Chapter 12 Tropical and Subtropical Root and Tuber Crops David Tay 12.1 Introduction Almost all root and tuber crops (RTC) in the world are of tropical and subtropical origin and they include potato (Solanum tuberosum L. and other diploid, triploid and pentaploid spp.), cassava (Manihot esculenta Crantz), sweet potato (Ipomoea batatas (L.) Lam.), yams (Dioscorea spp.), the aroids which include taro (Colocasia spp.), cocoyam (Xanthosoma spp.), and genera including Alocasia, Amorphophallus and Cyrtosperma (giant swamp taro), and a group of nine minor Andean RTC consisting of achira (Canna indica L.), ahipa (Pachyrhizus ahipa (Weddell) Parodi and two other species including the Mexican jicama (Pachyrhizus erosus (L.) Urb. a commonly grown species in Mexico and Southeast Asia), arracacha (Arracacia xanthorrhiza Bancroft), maca (Lepidium meyenii Walpers), mashua (Tropaeolum tuberosum Ruiz and Pavón), mauka (Mirabilis expansa Ruiz and Pavón), oca (Oxalis tuberose Mol.), ulluco (Ullucus tuberosus Caldas) and yacon (Smallanthus sonchifolius) (Poeppig and Endlicher Robinson). This group of crops is usually not traded widely as international commodities and thus is not subjected to wide price increases and fluctuation as that for grain crops such as rice, wheat and maize during international market crises in recent years. Additionally, their tropical origin allows them to be grown anytime of the year when there are available water and temperature for growth and they complement the growing of grain cereals as rotational crops and during the off-season. Some are also grown in marginal lands with limitations like drought, water-logging, salinity and poor soil conditions. Once they start to set storage roots and tubers, harvesting can be commenced periodically without waiting for a one-time maturation harvest as in cereal crops. Thus, they play an important role in stabilizing local and regional food security and prices. The current D. Tay (*) Genetic Resources Conservation and Characterization Division, International Potato Center (CIP), Apartado 1558, Lima 12, Peru e-mail: dt26012012@gmail.com 249 M.N. Normah et al. (eds.), Conservation of Tropical Plant Species, DOI 10.1007/978-1-4614-3776-5_12, © Springer Science+Business Media New York 2013 250 D. Tay low yield realized in most farmer fields in developing countries offers enormous, untapped potential for yield improvement, combating malnutrition and vitamin A deficiency specifically the orange-flesh cultivars with high beta-carotene, and improving livelihoods. They can produce better yields in poor conditions with fewer inputs making them particularly suitable for households threatened by displacement, civil disorders or diseases such as AIDS. They therefore play an important role toward food security in developing countries. Potato, the fourth most important food crop in the world ranked by production at 330 million T, is eaten by millions of people in Asia, Africa, and Americas (FAOSTAT 2009). Potato, commonly related as staple of temperate countries, in fact, has its origin in the Andean highlands in South America. It is still the main stable in the isolated and deprived regions of the Andes. In term of productivity, potato harvest index is up to 85% of the plant (Reynaldo et al. 1986). Upon cooking, potato diet provides significant daily needs of energy, protein, vitamins C, B6, and B1, folate, iron, potassium, phosphorus, calcium, zinc and other essential trace elements such as manganese, chromium, selenium, and molybdenum. It has high dietary fiber and is rich in antioxidants, including polyphenols and tocopherols. In most developing countries it is grown as a high value income generating crop considering that French fries has become one of the most popular fast food in the world. China, largest potato producing country in the world, is planning the development of more potato production to sustain its future food need because it is the only staple crop that new production areas are available for expansion (CCCAP on CIP website – www.cipapa.org). Cassava is predominately cultivated in developing countries of Asia, Africa, and Latin America. It ranks fifth in term of total production in the world at 234 million T (FAOSTAT 2009). It is thus an important energy source in the tropics and subtropics. The vitamin and mineral rich young leaves are used as vegetable green in Southeast Asia and Africa. The short shelf-life after harvesting means that it is mainly used and traded locally. In fact, the bulk of Asia production is processed into starch. Sweet potato is the seventh most important food crop in the developing countries with a total production of 102 million T (FAOSTAT 2009). It is one of the main staples in the Pacific including Papua New Guinea and Indonesia Irian Jaya. Sweet potato originated in tropical Americas and was taken across the Pacific as far as New Guinea before Columbus by ancient civilizations. In fact, the sweet potato culture is more elaborated in the Pacific than in the Americas as the ‘kumara’ in the Maori culture. The orange-flesh cultivars (OFSP) have very high levels of pro-vitamin A and are used to reduce vitamin A deficiency in the tropics and subtropics. As for cassava, the nutritious young leaves are eaten in Southeast Asia and the Far East as green vegetable, and the whole vine for animal feed. Yam, a multispecies crop with origins in Africa and Asia rank eleventh in global food crops with a total production of 49 million T (FAOSTAT 2009). Production is mainly in tropical Africa (96%) by smallholders consisting mainly of Guinea yams, D. rotundata (white yam) and D. cayenensis (yellow yam) of African origin. They are preferred for the organoleptic properties of the tubers. The water yam, D. alata, originated in Asia, is widely grown in the world as minor crop because of its wide adaptation. 12 Tropical and Subtropical Root and Tuber Crops 12.2 251 Genetic Diversity and Genebank Collections The genetic resources of a crop (germplasm collections) are the ‘building blocks’ consisting of genetic linkage groups available for plant breeders to put them together in the best combining ways to create the ‘winning varieties’. The gene linkage groups are the results of 1,000 years of selection by generations of ancient farmers to present days to adapt to the ever changing biotic and abiotic environments and the changes in the anthropological and aesthetic needs through time. The domestication of a crop could be said as the first big leap forward of the crop genepool from the wild ancestors. As the crop spreads and migrates to new territories it faces new selection pressure and thus new genetic linkage groups are created. When it comes into contact with new related species (both wild and cultivated) they intercross, introgression takes place and new genetic linkage groups are formed. When it reaches edges of near extreme environments founder effect due to chance and genetic drift happens and it adapts by polyploidization and often becomes selfpollinated to survive and new linkage groups are stabilized. Through time mutation accumulated, new alleles and genes are created adding another dimension to the total genetic diversity. A quality crop germplasm collection is a collection with a good representation of the total genepool of the crop where most of the genetic diversity specifically in term of the genetic linkage groups, genes and alleles is represented. Harlan and de Wet (1971) proposed a genecological approach to define the different segments of a crop genepool based on their ability to exchange genes where the primary genepool (GP1) contains relatives that readily intercross with the crop; secondary genepool (GP2) contains relatives that hybridize with the crop but show sterility problems in the progenies; and tertiary genepool (GP3) contains relatives that can be crossed but with difficulty. However, in most crops crossing information between a crop and its relatives is unavailable and thus this concept can be applied only to a certain degree. An alternative concept was thus proposed by Maxted et al. (2008) based on the taxonomy of a crop which to some degree reflects their genetic relationships and crossability. The classification is based on Taxon groups where Taxon Group 1a is the crop; Taxon Group 1b is the same species as the crop e.g. wild or semi-wild subspecies or varieties; Taxon Group 2 is of species in the same series or section as the crop; Taxon Group 3 is of species in the same subgenus; Taxon Group 4 is of species in the same genus; and Taxon Group 5 is of species in different genera. Information on taxonomic treatments and domestication of a crop is thus essential in managing the genetic quality of a crop collection in term of genepool representation. Currently, most root and tuber crop collections have poor GP2 and GP3, or poor Taxon Group 2–5 representations. The following crop summaries will provide some insight on the state of the collections for different root and tuber crops: Potato (tuber): Potato is in the family Solanaceae, genus Solanum, subgenus Potatoe, section Petota (formerly Tuberarium), series Tuberosa (Hawkes 1990). The local name in the Andes is papa. It is an ancient crop and was found in 252 D. Tay archeological remains in the coastal Peruvian pre-Inca civilizations as far back as 7,000 years ago (Ugent and Peterson 1988). Spooner et al. (2005) using AFLP data postulated a single domestication and origin for cultivated potato from S. bukasovii in the broad area of southern Peru. It then spread to the whole Andes from western Venezuela in the north to Argentina and Chiloe Islands in the south and evolved into multispecies with ploidy levels from diploid (2n = 2x = 24) to pentaploid (2n = 5x = 60). Through time introgression with wild potatoes, selection by the Andean ancient farmers, mutation, genetic drift and intercrossing between cultivated forms have created