistance to pota- to smut were conducted in Comas, Peru (3100 m). In the first trial , 11 cultivars previously reported to be resistant were retested in larger quantities in a highly infested field, and 7 were found to be highly resistant (Rosita, Revoluci6n, ASA- 69-1 , Mi Peru , Participaci6n , 69-56-52, and 375587.2). In the second trial, 71 cultivars, evaluated for the first time , were planted in a randomized complete block with four replications and five tubers per replication. Twenty-eight of the 71 were not infected by A. solani and will be retested. Pink rot (Phytophthora erythrosep- tica ). An on-farm field trial was estab- lished in Huancayo to study the residual effect of the fungicides Basamid (300 kg/ha)+ Ridomil 5G (30 kg/ha) for the control of pink rot. This chemical treat- ment once again gave excellent control: the yield of healthy tubers was increased 2.5 times with a 50-fold decrease in dis- eased tubers. The residual effect of both fungicides will be studied over the next two subsequent potato crops. Southern wilt (Sclerotium rolfsii). A second repetition of a rotation study, ini- tiated in 1980 at San Ramon, which in- cluded four rotation sequences (rice- beans-corn-potatoes) to be compared with consecutive potato crops, was again con- ducted at San Ramon in 1984. Each ro- tation included subtreatments with and without crop residue incorporation. The plot size of each experimental unit was 21.6 m2. During the rainy season, potato was planted and plants were inoculated with S. rolfsii; fifteen days later, 50°1o of the plants were dead. Before the first crop of the rotation was planted, the number of microsclerotia ranged from 8-24/500 g of soil. After residue from the first crop was incorporated in the soil, there was a general increase in micro- sclerotia, the number being higher (215°1o increase) in corn plots and lower in po- tato plots. At the end of the rotation se- quence , yields of potatoes on potatoes were lower (23 .1 kg/21.6 m2 ) and higher for the corn-bean plots (41.5 kg/21.6 m2 ). The final conclusion of this study will be available after the soil assays of microsclerotia content are analyzed. Verticillium wilt ( Verticillium dahliae ). In a field trial in Canete, a coastal desert valley south of Lima, 15 clones were planted and inoculated by three different methods to determine if a screening meth- od could be used to select clones resist- ant to Verticillium wilt. The three inocu- lum sources applied at planting were 1) infected wheat kernels, 2) dry microscle- rotia produced on potato dextrose agar (PDA) and mixed with peat moss, and 3) tuber dipping in an inoculum suspension. Tubers inoculated with dry microscle- rotia and peat moss induced the earliest and most severe symptoms. On the other hand, inoculation studies carried out in pots in CIP's greenhouse (Lima) indicated that the following two methods were the most reliable and reproducible under conditions at Lima. In the first, infected wheat kernels were mixed with the pot- ting soil ; and in the second, a 2-cm2 of PDA with a two-week-old culture of V. dahliae was placed below the tuber at planting. A study on the incidence and distribu- tion of Verticillium wilt in the Mantaro Valley of Peru has shown that the high- est percentage of plant samples infected with V. dahliae was obtained from farm- ers' fields in the lower zone of the valley (3200-3500 m), with no infection ob- served in the higher zone (3800-4200 m). There appeared to be no correlation be- tween stem and tuber infection. The cor- relation between plant infection and alti- tude seemed to be directly related to seed supply. Generally, farmers from the lower part of the valley buy seed from the coast where Verticillium wilt is a well-known problem, while farmers from higher zones produce their own seed. V. dahliae is the only species known to exist in Peru. 59 SURVEYS OF DISEASE INCIDENCE A sUivey of bacterial and fungal diseases was carried· out in Burundi , Rwanda , and Zaire in a collaborative contract with the Research Institute for Plant Protec- tion (IPO), Netherlands. During April and May , P inf es tans was, in general, the most serious pathogen; although in Burundi and in the southern part of Rwanda , P solanacearum was of equal importance (Fig . 4). The third most important dis- ease , affecting up to 35°/o of po tato plants in the field , was caused by E. chrys- anthemi and E. carotovora pv. carotovora . Disease symptoms included stem rot and wilt . In Rwanda , the relationship between resistance to late blight in clones and number of days to maturity was studied jointly by CIP and PNAP. The 40 clones included in the experiment were divided into two groups: late and early maturing. The mean late blight score on a scale of 1-9 was plotted against the maturity length of the two groups. Only a weak or nonexistent correlation existed between maturity and late blight resistance in the 40 clones tested. Late blight reduced ra- diation interception due to loss of leaf area, and thus the total photosynthesis of carbohydrates was reduced . In experi- ments with and without fungicide treat- ment, the fungicide treatment extended the duration of foliage and foliar soil cover considerably. The yields increased proportionally to increased intercepted radiation . Figure 4 . Potato plant with the classical unilateral wilt symptom of bacterial wilt dis- ease caused by P. solanacearum. 60 TRAINING Five scientists from Latin America stud- ied the control of bacterial and fungal dis- eases and methods of screening germplasm for resistance at CIP's research stations in Peru. The national potato program of Burundi held a two-day workshop on bac- terial wilt , a major problem for potato growers in East and Central Africa. The workshop was organized so that scientists from Burundi, Rwanda, Zaire, and Kenya could review the current status of bacte- rial wilt research in their countries and develop an integrated research program for studying this disease. 61 THRUST IV Potato Virus Research Major emphasis was placed on investigating the mechanisms of plant resist-ance to potato leafroll virus (PLR V) and the factors affecting this resist- ance. A system based on inoculating potato plants with different amounts of PLRV, by means of viruliferous aphids, proved reliable in distinguishing dif- ferent levels of resistance to infection among potato cultivars. Resistance to PLR V multiplication was assayed by determining the concentration of the vi- rus in graft-inoculated plants such as clones B71-240.2 and BR63.76. Studies to determine the factors affecting a plant's resistance to PLRV infection indi- cated that resistance to infection in clones was reduced dramatically in plants previously infected with potato viruses X or Y (PYX, PVY); whereas infection with potato virus S (PVS) had no effect . This interaction seems to explain the loss of resistance observed in resistant clones tested under field conditions. Differences among PLRV strains appear to be identifiable by using Solanum spp. as differential hosts. ELISA kits have been used successfully in several countries for diagnosing viruses. Detection of potato spindle tuber viroid (PSTV) by nucleic acid spot hybridization (NASH) has been adopted at CIP. A kit to test for PSTV in the regions has been developed and distributed to several developing countries. Extensive field-testing for PLRV virus resistance was done in Uruguay, Brazil, and Argentina by national institutions in collaboration with CIP. In a joint project with the national potato program of Tunisia, CIP scientists are studying an apparent inefficiency of aphid vectors to transmit PLRV and PVY in the field . Crystal-like structures of PLRV particles in the cytoplasm of aphid tracheal cells. 63 RESISTANCE TO VIRUSES Levels of genetic resistance to potato leaf- roll virus (PLRV) infection in clones. For many years the development of potato genotypes with high levels of resistance to PLRV has been attempted with little success. Two of the main difficulties ex- perienced have been lack of knowledge on the levels of resistance available in the sources used and little information on the mechanism of this resistance. Resistance to infection is the only type of resistance reported for PLRV, which is normally determined under field conditions. Plants having this type of resistance are not easi- ly infected with PLRV; however, once in- fected , the virus multiplies and reaches high concentrations in the plant tissue. To determine the nature and stability of resistance to infection, we had to care- fully control the conditions for virus ac- quisition by aphids and inoculation of the plant. To ensure that all aphids acquired a uniform "load" of PLRV, apterous aphids were given access to the virus-infected plants at a temperature of 22° ± 2° C for three days. Virus infection and multiplication was allowed to proceed in a growth chamber at 20° C for 16 hours in light (7000 lux) and at 16° C for 8 hours in the dark. To eliminate the possible occurrence of re- sistance to aphids in the plants being in- oculated, we observed aphid behavior and counted them several times for up to 72 hours after the access period . The different levels of resistance to PLRV infection were examined in a select- ed group of 16 clones inoculated with the virus by using 5, 25, and 50 viruliferous aphids per plant. Infection was later de- termined by the enzyme-linked immuno- sorbent assay (ELISA) and by grafting in- oculated plants onto indicator hosts. The levels of resistance to infection with PLRV were determined by the number of virulif- 64 erous aphids required to infect the clones. Mariva, Serrana, Pentland Crown, Edith, and BR63. l 5 were not infected with the largest number of aphids (50) used, sug- gesting the existence of even higher levels of resistance. In experiments to further discriminate higher levels of resistance , we inoculated Mariva and Serrana with 75 , 100, and 125 viruliferous aphids per plant. Mariva showed a higher level of resistance than Serrana, which is well known for its re- sistance to PLRV. Additional studies are in progress to assess the level of resistance in varieties already identified as being re- sistant. The use of different numbers of viruliferous aphids as a way of inoculat- ing plants with different concentrations of virus inoculum has yielded consistent results. Factors affecting resistance to PLRV infection. In spite of their high level of resistance to PLR V infection in green- house tests, Mariva, Serrana, and Pent- land Crown become infected with PLRV within a few years in the field . Several factors were studied to determine the inconsistent performance between plants grown in the greenhouse and field. Pota- to viruses X, Y, and S (PYX, PVY, and PVS) were almost always found in Mariva plants infected with PLRV. Several ex- periments investigated the interactions be- tween these viruses and PLRV in cultivars having resistance to infection. In one ex- periment, healthy plants of Mariva and Pentland Crown were infected with PYX, PVY, or PVS before their level of resist- ance to PLRV infection was determined . The results showed that pre-infection of plants with PYX and PVY lowers their resistance to infection (Table 1). Simi- lar results were obtained with the PLRV- resistant vars. Edith and Hualash. Pre- infection with PVS did not alter the level of resistance to PLRV infection of the Table 1. Percentage of potato leafroll virus (PLRV) infection in selected clones uninfected and infected with potato viruses X, Y, and S. No. of aphids/plant Level of resistance Clone+ viru s 5 25 50 to PLRVa Mariva Uninfected 0 0 0 R + PVX 0 40 MR + PVY 40 60 s +PVS 0 0 R Pentland Crown Uninfected 0 0 0 R + PVX 40 60 s + PVS 0 0 R a R =resistant; MR= moderately resistant; S =susceptible. four varieties. To our knowledge, this is the first time that an interaction of this nature has been reported for the potato or any other plant species. It seems to ex- plain why resistant clones become suscep- A405 x10 300 200 100 tible to PLRV within a few years under field conditions. Investigation on the nature of resist- ance to multiplication of PLRV. Previous studies, reported in 1983, have shown the possible existence of another type of re- sistance, which was tentatively called " re- sistance to multiplication." To determine the resistance to multiplication in clones, we side-grafted plants with PLRV-infected scions, and two weeks later the tops of inoculated plants were excised one centi- meter above the graft union and grown in flasks containing distilled water. At week- ly intervals, virus concentration was deter- mined by ELISA serology. The results indicated that the maxi- mum concentration of PLRV varied in the clones tested. Three to four weeks af- ter inoculation, a susceptible clone such as DT0-2 attained a maximum concentra- tion at least four times higher than that in the resistant clones B7 l-240.2 (Fig. 1) and DT0-2 ·--------871 -240 .2 ·-------Healthy controls T !----=====Q=========0 ~ o L-J~~~2L-~~~~~~--1.3~~~~~~~~4~~~~~~~--'5 Weeks after inoculation Figure 1. Concentration of potato leafroll virus (PLRV) in graft-inoculated plants of DT0-2 (susceptible) and 871-240.2 (resistant) at weekly intervals . 65 BR63. 76. The behavior of B7 l-240.2 and BR63.76 as a virus source of inoculum is being evaluated under field conditions. VARIABILITY STUDIES ON THE MOST IMPORT ANT POTATO VIRUSES Variability of PLRV. One of the main reasons to investigate the possible varia- tion of viruses is to assure that genetic resistance will not be overcome by natu- rally occurring strains of PLRV isolates. In previous years, 129 PLRV isolates were collected in Peru and compared serolog- ically and by their reaction on selected host species. Serological variation among the isolates was not large enough to de- fine strains ; however, three groups could be distinguished by their reaction on Phy- salis fl.oridana . The low level of serolog- ical variation among PLRV isolates was confirmed by using polyclonal and mono- clonal antibodies to PLRV through a re- search contract with the Federal Agricul- tural Research Station , Changins, Nyon, Switzerland. At CIP, isolate 01 from cv. Ticahuasi, isolate 10 from a wild Solanum species, isolate 29 from Solanum tuberosum ssp. andigena, and a Chinese isolate from cv. Shuang Feng grown in Shanghai were compared for their infectivity in some hosts. These four isolates produced unre- liable symptoms of varying severity in P. fl.oridana and on potato cultivars. Some differences, however, were obtained when the rate of infection of the four isolates was tested by means of aphids on wild So- lanum spp. (Table 2); S. chomatophilum, S. polytrichon, S. fendleri , S. peloquinia- num, and S. etuberosum showed differen- tial responses in their susceptibility to the four PLRV isolates. Others like S. chan- Table 2. The number of plants of some wild Solanum species infected with potato leafroll virus (PLRV) after inoculation with four PLRV isolates by means of aphids . PLRV isolatea Host 01 10 29 Chinese OCH-13200 (S. chomatophilum) 0 O O 2 OCH-13230 (S. pe/oquinianum) 0 0 4 4 OCH-14124 (S. po/ytrichon) 0 2 5 OCH-13070 (S. etuberosum) 2 O OCH-14196 (S. fend/eri) 4 3 5 O a Number of infected plants out of five. num were infected by all isolates ; whereas S. lycopersicoides, S. ochranthum, S. fer- nandezianum, S. brevidens, S. morellifor- me, and S. limbaniense were not infected by any of the four isolates. This suggests that there is a possibility of developing a set of differential hosts to identify and classify PLR V strains. Variability in PVY. In continuing our serological studies on PVY, we used 19 isolates and strains of PVY from six coun- trie.s and five different Peruvian localities to compare the efficiency of monoclonal and standard polyclonal antibodies to de- tect PVY by ELISA. The monoclonal antibodies were supplied by Dr. P. Gugerli of the Federal Agricultural Research Sta- tion in Switzerland. All isolates in the pyyo, pyyN and pyyc group of strains reacted with both types of antibodies, except pyyc_Arran, which reacted only with polyclonal antibodies. Background values, due to nonspecific reactions ex- amined 24 hours after enzyme substrate was added to the microtiter plates, were lower with monoclonal antibodies. The cayense, S. mochicense , S. medians x2, • high sensitivity and specificity of mono- s. violaceinarmoratum, and S. bulbocasta- clonal antibodies makes them more suit- 66 1 2 Figure 2. Separation of plasmid DNA extracted from