a wide diversity of many thousands of native Andean potato cultivars (not subjected to modern breeding). Ugent et al. (1987) reported wild potato remains in archeological sites in southern Chile as far back 13,000 years ago. Based on Ochoa (1999, 2003) cultivated potato can be classified into nine species, namely, Solanum stenotomum (a 2× species believed to be the first potato derived from S. bukasovii (Spooner et al. 2005)) and possibly other related wild species), S. goniocalyx (a 2× species with lesser distribution, generally yellow flesh, high dry matter and good eating quality, and classified as a subspecies of S. stenotomum by Hawkes 1990), S. phureja (a 2× species with early maturing, no tuber dormancy in the lower altitude down to 1,700 m asl in the eastern slope of the Andes toward Amazon from Colombia to Bolivia), S. x ajanhuiri (a 2× natural hybrid species between S. stenotomum and a wild species, S. megistacrolobum) (Huaman et al. 1980) with only two main forms – ajanhuiri (non-bitter) and yari (bitter with frost tolerance), S. x chaucha (a very variable 3× species resulted from the natural crosses between diploid species and tetraploid S. tuberosum ssp. andigenum or unreduced and normal gamete crosses of diploid species), S. x juzepczukii (a bitter 3× natural hybrid species between S. stenotomum and a wild species, S. acuale) (Schmiediche et al. 1982), S. tuberosum (a 4× species with two subspecies – ssp. andigenum and ssp. tuberosum which represents 78% of the diversity in the Andes and almost all the potato growing in the world, respectively), S. hygrothermicum (a 4× species from the lower altitude of Andes toward the Amazon (Ochoa 1984) and Hawkes (1990) classified it as a form of S. phureja) and S. x curtilobum (a bitter 5× natural hybrid species between ssp. andigenum and S. x juzepczukii with very narrow diversity) (Schmiediche et al. 1982). Recently, Spooner et al. (2007) using SSR markers and T chloroplast deletion data reclassified these cultivated species into four species – the three natural F1 hybrid species (S. x ajanhuiri, S. x juzepczukii and S. x curtilobum) accounting for only 1.3% of the known diversity in cultivated native potatoes in CIP Genebank, and lumping all the remaining diploids, triploids and tetraploids together as S. tuberosum in two groups, the Andigenum group (accounting for 74.3% of the diversity) and Chilotanum group from Chiloe region (3.8% of the diversity). This was concluded despite reasonable clear groupings were obtained in their analysis between the diploids and tetraploids. This lumping of 2×, 3× and 4× together as a species (98.7% of diversity) is not practical as it would create serious communication difficulty between researchers. These entities although have overlapping morphological characteristics are able to be distinguished to large extend in the field by field researchers (based on 70 man-year experience of CIP potato curators). 12 Tropical and Subtropical Root and Tuber Crops 253 Table 12.1 The global in trust potato collection held under the International Treaty on Plant Genetic Resources for Food and Agriculture at CIP in 2011 (CIP data) Species Acc Distribution Cultivated sp. (Ochoa 1999, 2003) Native potato 2n = 2x = 24 S. stenotomum 299 98 204 14 Argentina (2), Bolivia (88),Colombia (2), Ecuador (2), Perú (205) Bolivia (2), Chile (1), Peru (95) Colombia (99), Ecuador (85), Peru (20) Bolivia (13), Peru (1) 116 36 Bolivia (24), Ecuador (7), Peru (85) Argentina (1), Bolivia (20), Peru (15) S. goniocalyx S. phureja S. x ajanhuiri 2n = 3x = 36 S. x chaucha S. x juzepczukii 2n = 4x = 48 S. tuberosum ssp. andigenum 3,148 S. tuberosum ssp. tuberosum 163 2n = 5x = 60 S. x curtilobum To be classified 6 151 Landracesa 119 Improved material Wild potato sp. (section Petota) 141 species 92 2,174 Total 6,620 Argentina (183), Bolivia (375), Colombia (147), Ecuador (254), Perú (2,153), Venezuela (36) Argentina (13), Chile (142), Colombia (2), Ecuador (1), Perú (4), Venezuela (1) Argentina (1), Bolivia (1), Peru (4) Argentina (6), Bolivia (18), Colombia (3), Ecuador (12), Perú (112) Bangladesh (18), Bhutan (5), Costa Rica (1), Guatemala (32), India (2), Mexico (32), New Zealand (5), Philippines (3), Russia (11), Switzerland (8), Unknown (3) – Argentina (80), Bolivia (451), Chile (9), Colombia (48), Costa Rica (7), Ecuador (88), Guatemala (3), Mexico (106), Panama (2), Paraguay (17), Peru (1,281), Uruguay (47), USA (26), Venezuela (9) a Native potato types from outside the Andes The diploids are self-incompatible and thus outcross, the triploids are mostly sterile, the tetraploids are highly self-compatible and the pentaploids are crossable with tetraploids. The species intercross to produce a wider segregation of new forms. There are some 30 collections of potato worldwide conserving about 65,000 accessions. The major ones represent some 59,000 accessions are listed in the Global Strategy for the Ex situ Conservation of Potato, 2006 (http://www.croptrust.org/ documents/web/Potato-Strategy-FINAL-30Jan07.pdf). The collection at CIP includes 4,235 accessions of cultivated native potatoes, 2,174 accessions of wild potatoes (Solanum section Petota), 119 landraces, 92 bred cultivars, and 3,752 genetic stocks and advanced breeding lines (Table 12.1). These collections are underutilized in breeding work. For example, only 246 of the 4,235 native potato 254 D. Tay accessions representing about 5.6% were used in the breeding program at CIP in the last 40 years and they were represented in only 30% of the crosses, i.e. 6,324 out of 20,922 total crosses (based on 2010 data). The key causes contributing to this low level of utilization are the lack of evaluation information of the collection for important agronomic traits; the inadequate documentation on and ease of access of this information on the collection; and the need of a specific germplasm enhancement pre-breeding program to isolate useful genes and gene linkage groups of native potatoes. The classical example is the use of S. tuberosum ssp. tuberosum (female parents) and ssp. andigenum (male parents) crosses to exploit the resulting adaptation and heterosis in the Andes. Using this concept Carlos Ochoa bred more than ten released cultivars in Peru in the 1960s and 1970s (Ochoa 2008), and several of them have made their ways into the traditional potato production system and thus continue to be important cultivars to date, e.g. cv. Yungay is still one of the most important cultivars in cultivation in Peru. Similarly, the neo-tuberosum program to select for long photoperiod genotypes from new genepool of ssp. andigenum in the 1960s and 1970s in Scotland (Simmonds 1964; Glendinning 1975a, b, c, d) and in USA (Plaisted 1971) is another important event to widen the genetic base of the ssp. tuberosum genepool in the world. There is a lot of genetic diversity in the native cultivated potato of the Andes available for this purpose without having to resort to the use of wild related species which tend to introduce glycol-alkaloids (bitterness) into the tubers and many other unwanted agronomic characteristics that are difficult to breed out. There are 187 species of wild potato in the world (based on CIP revision of Petota under preparation) with a polyploidy series from diploids to hexaploids and they are distributed from southwest USA in the north continuously along the cordillera of the two Americas to Argentina to Pacific coast of Chile around Chiloe Islands in the south (Fig. 12.1). The differentiation between wild potatoes and other Solanum species is tuber bearing and this characteristic forms the section Petota. They are endemic from the high Andes of up to 4,300 m above sea level, to the west the edge of Pacific Ocean and to the east the foothills of the Andes and cloud forests toward the Amazon Basin. Along this distribution there are two centers of diversity with the South American center concentrates in Peru with 83 endemic species and the North American center in Mexico with 29 endemic species. The genetic diversity is many times richer than the cultivated native potatoes and thus a tremendous genetic resource for breeding because of their wide range of ecological adaptation. The useful traits include both biotic and abiotic stresses such as pest and disease resistance, and frost, drought, salinity and heat tolerance, respectively. Many of species are inter-specific cross-compatible and also with the cultivated species. In fact, the three natural hybrid native potatoes species, S. x ajanhuiri is the result of nature crosses of cultivated native species directly with S. megistacrolobum (2n = 2x = 24), and S. x juzepczukii and S. x curtilobum with S. acuale (2n = 4x = 48), meaning that ajanhuiri has a half of wild genome, juzepczukii has two thirds wild genome and curtilobum has two fifth wild genome. This is the reason for their bitter tubers. Since the formation of CIP in 1971 emphasis has been to collect, conserve, evaluate and use the wild species. Currently CIP genebank holds in trust the most 12 Tropical and Subtropical Root and Tuber Crops 255 Fig. 12.1 Geographical distribution of wild potatoes (Solanum section Petota) in their natural endemic habitats diverse collection of this germplasm with 2,164 accessions of 141 species (Table 12.1). This represents one third of the in trust Global Potato Collection maintained at CIP – the highest % holding of CWR germplasm in all the major crops. However, the use of these genetic resources in plant breeding is always faced with the occurrence of bitter tuber, day-length sensitivity, long stolon, small multiple tuber formation per stolon in tandem and other poor agronomic traits. The recommendation is that when a trait is present in the native potato germplasm breeding should focus on them first rather than going directly at the CWR. Currently, 256 D. Tay CIP is working with the Global Crop Diversity Trust in the implementation of the Global Strategy for the Ex situ Conservation of Potato, 2006 (http://www.croptrust. org/documents/web/Potato-Strategy-FINAL-30Jan07.pdf). Cassava (root): It is in the family Euphorbiaceae, subfamily Crotonoideae, tribe Manihotae, genus Manihota and species Manihot esculenta Crantz. The Neotropical genus has 98 species divided into 19 sections distributed from southwestern USA to Argentina (Rogers and Appan 1973) and the common characteristics are latex and cyanogenic glucoside production (Rogers and Fleming 1973; Bailey 1976). Rogers (1965) postulated two geographic centers of evolution in the genus Manihot: (1) the drier Mesoamerica, and (2) the dry northeastern Brazil; and Nassar (1978a, b) four centers of diversity: (1) central Brazil, (2) northeastern Brazil, (3) southwestern Mexico, and (4) western Mato Grosso, Brazil and Bolivia. None of the species are endemic in both geographic regions except for M. esculenta and M. brachyloba. The geographical distribution of Manihot sections was redrawn from Rogers and Appan (1973) in Bonierbale et al. (1997). Synonyms of M. esculenta include M. utilissima, M. dulcis, M. aipi and M. palmata (Rogers 1965). Cassava basic chromosome number is 9 and 2n = 4x = 36 (Magoon et al. 1969; Bai et al. 1993; Umanah and Hartman 1973). It is also commonly called manioc by French-speaking people, tapioca by English-speaking people, yuca by Spanishspeaking people and mandioca by Portuguese-speaking people. The Spanish name yuca is from Taino tribe of Antillas/Haiti, and it has distinct native names by different tribes from Mexico to Paraguay (Bonierbale et al. 1997). There are sweet (low cyanide) and bitter cultivars, and ethnobotanical names classify them accordingly, e.g. the sweet cultivars are called aipi or aipim and the bitter cultivars maniyua or maniva. Cassava is an ancient crop as archaeological evidence showed its use on the Peruvian coast before 4,000 BC (Ugent et al. 1986) and Hershey (1987) cited its cultivation in Colombia and Venezuela from 3,000 to 7,000 years ago. There are numerous proposals on its domestication. Alphonse de Candolle in 1886 (Smith 1968) and Vavilov in 1920–1940 (Vavilov 1992) indicated cassava origin in lowland tropical Americas and the Brazilian-Paraguayan center of origin, respectively. Sauer (1952) postulated northwestern South America and Rogers (1965) Mesoamerica from northwestern coast of Mexico to Nicaragua where wild species, M. aesculifolia, M. pringlei and M. isoloba could have involved in the forming of cassava. Rogers and Fleming (1973) indicated that M. esculenta is a complex species with multiple domestication sites. Allem (1987, 1994) indicated that cassava derived from two primitive forms where cassava is M. esculenta subsp. esculenta and the two wild primitive forms, M. esculenta subsp. peruviana and M. esculenta subsp. flabellifolia which is morphologically similar to cassava. AFLP studies (Roa et al. 1997) supported the close relationship with flabellifolia. Similarly, study on the single-copy nuclear gene coding glyceraldehyde 3-phosphate dehydrogenase (Olsen and Schaal 1999) and SSR markers (Olsen and Schaal 2001) also pointed to flabellifolia and that domestication occurred along the rim of southern Amazon Basin in the Brazilian states of Acre, Rondonia and Mato Grossa and probably extending south to Bolivia. Brucher (1989) indicated that the Arawak tribes of 12 Tropical and Subtropical Root and Tuber Crops 257 Central Brazil took cassava to the Caribbean and Central America in the eleventh century. After Columbus discovery, the Portuguese took it to west coast of Africa in the sixteenth century (Jones 1959), to east coast of Africa in eighteenth century (Barnes 1975; Jennings 1976), to India beginning of nineteenth century, and then to the Pacific by the Spanish (Jennings 1976). Since then cassava has developed wide diversity in different parts of the world especially in Africa (Gulick et al. 1983). There are more than 50 collections of cassava worldwide conserving about 10,000 accessions ex situ of the estimated 27,000 distinct landraces found in situ worldwide (Table 12.2). To represent the complete diversity of cassava 15,000 landraces have to be conserved with about half of them from the Americas. Two international centers (CIAT and IITA) conserve cassava germplasm where CIAT targets on Americas and Asia diversity and IITA on Africa. The collection at CIAT includes 5,301 accessions of landraces, 883 accessions of wild related species and 408 accessions of breeding material (2011 data provided by Daniel Debouck and Ericson Aranzales, CIAT genebank). The collection at IITA consists of 2,556 accessions (2011 data provided by Dominique Dumet, IITA genebank). Sweet potato (root): All the diversity of sweet potato belongs to one species, Ipomoea batatas (2n = 6x = 90), in the family Convolvulaceae, genus Ipomoea, subgenus Eriospermum, section Eriospermum, series Batatas (Austin and Huaman 1996). Austin (1977) studied a range of morphological 2n = 4x = 60 forms and considered all of them as synonyms to I. batatas. It is an ancient crop of American origin. Carbon-dated sweet potato remains in the Chilca canyon in Peru were estimated to be from 8,000 to 10,000 BP (Engel 1970; Yen 1974). However, Austin (1988) postulated its origin was between the Yucatan peninsula of Mexico and the mouth of Orinoco River in Venezuela and it was widespread by 2,500 BC from southern Mexico to southern Peru (O’Brien 1972). Austin (1988) described two main groups – the aje (an Arawakan word) group with starchy less sweet tuber and the batata group with starchy sweeter tuber. To date two distinct groupings between the Central American and the South American cultivars can be detected based on chloroplast and nuclear SSR marker studies and this has led to the suggestion of duo independent domestications, in Central/Caribbean America and in the north-western part of South America (Roullier et al. 2011). There is no wild I. batatas but it can survive in abandoned cultivated fields either directly from vegetative growth or seedlings of seed naturally produced. This could be the case as for accession, K123 with 2n = 6x = 90, that Nishiyama (1963) collected in Mexico as I. trifida and Jones (1967) concluded that it could be I. batatas derivative from morphological, crossing and chromosome studies. The hexaploid nature of sweet potato indicates its complex genetic origin. According to the Global Strategy for Ex Situ Conservation of Sweet potato Genetic Resources (http://www.croptrust.org/main/identifyingneed. php?itemid=513), the series Batatas in addition to sweet potato (I. batata) has 13 wild species of which all are endemic to the New World except I. littoralis from Australia and Asia. These species (Taxon Group 2 genepool) are therefore closely related to sweet potato and thus could all contribute to the genome of modern sweet potato. postulated that The origin of sweet potato was postulated by Nishiyama (1971) and Nishiyama et al. (1975) to come from 6× I. trifida which came from 2 29 93 2,000 72 Americas Argentina Bolivia Brazil Colombia Costa Rica Cuba Dominican Rep Ecuador El Salvador French Guiana Guatemala Guyana Haiti Honduras Jamaica Mexico Nicaragua Panama Paraguay 30 3,075 Region/country 27 (0.5%) 20 (0.4%) 106 (2.0%) 3 (0.1%) 47 (0.9%) 208 (4.0%) 92 (1.7%) 122 (2.3%) 7 (0.1%) 1,281 (24.7%) 25 (1.0%) 2,000 (38.5%) 81 (1.5%) 82 (1.5%) 5 (0.1%) 116 (2.2%) 10 (0.2%) In CGIAR centersb Status of ex situ collections GCDT surveya (2008) 1,800 70 75 25 80 8 0 50 25 0 20 0 75 10 40 300 160 18 1,600 3,000 100 100 50 250 25 50 75 50 100 50 50 200 100 75 500 250 300 8,000 1,000 19 18 45 134 25 50 0 50 100 23 50 94 97 28 292 128 293 6,719 2,500 100 100 25 200 20 50 100 50 75 25 25 100 75 50 400 200 200 4,000 Estimates of unique local landraces (excluding duplicates and breeding/ experimental material)c Estimate in situ accessions Proposed minimum ex Ex situ In situ missing from CGIAR situ no. of accessionse centersd Table 12.2 Status of ex situ cassava collections, estimates of unique local landraces, estimate of accessions not in CGIAR centers and proposed minimum number of accessions to be conserved in the world (based on Table 12.3 of the ‘Global Conservation Strategy for Cassava and Wild Manihot Species’; accessions for the two CGIAR centers (CIAT in light blue and IITA in purple) were based on 2011 data provided by Daniel Debouck and Ericson Aranzales, CIAT genebank, and Dominique Dumet, IITA genebank) 258 D. Tay Peru 639 Puerto Rico Suriname USA Venezuela Sub-total 5,940 Africa Angola Benin Botswana Burkina Faso Burundi Cameroon Cape Verde Central African Republic Chad 45 Congo, Republic of Cote d’Ivoire 170 D.R.Congo 140 Gabon Gambia Ghana 36 Guinea Bissau/Conakry 50 IITA (Unknown) Kenya Liberia Madagascar Malawi 192 50 200 300 1,000 75 25 400 175 200 100 200 175 200 10 2 40 150 250 300 40 5 300 120 150 75 4 150 179 (7.0%) 17 (0.7%) 2 (0.1%) 4 (0.2%) 50 (2.0%) 25 (1.0%) 27 (1.1%) 6 (0.2%) 264 (10.3%) 133 (5.2%) 24 (0.1%) 12 (0.5%) 8 (0.3%) 3 (0.1%) 6 (0.2%) 6 (0.2%) 300 400 20 15 50 300 20 200 1,000 15,925 1,500 25 75 10 300 10 10 225 5,148 550 17 0 2 (0.1%) 329 (12.9%) 10 (0.2%) 253 (4.8%) 4,933 421 (8.1%) 17 (0.3%) 50 50 100 100 25 50 100 500 50 10 100 75 100 100 100 20 20 25 250 500 9,835 1,000 15 25 (continued) Tropical and Subtropical Root and Tuber Crops 190 94 196 170 47 178 277 978 75 20 62 63 297 0 20 9 50 81 7 198 747 11,074 1,079 8 75 12 259 Rwanda Senegal Sierra Leone South Africa Sudan Swaziland Togo Uganda U.R.Tanzania Zambia Zimbabwe Sub-total Asia–Oceania Australia Cambodia China Fiji Islands India Indonesia Mali Mozambique Niger Nigeria Region/country Table 12.2 (continued) 130 4 1,272 103 118 0 10 10 209 25 124 40 GCDT surveya (2008) 253 (2.6%) 2 (0.1%) 6 (0.1%) 1 (0.1%) 2,549 128 (5.0%) 14 (0.5%) 3 (0.1%) 69 (2.7%) 10 (0.4%) 1,207 (47.0%) 19 (0.4%) 1 (0.1%) 1 (0.1%) In