Escherichia coli by isopycnic centrifugation in Cs Cl gradients. ( 1) E. coli chro- mosomal DNA, (2) plasmid DNA. In gradient (A), plasmid DNA con- tains monomer forms, whereas in (8), dimer forms of PSTVcDNA are shown. able than polyclonal for detection of PVY in potato. Four potyviruses isolated from the potato did not react significantly with any of the two types of antibodies. The possible natural existence of PYX and PYY strains that could break the im- munity present in some clones was stud- ied during two seasons in Lima and Huan- cayo. Clones having immunity to PYY and PYX were not infected, indicating that resistance-breaking isolates are not common and that the stability of this type of resistance is guaranteed. TECHNIQUES FOR DIAGNOSING YIROID AND VIRUS INFECTIONS Nucleic acid spot hybridization {NASH). Purification of plasmid pYC9, containing monomer and dimer forms of DNA com- plementary to potato spindle tuber vi- roid RNA {PSTY cDNA), was improved by using the boiling lysis procedure. Af- ter two isopycnic centrifugations in CsCl gradients, as much as 500 µg of pure PSTYcDNA was recovered {Fig. 2). Stud- ies directed toward replacing the radio- active label (32P) by an enzyme were 67 unsuccessful. Nonspecific reactions oc- curred in all experiments in which a biotynilated , enzyme-labeled PSTVcDNA probe was used to detect PSTV. Because neither monomeric nor polymeric forms of alkaline phosphatase were satisfactory for labeling the cDNA, efforts were di- rected toward developing methods for routine detection of PSTV by radioactive probes, which could be used at CIP head- quarters and in the regions . A small laboratory has been set up for this type of work, and because 32p is not available in Peru, hybridizations have been scheduled every 30 to 45 days using radioactive label imported from the United States. This laboratory will per- mit us to carry out sensitive detection of PSTV and to also do experiments on the control of this troublesome viroid. More- over, the technology developed for viroid diagnosis can also be used to diagnose vi- rus infections in situations where immu- nological techniques may not be adequate. Based on the principles used to develop ELISA kits for virus detection in develop- ing countries, we have now produced a kit for PSTV detection by using the NASH test (Fig. 3). This kit contains a concen- trated sample extraction buffer, nitrocel- lulose membranes to accommodate 100 samples each , and other items. By using this kit , scientists in the regions can mail the samples spotted on membranes to CIP headquarters, where hybridization and autoradiography will be performed and the results sent back to the regions. This kit will be especially valuable for use in Figure 3. Contents of a kit for detecting potato spindle tuber viroid (PSTV) by nucleic acid spot hybridization (NASH) . Included are nitrocellulose membranes protected between two carboard sheets, tweezers, plastic gloves, chemicals for preparing the extraction buffer, and instructions. 68 CIP redistribution centers by eliminating the need for installing costly electropho- resis facilities for detecting PSTV. Alternatives for producing antisera for developing countries. For ten years CIP has been providing antisera to developing countries for research and routine detec- tion of viruses in their seed stock. As the demands increased, CIP implemented two approaches to help national programs procure their own antisera. In the first approach, a country in each of the seven CIP regions is selected to produce virus antisera for other countries in a region. Presently, Brazil (Region II) and Colom- bia (Region I) have each started a project, with CIP's assistance, to produce antisera. Several countries. in other regions are un- der evaluation for this type of work. In the second approach, organizations such as INIP A (Peru) and the country network PRECODEPA (Region II) pro- duce the antisera they require using CIP technology and facilities. A procedure for purification of viruses on a large scale, except PLRV, has been adopted for mass production of antisera. Three basic steps are involved: 1) Clarification of virus ex- tracts such as PVY by chloroform treat- ment followed by incubation in Triton X-100 (detergent). PLRV, however, re- quires a pectinase-cellulase incubation to release virus particles and it is then clari- fied with a chloroform-butanol mixture. 2) Concentration of virus particles by pre- cipitation with 4°/o to 8°/o polyethylene glycol (MW 6-8000). 3) Separation of the virus from host components performed by three cycles of centrifugation in su- crose gradients. As shown in Figure 4, the final virus preparation is completely free of host components and is ready to be in- jected into rabbits to produce a highly specific antiserum. Improvements and simplification of ELISA. During the year, 44 ELISA kits for detection of PLRV and PVY in 600 samples each were sent to several develop- ing countries. Short questionnaires filled in by those using the kits indicated that good-to-fair results were obtained. In on- ly one case did PLRV-lgG lose its activ- ity due to a defective silicone coating of the plastic storage vial. Antibodies (IgG), stored at 4° C for one year, were almost as sensitive as a fresh sample (A405 read- ings for stored and fresh lgG were 1.388 and 1.523, respectively). The enzyme substrate remained active for at least five months at room temperature and for one year at 4° C if stored in the dark in a tightly sealed vial. Studies on recovering the expensive microtiter plates allowed us to develop a system for complete dissociation of coat- ing antibodies and PVY. The results ob- tained after five consecutive dissociations and re-uses, in which positive and nega- tive samples were alternated in the same well, are shown in Table 3. Virus and IgG were completely dissociated from the Table 3. Absorbance values (A405 )a in a micro- titer plate used five times to test samples that were healthy or infected with potato virus Y (PVY) after dissociation with a 10°/o NaOH solution. Dissociation and re-use no. Sample 2 3 4 5 Dissociated plateb PVY 187 111 120 101 76 Healthy 20 12 14 16 14 New plate PVY 113 199 154 100 Healthy 12 16 15 14 a Readings were recorded 30 minutes after wells were filled with the enzyme substrate and are an-average of six replications. bThe same plate was dissociated and re-used suc- cessively five times. Wells containing PVY sam- ples were loaded with healthy samples for the next re-use and vice versa. 69 Relative absorbance 1.0 P, R 0 0.4 0 0.4 0 Top a b c Bottom Figure 4 . Absorbance profiles of a potato virus Y (PVY) preparation in three con- secutive (a, b, and c) 10-40°/o sucrose gradients. The positions in the gradient for phytoferritin (P), ribosomes (R), and virus (V) are indicated . Preparations were centrifuged for one hour at 27 ,000 rpm in a Beckman SW28 rotor . wells, since no reaction occurred with neg- ative samples in previously positive wells . Although there was a reduction in A405 absorbance values for PVY samples com- pared to a new plate , these values are not significant in routine detection. The same procedure can be applied to recover plates from a number of other viruses . In con- junction with the production of antiserum, ELISA can be used effectively to diagnose virus infections in potato programs with limited laboratory facilities . In conjunc- tion with CIP's efforts in implementing antiserum production in developing coun- tries, sensitive serological detection of vi- ruses should no longer be a problem. 70 Efforts to increase the sensitivity of ELISA to detect viruses were continued during 1984. The use of Mcllvine's citric acid pH 7 .0 increased sensitivity by 30°1o over the standard phosphate buffered sa- line (PBS). Identification of other virus diseases. Alfalfa mosaic virus (AMY) was identified from potato plants showing calico symp- toms in the highlands of Peru. Of the plants inoculated with AMY, severe mot- tle and mosaic symptoms developed in plants of cvs. Renacimiento, Huagalina, Maria Tropical, Serrana, Bolona, and the clone DT0-33, but only mild mosaic or symptomless infection occurred in plants Figure 5 . Location and damage caused by potato leafroll virus (PLRV) in potato tissue : A. General view of phloem and ph loem parenchyma tissue showing electron-dense areas, aggrega- tion of virus particles (V), and degraded chloroplasts (C) . B and C. Sections through phloem cells showing loose virus particles and aggregates, and distortion of cell walls (Ca). D. Virus particles from a purified preparation. 7 1 of cvs. Kennebec, Chata Blanca, Radosa , and Molinera . This virus was seed-borne in Nicandra physalodes ( 43 °lo) and Nico- tiana glutinosa (36°/o ) . Seed transmission in the potato is being investigated. A potexvirus (PYX-type), code-named GUA-2, was found during a survey in Gua- temala in potato plants showing severe mosaic symptoms. This virus did not re- act with latex PVX antiserum and showed only a low reaction with PVX in ELISA. The virus has a widespread distribution in Costa Rica and Mexico and seems to be one of the most widely disseminated vi- ruses in Central America. An antiserum is being produced at CIP and the relation- ship of GUA-2 to other PVX strains is under study. In an attempt to understand the rela- tionships between hosts and viruses , we examined PVX, PVY, PLRV, PVS, APMV, and APL V in thin tissue sections by elec- tron microscopy. The results showed that each virus was associated with a partic- ular type of leaf tissue and produced specific virus inclusions or characteristic host structures. For instance, PLRV was limited only to phloem parenchyma cells where virus particles could be found loosely aggregated (Fig. 5). Andean po- tato latent virus (APLV), however , was found mainly in epidermal and mesophyl cells; it was located inside and outside the nucleus and caused vesicles in chloro- plast membranes, characteristic of infec- tion with tymoviruses. TESTING FOR VIRUS RESISTANCE Clones were tested against PLRV in three cooperative projects with national potato programs in Uruguay , Brazil , and Argen- Figure 6 . Testing clonal material for PLRV resistance by means of ELISA. A. Extracting sap from a tuber using an automatic borer. B. The diluted sap is being placed in the well of the ELISA plate . 72 tina. The first trial was planted in Uru- guay during the fall in 1984. A total of 118 test clones and 23 resistant and sus- ceptible cultivars were used as controls. In Brazil, 21 of the 48 clones selected pre- viously in 1983 were again planted and ex- posed to PLRV infection. Clones selected in early tests prior to 1983 were exposed to field infection of PLRV for the fifth season. Eleven of these clones were se- lected for good agronomic characteristics and adequate levels of resistance. Three of these are presumed tolerant to PLRV as they have shown no symptoms and only reacted very weakly with PLRV antiserum in ELISA (Fig. 6). The 11 clones are now being cleaned of viruses by CNPH/EMBRAPA for subsequent fur- ther commercial multiplication in Brazil. The epidemiology of PLRV and PVY in Tunisia is being studied by a joint CIP- INRAT project to correlate aphid popula- tions and virus spread. Surprisingly, field inspections of the potato crop have shown that virus infection has remained low in spite of buildup of the most important aphid vectors. This indicates that at least two consecutive multiplications of im- ported European seed can be made with- out significant decline in seed quality. The explanation for the apparent ineffi- ciency of aphid vectors to transmit virus diseases is being studied by CIP scientists. TRAINING CIP has continued its assistance to coun- tries with their own seed tuber produc- tion schemes and to those who are in the process of establishing these programs. Pathologists and other scientists have been trained in the detection of virus diseases by serological methods, as well as in other virological techniques such as electropho- retic identification of PSTV. During the year, six visiting scientists from South America, three from Asia, and one from Africa came to Lima for a total of 42 weeks' training. 73 / • THRUST V Integrated Pest Management Fallowing mass seedling screening, 21 families from the 1984 breeding cycle were found resistant to Globodera pallida pathotype P 4 A, 66 to P5 A, and 84 had combined resistance to both pathotypes. Results of the national potato program of INIAP, Ecuador , showed a significant reduction of G. pallida P 4 A multiplication rate when using CIP's advanced clones. Two clones showed significantly higher yields than the local cultivar Gabriela. In screening trials for resistance to Meloidogyne incognita, 17°/o of progenies from crosses with a resistant diploid parent segregated as resistant. In ultrastructural and biochemical studies, the eggshell of M. incognita appeared to be simple in structure , while that of Nacobbus aberrans was complex. The complex eggshell structure of N aberrans contributes to its ability to withstand desiccation and to resist penetration by parasitic fungi . Exopathic compounds produced by P. lilacinus and isolated from a dextrose culture filtrate stimulated G. pallida eggs to hatch, while a hyphal extract of Penicillium anatolicum reduced hatching. Of 1820 clones tested for resistance to potato tuber moth (PTM), Phthori- maea operculella, 53 were selected and will be intercrossed to increase the frequency of resistance. In a separate study in Colombia, the clone Parda Pastusa caused a four-day delay in PTM pupation, while pupation on clone Criolla occurred four days earlier than on other clones. In diffused-light stores, PTM was controlled by Phenthoate dust or chopped, dried leaves of Lantana, Minthostachys, and Eucalyptus used singly or in a 1:1:1 mixture. Unpurified PTM sex pheromone was as effective in controlling PTM in stores as purified preparations, thus reducing cost of control. In the control of leaf- miner fly , Liriomyza huidobrensis, light green or yellow sticky traps were highly effective in monitoring populations. Soil solarization was comparable with Phenamiphos and Dazomet in con- trolling M. incognita in the greenhouse , seedling nursery , and field. In the field , thirty-day solarization was as effective as a sixty-day treatment, and it also resulted in a highly effective weed control. When soil solarization was combined with the application of P. lilacinus, a more efficient control of M. incognita was observed than when either treatment was used alone. Roots of test plants are examined to determine severity of infection by root-knot nematode. 75 POTATO CYST NEMATODE Screening for resistance. Early and effi- cient selection of segregating progenies resistant to pathotypes P 4 A and P5 A of Globodera pallida was achieved by a mass seedling screening technique. This tech- nique makes use of a modified petri dish test , which includes a single , vigorous, sprout treated with hormones. Intercross- ing of double-resistant clones selected by the petri dish test produced the highest predictability value of resistance to G. pallida (Table 1). In field tests, 10,000 seedlings from the 1983 breeding cycle were trans- planted to the field and evaluated for G. pallida resistance. From 94 families , clones 280174.4, 280236 .6, 280189 .l, 286090.l 0, and 280240.11 were found to be the best combiners, with the lat- ter two producing excellent progenies in terms of tuber shape and yield. A total of 257 families , from the 1984 breeding cycle, were tested by mass screening. Twenty-one families were re- sistant to P4 A, 66 to P5 A, and 84 had combined resistance. Clones selected from six breeding cy- cles during 1975-1980 were pot-tested for resistance to P 4 A; the sixth cycle showed a significant improvement in resistance. Recurrent selection and the use of resist- ant clones from the Foundation for Agri- cultural Plant Breeding, Netherlands , were important factors in achieving high levels of resistance (Pf/Pi= 0.27). Variability of potato cyst nematode populations. The P5 A pathotype of G. pallida is suspected of being the only pathotype present in the Andean region of northern Peru. Twenty populations of this pathotype were collected from three main potato-growing areas of northern Peru (Otuzco , Huamachuco , and Santiago de Chuco) . The populations were identi- fied as G. pallida by female color changes, morphometrics of second-stage juveniles and cysts, and their multiplication on CIP and European standard clones. A greater variability was found among the populations when their multiplication rate on CIP clones was compared with that on European standard clones. This differ- ence in variability indicated the presence of a wide spectrum of genes for aggres- siveness. Populations from Huamachuco were the most aggressive (aggressiveness index or a.i . = 82.3-88.2°/o), followed by those of Santiago de Chuco (a.i. = 35 .3- 41.2°1o), and Otuzco (a.i. = 11.8-23.5°/o). The inclusion of CIP clones 280090.10 and 280236 .10, along with standard Table 1. Reaction of the progenies of various families to G/obodera pa/Iida P4 A in a mass seedling screening test. No. families Families tested R* x R P4A, P5A (petri dish test) 25 R* x R P4A, P5A (pot test) 24 R* x R P4A (pot test) 24 R* x R P5A (pot test) 24 R* x S 32 SxS 2 *Female parents selected as resistant to P4 A and P5A by the petri dish test. R =resistant; S =susceptible. 