CGIAR centersb Status of ex situ collections 10 5 600 150 125 10 100 5 10 10 100 250 250 75 6 3,743 1 75 50 500 25 15 25 750 1,000 150 50 200 25 10 20 200 1,000 1,000 200 25 7,480 25 250 75 800 25 13 19 750 864 148 50 90 25 10 20 24 986 997 200 25 5,368 24 250 65 253 10 20 20 200 500 75 25 100 10 10 10 100 500 500 150 10 3,675 20 150 20 200 Estimates of unique local landraces (excluding duplicates and breeding/ experimental material)c Estimate in situ accessions missing from CGIAR Ex situ In situ Proposed minimum ex centersd situ no. of accessionse 260 D. Tay 11 150 31 473 7,685 95 52 9 (0.2%) 375 7,857 37 (0.7%) 6 (0.1%) 61 (1.1%) 7 75 130 0 50 10 120 20 1,132 10,068 50 100 25 50 100 500 25 100 11 50f 50 2,965 26,986 39 25 50 100 494 25 100 6 150 41 2,708 19,954 50 10 20 50 250 10 50 11 25 25 1,170 14,791 b Information provided by survey respondents Accessions for the two CGIAR centers (CIAT in light blue and IITA in purple) were based on 2011 data provided by Daniel Debouck and Ericson Aranzales, CIAT genebank, and Dominique Dumet, IITA genebank c These are approximations based on region (primary or secondary center of diversity), area planted, ex situ accessions reported, and personal knowledge of the author about diversity in individual countries d Estimates of in situ unique landrace varieties minus number of accessions in CGIAR centers e Estimated number of accessions that would be required to fully represent a country’s cassava genetic diversity. More accurate estimates will be possible as more molecular information becomes available on genetic variation f There appear to be a large number of landrace varieties lost from farmers’ fields and home gardens in the past two decades due to declining cassava production a Malaysia Micronesia Myanmar Papua New Guinea Philippines Polynesia Sri Lanka Thailand Vanuatu Vietnam Sub-total Total 12 Tropical and Subtropical Root and Tuber Crops 261 262 D. Tay 3× I. trifida and in turn came from the cross of I. littoralis (4×) and I. x leucantha (2×) where the former derived from the latter. However, most of I. trifida are diploid. Austin (1988) postulated that I. trifida, I. triloba and I. tiliacea all contributed to the genome of sweet potato. There are some 36 collections of sweet potato worldwide and conserving about 29,000 accessions (Table 12.3). The related wild species are poorly represented in Table 12.3 Overall composition and size of the sweet potato collections included in this assessment (Source: the Global Strategy for Ex Situ Conservation of Sweet potato Genetic Resources – http://www.croptrust.org/main/identifyingneed.php?itemid=513) No. of accessions Region/collection/countrya Wild Latin America and Caribbean 1. International Potato Center – PER 1,160 2. Instituto Nacional de Tecnología Agropecuaria Castela 122 – ARG 3. Empresa Brasilera de Pesquiza Agropecuaria – BRA 4. Instituto Nacional de Investigaciones de Viandas 95 Tropicales – CUB Sub-total 1,377 North America 5. United States Department of Agriculture’s Agricultural 447 Research Service – USA Sub-total 447 Asia 6. CIP-East South East Asia and Pacific – IDN 7. Indonesian Agriculture Biotech and Genetic Resources Institute – IDN 8. The Philippines Root Crop Research and Training Center – PHL 9. Xuzhou Sweetpotato Research Center – CHN 40 10. MOKPO Experiment Station – PRK 11. Plant Genetic Resources Center – VNM 12. The National Plant Genetic Resources Laboratory – PHL 13. National Institute of Agrobiological Sciences – JPN 14. Central Tuber Crop Research Institute – IND 84 15. Northern Philippines Root Crops Research and Training Center – PHL 16. Malaysian Agricultural Research and Development Institute MYS 17. PHRC – THA 18. Central Agricultural Research Institute – LKA 19. South Korea – KOR Sub-total 124 Africa 20. Centre de Developpement Rural et de Recherche Appliquee – MAG Cultivated Total 6,360 362 7,520 484 1,024 535 1,024 630 8,281 9,658 755 1,202 755 1,202 1,366 1,520 1,366 1,520 801 801 1,044 497 480 183 1,084 497 480 183 1,600 3,778 180 1,600 3,862 180 72 72 236 131 430 12,318 236 131 430 12,442 98 98 (continued) 12 Tropical and Subtropical Root and Tuber Crops 263 Table 12.3 (continued) No. of accessions a Region/collection/country Wild 21. National Crops Resources Research Institute – UGA 22. CIP-South Saharan Africa – UGA 23. Mulungu Research Center – COD 24. Kenya Agricultural Research Institute – GHA 25. University of Ibadan – NGR 26. Mpnza Research Station – ZMB 27. Agricultural Research Institute – MWI 28. Instit. Investigacao Agrarian de Mozambique – MOZ 29. Vegetable and Ornamental Plant Institute – ZAF 30. Agricultural Research Institute – AGO 31. EARI, Awasa, Ethiopia – ETH 32. Kenya Agricultural Research Institute – KEN 33. Horticulture Research Institute – TNZ 34. Rwanda Agricultural Research Institute – RWA 35. INIDA, S.J. Orgaos – CPV Sub-total 0 Melanesia 36. National Agricultural Research Institute – PNG Sub-total 0 Total 1,948 Cultivated Total 1,808 141 120 167 90 258 139 102 444 34 319 120 584 159 11 4,594 1,808 141 120 167 90 258 139 102 444 34 319 120 584 159 11 4,594 1,120 1,120 27,068 1,120 1,120 29,016 a Data of 18 collections: 1–5, 6–15, 20–21 and 36 were obtained from the survey’s questionnaires and make a total of 25,459 accessions; the remaining 18 collections are from the Manila workshop and make a total of 3,557 accessions these collections. The collection at CIP includes 7,777 accessions of sweet potato from 59 countries and 1,178 accessions of 67 wild species including 183 accessions of I. trifida. It consists of 2,089 Peruvian landraces of which about 50% are of duplicates, 1,568 Latin American excluding Peruvian landraces of which an estimated 50% are duplicates, the AVRDC collections with Asia, Oceania and to great extent worldwide representations of landraces and improved germplasm, and the IITA breeding lines. These collections are underutilized in breeding work due to the lack of evaluation information for important agronomic traits. Major disease of sweet potato is sweet potato virus disease complex (SPVD) which consists of the combination of two viruses – sweet potato chlorotic stunt virus and sweet potato feathery mottle virus and the main pests are sweet potato weevils (Cyclas spp.). The crop has large genetic variation for crop duration, adaptation, nutrient composition, etc. Currently, CIP is working with the Global Crop Diversity Trust to introduce germplasm from Southeast Asia, Oceania and Africa in the implementation of the Global Strategy for Ex Situ Conservation of Sweet Potato Genetic Resources (http://www. croptrust.org/main/identifyingneed.php?itemid=513). Yams (corm): They are in the family Dioscoreaceae and genus Dioscorea with over 600 species. The cultivated species are in the following sections from both the Old and New World: (1) Section Enantiophyllum – Dioscorea alata L. (water yam, greater yam, white yam), D. glabra Roxb., D. nummularia Lam., D. transversa 264 D. Tay Br. of Asia and Oceania origin; D. japonica Thumb. (Chinese yam, igname de Chine), D. opposita Thumb. of Sino-Japanese origin; and D. cayenensis Lam. (yellow yam), D. rotundata Poir. (white Guinea yam, white yam) of Africa; (2) Section Lasiophyton – D. pentaphylla L., D. hispida Dennsdest, D. dumetorum (Knuth) Pax (bitter yam); (3) Section Opsophyton – D. bulbifera L. (aerial yam); (4) Section Combilium – D. esculenta (Lour.) Burk. (Chinese yam, lesser yam); and (5) Section Macrogynodium – D. trifida L. (cush-cush yam) of tropical America (Martin 1974a, b, 1976; Martin and Degras 1978a, b; Martin and Sadik 1977). Hanson (1985) named in total 13 food and seven medicinal species with different ploidies. Dumont et al. (1994) described 16 wild and 7 cultivated species in the domestication of yams in Cameroon. They are mainly dioecious. D. rotundata (2n = 40) and D. cayenensis (2n = 60 and 80), the two major species cultivated in Africa because of their preferred tuber organoleptic properties represent 95% of yam production in the world (FAOSTAT 2009). However, Martin (1976) considered D. alata (2n = 40, 60 and 80) from Southeast Asia the most important species because of its wide introduction to both Africa and America for its agronomic and nutritive value, and wide acceptance. D. rotundata and D. cayenensis, originated in West Africa, are related (Martin and Rhodes 1978; Akoroda and Chheda 1983; Terauchi et al. 1992) and some taxonomic treatments put them together as a single species complex. Terauchi et al. (1992) using RFLP analysis on chloroplast and ribosomal DNA postulated that D. rotundata was domesticated from either D. abyssinica, D. liebrechtsiana or D. praehensilis or their hybrids and D. cayenensis from hybrids of D. burkilliana, D. minutiflora or D. smilacifolia as father and D. rotundata, D. abyssinica, D. liebrechtsiana or D. praehensilis as mother. Hamon et al. (1995) using morphological studies also proposed the involvement of D. burkilliana, D. abyssinica and D. praehensilis in their domestication. There are 21 yam collections in the world which include the IITA collection of 3,166 accessions (Table 12.4). The global conservation strategy for yams is under development to identify the status of the major collections globally and the missing gaps, to prioritize genepools for collecting and safe duplication at another site, and to formulate a global conservation strategy. Conservation of yams in field genebank requires a period of storing some huge tubers between annual harvesting and planting time and at IITA controlled environment room of 18°C and 50–60% RH is used (Ng 1993). Edible Aroids (corm): The family Araceae has the following food genera: Alocasia, Amorphophallus, Colocasia, Cyrtosperma and Xanthosoma. Among them, Colocasia (taro) and Xanthosoma (cocoyam, tannier) are the most commonly grown in Southeast Asia to China, Korea and Japan, Melanesia, the Pacific Islands, New Zealand, Mediterranean