76 No. females / tray 57 .5 84.6 76.5 88.6 255.0 900.0 Table 2 . The average multiplication rate (Pf/Pi) of four G/obodera pa/Iida P4 A populations on 26 CIP clones determined at four sites in Ecuador. Sites and populations Sta . Catalina Pillaro Sabaiiag Chutan Bajo Clones population population population population x 26 clones 0 .29 Gabriela (control) 6.6 Data provided by INIAP, Ecuador. differentials, confirmed the genetic varia- bility within the P5 A pathotype. Use of resistant material. Clones were tested in three geographical locations of Peru to compare their reaction to G. pal- lida. Seventy percent of the clones tested were resistant to P 4 A in the central and P5 A in the northern highlands, while 85°/o were resistant to P 4 A in the south- ern highlands. A field trial of eight CIP advanced clones was carried out in collaboration with the national program of INIAP, Ecuador, to compare G. pallida multipli- cation rates. The results showed a signif- icant reduction in the Pf/Pi of the test clones (avg Pf/Pi= 0.25) in comparison to the local cv. Gabriela, which had a Pf/Pi of 2.5. The multiplication rate of G. pa/- Iida on 26 clones was determined in four field sites in Ecuador. The mean multipli- cation rate on the 26 clones was consis- tently less in all sites when compared with the multiplication rate on the control cv. Gabriela (Table 2). ROOT-KNOT NEMATODE Clones with desirable agronomic traits and resistance to Meloidogyne ( 4 major species and 8 races) were tested for their reaction to M. incognita, along with prog- enies of crosses from tropically adapted clones. Only a few clones and progenies 0 .27 0.22 0.13 6.90 16.30 4.15 had a high degree of resistance to M. in- cognita. Further screening tests were carried out with new material derived from 4x- 2x crosses in which wild species were used as a source of resistance (see Thrust II). The results of these tests indicated that segre- gation of resistant genotypes from fami- lies with at least one resistant parent was significantly higher than the susceptible check (Table 3). This finding showed clearly that resistance of wild diploid spe- cies can be transmitted to cultivated tetra- ploid genetic material, and that highly re- sistant genotypes can be readily selected. BIOLOGICAL, CHEMICAL, AND CULTURAL CONTROL OF NEMATODES In Burundi, biological control of root- knot nematode (Meloidogyne incognita) by the fungus Paecilomyces lilacinus was compared with five common nematicides and an untreated control. At 35 days, the Paecilomyces-treated plants were more vigorous and had 50°/o less nematode- infected hills as compared with the un- treated control. The results from replica- tions were very irregular due to the severe drought in East Africa and experiments will be repeated in 1985. Control by solarization. Soil solariza- tion under greenhouse conditions was as 77 Table 3. Levels of resistance to root-knot nematodes in 4x seedling families derived from 4x-2x crosses. Root galling indexa Pedigree 2 3 4 5 Mean* Atzimba x bulk 2x (R) 0 3 3 0 0 2.5 a Unzen x bulk 2x (R) 3 0 8 1 0 2.6 a DT0-2 x bulk 2x (R) 1 3 10 3 0 2.9 ab BR-63.74 x bulk 2x (R) 0 10 1 0 3.0 ab DT0-33 x bulk 2x (R) 0 14 3 0 3.1 ab L T-1 x bulk 2x (R) 0 1 5 5 0 3.4 b Atzimba x lvP 35 (S) 0 0 12 30 14 4.0 c DT0-2 x 378916.13 (S) 0 0 6 26 22 4.3 d a 1 (highly resistant) to 5 (highly susceptible). •Means followed by the same letter are not significantly different at the 50/0 level . effective as the nematicide Phenamiphos in controlling M. incognita on seedling tu- bers and true potato seed (TPS). In TPS nursery trials, there were no differences between the efficiency of Phenamiphos, Dazomet, and solarization to control M. incognita; however, a 60-day solarization was superior to that of 30 days (Fig. 1 ) . Under field conditions at San Ramon, plants in solarized-treated (30 days) and Dazomet-treated plots had less M. incog- Phenamiphos Dazomet 60-day solarization 30-day solarization Control 2 nita infection than those in untreated plots, and both treatments were equally effective in controlling weeds. In Yurima- guas, both treatments were used to con- trol weeds in experimental plots and had results similar to those in San Ramon. In San Ramon , the combination of soil solarization and P. lilacinus was found to be the most efficient method in con- trolling M. incognita in a seedling tuber nursery. In the second cropping season , 3 4 Root galling index Figure 1. Results of four treatments to control M. incognita in a seedling tuber nursery, San Ramon . Root galling index: 1 =no galling or nematode reproduc- tion; 5 =severe galling or high nematode reproduction . 78 Table 4. Combination of soil solarization and Paeci/omyces li/acinus for controlling Me/oido- gyne sp . in a seedling tuber nursery,San Ramon. Root galling indexa 1st planting 2nd planting Treatment (May 1984) (Aug 1984) P. lilacinus 4 .3 2.5 30-day solarization 1.9 3.0 P. lilacinus plus 30-day solarization 1.2 1.1 Control 4 .5 3.6 LSD (50/o) 0.9 1.1 a 1 =no galling or nematode multiplication; 5 = severe galling or high nematode multiplication . when no additional treatment of solariza- tion and P. lilacinus was applied , notice- able reduction in the root galling index was found in the plots previously treated by this combination (Table 4) . Further reduction of root galling index in plots previously treated with P. lilacinus indi- cates the long-term effect of the bio- control application. Ultrastructure and biochemistry. Stud- ies on the ultrastructure of eggs of M incognita and Nacobbus aberrans deter- mined the differences in their eggshell composition as it relates to the action of various biocontrol agents. The eggshell of Meloidogyne species appeared to have a simple structure, while the eggshell of N aberrans was notably complex. This com- plex structure may account for the ability of N aberrans to withstand desiccation as well as to resist fast fungal penetra- tion and to limit the adverse effect of exopathic fungal compounds on embryo development. Exopathic compounds produced by the fungi P. lilacinus , Gliocladium roseum, and Trichocladium asperum in culture fil- trates or on their mycelia and extracted in methanol or ether had varying effects on the hatching of G. pallida eggs. Appar- ently, the compounds extracted (in meth- anol and evaporated at 80° C) from the mycelia of these fungi had a stimulatory effect on hatching the eggs. A 3°1o dex- trose culture filtrate of P. lilacinus stimu- lated hatching, while a hyphal extract (ex- tracted in methanol) of the fungus Peni- cillium anatolicum reduced hatching. POTATO TUBER MOTH Screening for resistance. More than 1800 clones were screened for resistance to potato tuber moth (PIM), Phthorimaea operculella, in both laboratory and field under high PIM-population pressure in Lima. In one test, 38 of 900 clones were selected for future trials. In another trial, consisting of one field and two laboratory tests, 15 of 920 clones were selected. All selected clones will be intercrossed to in- crease the frequency of PIM resistance . In a cage isolation study in Lima, clone F743.4 from Cornell University was found to have a high density of glandular trichomes, which may have contributed to the high level of nonpreference for PIM oviposition in this clone. Out of 20 clones tested in Colombia for PIM pupa- tion, one clone, Parda Pastusa, caused a four-day delay in pupation; while pupa- tion on clone 4751 (Criolla) was four days earlier than on other clones. Field control with pheromones. In col- laboration with Imperial Industries, U.K., a PIM sex pheromone has been formu- lated as a microencapsulated spray. Trials using this spray conducted by the Tropi- cal Development Research Institute , U.K., indicated that 80°/o of the pheromone persisted on test plants for 24 days under shaded conditions and 3°/o under non- shaded conditions. In field-trapping stud- ies in Lima, plastic vials impregnated with purified PIM 1 (0.4 mg) plus PIM 2 (0.6 79 mg) gave the highest trap capture (7 male PTM /day). A 2: 3 ratio mixture of the unpurified PTM 1 and PTM 2 at 2.5 mg loading per dispenser was as effective as the purified pheromone mixture at 1 mg loading. The use of the unpurified phero- mone mixture would reduce costs for po- tato growers in developing countries. A joint CIP-Ministry of Agriculture team in Egypt is studying the population dynamics of PTM in the central area of the Nile delta. A series of water traps baited with PTM sex pheromones were placed at several potato-growing sites in the delta. The number of male moths started to build up rapidly during the first week of May, nearly three weeks earlier than in Tunisia, another site representative of north African potato-growing conditions. Control of PTM in the field was studied by applying the insecticide Profenofos at specific periods during the season on a crop planted in mid-February. The first treatment was applied at four weeks af- ter planting. No significant yield response was recorded until the treatment was ap- plied ten weeks after plant emergence. This timing correlated closely with the maximum catches reported in the phero- mone traps. In Tunisia, populations of PIM were monitored with pheromone-baited water traps in two potato-growing areas. At the site in Saida, located in a minor produc- tion area , there were lower PTM popula- tions than at Bory-el-Amri, located 2 km away in a major production area. At Saida, however, the male moth catches continued to increase even after the crop was harvested at Bory-el-Amri, indicating that adult moth migration was important at least over a distance of 1 to 2 km. These initial studies showed that in this area of Tunisia, there were three weeks between mid-May and early June when tu- ber bulking ceased and PTM population 80 was low. Potatoes harvested during this period had a low initial infestation in the field, thus losses in stores were reduced. National scientists in Morocco have also been using pheromone traps to monitor PIM in the field. The first results have indicated that the epidemiology of male PIM populations is similar to the situa- tion in Tunisia. Studies on the field control of PTM with sex pheromones in Colombia indi- cated that the combination of sex phero- mones and water traps was superior to that of dry funnel traps with pheromones in capturing PTM males. In other field experiments , utilizing microencapsulated formulation of PTM sex pheromone , 50°/o mating disruption was observed and the damage by PIM was reduced significantly. Control in stores. Mechanical barriers to prevent moth entry in rustic stores, coupled with the use of pheromone traps, were tested in Tunisia to control PTM in- festation; however, neither measure was particularly effective in controlling the rate of PIM increase in stores. This con- trasts with results in Egypt, where me- chanical barriers proved to be effective in traditional stores. Possibly , the differ- ences in store construction or initial tuber infestation were determining factors. In Peru, tuber moth Symmetrischema plaesiosema was efficiently controlled in diffused-light stores in Huancayo when tubers were dusted with Phenthoate at 3 g/ton prior to storage and covered with the insect-repellent weed Lantana. In San Ramon, P. operculella populations were high in dry stores, but when tubers were treated with Phenthoate dust prior to storage and at sprouting, moths were con- trolled effectively. Good control was also obtained by using either chopped and dried Lantana sp., Minthostachys sp., Eucalyptus sp., or a mixture of all three (Table 5). Table 5. Effect of insect-repellent weeds (dried and chopped) to control potato tuber moth (PTM), Phthorimaea opercu/el/a, damage in stores. San Ramon, 1984. Tubers Sprouts rotten damaged Holes/tuber Treatment (O/o) (O/o) (xl Flesh damagea Lantana sp . 7.5 12 .3 0.4 Minthostachvs sp. 9 .0 9.3 0.5 Eucalyptus sp . 6 .0 13.8 0 .5 Mix (1:1 :1) of3weeds 9 .5 8 .8 0.8 Control 85 .0 62.3 5 .7 4 LSD (5°/o) 23.4 22.6 2 .7 a Area mined by PTM larvae in cut tubers : 1 = 0-1 /8; 2=1 /8-1 /4; 3=1 /4-1 /2; 4=1 /2 and above. LEAFMINER FLY Tests were conducted to determine the relationship between leafminer fly (Lirio- myza huidobrensis) population and dam- age and fly capture on sticky traps. There was a significant correlation between feed- ing punctures on terminal leaflets and the number of adult flies (r=0.73). There was also a significant correlation between larval infestation in foliage and the num- ber of adults captured on light green or yellow sticky traps (r = 0.90). The data confirmed that sticky traps can be use- ful tools in monitoring L. huidobrensis populations. In control studies , plots treated with Decis 0.2°/o plus Vydate 0.4°/o applied every 10 days from 35 days after emer- gence were compared with plots where light green and yellow sticky traps were used . The leafminer fly population was slightly higher in plots with traps; how- ever, there were no significant differences in yields in plots treated with insecticides or sticky traps. This finding suggests that either treatment could be used effectively in controlling this insect. TRAINING Two training activities, a nematology workshop in Panama and a potato tuber moth course at headquarters, were held during the year. The 13 scientists from Central and South America who attended the Nematology Follow-Up Workshop had been previously trained at CIP in the 1982 course or through individualized training. They reviewed the progress made by their research programs as a result of a stan- dard methodology adopted at the 1982 course and developed new projects on Globodera , Nacobbus, and Meloidogyne . CIP's first International Course on Po- tato Tuber Moth , attended by seven par- ticipants from South America and Asia, focused on the biology of this major pest and its control in diffused-light stores and the field. An important subject in the course was innovative methods for the in- tegrated control of PTM in diffused-light stores, especially the use of weed species as repellents and physical barriers. This type of low-cost technology is highly ap- propriate for small-scale farmers in many developing countries. 81 THRUST VI Warm Climate Potato Production Agronomic practices suited to warm climate potato production remain a high priority. Physiological studies provide the essential background for improved adaptation of the potato to warm climates. Planting on cool side of ridges, although giving an initial benefit in terms of emergence, light intercep- tion, and tuber yields, did not improve final tuber yield. When planting posi- tion was studied in the presence or absence of mulch, planting on warm side of ridges in combination with mulch led to the greatest yields. Due to wet field conditions at Yurimaguas and San Ramon after planting, shallow planting (2 cm) or planting in ridges or beds resulted in improved yields, compared to deeper (7 or 15 cm) planting, planting on the flat, or in furrows. Studies on the role of potato in cropping systems suggested that potato can be planted simultaneously with maize at a ratio of 9: 1, leading to efficient use of radiation and a land equivalent ratio of 1.64. Bacterial wilt incidence was reduced in Yurimaguas following either a rice -maize or Brachiaria sp. (pasture) cropping sequei:ice, particularly after two years without potato; how- ever, the bacterial population increased with two years of natural vegetation. With respect to selection of clones adapted to heat, further improvement in heat tolerance is necessary as is the efficiency of light interception. Rarely more than 50°/o of available light energy over a season is intercepted by the crop. To date, application of growth hormones has not improved heat toler- ance or light interception. High glycoalkaloid values (>20 mg/100 g fresh weight) have been recorded under severe temperature and water stress. In clonal and agronomic field evaluations, yields were obtained at a coastal site in Kenya of up to 26 t/ha with acceptable dry matter content and good cooking quality. Similarly, in the Philippines, a heat-tolerant clone gave yields in two trials at Canlubang of 34 and 38 t/ha in 90 days with a specific gravity of 1.07. In Mindanao, two clones with Solanum phureja in their parentage were selected for good yield and superior bacterial wilt resistance . Three clones selected from CIP introductions now occupy 100°/o of the cultivated area at Dalat, Vietnam. Lowland variety trials were conducted by national scientists in ten countries of Southeast Asia with seed supplied by an Austral- ian contract. Clone B71-240.2 had the best overall attributes, including adap- tation to higher altitudes, and will be a potential variety for Asia and Africa. Harvest of clone B71-240.2 at San Ramon. 83 AGRONOMIC PRACTICES FOR WARM CLIMATES Emphasis has continued on identifying agronomic techniques that are favorable for potato growth and yield in warm cli- mates. Crop protection and combining insecticidal and cultural techniques are of increasing importance, as well as the ex- perimental data on alternatives to the use of tuber seed as planting material. Mulching and row orientation. Earlier work at Yurimaguas (lat. 6° S) has shown that planting on the cool side of rows, orientated east-to-west, improved plant emergence and tuber yield. Similar ex- periments comparing various row orien- tations and planting positions within the row were run at San Ramon and repeated again at Yurimaguas in 1984. Positioning of tubers on the south (cool) side of east- to -west orientated rows resulted in the fastest initial emergence . Although crop cover and total radiation intercep- tion (381.6 vs. 296.0 MJ/m2 ) were mar- ginally improved in the treatment leading to fastest initial emergence , no difference in yield was evident at harvest between the treatments. In a further experiment at San Ra- mon during the dry season, mulch was in- cluded as an additional treatment. Since this experiment was planted on a south- facing slope, soil heating per se was min- imized. Nevertheless , mulch significantly improved tuber yield , due mainly to im- proved light interception (412 .8 vs. 348.6 MJ /m2 ). Mulch also modified the crop's response to planting position in the row: yields on the warmer side (N of E-to-W rows) with mulch reached 460 g/m2 tu- ber dry weight; whereas in all treatments without mulch, yields did not exceed 330 g/m2 tuber dry weight . Mulch re- duced the temperature differential be- tween north- and south-facing sides of the row ; however, light interception later was 84 greater on the north , sun-orientated side of east-to-west rows , which contributed to greater yields . In Vietnam, lack of adequate irrigation is the major constraint to further yield increases. The use of mulch can partially compensate by conservation of soil mois- ture . In Bangladesh, results of mulching ex- periments carried out by the Bangladesh Agricultural Research Institute indicated that use of mulch at planting allows the crop to be planted one month earlier than the normal optimum planting date. This measure and other measures such as early sprouting of the tubers can be used in the northern areas of the country to give more flexibility in dates of planting and spread of harvest period , thus helping to maintain the price level for farmers. Form of planting. Four systems of planting were evaluated in San Ramon and Yurimaguas during the dry season : planting on the flat , in beds, on ridges , and in furrows. The furrow method has been used successfully in the free-draining soils of Puttalam, Sri Lanka, to capitalize on the soil moisture provided by surface irrigation. At both sites , however , the rainy sea- son was unusually long and conditions at planting were wet. Emergence and devel- opment, therefore , were favorable in well- drained plots planted in beds or ridges as opposed to those on the flat or in furrows. At San Ramon, improved crop cover and light interception increased tu- ber yield (t/ha) as follows : bed, 25.70; ridges, 26.93 ; flat , 17 .21; furrow, 13.8 (P < 0.01). At Yurimaguas, excessive soil moisture was also detrimental to crop growth and yield. Emergence was reduced due to tuber rotting, and rapid leaching of soil nitrogen led to early yellowing and a reduction in the light use efficien- cy (LUE =the total potato dry weight produced per unit of intercepted light energy) . Under warm, wet conditions, planting in beds or ridges is the most reli- able technique. In areas where rainfall or irrigation is limited, methods to econo- mize on water use by choice of planting in furrows or on the flat may be advisable. Earlier results on planting depth at San Ramon during the dry season indicated an optimum depth at 7 cm. A similar ex- periment run at Yurimaguas (planted at the tail end of the rainy season) compared three depths of planting (2 , 7, or 15 cm) with or without mulch. Light intercep- tion and tuber yield (71 days after plant- ing) were greater at 2 cm than at 7 or 15 cm (6.82 , 5.16, and 2.34 t/ha, respec- tively, P < 0.05). There was no interac- tion between planting depth and mulch. The latter, although marginally improving Light interception (O/o) 100 80 60 40 20 light interception, was itself ineffective in improving yield under the prevailing wet conditions at Yurimaguas. Intercropping. To produce shade later in the season when soil temperature re- duction by mulch is ineffective and to control insect populations, we planted po- tato and maize simultaneously within the same plot in a 9: 1 ratio at San Ramon. The maize was planted in a systematic design that gave minimum clustering and an evenly distributed shade during the lat- ter part of the potato crop. Sole crops of potato and maize were also planted as controls, and all plots were mulched at planting. The development of light inter- ception by the sole potato and potato : maize mixture is presented in Figure 1. Tuber yield was reduced marginally in the intercrop (19 .57 vs. 22.71 t/ha, Days after planting Figure 1. Light interception of sole potato ( 0 ); potato alone in a mixture of po- tato and maize (9 :1 respectively) (•);and the combination of the potato : maize mixed crop !*l. 85 Bacterial wilt (o/o) 80 60 40 20 0 30 A 40 50 60 Days after planting Figure 2. The influence of two years of cropping systems on bacte rial wilt inci- dence in a subsequent potato crop : O =natural weed population; 6 =manual weeding every 20 days ; T =maize : rice cropping sequence; o = Brachiaria de- cumbens (pasture) . P>0.10), with maize yielding about 50°/o of the sole crop (203 vs. 426 g/m2 dry weight grain). The land equivalent ratio (LER) of the intercrop at 1.64 was markedly greater than unity. The LUE tended to be greater in the shaded than in sole potato crop. Tuber percent dry matter was also greater in the intercrop (17.05 vs . 15.72n5 ) , which suggests that LUE is less under saturating levels of so- lar radiation. Similar trends were appar- ent in duplicate experiments in Yurima- guas; however, crop cover and yields were much lower in general. Rotation. The ability to reduce bacte- rial wilt (BW) incidence is a major deter- mining factor for the expansion of potato into warm climates. Results from a rota- 86 tion experiment on highly infested land at Yurimaguas showed that a one-year maize : rice rotation or continuous pasture (Brachiaria spp.) reduced BW incidence. Even further reductions were evident after two years without planting potato (Fig. 2). In contrast, if natural vegetation is maintained for two years, there is an in- crease in BW incidence. Reported obser- vations have indicated that potatoes show little BW symptoms when planted after a sugarcane or paddy rice crop. To validate such reports, a one-hectare rotation exper- iment has been established at Yurimaguas incorporating these gramineous crops. Soil management. Previous reports by the Soils Department of the National Agrarian University in Lima have empha- .. sized the importance of phosphorus avail- ability and uptake. Present studies in collaboration with the University have concentrated on the effect of potassium and soil salt content on tuber yield and on the use of the mycorrhizal fungus Glo- mus fasciculatus in improving phosphorus nutrition. Inoculated rooted cuttings of three clones were transplanted to low fertility conditions in the field and to nursery beds containing the same soil but steril- ized. In the field, plant survival was en- hanced by the presence of G. fascicu- latus, but the yield was not improved significantly; however, in beds, all growth parameters measured were improved by the fungal association. Tuber yield of in- oculated plants in beds was three times greater than the yield of noninoculated plants 45 days after transplanting. In pot experiments, plant growth in- creased when potassium was added up to 240 ppm K 2 0, particularly at low soil- moisture range between 25°/o and 50°1o field capacity. Also, single eye sprouts grown in pots with soil of electrical conductivity ranging from 2.23 to 9.80 mmho/ cm showed yield reductions of 30°/o above 6.16 mmho/cm. Alternatives to tuber seed. There are warm areas in the developing world with PLANT CHARACTERS FOR POTATO ADAPTATION TO WARM CLIMATES Light interception and conversion to dry matter. The efficiency of light intercep- tion, measured as the proportion of light intercepted to that available over the growing season, rarely exceeded 50°/o at Lima (summer), San Ramon, and Yuri- maguas. Within a site, light interception was closely related to the maturity of a clone, the later-maturing clones having a greater efficiency of light interception (e .g., 35.6°1o for early clone DT0-33 vs. 50.5°1o for late clone Mariva). The LUE, as indicated by the relationship between harvest index and total (plant plus tubers) and tuber dry weight efficiencies (Fig. 3), was 30°/o to 50°/o less in the warmer environment of Lima (summer) than in 0 0- x Q) "O 100 80 .~ 60 >- Tuber dry weight efficiency (g/MJI 0.5 1.0 1.5 2.0 2.5 I \ I \ I I I I \ I I I \ I I I \ I I \ \ I I \• \ I I \ I I \ \ I ~- ,, . ' ' I I \ \ I \ e\ I \ I °' \ 90 ' \ ' 0 \ ' \ ' \ ' the potential for potato production; how~ ~ ('. ever, lack or high cost of seed tubers "' I ~ \ \ \ \o \ ' ' ' ' ' may prohibit potato cultivation in these areas. In addition to the use of true seed (see Thrust IX), other alternatives to the use of seed tubers are under study. Rapid multiplication of rooted cuttings originating from in vitro plants or tu- bers has been successful under warm con- ditions. Rooted cuttings have compared favorably alongside TPS in intensive, garden-scale production systems devel- oped for their efficient use of available land space. \ 0 ' ' ' ' ' ' ~ ' ' ' 40 ' ' ' ' >-- ' 0 ' ' ' ' I ...... ....__ 0 0.5 1.5 2 2.5 Total dry weight efficiency (g/MJ) Figure 3. Relationship between the harvest in- dex and the total and tuber dry weight efficien- cies of seven clones grown in Lima (summer) (O) and Huancayo (•). 87 the cooler climate of Huancayo . Within sites, the small variation in LUE among clones was not related to heat tolerance as measured by the ability to tuberize un- der warm conditions. In studies on the LUE and light inter- ception under warm conditions, maximum tuber yields were achieved by clones that reached maximum cover before tuber ini- tiation. Preliminary data suggest that syn- chrony of tuber initiation with maximum cover is the most appropriate growth pat- tern for warm climates. Studies will con- tinue on the relationships between tem- perature and canopy characteristics. Harvest index. The continued parti- tion of assimilates to tubers during the latter part of tuber bulking is essential for high yields. Although clones adapted to warm conditions can tuberize freely un- der such conditions, the harvest index is generally below that of traditional clones in cooler climates. To improve the harvest index, we reduced stem growth by apply- ing the growth retardant Daminozide to the potato crop in San Ramon. The har- vest index was improved, but total dry matter production was reduced , and tu- ber yield was the same in both treated and control plots. Clonal selection. Selection of adapted clones continues at Yurimaguas and San Ramon. CIP clones 377852.1 and Desi- ree x 378015.16 outyielded a group of 360 Dutch and Canadian clones during the summer at Yurimaguas, yielding 250 g/plant in 75 days . During the winter, clones with LT-7 , Maine-40, or Atlantic as one parent performed well, with a no- table absence of growth cracks often asso- ciated with heat stress. One outs tan ding clone of the cross Aphrodite x 378015 .16 yielded 600 g/plant in 75 days during that season. Three additional plant characters that will merit incorporation into CIP's selec- 88 tion program are 1) storability in warm climates, 2) aluminum tolerance , and 3) redu ction in glycoalkaloid content. Trials have been set up to study the temporal stability of various clones produced and stored in succession in warm climates. A method is being developed to screen for aluminum tolerance by using rooted cuttings in a nutrient solution containing aluminum. Rau tine analyses of total gly- coalkaloid levels have indicated values ranging from 9 .31 to 37 .56 mg/ 100 g fresh weight. Further studies to account for the variability in glycoalkaloid levels and tolerance to aluminum are in progress. East Africa. At a lowland coastal site in Kenya, the mean yield of CIP clone 720045 was 26 t/ha compared with 9.2 t/ ha for Desiree, a common variety. Cook- ing quality tests and analyses, carried out by the Ministry of Agriculture Research Station Tigoni , indicated that potatoes from the coastal site had a higher con- centration of reducing sugars than those from the highland trials; however, , mean dry matter content at the coast was ac- ceptable, about 19°/o. Southeast Asia. The potential potato- growing areas of Southeast Asia have warm climates and generally do not ex- ceed 1000 m. Suitable techniques for growing potatoes under these conditions are being studied by CIP scientists in collaboration with public and private or- ganizations in the Philippines. At a sugar estate at Canlubang (sea level) , clone 378597 .1, selected from a heat-tolerant tuber family, gave yields in two trials of 34 and 38 t/ha in 90 days with a specific gravity of 1.07. Clones DT0-28, Spunta, and Desiree had yields of 29, 38, and 31 t/ha , respectively , with a specific gravity of less than 1.06. Cosima, the most wide- ly used variety in the Philippines, yielded 21 t/ha in the same trial. At the Bureau of Plant Industries in Mindanao (900 m), clones 381064 and 381065 were selected for good yield and superior BW resistance. Both of these have Solanum phureja and clone AVRDC 1287.19 in their parentage. To study optimal cultivation practices for mid-elevation and lowland sites, CIP planted a trial at Canlubang in which yields in excess of 20 t/ha were obtained from experiments on 0.5 ha. It was appar- ent that seed from the highlands yielded better than lowland seed stored for nine months in cold storage. In South Vietnam, clones B71-240.2, CFK 69.l , and Atzimba, selected by Viet- namese scientists from CIP introductions, now occupy 100°/o of the cultivated area at Dalat. Clones selected from CIP tuber families bred for highlands and lowlands have, in their pedigree, a DTO parent crossed to one of the three clones men- tioned above . Clones 65-ZA.5 and CGN 69 .1 have also proved to be good parents, appearing in 34 progenies tested since 1982 from which 178 clones have been initially selected. Regional lowland variety trials were conducted by national scientists in ten countries of Southeast Asia. The seed was supplied through a CIP contract with the Plant Research Institute, Victoria, Australia. The most superior clone overall was B71-240.2; other clones and varieties with above-average yields were Sequoia, Red Pontiac, N-565.1, AVRDC 1282.15, and DT0-2. Clone B71-240.2 had the best adaptation and has the greatest po- tential to be named as a variety in many countries. TRAINING The first regional course on Agronomy for the Potato in the Hot Tropics was held in East Java, Indonesia, for research- ers from Asian countries. The course was organized in collaboration with AARD's Malang Research Institute for Food Crops and attended by 26 scientists, 10 of whom where sponsored by the Southeast Asian country network SAPPRAD. During the course , participants were acquainted with agronomic practices suited to potato pro- duction under high temperatures. Experi- ment station and on-farm trials were used to illustrate the physical and biological principles involved and, with this informa- tion, participants planned future research activities suited to their own particular conditions. 