and tropical Africa and America. Taro is an important staple in South Pacific islands such as Tonga and Samoa, and parts of Papua New Guinea. The minor aroids, Alocasia, Amorphophallus, Cyrtosperma (giant swamp taro) are used only in specific regions and countries. For example, the giant swamp taro is mainly grown in the atoll countries of the Pacific and the Amorphophallus in Japan and Taiwan as a functional food. There are no organized 12 Tropical and Subtropical Root and Tuber Crops 265 Table 12.4 Number of yam accessions and percentage of the collection maintained in ex situ conditions per species (Source: draft of the global strategy for the conservation and use of edible yam including 2010 report on the state of the world’s plant genetic resources from 57 countries (FAO 2010) and the yam global strategy survey) FAO data 2010 GCDT survey data Species D. alata D. bulbifera D. cayenensis D. esculenta D. nummularia D. opposita-japonica/ japonica D. pentaphylla D. rotundata/rotundatacayenensis D. transversa D. trifida Others/unknown Total No. of accessions Percentage of the collection No. of accessions Percentage of the collection 3,904 334 843 662 43 118 24.5 2.1 5.3 4.2 0.3 0.7 2,763 164 393 215 81 20 35.9 2.1 5.1 2.8 1.1 0.3 68 4,208 0.4 26.5 65 3,631 0.8 47.2 2 154 5,567 0.0 1.0 35.0 10 35 320 0.1 0.5 4.2 15,903 100.0 7697 100.0 collections. However, many of their species are valued as ornamentals and therefore some unique collections are found in botanic gardens and arboreta. Effort should be made to collect and conserve them because they have shown to be more resistance to pests and diseases compared to taro and have been reported to be used as substitution in some countries. The center of origin and domestication of Colocasia esculenta is in Southeast Asia more specifically the region from Myanmar to Bangladesh (Plucknett 1976) include northeast India where several Colocasia species occur (Matthews 1990; Edison et al. 2004). C. esculenta var. aquatilis, which is distributed in IndoMalaysian region, China, Japan, Melanesia, northern Australia and Polynesia and has wide diversity across its distribution, is postulated to be the progenitor of cultivated taro (Matthews 1991, 2004) and that domestication in Southeast Asia and Melanesia was from their respective native var. aquatilis populations thus forming two separate genepools overlapping in Indonesia with high diversity if diploids (Matthews 1990, 1991, 2004; Irwin et al. 1998; Lebot 1992, 1999; Kreike et al. 2004; Lebot and Aradhya 1991; Yen 1993). Their overall total diversity is low in term of isozyme, RAPD, AFLP and SSR markers used on the Taro Network for South Asia and Oceania – TANSAO’s collection of 2,300 accessions from Indonesia, Malaysia, the Philippines, Thailand, Vietnam and the Pacific countries of Papua New Guinea and Vanuatu (Kreike et al. 2004; Quero-Garcia et al. 2006; Noyer et al. 2004). Southeast Asia, Papua New Guinea and Solomon Island have greater diversity than in the Pacific. With its eastward migration to Polynesia its diversity progressively decreases away from Melanesia (Lebot 1992; Yen 1993). The diverse 266 D. Tay morphotypes in Polynesia are likely somaclonal variation derived from a narrow genetic base of a few mother clones (Irwin et al. 1998; Lebot and Aradhya 1991; Lebot et al. 2004). Purseglove (1972) described two cultivated forms – the dasheen (C. esculenta var. esculenta) and eddoe (C. esculenta var. antiquorum). The dasheen usually has a large central corm and higher dry matter content, and the eddoe has a small central corm with a large number of smaller cormels with lower dry matter content and slimy even after cooking (personal experience). Intermediate forms exist and isozymes, AFLP, RAPD or SSR markers have not shown consistent difference between them (Vincent Lebot of CIRAD in Edible Aroid Conservation Strategies – http://www.croptrust.org/main/identifyingneed.php?itemid=513). The trueness of the two botanical varieties was challenged (Hay 1998). The differences between the ‘wild’ and cultivated forms are likely the alkaloid content which causes irritation to skin and the corm size. Wild forms are used as pig fodder and sometimes leaf petioles are eaten and their leaf blades are preferably used as food wrapper than that of the cultivated forms (personal experience in Sarawak). Other wild taros – C. fallax and C. affinis (both in the arc of Himalayan India, Nepal to Myanmar) and C. gigantea (eastern China, Indonesia, Myanmar, Sri Lanka, southern Japan, Thailand and Vietnam) and C. gracilis (Sumatra), C. mannii (Assam) and C. virosa (eastern India) are yet to be collected and studied in details. For example C. gigantea has closer affinity to Alocasia based on mitochondrial DNA analysis (Matthews 1990). A comprehensive DNA analysis of the wild and cultivated diversity is needed to clarify the taxonomy of the genus Colocasia, and the origin and domestication of taros. The major collections of taro are in Asia and the Pacific. These are some of the results of TANSAO (1998–2001) and Taro Genetic Resources Network – TaroGen (1998–2003) projects (The Edible Aroid Conservation Strategies – http://www. croptrust.org/main/identifyingneed.php?itemid=513). Under TANSAO, 2,300 accessions from Indonesia, Malaysia, the Philippines, Thailand, Vietnam and the Pacific countries of Papua New Guinea and Vanuatu were collected and 168 accessions were selected based on morphological and isozyme diversity of each country to form a core collection for network exchange and utilization. TaroGen project collected some 2,199 accessions in network countries of Pacific Islands (Cook Islands, Fiji, Niue, Papua New Guinea, Samoa, Solomon Islands, Tonga and Vanuatu) and 211 accessions were selected accordingly as regional core collection. Both the two core collections are among the 857 accessions (December 2009) that are safely conserved as in vitro collection at the Centre for Pacific Crops and Trees (CePaCT) of the South Pacific Commission in Fiji, a regional germplasm center for the conservation of core collections, back-up national holdings, and virus index, multiply and disseminate germplasm. The genus Xanthosoma is originated from tropical America, probably northern South America (Clement 1994; Giacometti and Leon 1994). The edible species according to Wilson (1984) include X. violaceum, X. atrovirens, X. caracu, X. jacquini, X. maffafa, X. belophyllum and X. brasiliense. Brown (2000) named X. sagittifolium and X. violaceum as the main species and Reyes Castro (2006) reduced all of them to X. sagittifolium as the differences between them are leaf 12 Tropical and Subtropical Root and Tuber Crops 267 shape, pigmentation and other morphological features. Xanthosoma is the most grown aroid in the world (Matthews 2002). The collections in the world based on the survey in the formulation of the Edible Aroid Conservation Strategies are available at – http://www.croptrust.org/main/identifyingneed.php?itemid=514. Minor Andean root and tuber crops (ARTC): They consist of nine underutilized crops domesticated from different botanical families to exploit all the agroecosystems of the Andes (Table 12.5). Three are tuber crops, mashua, oca and ulluco, usually grown in mixed stand with native potato in traditional cropping system for their starchy swollen stolons. Their domestication and use are parallel to that of potato. Like potato they are annual, produce seed and tubers are used in propagation. In recent years, these tubers are being developed as new crops in countries like New Zealand (King 1988). Achira is grown for its swollen starchy rhizomes in warm Andean valleys. The main use is its starch for baking local recipes but in some communities the fresh rhizomes are fermented to convert the starch into sugars for use as traditional regional snack. Ahipa, arracacha and mauka are starchy root crops grown mostly for subsistent use. However, arracacha has potential to be developed into an important specialty crop because of its easily digestible starch and this is exploited in Brazil. The Andean ahipa unlike the Asian sweet juicy type is not used as snack. Yacon is a sweet juicy root crop for use raw as refreshing snack. It is a functional food for people on diet and with diabetes because of its high contents of low calorie fructans and human unmetabolized inulin. Maca, a turnip relative, is a swollen hypocotyl crop grown at high altitude at frost zone for its nutraceutical value. ARTC are mainly cultivated as part of the food diversity and security system in the Andes from Venezuela to northern Argentina. However, in recent years maca and yacon have been developed into commercial crops because of their nutraceutical value as energy and diabetic supplement, respectively. Table 12.5 Estimated accessions of Andean root and tuber crops maintained by Andean germplasm banks (September 2011) Ecuadora Perub Boliviac CIPd Total Oca Olluco Mashua Yacon Achira Arracacha Mauka Ahipa Maca 130 245 26 35 35 20 12 35 – 2,961 1,689 828 311 297 286 103 – – 334 140 39 36 19 37 – 13 – 492 420 54 29 35 7 4 54 30 3,917 2,494 947 411 386 350 119 102 30 Total 538 6,475 618 1,125 8,756 a INIAP b INIA, UNSAAC, UNSCH, UNMSM, UNC c INIAF (IBTA-PROINPA) d CIP (only in trust materials under ITPGRFA) 268 D. Tay Achira (rhizome): It belongs to the family Cannaceae, species Canna indica L. C. edulis Ker-Gawler is its synonymy (Maas and Maas 1988; Brako 1993). The name is Quechua. The genus consists of 25–60 species in America and Asia. In addition to C. indica, C. iridiflora from the Peruvian Andes and C. paniculata in Peru, Brazil and Chile also produce tuberous rhizomes, and the New World ornamental species are C. glauca, C. iridiflora and C. flacida (Maas and Maas 1988; Brako 1993). Achira comprises of both diploid (2n = 2x = 18) and triploid (2n = 3x = 27) cultivars (Darlington and Janaki-Ammal 1945; Gonzales and Arbizu 