89 THRUST VII Cool Climate Potato Production Two populations that combine frost tolerance with desirable agronomic attributes and earliness are being gradually improved to fit two target areas: 1) the Andean highland tropics, and 2) the non-Andean highland tropics and subtropics. Two different populations of seedlings were screened for frost tolerance in a growth chamber at -3°C and -4°C with 10°/o and 15°/o survival, respec- tively. The survivors were transplanted to the field for further multiplication and future testing at high altitudes in Peru . Daylength at subtropical locations may be up to three hours longer than at sites near the equator. A single leaf-node cutting test for tuberization un- der artificial daylength has proved to be effective. The identified clones sub- sequently proved to be adapted to long-day conditions in subtropical lati- tudes. The use of potassium indirectly reduced freezing injury to plants in both laboratory and field tests. Preliminary fertilizer trials have been con- ducted to determine basic levels of fertilizer that would be suitable for acid soils in the Andes that have excessive aluminum saturation. Resistant (left) and susceptible (right) potato seedlings exposed to late blight in the field at Huanuco, Peru (2600 m). 91 BREEDING FOR FROST TOLERANCE AND ADAPT ABILITY The traditional potato-growing areas of most developing countries are generally located at mid and high elevations where the crop is rainfed , or at low elevations where the crop is grown during the cool season under either rainfed or irrigated conditions. Much of the potato produc- tion technology from developed countries is applicable to developing countries with cool climates, particularly to the non- Andean countries. However , there still re- main important research areas where CIP has a comparative advantage for further improving frost tolerance and late blight (LB) resistance , especially for the cool cli- mates of these countries. In tropical and subtropical countries, frost occurs at high altitudes anytime dur- ing the growing season, and in the cool climates of the subtropics during the early or late part of the cropping season. Breeding is therefore directed toward combining frost resistance , earliness, and tuberization response to the effects of long days, particularly those of subtropi- cal latitudes. During 1984, we screened more than 9000 seedlings from crosses between the most advanced clones with frost resist- ance and early maturing clones from a lowland tropic population. Screening was done at - 3° C in a growth chamber with lO°lo seedling survival. Another 12,000 seedlings from intercrosses among the most advanced frost-resistant clones were screened at -4°C with 15°/o survival. Both groups of survivors were trans- planted to the field for further multipli- cation. The clones will be evaluated in the field for frost resistance and desirable agronomic characters, which are priority criteria for final selection. In replicated trials at Usibamba, Peru (3800 m), the field performance of the latest selections for frost resistance , earli- ness (130 days) , and good tuber appear- ance indicated that, although frost inci- dence was not severe (-2° C) , prolonged drought lowered the yields considerably. The selected clones, however, were supe- rior in yield to the local cultivars . At another site , a group of clones from ad- vanced stages of selection with resistance to both frost and LB was evaluated at Huancayo (3200 m) , with a plant density of 27,777 /ha (Table 1). Yields were two- Table 1 . Yield of a sample of advanced clones selected for resistance to frost and late blight in Huancayo, Peru (3200 m) . CIP no. Pedigree Y ield/plant (kg) 379454.1 374069.7 x LB Hyb bulk 3.24 a* 377427.1 1-832 (tub) x 702449 3.15 a 380474.6 376181.5 x LLT XY bk 3.13 ab 380482.1 Monserrate x LL T XY bk 2 .91 ac 380426.1 374068.4 x CN bk 2.90 ad 380446.4 374080.3 x CN bk 2.88 ad Mariva Local cv . 2.56 ad Revolucion Local cv . 1.60 ce CV (O/o) 37 .1 *Means followed by the same letter are not significantly different at the 5<>/o level. 92 ' thirds higher than those at Usibamba, which indicates the yield potential of the material when grown under less severe cli- matic stress. ADAPTATION TO SUBTROPICAL DAYLENGTH In collaboration with the national pota- to program of INIA in Chile , CIP evalu- ated a sample of clones from the highland frost-resistant population under subtrop- ical daylengths in the field at Osorno, Chile (lat. 40° S). Two field experiments were conducted in 1984. The first in- cluded selected clones from five families introduced earlier. These clones were re- evaluated, under subtropical daylengths, for yield performance in a simple 10 x 10 lattice. The results indicated that average yields obtained per family were compar- able to those of local cultivars (Table 2). In the second experiment, a larger sample of clones from 20 families, re- cently introduced, was also evaluated for yield performance in five-hill observation plots, with a plant density of 47 ,619 ha (Fig. 1 ). Results indicated that the yields of these clones adapted to subtropical lat- itudes were equal to or higher than yields of locally adapted cultivars (Table 3). Both clonal samples, before being evalu- ated under subtropical latitudes, were pre- screened for tuberization in Lima under an artificially extended 15-hour day by using a single leaf-node cutting method. It is evident from the results of both ex- periments that populations with frost re- sistance can be preselected under artificial daylengths for their adaptability to natu- ral long days of subtropical latitudes. Distribution of frost-resistant material. CIP distributed 73 tuber families , contain- ing 1889 different individual clones, to five countries for further trials (Table 4). These families had been screened for frost Table 2. Average yields calculated for three characters of selected clones within five families under long days at Osorno, Chile. Marketable Total Marketable yield yield tuber wt Family (g/plant) (g/plant) (g/tuber) 380470 (5)a 719 .8 780.4 88.6 380473 (5) 1112.4 1215.2 95.2 380554 (29) 933.8 1127.7 60 .6 380553 (29) 987.5 1104.3 80.8 380182 (29) 1054.6 1173.6 79 .0 Local control: Yagana 930.0 1050.0 78.0 Mirka 1005.0 1100.0 67.0 Ultimus 965.0 1140.0 71.0 CV (O/o) 20 .7 17 .1 18.7 SD 203.8 190.0 14.0 a Number of clones evaluated within a family. Table 3. Yield of the 10 best clones from 20 frost-resistant families tested under long days at Osorno, Chile. Total yield/plant Clone no. (kg) FH 381135.1 2 .30 FH381125.35 2.27 FH 381123.47 2.30 FH 381130.46 2.08 FH 381132 .89 2.00 FH 381116.84 2.02 FH 381134.85 2 .1 4 FH 381125 .37 2.01 FH 381132.12 1.82 FH 381123.37 2.10 Control: Yagana 1.34 Ultimus 1.23 resistance and they are also segregating for earliness. An additional amount of 400 true potato seeds (TPS) , contained in four families , was sent to the Philippines for evaluation of frost resistance. 93 94 Figure 1 . Tuberization response of a sample of a highland tropic popu- lation to long daylengths in Osorno , Chile (lat. 40°S) . Top : family performance . Middle : yield of a selected clone compared to a local cultivar . Bottom : the most outstanding clone, selected for yield and appearance . Table 4. CIP di stribution of tuber famil ies from advanced clones with combined frost resistance and early maturity, 1984. Country Fami lies Clonesa Brazil 11 113 Turkey 14 276 Pakistan 8 54 Chile 20 902 Bolivia 20 544 Total 73 1889 a Number of clones included in the families sent to each country . INDUCED F ROST RESISTANCE Preliminary results from both laboratory and field tests on the use of potash (K2 0) to contro l fros t damage indicated, at three different levels of potassium (Table 5), that K + ion concentration in the leaves Table 5. Concentration of K+ (ppm) in the leaves of two clones after frost (-4°C) at three levels of potassium . Clone 377427 .1 (R) Rosita (S) K20 supply (kg / ha) 0 100 200 3.3 2.2 4 .2 2.0 4 .7 3 .9 R = res istant; S = susceptible . was higher in frost-resistant than in sus- ceptible clones. This suggests that potas- sium may play a role in reducing plant injury due to freezing temperatures. Lab- oratory and field experiments have been designed to obtain additional information on the role of potassium and its potential to strengthen a plant's ability to with- stand frost injury. In contract research at the National Agrarian University, Lima, an experiment was conducted in the Mantaro Valley, Peru , in a field representative of highland Andean soil to determine basic levels of fertilizer application for the potato. The soil was very acid (pH 4.1 ), high in or- ganic matter, low in available P, medium in K, and had more than 80°/o aluminum saturation . When 4 t/ha of CaC03 was added , tuber yield increased from 7 .7 to 18.4 t/ha , and with 8 t/ha of CaC03 tu- ber yield increased almost twofold (27.4 t/ha) . Increasing the level of P2 0 5 from 160 to 240 kg/ha increased the tuber yield from only 16.7 to 19 .0 t/ha , indi- cating that 160 kg/ha of P2 0 5 would be adequate to obtain satisfactory yields. In- creased levels of K2 0 from 80 to 240 kg/ha did not increase yield, suggesting that 80 kg/ha of K2 0 or less was suffi- cient under the prevailing experimental conditions. 95 THRUST VIII Postharvest Technology Two years of on-farm trials on the storage of consumer potatoes in the Mantaro Valley of Peru have clearly demonstrated the technical advan- tages of both improved storage structures and the application of chemical sprout suppressants. In Peru it is estimated that 40°/o of potatoes produced are stored annually at the farm level for home use and for sale in local mar- kets as a source of income . In East African countries such as Kenya, Malawi, Madagascar, and Tanzania, construction and on-farm testing of consumer stores has received the support of national potato programs. The storage of seed tubers in low-cost diffused-light stores (DLS) has been accepted widely in many potato-producing countries. In the Philippines, it is estimated that 40°/o of all potato farmers now use this technology . Research on DLS has focused on problems associated with seed tubers stored in various environments. Simple methods to break the dormancy of seed tubers have been developed in Rwanda and Burundi. Under the hot summer conditions in Tunisia , long-term storage in DLS requires an interval in cold stores. In Viet- nam , diffused-light stores with a clay tile roof and rustic brick construction proved superior to bamboo structures. Traditional nawalla stores in Egypt have been improved by better ventilation combined with screening to exclude tuber moth and rodents . Seed tubers stored in DLS in Rwanda for four months gave yields significantly greater over seed stored in local traditional stores. In contract research in Scotland, the effect of irradiance levels and tem- perature in suppressing sprouting was investigated. While it is clear that there are varietal differences in sprouting, an irradiance level of about 330 mW m-2 and a wavelength of 5 50 nm (blue light) was effective in sprout suppression. In postharvest pest and disease control, research concentrated on the con- trol of potato tuber moth, the buildup of viruses, and the interaction between Erwinia soft rot and tuber moth infestation. Soil treatment with calcium sul- fate reduced soft rot slightly in storage . Seed tubers stored in DLS were pro- tected from tuber moth infestation by a combined treatment of the insecti- cide Phenthoate together with a covering of insect-repellent weeds . Testing of prototype dried food mixes throughout 1984 continued to show consumer acceptability of the M-6 potato-cereal-legume mixture . This solar- dried product should be nutritionally advantageous and can be produced simply at various scales of operation at a low cost. Peeling potatoes for preparation of dehydrated food mixes. 97 STORAGE OF CONSUMER POT A TOES A second series of six on-farm storage trials was conducted during 1984 in the Mantaro Valley, Peru (3200 m) . During the 1983 trials, consumer potatoes were stored for a fixed six-month period. In these 1984 trials, the farmers determined the storage periods, which ranged from four to six months , with an average of 4.8 months. The monthly storage losses were similar for both trials (Table 1 ). In one six-month storage trial in 1984 with the cv. Mariva (a vigorous sprouter), the sprout inhibitor CIPC, applied as a dust , reduced sprouting losses from 12°/o in undusted treatments to below 0 .2°/o. When dry Muna (Minthostachy s spp .) fo- liage (commonly used by Peruvian farm- ers to control insect damage) was present , sprouting was not reduced (Fig. 1 ). In two farms where moderate levels of tuber spoilage occurred - one due to potato tu- ber moth and the other to a combination of dry and soft rotting - the total level of spoilage was reduced to below 3.0°/o in naturally ventilated 0.5-ton storage boxes kept inside farm buildings. The combined use of CIPC in ventilated storage boxes held storage losses to 1.4°/o per month in both years. While there are technical benefits to be derived from using chemical sprout in- Table 1. Monthly storage losses of consumer potatoes in on-farm trials, Mantaro Valley, Peru. Storage method Traditional Traditional+ CIPC Ventilated box Ventilated box+ CIPC Mean monthly Iossa (O/o) 1983 1984 4.3 3 .7 2.0 1.9 3.3 3.2 1.4 1.4 a 1983 = five trials for a fixed 6-month period; 1984 = six trials with mean storage period of 4.8 months. 98 hibitors on consumer potatoes, their use requires great caution. The persistence of chemical residues in building materials such as adobe and timber requires that sprout inhibitors such as CIPC should not be used in stores that may be used in the future to store seed tubers or seeds of other crops. Such chemicals should only be used in specifically constructed stores or in naturally ventilated storage boxes and should be used in strict accordance with a country's regulations and the man- ufacturer's recommendations. Extensive social science studies in the southern highlands of Peru have clear- ly demonstrated that farmers frequently make no distinction between their meth- od of storing consumer potatoes and seed tubers, which complicates the rationale behind storage practices. For example, within the different highland potato- producing areas of Peru, the seasonal avail- ability of fresh local potatoes and trade in those from coastal harvests makes com- mercial storage risky . Consumer prefer- ence for fresh potatoes and the pressure of credit agencies for farmers to repay production loans by immediate sale of their crops also influence the motivation and practice of storing consumer potatoes for a profit . Because farmers in the south- ern highlands are remote from coastal pro- duction zones and the large Lima market, they store larger quantities of consumer potatoes for commercial profit. CIPC is used in this region to inhibit sprouting. In both the central and southern high- land regions, however, a large propor- tion of stored consumer potatoes are not stored for a commercial profit motive, but for home consumption. The term "home consumption" encompasses a whole range of home uses beyond that of supplying the immediate farm family with potatoes from one harvesting period to the next. It also includes such important activities / Figure 1. In on-farm trials to examine the potential of 500-kg naturally ventilated storage boxes and different storage treatments, the presence of dried foliage of Muna did not prevent excessive sprouting. as weekly sale in the local market, almost irrespective of price , as a means to main- tain a cash flow for the purchase of other foods and household necessities. It is estimated that 500 kg of potatoes per farm are stored to satisfy cash flow needs throughout the year. From the data and additional informa- tion made available by the national po- tato program of INIPA, one can estimate that about 650 ,000 tons of potatoes, or 40°/o of total national production , are stored annually at the farm level for var- ious home uses. Since potatoes are gen- erally stored in less than one ton units, this greatly influences the approach and technologies required to make improve- ments in existing practices. This infor- mation helps to explain why centralized, community, or government storage facili- ties for consumer potatoes have not been fully utilized and why emphasis should be placed on improving individual farm stor- age practices. To better understand storage prac- tices and to define priority research needs within potato production systems, CIP cooperated with national scientists from the PROClPA and PRACIPA country net- works in South America to define major technical problems in existing storage practices for both consumer and seed po- tatoes (Tables 2 and 3). In East Africa , new and appropriate storage technology for consumer pota- toes is being adopted in Kenya, Malawi, Madagascar, and Tanzania. Construction and on-farm testing of consumer and seed stores is underway. In Kenya , the Ru- ral Structures Unit of the Ministry of 99 Table 2. Major problems encountered during storage of consumer potatoes in nine South American countries. Argentina Bolivia Brazil Peru Storage problems Uruguay Venezuela Chile Colombia Ecuador Unsuitable stores x x x x Poor tuber quality x x x x x Sprouting x x x x Tuber moth x x x Andean weevil x x x Erwinia x x x x Fusarium x x x x x Phytophthora x x Table 3. Major problems encountered du ring storage of seed tubers in nine South American countries. Argen- Colom- Vene- Major problems tina Bolivia Brazil Chile bia Ecuado r Peru Uruguay zuela Unsuitable stores x x x Poor seed selection x x x Young seed tubers x x x Old seed tubers Andean weevil x Erwinia x x x Fusarium x x Phytophthora x x x Management of imported seed x x Agriculture has prepared final designs for stores, based on earlier work by CIP spe- cialists in Nairobi. The project in Malawi is supported jointly by the Netherlands Technical Assistance and CIP; while in Madagascar, the Ministry of Agriculture has created a revolving fund to assist farmers in store construction. STORAGE OF SEED TUBERS Research has continued in Sou th America on manipulating the physiological con- dition of seed tubers stored in different 100 x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x environments. Preliminary studies on the physiological condition of seed tubers did not indicate an overall optimum time of desprouting ; the effect of desprouting time on final yield was influenced by the cultivar used and storage and replanting location. Yields were consistently reduced when lengthy transportation of seed tu- bers from storage to planting location was required. The reduction was greatest in tubers with the most developed sprouts , which resulted from early desprouting. Research continues on determining and measuring parameters for evaluating the storage behavior of seed tubers in a col- lection of cultivars selected from CIP's pathogen-tested list. Methods for breaking dormancy. In Rwanda, excellent results for breaking dormancy were obtained when seed tu- bers were buried for two weeks in a straw- lined pit, immediately after harvest , and planted four weeks later. This treatment resulted in 100°/o ground cover five to six weeks earlier than untreated seed tubers and gave 10°/o higher yield. In Burundi, heat shock treatments were used to break dormancy. Seed tu- bers were stored in sacks hanging from the roofs of watchmen's huts, where night temperatures rose to 50° C due to cook- ing fires. The length of treatment varied, but 15 days seemed optimal for breaking dormancy . Forty-two days after harvest, treated tubers developed an average of 4.7 sprouts, whereas those from farmers' normal dark storage had hardly started to sprout. The use of diffused-light stores. In Tu- nisia, seed tubers stored throughout the hot summer in diffused-light stores (DLS) suffered high weight loss and resulted in weak plants. The combination of careful selection of cultivars may permit the use of DLS for 150 days. For longer periods of up to 230 days , an interval in cold stores seems necessary, but this may be decreased if varieties with longer dorman- cy are used. The importance of selecting the appro- priate construction materials for DLS was demonstrated in Vietnam, where stores made of rustic brick and clay tile roofs had superior storage conditions over stores made from bamboo. Higher humidity and slightly cooler temperatures were the main advantages of the improved store. In Egypt, two modified traditional nawallas (seed stores) were built to test their performance for potato storage. Bet- ter ventilation was introduced, and physi- cal harries of fine mesh to exclude potato tuber moth (PTM) and a strong metal screen to keep out rats were both placed over the ventilation holes. These modifi- cations were extremely effective and local growers are showing interest in adopting these changes. Seed tubers stored in the unmodified nawalla and in a DLS built inside a modified nawalla were compared with tubers from a cold store . Although tubers in cold stores had the lowest weight loss of all three treatments, tubers from D LS lost less weight and had stronger, healthier sprouts than those in unmodi- fied nawallas . National scientists in Rwanda evaluat- ed low-cost methods for storing both con- sumer and seed potatoes in which modi- fied traditional designs were used. Seed tubers of the var. Sangema were stored for 3-1/2 months. Total tuber weight loss of 10°/o in the experimental stores was low compared with normal farmer losses. Moreover, seed tubers stored in DLS for four months gave significantly better yields of 6.1 t/ha over seed from tradi- tional stores. Because of the double crop- ping season in Rwanda most farmers prefer to plant with only 2-1/2 months between seasons, thus the advantage from using DLS is not appropriate for such con- ditions. But rural development projects multiplying larger quantities of seed for the national program have adopted DLS to store over 2000 tons of seed annually. The introduction of DLS technology into New Caledonia permits growers to keep their own seed, which up to now has been imported. Yields of over 30 t/ha have been obtained from seed tubers stored in DLS. In the Philippines, it is estimated that 1300 farmers or 40°/o of all potato farmers are now using DLS technology, which was first introduced six years ago. 101 Studies on sprout growth in diffused- light stores. The effect of diffused light on potato sprout growth during storage was investigated in a research contract at the University of Glasgow by providing a framework within which a study of sprouting in a range of locally grown cul- tivars could be assessed. Two tempera- ture regimes were used : I) night - 22° C: day-33°C, and 2) night- I0°C : day- 200 C; and an irradiance range from 330 to 18 mW m- 2 . Sprout growth was inhibited by both high irradiation and the high temperature regime (Table 4) . The opti- mum temperature for sprouting was about 18° C. Significant differences were appar- ent in the cultivar response to irradiance levels and temperature . In the field , emer- gence was earlier from tubers stored under high irradiation. To determine the relationship between the wavelength of light and sprout sup- pression, studies were done at Glasgow on producing an action spectrum for po- tato sprouting. Incandescent lamps and diffraction filters were used to generate a range of narrow wave band light sources covering the 400-750 nm region. The two spectral regions , in which sprout growth was suppressed , were around 710 nm (red) and below 550 nm (blue). Only blue light appeared to cause greening and photo- tropism, and the sprouts that received blue light seemed more vigorous than those receiving red light. CONTROL OF POSTHARVEST PESTS AND DISEASES Research in 1984 concentrated on 1) con- trol of potato tuber moth (PTM) in stores , 2) buildup and dissemination of viruses in stores, and 3) the interaction and control of Erwinia soft rot and PTM in both field and stores. In the Mantaro Valley of Peru, the damage caused by the tuber moth Sym- metrischema plaesiosema in stores is of increasing concern to farmers. The chem- ical insecticide Phenthoate (Cidial) was an effective chemical treatment in stores, resulting in less than 10°/o sprout and tu- ber damage as compared with over 60°/o damage in untreated controls (Fig. 2) . Al- though the use of insect-repellent weeds was not as effective against S. plaesio- sema in Mantaro Valley stores as it was against Phthorimaea operculella (PTM) in San Ramon stores; the weeds reduced both tuber and sprout damage (see Thrust V). Trials on the buildup and dissemination of potato leafroll virus (PLRV) and po- tato virus Y (PVY) in stores in Huancayo (sierra) and lea (coast) concentrated on the control of aphid vectors . A range of cultivars known to differ in their reaction to these two viruses was used. One treat- ment , regular spraying with an antifeedent (neem oil) , caused phytotoxicity and re- sulted in tuber death and rotting. Prelimi- nary results from insect-repellent weed Table 4. Potato sprout growth (mm) during storage at two temperature regimes and four levels of irradiation . Glasgow, Scotland . Cultivars Majestic King Edward Desiree Home Guard 102 Day / night, 200 / 1 oo C Visible irradiance mW m-2 330 133 72 18 61.4 54.7 57 .1 44.9 17.4 28.0 31 .0 38 .8 33.8 46 .6 64 .8 99.7 106 173 237 303 Day /night, 330122oc Visible irradiance mW m-2 330 133 72 18 3.4 19.4 14.2 8 .1 3 .5 15 .6 13.9 5.2 6 .6 14.1 14.7 9.6 6.0 13.5 18.4 15.2 Control • Phenthoate ., .. 70 60 10 0 0 Sprouts damaged (D/o ) II Damaged • Rotten 10 20 30 40 50 Tubers damaged (0 /o) LSD (50/o) 60 70 Figure 2. Effect of the chemical insecticide Phenthoate on tuber moth Symme- trischema plaesiosema damage in stores, Mantaro Valley, Peru . 50 Protected against PTM Desiree { d de Revoluci6n { de de Rosita { 25 Exposed to PTM 0 25 50 Soft rot in tubers (D/o) • No postharvest calcium sulphate • With postharvest calcium sulphate a a 75 100 Bars followed by the same letter are not sign ificantly different at th e 1 D/o level. Figure 3. Effect of protection against potato tuber moth (PTM) infestation and postharvest application of calcium sulphate on the percentage of tuber soft rot in stores. 103 treatments indicated that growing sprouts were only protected from aphids when completely covered with the dried fo liage. The insecticide Tamaron effectively con- trolled the buildup and spread of PLRV but had little effect on PVY. The reac- tion of the cultivars to these two severe vi- ruses appeared to be similar in stores and on the growing plants. Testing of sprout sap by ELISA gave results similar to those obtained from leaves in the field; how- ever, when tuber sap was used for ELISA testing , the results were unsatisfactory. Thus, when field space is unavailable for virus evaluation , tests may be performed using sprout sap. Observation trials were established in the field and stores at San Ramon to re- cord the interaction between PTM dam- age and Erwinia soft rot. During the rainy season, the cv. Desiree showed less visible field symptoms of blackleg and tuber soft rot at harvest than cvs. Rosita and Revolu- ci6n. The application of soil calcium sig- nificantly reduced blackleg and tuber rot in both Desiree and Rosita . In these two cultivars, about 50°/o of the plants in- fected were with E. carotovora pv. caro- tovora and 50°/o with E. chrysanthemi, but in Revoluci6n, a higher percentage (75°1o) of E. chrysanthemi was isolated. At harvest, no tubers were in feste d with PTM , but after six months in DLS during the dry season, all unprotected tubers became infested. No PTM dam- age was found in stored tubers protected by a combination of one application of the insecticide Phenthoate, a covering of the repellent weed Lantana sp. , and sex pheromone traps. A significantly lower incidence of soft rot was found in stored tubers of all three cultivars protected against PTM (Fig. 3). While postharvest application of calcium sulphate did not significantly reduce soft rot (Fig . 3), less rot occurred in stored tubers of the cv. 104 Desiree that had been grown in calcium- treated field plots (Fig . 4). The results demonstrated an interaction between tu- ber soft rot in storage and PTM infesta- tion. The use of calcium sulphate in field applications merits further investigation. POTATO PROCESSING Several prototype food mixes based on potato have been produced at the CIP processing plant in Huancayo as a result of consumer studies and preferences. Test resu lts of the M-6 mixture during 1984 in Peru continued to show good consumer acceptability. M-6 contains 30°/o potato , 14°/o each of rice, oat, barley, and beans , 12°1o maize , and 2°1o sa lt. The quantities of raw and prepared ingredients to pro- duce 100 kg of dried produ ct are shown in Table 5. Potato-based food mixes such as the popular M-6 can be modified ac- cording to consumer taste preferences, availability of ingredients, and cost. Chemical analysis of M-6 by the Insti- tute of Nutrition of Central America and Table 5 . Quantit ies of raw and prepared ingre- dients suggested for family level production of M-6 potato food mix.a Ingred ients Kg raw kg prepared Potatoes 170 raw 120 cooked and mashed Broad beans 21 beans 16 flour Rice 17 grai n 16 flour Oat 21 grain 16 flour Barley 23 grain 16 flour Maize 12.5 grain 12 flour Salt 4 4 a 100 kg dry mix = 5000 portions of 20 g dry mix/ 250 ml water, which allows a family of six to use the mi x 3 times /day for nine months . The quantities of ingred ients can be scaled by a factor X25 to provide 125,000 portions for a community of 992 families (6 members each family) using the mix 3 times /day for one week . / Protected against PTM Exposed to PTM { d Desiree d b { de Revoluci6n de a a Ro•;,. { 50 25 0 25 50 75 100 Soft rot in tubers (O/o) • No soil application of CaS04 . • CaS04 distributed and incorporated in soil (12.6 t/ha). LJ Caso 4 applied to ridge (0.22 t/ha). Ill CaS0 4 incorporated in soil and applied to ridge (12.6 t/ha + 0.22 t /ha) . Bars followed by the same letter are not significantly different at the 50/0 level. Figure 4. Effect of calcium sulphate (CaS04 ) in soil on the percentage of soft rot in tubers of three cultivars exposed to or protected against potato tuber moth (PTM) infestation. Panama (INCAP), Guatemala (Table 6), agreed closely with calculated theoretical data based on food tables. Two independ- ent commercial bacteriological analyses of M-6 confirmed that satisfactory products can be produced using simple equipment and sun-drying techniques such as those used at the CIP pilot plant. The Huancayo plant and sun-drying fa- cilities were remodeled (Fig. 5) to assist in evaluating techniques for producing dried food mixes. With the assistance of a grant from the International Development Re- search Centre (IDRC), Canada, simple equipment for producing M-6 at both the family and community level was designed , manufactured locally , and is being eval- uated (Fig. 6). The essential steps in po- tato processing are peeling, cooking, and mashing. The other ingredients are first premilled and then thoroughly mixed into the wet mashed potatoes, and the 105 Figure 5 . The new cooking facilities in CIP's pilot processing plant, Huancayo . mixture is then dried by using solar or Table 6 . Analysis of a 100-gram sample of M-6 artificial energy. The sequence and pro- potato food mix .a cessing details may vary with different ----------------- production scales, conditions, and needs , and thus should not be regarded as fixed. The major cost for a product such as M-6 is for the individual ingredients . In Peru , the final product can be sold profit- ably at about US$1.00 per kilogram , or two US cents per ration (20 g dry mix in 250 ml water). CIP costs were 60°/o in- gredients, 14°/o processing with solar dry- Calories Protein Fat Fiber Ash Lysine Phosphorus Calcium Iron 409 .0 10.8 g 1.3 g 2.2 g 3 .9 g 695 .0 mg 208 .1 mg 13.0 mg 10.2 mg ing , and 25°/o remaining costs and profit. a Analysis performed by INCAP, Guatemala . 106 Figure 6. Plant equipment is being evaluated for performance and operational costs. A. Hand masher. B. Mixer for combining mashed potato with dry flours . C. Motor-driven cutter for pre- paring mixture for drying. D . Mixture is placed on trays to dry in solar dryer. 