1995) and the diploids produce dark hard seed through mainly self-pollination. It is a perennial and grows from 1,000 to 2,900 m asl. The centers of genetic diversity and production are in the upper valley of Apurimac (Arbizu 1994; Meza 1995), and low valleys of Ayacucho in Peru, in the Patate of Ecuador (Espinosa et al. 1993), and in the departments of Huila and Cundinamarca in Colombia (Morales 1969). However, it is grown from Mexico to Argentina but in small scale. Vietnam reported growing about 30,000 ha where the starch is used mainly for making noodle (Ho and Hao 1995). There are 386 accessions in Andean genebanks (Table 12.5) which include 35 accessions maintained at CIP. The number of unique accessions among the different collections is unknown. Ahipa (root): It is a Leguminosae, genus Pachyrhizus with three cultivated species, namely, P. ahipa (Weddell) Parodi, P. erosus and P. tuberosus, and two wild relative species – P. panamensis and P. ferrugineus (Sørensen 1988). P. ahipa is mainly cultivated in Bolivia and some in northern Peru (Orting et al. 1996) and in northwest Argentina (Towle 1961). P. erosus (known as jicama in Mexico) from southwest Mexico to northwest Costa Rica is widely used there and worldwide including Southeast Asia, Far East, Indian Subcontinent and west coast of Africa (Sørensen 1988). P. tuberosus from the Amazonia is still in cultivation in Peruvian Amazonia. P. panamensis is from Panama and southwestern Ecuador to 800 m asl and P. ferrugineus from Mexico to Colombia to 1,600 m asl (Sørensen 1988). The name ahipa is from Quechua word aqipa or asipa and its other names in Aymara are konori and villu, in Spanish jiquima in Peru (Yacovleff 1933) and in English yam bean (which is more referring to P. erosus in Asia). The domestication of ahipa is poorly known. Brucher (1989) postulated its derivation from wild forms in the eastern slope of Andes and Rea (1995) reported wild forms in the department of La Paz, Bolivia. Archeological evidences in Peru show its cultivation in the Nazca and Mochica cultures (Yacovleff 1933; Yacovleff and Herrera 1934–1935; Brucher 1989). It was described as a ‘very watery and sweet’ and ‘used as a fruit’ by the Spanish chronicler Bernabe Cobo (Yacovleff and Herrera 1934–1935). In fact, in Asia P. erosus is a common vegetable and is used sometimes like a fruit in vegetable sweet salad and as refreshing snack when consumed raw after removing the peel (personal experience). This is because the dry matter is 19–25% and about half is sugar and the remaining half is 10% protein and 40% starch (Orting et al. 1996). The seed extract of P. erosus is used in Southeast Asia as insecticide (personal experience) due to the presence of rotenone, pachyrhizid and erosone. Propagation is by seed and as in many legumes ahipa is self-pollinated. 12 Tropical and Subtropical Root and Tuber Crops 269 The Andean genebanks have 102 accessions of Pachyrhizus (Table 12.5). Presently, CIP has a project to collect P. tuberosus in the department of Junin, Peru and to date 54 accessions have been collected for research and conservation. Arracacha (root): It is an Apiaceae (Umbelliferae), species Arracacia xanthorrhiza . This is the only species in the family domesticated in the New World (Leon 1967) out of 30–36 wild species of this genus in the mountain ranges of Mexico, Guatemala, Costa Rica, Panama, Peru and Bolivia (Constance 1949; Mathias and Constance 1962, 1976; Hiroe 1979). The name is from Quechua word raqacha and other names in Aymara is lakachu, Amusha (Amazonian tribe) pueb, other Spanish names virraka, zanahoria blanca and apio criollo, and in English white carrot, Peruvian carrot and Peruvian parsnip. The names are referring to celery and carrot because the plant is like celery and the taste of the root is that of carrot. The leaves can be eaten like celery. The root is white to yellow and purple. It is an ancient crop (Bukasov 1930) and the ancestor is unknown. The genetic diversity is in Andean valleys of 1,500 to 3,000 m asl with warmer temperature where potato cannot be grown in Colombia, Ecuador, Peru and Bolivia. The volume of production is limited. However, starch of arracacha is easily digestible and is used in baby food production and other processed food. There are some 350 accessions in Andean genebanks (Table 12.5) and CIP has a collection of seven accessions. The number of distinct cultivars in these collections has not been compared. Tapia et al. (1996) reported only 17 distinct morphotypes out of 93 studied in the Ecuadorian collection, and Blas and Arbizu (1995) in Peru indicated 16 out of 32 accessions studied. Maca (hypocotyls): It is a Brassicaceae, species Lepidium meyenii Walper. L. peruvianum Chacón (Chacón 1990) is considered within L. meyenii in a recent revision of the genus (Al-Shehbaz 2010). The genus consists of some 150 species of annual, biennial or perennial mainly in temperate region of the world and L. sativum is the other cultivated species from the Old World (Bailey 1976). The name is a Quechau word, maca. The species is a biennial but the crop is managed as an annual in the high Andes (4,000 m) in order to harvest its swollen hypocotyls which are a traditionally functional food for impotency, stamina and female fertility. This may be attributed to its high protein content (10–14%) among tuber and root crops, high iron and calcium, high leusine and isoleucine, high palmitic, linoleic, oleic and stearic fatty acids, and high sterols (Tello et al. 1992; Dini et al. 1994). The planting propagule use is botanical seed and not vegetative sets. The domestication of maca is postulated to be in central Andes of Peru around Lake Chinchaycocha, Junin about 2,000 year ago (Rea 1992) but its ancestor is unknown. It is an octoploid (2n = 8x = 64) and self-pollinator (Quiros et al. 1996). Wild Lepidium occur from Ecuador to Argentina but their relationship with maca has not been reported. The center of diversity and production is in Central Highlands of Peru in the department of Junin and Pasco at altitude of above 4,000 m asl. It is the only crop that cans tolerant frost, hail and snow at these altitudes in addition to the bitter potato. The variation in term of foliage is low but the hypocotyl skin has variable color (Tello et al. 1992). CIP holds the only maca collection with 30 accessions (Table 12.5). 270 D. Tay Mashua (tuber): It belongs to the family Tropaeolaceae, genus Tropaeolum, section Mucronata, species Tropaeolum tuberosum Ruis and Pavon with two subspecies (42 chromosomes) – tuberosum and silvestre. The silvestre is the wild forms that do not produce tubers. In addition, there are 86 wild species endemic from Mexico to temperate South America including the ornamental nasturtium (Sparre and Anderson 1991). The name mashua is derived from Quechua names maswa and mashwa and other names are añu in Quechua, isaño in Aymara, mashua in Spanish in Peru and Ecuador, and cubio or navo in Colombia. The plant is similar to nasturtium but with smaller orange long peduncle flowers. The tuber shape is typically claviformis with tapered stolon end, and peel and flesh colors are diverse from whitish cream to dark purple (usually refer to as ‘black’ mashua) as in native potato. In Peru, the ‘black’ cultivar is believed to have the property against cancer (traditional knowledge) and in fact Noratto et al. (2004) reported that mashua extracts suppress tumor cell proliferation. It is also said to have anti-aphrodisiacal property (Yacovleff and Herrera 1934–1935; Johns et al. 1982) and as a diuretic for kidney ailments. The main area of diversity and production is from central Peruvian Andes to central Bolivia and in Ecuador the provinces of Carchi and Cañar but it is grown from the Andes of Venezuela to northwestern Argentina from 2,600 to 4,000 m. It is an ancient crop based on archeological evidence in ceremonial pottery representation of Wari culture in Peru (600–1,100 AD). In traditional mixed stand Andean planting system mashua is known as the ‘guardian of potato’ and it is inter-planted and surrounding the potato field because it repells pests. This could be due to its isothiocyanate content (Johns et al. 1982) and for consumption the tubers have to be cured under the sun for 4–6 days before cooking to remove the chemical odor. Some 947 accessions of mashua are conserved in genebanks in the Andean countries including 54 accessions in CIP collection (Table 12.5). These collections have not been compared to eliminate the duplicates so that the number of unique cultivars can be estimated. Mauka (root): It is a Nyctaginaceae, species Mirabilis expansa Ruiz and Pavon, the only species in the genus with edible roots. The name is of Aymara origin, mauka and other names include arracacha de toro, chago, miso, pega-pega, tazo and yucca inca. It is a perennial and the edible part is the thickened long fusiform storage root. Propagation is by cutting from underground and basal stems (Rea and Leon 1965; Seminario 1993). It is rarely found in Peru and the Andean region and thus disappearing as a crop as compared to its ornamental relative, Mirabilis jalapa (The four o’clock flower or marvel of Peru) which is popular in Peru. The reasons could be that it has no reported functional food value and the root is bitter if not cured properly in the sun before use. Its domestication and ancestor have not been studied and no archeological evidence has been reported. There are 60 species distributed in the Americas from Mexico to Chile from sea level to more than 3,000 m asl (MacBride 1937; Weberbauer 1945; Rea 1992). The Andes has the most diversity with ten species in Peru (Liesner 1993). Its cultivation is reported in Cajamarca, Amazonas and La Libertad department in northern Peru (Seminario 1993), Puno department in 12 Tropical and Subtropical Root and Tuber Crops 271 southern Peru (Vallenas 1995), La Paz and Cochabamba