107 The product is prepared by reconstituting in water (80 g product per liter water) and boiling for approximately 25 min- utes . During the final stages of boiling, a range of flavor ingredients are added ac- cording to taste preferences and end-use of the product, which adds to consumer acceptability. Within Peru, commercial interest is being shown in producing these mixes at the small factory level. In collaboration with national institutions, CIP is using its pilot plant for demonstrating production and processing to interested parties. In a joint effort between CIP, the Ministry of Health, and the national potato program of INIP A, several communities have been selected in the central and southern high- lands for demonstrating the product and evaluating its potential production at both family and community levels. TRAINING Storage. Three training activities on stor- age were conducted in Africa, Asia , and South America and attended by a total of 46 scientists. In South America, the par- ticipants of a workshop visited Colombia, Ecuador, and Peru to assess the progress made in research on DLS technology and its acceptance by farmers. The visits to the different countries also afforded an opportunity to diagnose and discuss prob- lems associated with the storage of con- sumer potatoes in the region. The coun- try network SAPPRAD and CIP were joint organizers of a storage course in Thailand, the lead country for postharvest technol- ogy in SAPPRAD. This course also had a strong component on the control of PTM, which can be a limiting factor to farmer acceptance of DLS technology because of the storage losses caused by this insect. During the storage workshop in South America, a farmer explains his experiences of diffused-light storage to the evaluation committee consisting of course participants. 108 A training workshop in Kenya, one of the many storage activities within the framework of the UNDP project on Technology Transfer on Root and Tuber Crops, was attended by researchers and extensionists from East African countries. This was one of a series of storage courses planned to foster the diffusion of appro- priate DLS technology into more coun- tries in the region. Potato processing. Considerable inter- est in CIP's approach to simple potato processing has been shown by several La- tin American and Asian countries. Scien- tists from Guatemala and Bangladesh were trained in the consumer-oriented ap- proach to simple processing. Preliminary trials on consumer acceptability of a test mixture of potatoes, rice, wheat, lentils, peas, and chickpeas have shown promising results in several communities in Bangla- desh. Similarly, in Sri Lanka, both potato- and sweet potato-based mixes have had good acceptability . Institutions in Bhu- tan, Bolivia, and Colombia are interested in producing potato-based mixes, and ar- rangements have already been made to train scientists from these countries at CIP headquarters. 109 THRUST IX Seed Technology Increased demand for seed of hybrid progenies has emphasized the need for research aimed at production of true potato seed (TPS). One of the factors limiting TPS production has been the long-day requirements for flowering of many superior parental selections. Profuse flowering and abundant TPS pro- duction have been achieved under the long-day conditions of southern Chile . Research to overcome environmental flowering constraints has shown that hormones and other chemicals can be effective. Improved fertility has re- sulted from an increased understanding of gamete and seed tuber quality, improved pollen handling, the effect of multiple pollinations, observations of flowering and berry set behavior, and appropriate fertilizer regimes. Research on the control of potato seedling diseases has resulted in improved man- agement practices under warm, humid conditions where TPS use has high potential. In agronomic research, selected hybrids have shown superior transplant survival over open-pollinated progenies. The regeneration of roots after trans- planting has been identified as a major factor conveying increased field sur- vival of transplants. The use of TPS for seedling tuber production as an alter- native to conventional seed tuber programs appears highly applicable in developing countries. The number of useable seed tubers obtained in nursery production has increased significantly with increasing plant population. Con- siderable advances have also been made in small tuber utilization through better combinations of planting density and spatial plant arrangement. Field research on TPS has been active in Asia, Africa, and South America. Research in Egypt and Tunisia focused on improving nursery production of low-virus seedling tubers. In Rwanda and Kenya, TPS research was divided between on-farm evaluations and the selection of improved parental clones. Under field conditions in Bangladesh, two hybrid progenies gave yields com- parable to the standard cultivar Patrones. In India, research concentrated on the more basic aspects of TPS production, while in Sri Lanka, the Ministry of Agriculture was active in extending TPS technology to farmers in the main potato-producing region. Extensive progress in conventional seed tuber pro- duction is reported from Burundi, Rwanda, Ecuador and Vietnam. The prac- tical and rapid in-vitro multiplication system developed in Vietnam is being evaluated in Burma, the Philippines, Indonesia, and Thailand. Potato flowers are being pollinated for hybrid TPS production in Osorno, Chile . 111 PRODUCTION OF TRUE POTATO SEED A key factor to the extensive use of true potato seed (TPS) in the future is the de- velopment of simple and low-cost tech- niques that permit large-scale production and availability of TPS. Research at CIP has concentrated on developing the ap- propriate techniques for large-scale TPS production (Fig. 1). The results have pro- vided preliminary data that are already being used in a contract with the national potato program of Chile to produce sev- eral kilograms of high quality TPS of se- lected hybrid combinations. The use of growth regulators for pre- venting flower bud drop and increasing pollen production and fertility was investi- gated at CIP, Lima, in the winter by using a clone (DT0-33) with known low flower production and fruit set. The number of flowers and amount of pollen produced were increased two- to threefold after ap- plying a solution of 20 ppm kinetin and 50 ppm of gibberellic acid (GA3 ) to the developing truss at first macroscopic vis- ualization . In another experiment , differ- ent solutions of GA 3 and 6-benzylamino- purine (BA) of varying concentrations increased flowering, total pollen produc- tion , and fertility. Spermidine , a poly- amine, did not influence the number of flowers produced but did increase pollen germination significantly (Table 1). A one-time application of 200 ppm GA 3 in- creased pollen yield without a significant increase in germinability ; however, when a 100 ppm of GA 3 solution was applied with a 40 ppm solution of BA, a similar increase in yield was accompanied by a significant increase in germinability . BA and spermidine alone did not have an ef- fect on preventing bud drop. All treat- ments, except BA and GA 3 at 200 ppm Figure 1. Potato vine training is used to facilitate hybridization work and to prevent soil-berry contact. 112 alone, significantly (Table 1) increased in vitro germination of pollen. A 1 OO°lo in- crease in pollen germination was achieved when spermidine and BA 20 ppm+ GA 3 50 ppm were applied . Three polyamines applied to clone DT0-33 during the win- ter in Lima significantly increased in vitro pollen germination , but pollen production was not stimulated (Table 2) . In another experiment during two dif- ferent planting dates (Lima, winter), four concentrations of GA 3 were applied three times at weekly intervals, beginning one week after emergence. In the two plant- ings, GA 3 increased flower production per plant about 3.5 times in the first and 5.5 times in the second planting (Table 3). In the GA-treated plants , a larger propor- tion of stems formed an inflorescence and more flowers developed per inflorescence. Open-pollinated (OP) berry set in GA- treated plants was sharply reduced , possi- bly due to greater stigma exertion. Flower intensity was reduced in the second plant- ing , and since the DT0-33 seed tubers used in both plantings were of the same origin and harvest date , it is assumed that the physiological condition of the tubers had an effect on flowering . Several methods were evaluated for as- sessing in-vitro gamete fertility and the accuracy of the methods in predicting seed set in the field. The technique of germinating potato pollen in vitro was Table 1 . Number of flowers and characteristics of pollen produced under the influence of different growth regulator treatments. Total Total wt Pollen no . of pollen germination Treatmenta flowers (mg) (O/o) BA 20 ppm 20 20.9 16.6 GA3 50 ppm 105 200.3 22.2 GA3 200 ppm 352 232 .9 20.1 Spermidine 36 50.5 33 .1 BA 20 ppm + GA3 25 ppm 96 91.4 23.5 BA 20 ppm + GA3 50 ppm 187 143.2 32.1 BA 40 ppm+ GA3 100 ppm 299 226 .5 26 .3 Control (H 20 +Tween 20) 37 62.9 16.3 LSD (5°/o) 4.01 a BA= 6-benzylaminopurine ; GA= gibberellic acid. Table 2. Effect of polyamines on pollen germination and pollen weight. Pollen germination (0 /o) No. days after spraying Pollen wt Treatment 12 19 21 (mg/flower) Putrescine 30.4 29.9 40 .5 1.63 Spermine 29.4 28.9 37 .5 1.09 Spermidine 40.5 37 .6 37 .0 0.99 Control 15.2 22 .4 23.4 1.18 LSD (50/o) 1.1 4 .0 2.9 113 Table 3 . The effect of consecutive GA 3 applications on the flowering of clone DT0-33 during two winter plantings, Lima . GA3 concentration (ppm) Planting 0 25 1st planting (30 June) No. flowers /plant 8 33 No. berries / plant 5 7 Berry set (O/o) 54 24 2nd planting (26 July) No. flowers/plant 2 8 No. berries/ plant 1 2 Berry set (O/o) 30 22 * = significant at 5°/o level. * * =significant at 1°/o level. ns = not significant. modified to yield consistent data on po- tato pollen. Some of the pollen stainabil- ity tests being investigated were a redox dye (nitro blue tetrazolium) and the use of florescein diacetate. Mayer's hemalum whole ovule stain and clearing technique is being evaluated to study female fertility. When producing large amounts of hy- brid TPS , it is necessary to store the pollen; however, the condition of pollen storage and management influence pol- len fertility. Preliminary data from recent studies have shown that pollen stored dry under low tempera tu res (-10° to - 20° C) can retain its fertility longer than two months, i.e ., for an entire flowering peri- od of female parent plants. When flowers were pollinated two or three times , the number of seeds per berry increased . The results indicated that pollinating twice produced sufficiently high seed number and seed weight; seed weight was reduced in small berries obtained from flowers pol- linated once. As seed size increased there was a significant increase in seed with A- and B-type embryos. Several methods to improve the effi- ciency of TPS production were studied in 114 50 75 Significance 29 34 6 5 ns 19 16 13 6 2 17 15 ns Huancayo . Results showed that flowers of the first level of inflorescence produced a higher number of larger berries with more and larger seed than secondary in- florescences, possibly because berries de- veloped shortly before plants started to mature. Results also showed that the per- centage of flowers that produce berries increased with a decreasing number of flowers per inflorescence. These observa- tions suggested that pruning may improve seed quality while at the same time syn- chronizing berry maturity. It was also noted that flowering intensity was af- fected by seed tuber condition at planting and by the subsequent vigor of the plant . An experiment on nitrogen (N) require- ments for TPS production was conducted in Lima during the winter. Increasing levels of N (from 100 to 300 ppm N) increased flower production and in-vitro pollen germination in the clone DT0-33, but decreased flower production in the clone DT0-28 . By fraction ing the second application of N at hilling and during flowering, we were able to improve flower production and pollen germination for both DT0-33 and DT0-28. Waiting until flowering to apply the second application of N was disadvantageous, since a smaller percentage of flowers was retained in both clones , and pollen germinability was de- creased slightly in DT0-33. N and K (po- tassium) improved in-vitro pollen germina- tion, while phosphorous alone at 200 ppm reduced germination. Seed extraction. A method used in the tomato seed industry was modified and applied to processing large volumes of potato berries. Mashed berries were fer- mented for 48, 72 , and 96 hours at 25° and 30° C after which seed was treated with sodium hypochlorite and a 1500 ppm GA 3 solution. Seed germination was significantly improved with all treatments using freshly extracted seeds; however, when seeds were tested after eight months of storage , germination was reduced by 72 and 96 hours of fermentation. Emasculation and pollination. Studies were conducted in Lima to estimate the cost of producing large volumes of TPS. The total cost per kg was US$307 , a sur- prisingly low figure for production under experimental conditions. The main cost component was emasculation, represent- ing about 60°/o of total production cost. When comparing costs of TPS produc- tion with and without emasculation and open pollination, production costs de- creased dramatically when emasculation was eliminated, and they were reduced even further for open pollination. For producing 1 kg of TPS with emasculation, only 100 m2 of land and no more than 15 man days were needed. According to these figures, the market price of hybrid TPS would probably be less than the cost of equivalent amounts of tomato seed currently used in most developing coun- tries. One kilogram of TPS would provide sufficient seedlings to plant approximately ten hectares. PATHOLOGICAL STUDIES ON TPS Damping-off, caused by the pathogen Rhi- zoctonia solani, is often a serious problem in raising potato seedlings and for seed- ling tuber production in nursery beds. In an experiment designed for controlling damping-off, soil was treated with Basa- mid 30 days before sowing. Five days prior to sowing, seedbeds were inoculated with wheat kernels infected with R. so- lani at the rate of 2 g infected seed/kg of soil , followed by the application of fun- gicides. Results showed significant differ- ences among treatments for several of the variables analyzed (Table 4). In general, Table 4 . Chemical control of Rhizoctonia damping-off in nursery beds used for seedling tuber production. Seedling Plant height survival at at 63 days Yield No. Treatment 30 days (0 /o) (cm) (kg/m2) tubers/m2 Basamid 100 a* 32.5 a 12.1 a 1,293 a Basamid + inoculum 28 b 19.6 c 7 .7 c 693 c Basamid + inoculum + Rizolex (7 g/m2) 96 a 32.5 a 11.3 a 1,080 b Basamid + inoculum +Ben late (8 g/m2) 99 a 33.3 a 11 .7 a 1,341 b Basamid + inoculum + Campogran (5.5 g/m2) 97 a 28.4 b 9.8 b 937 b *Means followed by the same letter are not significantly different at the 5°/o level. 115 plots treated with Basamid (without inoc- ulum) , Rizolex , and Benlate yielded bet- ter than the untreated control. During the rainy season in San Ra- mon, seedling survival after transplanting was seriously affected by damping-off fungi. Pythium sp. was isolated in 70°/o of the affected seedlings after transplant- ing, while R. solani was the major cause of damping-off after hilling. In a previ- ous sampling of a large number of plots in San Ramon, Pythium sp. was also identified as the most important cause of damping-off after transplanting seed- lings during the rainy season. Of six dif- ferent isolates of Pythium sp. collected, two caused about 80°/o of seedling mor- tality . To control Pythium damping-off, we applied Ridomil to the soil and seed- ling survival in the field was improved, particularly during the rainy season. Un- der greenhouse and laboratory conditions, seedling survival was also significantly im- proved when Ridomil was applied to soils infested with Pythium sp. 377981 .3 DT0-2 x 7XY.1 CFK69.1 x DT0-33 0 SEEDLING PRODUCTION AND TRANSPLANTING Although agronomic techniques for re- ducing the shock of transplanting seed- lings to the field have been devised, the use of improved genetic materials is a more promising approach. There is a large variation in the reaction of different prog- enies in relation to their capacity to with- stand stress and for recovery after trans- planting. In general, hybrid seedlings have higher recovery rates than open-pollinated (OP) material. In experiments involving the progenies of more than 30 clones un- der controlled environmen ta! conditions, hybrid seedling survival was 20°1o better than that of OP progenies. The growth factor most responsible for seedling recovery from transplant shock was the rapid regeneration of adventitious roots. New root formation in the period immediately after transplanting account- ed for 87°1o of the recovery response. Root regeneration was measured in seed- lings of three progenies selected for their 50 0 /o Plants No regeneration Moderate High 100 Figure 2. Proportion of plants (O/o) from three progenies in three categories of root regeneration four days after induced transplanting shock . 