department in Bolivia (Rea 1992) and Cotopaxi and Pichincha province in Ecuador (Tapia et al. 1996) growing in altitude between 2,000 and 3,000 m asl. The Andean genebanks have some 119 accessions (Table 12.5) and the number of unique cultivars has not been studied. CIP is conserving four accessions. Oca (tuber): It belongs to the family Oxalidaceae, genus Oxalis, section Tuberosae, species Oxalis tuberosa Mol (octoploid with 2n = 8x = 64). There are about 80 wild species in the Andes with many endemic in Peru (MacBride 1949; Ferreyra 1986; Pool 1993) and they have different ploidy levels diploids, tetraploids and hexaploids (de Azkue and Martinez 1990) and their relationships were illustrated by Emshwiller and Doyle (2002). The name oca is derived from Quechua names okko, oqa and uqa and it known as apilla in Aymara. As in potato there are sweet and bitter cultivars. The former is for direct cooking and the latter processed into kaya, the dehydrated storable form as for chuño in potato. Flores (1991) reported that during the processing of kaya antibiotics including penicillin, streptomycin, ampicillin and nystatin were found and postulated that the traditional consumption of kaya after child birth help in fast recovery is due to the antibiotics. Oca is also an ancient crop domesticated probably 4,000 BP (Hawkes 1989). Its present cultivation ranges from the Andes of Venezuela to northern Argentina and Chile at 2,500 to 4,000 m asl. However, the main diversity and production concentrate in the central highlands of Peru to central Bolivia (Rea and Morales 1980; Arbizu and Robles 1986; King 1988). The tuber can easily be confused with that of mashua by inexperience eyes. In fact, its cylindrical shape instead of the tapering shape of mashua is quite distinctive. As in potato and mashua the variability is diverse in term of tuber skin and flesh color. Nearly 3,917 accessions of oca are conserved in genebanks in the Andean countries including 492 accessions in CIP collection (Table 12.5). These collections have not been compared to eliminate the duplicates so that the number of unique cultivars can be estimated. Ulluco (tuber): It belongs to the family Bassellaceae, genus Ullucus, species Ullucus tuberosus Caldas with two subspecies where subsp. tuberosus is the cultivated forms and subsp. aborigineus the wild forms (Sperling 1987). Both subspecies are diploid with 2n = 2x = 24. However, cultivated triploid (Cardenas and Hawkes 1948; Gandarillas and Luizaga 1967; Larkka et al. 1992) and tetraploid (Mendez et al. 1994) forms are also found. Ulluco came from the Quechua word ulluku relating to male organ probably referring to its shape. It is called ulluma or illaco in Aymara and also called papa lisas, melloco and other names. As for oca it is said to be cultivated some 4,000 BP in central Peruvian Andes to Bolivia (Hawkes 1989; Martins 1976) from the wild subsp. aborigineus (Sperling 1987). Presently, it is grown from Colombia and Venezuela in the north to northwestern Argentina in the south and in Peru it is most widely eaten among the three minor tubers. Its leaves are also eaten in some Andean communities as nutritive vegetable as in Asia for Basella alba and nigra belonging to the same family. However, the center of diversity and production is in central Peruvian Andes to 272 D. Tay central Bolivia (Rea and Morales 1980; Arbizu and Robles 1986; King 1988). In Ecuador, high diversity occurs also in the provinces of Canar, Pichincha, Imbabura and Chimborazo (Castillo et al. 1988). There are some 2,494 accessions maintained in genebanks in Andean countries (Table 12.5) including 420 accessions in CIP genebank. However, these collections have not been compared so the number of unique cultivars is not known. Morphological study at CIP showed that about half of the collection is of duplicates with 86 morphotypes out of 160 accessions (Vivanco and Arbizu 1995) and in Ecuador 57 out of 287 accessions (Tapia et al. 1996). Yacon (root): It is an Asteraceae (Compositae), species Smallanthus sonchifolius (Poeppig and Endlicher) (Robinson 1978). It was previously Polymnia sonchifolia (Wells 1965). The genus has 21 species endemic in the New World concentrating in Peru, Colombia and Venezuela at altitude range of 500–4,000 m asl (Wells 1965; Robinson 1978). Yacon comes from the Quechua word yakun referring to its sweet juicy storage roots of some 86% water content. In Aymara it is called aricoma, in Spanish jicama and arboloco and in English yacon. It thus makes a refreshing snack after peeling and eaten fresh like fruits. However, its value is the fructans, a group of low-calorie compounds that aid human intestinal flora and hyperpilemia (Hata et al. 1983) and inulin, a polymer of mainly fructose which is not metabolized by human (NRC 1989) and thus favor by dieters and people with diabetes. Other species with functional food value are S. uvedalius, S. glabratus and S. maculatus (Wells 1965; Uphof 1968; Robinson 1978). Archeological evidences showed that yacon was grown during Candelaria culture (1–1,000 AD) in Argentina (Zardini 1991) and Nazca culture (100– 1,000 AD) in Peru (O’Neal and Whitaker 1947). Its domestication and ancestor are not known. A species that produces tuberous roots is S. conatus from Argentina, Brazil, Uruguay and Paraguay. Yacon is widely grown in the Andes from Venezuela to northwest Argentina and the production is increasing because of its functional food value for fresh use and processed into medicinal products including tea making from its leaves. The genebanks in Andean countries maintain 411 accessions (Table 12.5) and CIP conserves 29 accessions. The number of duplicates within and among the different collections has not been studied. 12.3 Conservation Strategy The RTC are usually conserved as individual genotypes (clones) by vegetative propagation methods to ensure that they remain true to type. These clones usually can also sexually reproduce and some especially the balanced polyploids self-pollinate. However, the resulting generations segregate because of their genetic heterozygous nature. This means that most RTC genebanks use clonal conservation methods mainly as field and in vitro collection where the whole collection has to be regenerated in very short periods of a few months to a couple of years. In recently years, cryopreservation 12 Tropical and Subtropical Root and Tuber Crops 273 is being introduced and tested in well equipped genebanks as the long-term storage method. Because of all these the maintenance cost of RTC is several times higher as compared to seed conservation. To date, the debate continues on whether RTC should be conserved only as seed collection to reduce cost. This is a question on whether linkages of beneficial genes (genotypes) or individual genes/alleles (seed populations) should be the conservation objective. Many of the landraces might be the results of 100 years of selection and adaptation carried out by our farmer ancestors. For example, the ancient Inca artifacts of potato in pottery and stone models are very similar to some of the present day native potato cultivars and, thus, they represent the ‘winning’ linkages of genes bundled together. In RTC genebanks these linkages of genes are what are being conserved. On the contrary, when these clones are converted to seed populations many of the ‘winning’ linkages segregate and become displaced. On the other hand, the segregating seed population of an accession will provide a generation of head-start for breeders to evaluate and select the best individuals for further selection or for use as parents in breeding crosses. The cost in conserving a RTC collection is primarily determined by the size (number of accessions) of a collection. Take the case of the native potato collection at CIP which used to be more than 17,000 accessions and after the elimination of those duplicates through both morphological, and general protein and isozyme studies only 4,235 distinct accessions are currently conserved. The cost of maintaining the collection is thus reduced by four fold. Duplicate identification and elimination are the first priority in RTC genebanks. The RTC wild relatives (wild species) are conserved using seed conservation methods as populations to represent the genepools as being collected. Most RTC both wild and cultivated species have orthodox seed and thus suitable for long-term storage at −20°C. Similarly, the duplicates of the CIP potato collection have been converted to true seed for long term storage at −20°C. These seed collections (both CWR and cultivated duplicates) are the ones that are being put in safe duplication in the Svalbard genebank in Norway. Ex situ Conservation: The ex situ methods include field (including in greenhouse), in vitro, cryopreservation, and seed when the focus is on living plant conservation. Additionally, a pollen genebank should be explored because pollen can be conserved well at freezing temperatures and under cryopreservation. DNA samples can be frozen at −70°C for many years and CIP has initiated a DNA bank for potato, sweet potato and ARTC. Herbarium collection is another form of preserved DNA of each genotype in a collection. CIP has established a herbarium collection of all its collections. Each of the conservation methods has its advantages and disadvantages, and thus in most genebanks a combination of methods is employed to safeguard a collection. Field genebank: This is the most common method used especially in smaller genebanks where there is no tissue culture laboratory. Collections are either grown in the field or in containers, usually under cover in greenhouses. A new field is established when plants in the current field start to deteriorate. Similarly, new containers are planted to replace degenerated ones as required. The main advantages of this method are that it can be applied without a sophisticated laboratory