116 377981.3op CFK 691xDT0-33 Figure 3. A rapid screening test for root regeneration following transplanting of seedlings . Seed- lings of progeny 377981.3 OP regenerated adventitious roots more slowly after transplanting than seedlings of the hybrid progeny CFK69.1 x DT0-33. reaction to transplanting shock: sensi- tive (377981.3), intermediate (DT0-2 x 7XY.1), and tolerant (CFK69.lxDT0- 33). A significantly larger proportion of seedlings of the sensitive progeny did not regenerate roots after transplanting (Fig. 2). A simple screening test that could help breeders to identify superior mate- rials at the early stages of a TPS breeding program is being developed (Fig. 3). A number of hybrid and OP progenies, both selected and new combinations, were transplanted to the field in Lima, Huan- cayo, and San Ramon for evaluating their general agronomic characteristics, adapta- tion to a wide range of environments , and yield (Table 5). Yields from transplanted seedlings of these materials can be as high as the yields of clonal material grown in these three diverse environments. Transplanting seedlings to the field has proved to be a practical method of produc- ing seedling tubers for subsequent propa- gation of the crop in a vegetable-growing area on the coast of Peru (Callao). Seed- lings were transplanted into a 400-m2 plot at double the plant density normally used in this area for producing potato for con- sumption . Only 8 g of TPS was required to produce enough tubers for planting one hectare the next season (Fig. 4) . Early vigor is important for a rapid emergence and establishment of seedlings in the field. Several methods were inves- tigated for sowing seed directly into large field areas and for enhancing early emer- gence and growth of seedlings. By fluid drilling pregerminated seed in a 4°1o Ben- tonite gel with fertilizer , the sowing op- eration and time to emergence were sig- nificantly reduced, and seedling growth was subsequently improved (Table 6) . Al- though Bentonite is a relatively common product, other gels made out of potato, 117 Table 5. Total and marketable (Mktbl) yield of selected hybrids in Lima, Huancayo, and San Ramon , Peru . Lima Huancayo San Ramon Total Mktbl Total Mktbl Total Mktbl Hybrid (t/ha) (O/o) (t/ha) (O/o) (t/ha) (O/o) Atzimba x 380700.79 48.3 73 .3 55.7 83 .5 24.5 87 .0 CFK69.1 x 380700.79 43.8 70.8 57.3 83.3 25 .7 84.0 LT-1 x R128.6 40.9 81.4 40.0 87.8 17.0 85 .0 CGN69.1 x 380701.12 36.5 72 .1 59 .7 83.2 26 .8 78 .0 Atzimba x 380701.12 36.8 66 .6 56.4 85.4 19.5 68.0 CFK69.1x380701.12 34 .9 66 .9 54.4 78.2 21.2 70 .0 CEX69.1x380701.12 34.6 74.5 43 .8 75.6 22.8 73.0 CFK69.1 x R128.6 55.0 80.5 37.7 78 .1 Atzimba x R128.6 50.6 83.6 22.3 87.0 DT0-28 x R 128.6 44 .0 79.5 24 .2 87.0 CEX69.1 x R128 .6 72.8 82.2 BR6365 x R128.6 64.9 82 .3 377935.27 x 377964.5 40.1 82.0 Table 6. Seedling emergence and characteristics 30 days after pregerminated TPS was fluid-drilled in fertilized Bentonite gel. Leaf Emergence Weight Height diameter Treatment (d) (g/plant) (cm) (cm) Bentonite 4°/o +fertilizer 3 1.85 a* 7.6 a 1.8 a Bentonite 40/0 4 1.55 b 5 .7 b 1.4 b Water 3 1.30 c 5.1 c 1.4 b Control 8 1.20 c 4 .9 c 1.3 b *Means followed by the same letter are not significantly different at the 50/o level. Table 7. Total and tuber fresh weight per plant 75 days after direct field sowing by different methods. Fresh wt (g) Sowing method Total Tubers Fluid drilling-clusters 47 .7 a* 23.20 a Fluid drilling- continuous rows 42.9 a 23 .23 a Direct sowing- clusters, mulch 35.9 ab 15.20 b Plug mix-clusters 30.5 b 15.37 b Direct sowing-clusters 20.2 c 7 .87 c *Means followed by the same letter are not sig- nificantly different at the 50/0 level. 118 cassava , maize or sweet potato starch can also be used with good results . The addi- tion of the fungicide Tiabendazole (25 ppm) to organic gels gave excellent con- trol of fungal contamination. The incor- poration of P2 0 5 (1000 ppm) into the gels and seedbed substrate enhanced seed- ling growth and establishment . In a field experiment in Lima, the ad- vantage of fluid drilling seed , either in clusters or in continuous rows, was eval- uated compared to other sowing meth- ods, and early field establishment was obtained (Table 7). Improved seedling Figure 4. Seedling production in a farmer seedbed for transplanting into a 400-m2 plot. The seedling tubers produced in that area will be used for planting the next commercial crop. development was evident in both seedling size and greater weight of tubers 75 days after sowing. Mulching the soil in direct- ly sown plots was also beneficial in early field establishment of plants. SEEDLING TUBER PRODUCTION AND USE In the production of seedling tubers in beds, it was found that an increase in seedling density gave more tubers per unit area in all size grades, except the largest ( > 40 g), in which the number of tubers was similar for all densities (Table 8). By increasing plant density in beds, we obtained a greater yield of useable tu- bers (1 g), while the number of relatively large tubers was not reduced. Studies in Sri Lanka showed that the optimum plant density in high rainfall areas was 50-100 plants/m2 , while for Lima conditions, the optimum density was 100-150 plants/m 2 . In field experiments with single-sprout seedling tubers, ranging in size from 2.5 to 20 g, early plant growth, rate of ground cover (Fig. 5), tuber yield, and proportion of large tubers increased with increasing 119 Ground cover (O/o) 100 80 60 40 20 0 25 30 35 40 45 50 No. days after planting Figure 5. Effect of four different weights of single-sprout tubers on rate of ground cover. tuber weight. The positive yield response to increased stem density was particularly great with the smaller tubers, although they had a longer optimum sprouting period than larger tubers. In studies on the effect of plant spatial arrangement on early soil cover by foli- age, a positive interaction was observed between seed tuber weight and spatial arrangement, indicating that small tubers benefited more from a less rectangular spatial arrangement than larger tubers (Table 9). Small seedling tubers required planting at a high stem density and a square planting pattern for optimum mul- tiplication efficiency. Also, small seed tu- bers (1-5 g) produced more efficiently per unit of planted weight than larger tubers. Table 8. Effect of seedling density on yield and size distribution of seedling tubers in nursery beds .a Tuber yield (no.fm2) Total >1 g Plants/m2 <1 g 1-5 g 5-10 g 10-20 g 20-40 g >40g No ./m2 kg /m2 6 75 133 61 59 40 23 316 4.25 12 119 175 73 89 53 19 409 4.99 24 183 268 116 116 68 21 589 6.58 48 283 390 145 161 73 22 791 7.92 96 434 550 160 175 74 18 977 8.76 LSD (50/o) 71 53 31 28 14 ns 88 1.04 a Mean of two TPS progenies. 120 Table 9. Effect of seed tuber weight and spatial arrangement on percent soil cover 55 days after planting multiple-sprout tubers .a O/o Soil cover Seed tuber Spatial arrangement (cm) wt (g) 85 x 18.8 70 x 22 .9 55 x 29.1 40 x 40 Mean 1-5 53 51 84 83 68 5-10 70 83 98 100 88 10-20 80 92 100 100 93 20-40 97 100 100 100 99 40-60 100 100 100 100 100 Mean 80 85 96 97 a Mean of two TPS progenies. The interaction between seed tuber weight and spatial arrangement is significant at the 1°/o level. CV seed tuber weight = 120/o. cv spatial arrangement = 9°/o. Table 10. Number of above-ground stems and the total yield produced from seed tubers of dif- ferent weights planted at the same spacing. Seed No . tuber wt Planted wt above-ground Yield (g) (t/ha) stems/m2 (t/ha) 1-5 .188 6.9 30 .7 5-10 .469 9.5 37 .5 10-20 .938 12.3 43.8 20-40 1.875 17 .8 51.1 40-60 3.125 21 .8 54.9 LSD (5°/o) 1.6 5.4 With larger seed tubers ( 40-60 g), the planted weight was 17 times that of 1-5 g seed tubers, but the larger seed produced only three times the number of stems and less than twice the yield of the small seed tubers (Table 10). ON-FARM EVALUATION OF TPS TECHNOLOGY On-farm trials to evaluate the potential of alternative potato production systems that use TPS were conducted in farmer fields on the coast of Peru (Callao, Hua- chipa, and Canete). In intensive cropping areas such as Callao and Huachipa, farmers clearly pre- ferred seedling transplanting for the pro- duction of either consumer potatoes or seedling tubers for planting the following season. In early season trials in Callao, transplanting seedlings was more accept- able under conditions where farmers were familiar with vegetable growing. In Canete , a traditional lowland po- tato area where vegetable crops are of secondary importance, farmers preferred seedling tubers produced in seedbeds or directly sown into field plots. CIP tech- nology for producing and using seed tu- bers from TPS was evaluated on two farms in Canete for two consecutive sea- sons. Several modifications in the original system of production in densely sown beds were proposed by the farmers : fur- row sowing and ridging at a distance of 0.40 m. Although yields obtained in the modified system were about 20°/o lower than the original system, the simplifica- tion in management practices was more acceptable because of lack of labor in 121 the area and production costs were also reduced . A benefit/cost analysis of this year' s results, together with those obtained in previous years , including evaluations in a traditional potato-growing area in the highlands, has indicated the following: The cost of producing consumer potatoes from TPS was , in general , lower than the cost of producing potatoes from com- mercial seed tubers on a per hectare ba- sis as well as per kilogram of output. In vegetable-growing areas, the transplanting system reduced production cost per hec- tare between 1 O°lo and 30°/o and the cost per kilogram of up to 50°1o . In more tra- ditional potato-growing areas , the use of seedling tubers reduced the cost per kilo- gram of output up to 20°/o, but no reduc- tion in cost per hectare was observed. The best economic returns from the use of TPS were observed in the coastal areas of Peru and early in the season when high-quality seed tubers from the high- lands were not available. At that time , the farmers' only alternative was to plant tubers highly infested with virus which they had saved from the previous harvest. PROGRESS IN TPS RESEARCH IN DEVELOPING COUNTRIES Region I. In Colombia, CIP tested the potential for seedling tuber production of 16 TPS hybrid families as an alternative method of seed production. The four best families produced between 40,000 and 84,000 small tubers per 100 m2 of nursery , sufficient to plant up to two hectares. Region III . TPS research conducted by the national potato program (PNAP) in Rwanda is moving from the research station to on-farm trials . A mid-season survey by a CIP anthropologist showed that seedbed preparation was already well 122 known to farmers. In general, farmers encountered no serious difficulties in es- tablishing seedlings, although the plant density varied considerably . An addition- al survey will be conducted after harvest. In Kenya, 20 progenies were planted in screenhouses and 85°/o to 90°/o germina- tion was obtained. Tuberization occurred 50 days after germination; OP progenies from clones 800169 and 800176 tuber- ized earliest . Region IV. In Egypt , where CIP has its regional headquarters in Cairo , re- search has been conducted jointly be- tween Egyptian scientists and CIP region- al staff. The first crop of seedlings from TPS was produced in Egypt in fall 1983. The progenies available were not adapted , but good progress was made in evaluating the best agronomic practices to produce a consumer crop under local conditions. Seedling tuber yields for planting ranged from 300 to 500 small tubers per m2 of nursery. Differences between plants grown from seedling tubers of various sizes above 5 g rapidly disappeared as the plants matured. When tubers are very small (1-5 g) , the plants have lower yields , but this may be compensated for on a unit area basis by closer planting of tubers. In trials to produce TPS , 11 varieties and one CIP clone were planted in the Sinai Desert under mild winter condi- tions, but there was little or no flowering. Of another 34 European varieties planted , only 13 flowered and set seed . By con- trast , however, European varieties will flower profusely under the cool summer at Bozdag, Turkey. The trials will be con- tinued in other high-altitude areas of the Middle East to identify suitable areas for TPS production. At CIP regional headquarters in Egypt, a series of experiments tested the best agronomic methods for potato production from TPS. In studies on nursery manage- ment, small amounts of soil (20°1o) had a negative effect on seedling growth and tuber production, but a peat moss/sand mixture (1: 1) gave consistently good seed- ing emergence and development. Due to the high cost of peat , substitutes such as compost derived from wood shavings, ba- gasse, and maize stalks are being investi- gated for nursery mixes . The principal problem from using soil in the nursery mix is that of crusting and high weed pop- ulations; however, mulches of sawdust, straw, or paper reduced this problem. Wood shavings should be used cautiously as the wood preservatives have induced chlorosis in seedlings. Seedling emergence was ideal when the local seedbed construction was used , which consisted of basins that are flooded every three days. Good results were ob- tained with a simplified fertilizer regime of 80 g P 2 0 5 per m2 of seedbed before sowing, and 18 g each of N and K2 0 in three doses, applied as a water solution at 14, 30, and 40 days after emergence. Al- though systemic fungicides gave partial protection against damping-off of seed- lings, the use of low cost subsoil in the nursery mix helped reduce this problem. Since first generation seedling tubers have relatively low virus content, it is necessary, under Egyptian conditions, to sow the TPS in nurseries in early August for harvesting tubers in November and replanting in January. The germination of seedlings was improved 80°1o to 90°/o when they were lightly shaded by cheese cloth; however, damping-off was a seri- ous problem and seedlings were etiolated. Seedling growth during August was im- proved by using a mulch of shredded maize stalks or paper. The effect of two different types of stores - cold ( 4° C) and traditional non- refrigerated (nawalla) - on seedling tuber losses was studied. In traditional stores, only 15°/o of the tubers decayed during a 150-day period. This compares well with the 10°/o loss experienced in cold stores over an 89-day period; however, as was ex- pected, weight losses in the nawalla were greater (Table 11). Region V. The use of TPS for pro- duction of seedling tubers and consumer crops was studied in Tunisia during the main planting season (January-March). The local method of raising tomato plants in nurseries was used to produce potato seedlings. The emergence of both hybrid and OP seed supplied by CIP, Lima, was satisfactory , but the tuber characteristics of the hybrid were not acceptable in Tu- nisia . The tubers derived from OP seed of the cv . Pentland Ivory, however , had excellent characteristics and were highly uniform. The initial results indicated that consumer potato production in the main season was not satisfactory, as plants could not reach full maturity before the onset of the hot summer. Thus, earlier Table 11 . Effect of two types of storage on seedling tuber loss during summer, Kafr El-Zayat, Egypt . Decayed Total Total Storage period tubers wt loss moisture (d) Store type (O/o) (O/o) loss (