and that the 274 D. Tay collection can be used for characterization, genetic identity monitoring and is readily available to provide planting materials for field trials. The disadvantages are that it is costly to plant and manage large collections yearly and the collections are subjected to the elements of natural disasters such as flood, frost, drought, and pest and disease infestation. In the latter, a collection through years of growing accessions collected and acquired from different places together in same fields allows cross-contamination of systemic diseases like viruses, phytoplasmas, bacteria, etc. In addition, adaptation is a problem where accessions collected from very different geographical regions and habitats often grow poorly at the genebank site. As the result some of the accessions become too weak to survive and this is one of the main causes of losing accessions in a collection. This also creates quarantine issues in their distribution and use. In most RTC genebanks field materials are not used for distribution. This could be minimized to certain extent by growing collections in quarantined greenhouses using stringent maintenance protocols. However, in this case the greenhouse and labor costs to manage the plants could be extremely high. At CIP the Peruvian and Latin American sweet potato collections are maintained in this manner in a slow-growth state and, similarly, the cassava collection at CIAT as ‘bonsai’ plants. Alternately, a cleaner growing field area has to be identified for growing the field collection with clean planting propagules. This is the case in the maintenance of the native potato collection at CIP where clean plants from tissue culture program are reconstituted into a set of clean field collection for growing in high Andes where there are fewer insect vectors to readily re-infest the clean stock. Coupled with a stringent selection of the best plants to be harvested for the next growing cycle seed tubers, this program has been very successful to reduce the recontamination of the clean stock by viruses and the resulting harvests are used for the repatriation program of cleaned accessions back to their original owner communities in CIP’s ‘Ruta Condor’ project. The management of field collection is easily subjected to mechanical mix-up of accessions due to two main causes: (1) handling of yearly regeneration of field collection which includes selection of suitable field plot free of pests, diseases and volunteer plants, planting, field management including accurate labeling, harvesting, storage (in potato at 4°C and 80% RH) and documentation; and (2) in vine propagated crops such as sweet potato and yams an accession with vigorous vine growth, if not managed well, can grow over the neighboring accessions and be mistakenly used for the next season planting. A protocol to compare individual accessions in the new field with that in the old field is absolutely essential. This combines with comparison of accessions in the new field with photographs or images of authentic genetics will minimize this error. The field genebank is therefore a costly conservation procedure. In vitro genebank: This is the storage of RTC collections as meristem culture in well controlled environment. Meristem culture method is chosen because of its reduced risk of somaclonal variation (mutation) as compared to other forms of tissue culture methods such as callus culture and embryogenesis. The growth of the in vitro plantlets in storage is slowed by controlling the light, temperature and osmotic pressure in the growing medium. The specific protocols for cassava, potato, sweet potato and yam are given in Table 12.6. The most well developed protocol is 12 Tropical and Subtropical Root and Tuber Crops 275 Table 12.6 Slow-growth in vitro collection protocols used in cassava at CIAT, potato and sweetpotato at CIP and yams at IITA (Source: final report on GPG2-1.2 collaborative activity: refinement and standardization of storage procedures for clonal crops – http://www.sgrp.cgiar.org/sites/ default/files/1_2_FullReport_Final_OrigReply_1April.doc) CGIAR center – crop Slow-growth in vitro protocol CIAT – cassava CIP – potato CIP – sweetpotato IITA – yams Conservation (SN – silver nitrate) medium: MS (2% sucrose) + 0.02 mg/l BAP + 0.1 mg/l GA + 0.01 mg/l ANA + 10 mg/l silver nitrate. Agar 0.7%. pH 5.7–5.8 Storage growing conditions: temperature 23–24°C; light 18.5 mmol. m−2.s−1; photoperiod 12 h; light quality fluorescent lamps, light day type; relative humidity 50–70% Conservation (S42) medium: MS based medium with 2 mg/l glycine, 0.5 mg/l nicotinic acid, 0.5 mg/l pyridoxine, 0.4 mg/l thiamine, 2.5% sucrose, 4% sorbitol, 7 g/l agar Storage growing conditions: temperature of 6–8°C, photon flux density of 5–20 mmol/(m2.seg) with a 16 h/8 h photoperiod of light and darkness (fluorescent lamp COOL DAYLIGHT, 36°W) Conservation medium: MS based medium with 0.2 g/l ascorbic acid, 0.1 g/l calcium nitrate, 2 mg/l calcium panthotenate, 0.1 g/l L-arginine, 20 mg/l putrescine, 30 g/l sucrose, and 3 g/l phytagel Storage growing conditions: temperature of 19–21°C, photon flux density of 45 mmol/m²/s with a 16 h/8 h photoperiod of light and darkness (fluorescent lamp COOL DAYLIGHT, 36 W) Conservation medium: MS based medium with 100 mg/l myo-inositol, 30 g/l sugar, 1 mg/l kinetin, 20 mg/l L-cysteine and 7 g/l purified agar Storage growing conditions: temperature of 18–20°C, photon flux density of 43 mmol/m²/s with a 12 h/12 h photoperiod of light and darkness (fluorescent lamp COOL DAYLIGHT, 36 W) for potato developed at CIP where meristem culture is stored in a chamber under controlled conditions: temperature of 6–8°C, photon flux density of 5–20 mmol/(m2. seg) with a 16 h/8 h photoperiod of light and darkness (Fluorescent lamp Cool Daylight, 36 W) and sorbitol of 30 g/l medium for an average of 2 years in more than ten thousand clones. For cassava at CIAT silver nitrate medium is used at 20°C (day)/15°C (night) temperatures, 12-h photoperiod and 500 to 1,000 lux illumination. Similarly, yams are maintained at IITA, and sweet potato and ARTC at CIP with varying storage periods as shown in Table 12.6. This is known as the slowgrowth protocol and in genebanking terminology the medium-term storage of clonally propagated crops. It is becoming the standard method in the conservation of RTC due to the fact that with the in vitro state, a collection can be cleaned of systemic diseases and contaminates such as viruses, bacteria, phytoplasmas and fungi, and then maintained in the clean state for safe international distribution to clear both international and national quarantine requirements. The combination of slowgrowth protocol and safe movement status of a collection for the first time allows the implementation of safety duplication of a collection, also known as a ‘blackbox’ at another site of different risk factors, i.e. in another country, both from natural disaster and national politics. It is also in the in vitro state that sufficient clean 276 D. Tay meristems can be easily multiplied for cryopreservation in liquid nitrogen at −196°C for long-term conservation (see below on this method). These are some of the advantages of conservation as in vitro collection. However, the establishment of an in vitro genebank requires a major infrastructure investment including a well equipped laboratory with the following rooms: slowgrowth storage, incubation growing room, transfer room, media preparation room, washing room and backup electric generator in case of main power line cut, and virus and bacteria elimination thermo-therapy precision incubator and insect-proof greenhouse for virus diagnostic works. The laboratory and greenhouse complex should have air-locked anteroom to prevent the entry of insects and micro-organisms from outside and the air-conditioning system HEPA filtered to prevent dust, mist and spores in outside air from getting into the genebank. Ant infiltration through building gaps and conduit causes mite infestation and contamination. Maintaining stable quality technicians and equipment quality of the tissue culture laboratory are fundamental to maintain consistent standards. The capital and maintenance costs are expensive and more importantly annual budget has to be obligatory to cover staff salary, utility costs, consumable and equipment, and infrastructure maintenance and replacement costs. Technicians have to be well trained and disciplined because the frequent subculturing in the regeneration cycle allows plenty of opportunities to commit errors, such as mixed labeling, mix-up of accessions, missed place in wrong position in the shelving system, etc. At CIP, the application of a fully wireless barcode system in the management of the in vitro genebank has prevented many of these mistakes. The CIP’s in vitro genebank management software is custom-made to suit the different component protocols and all these are held together and institutionalized by the ISO 17025 accreditation system (see below). Finally, the genetic stability of collections going through cycles of regeneration in stressful conditions has not been extensively studied. To date, decision to replace field genebank with only an in vitro genebank is not possible. Cryopreservation genebank: This is the preservation of meristems in liquid nitrogen (LN) at −196°C. In RTC germplasm conservation it is the long-term storage system because it is generally believed that meristems frozen at this ultra low temperature will remain alive from hundreds of years or more. Potato and cassava have stable cryopreservation protocols (Source: Final report on GPG2-1.2 collaborative activity: Refinement and standardization of storage procedures for clonal crops – http://www. sgrp.cgiar.org/sites/default/files/1_2_FullReport_Final_OrigReply_1April.doc). In potato, research commenced some 40 years ago (Grout and Henshaw 1978) and, currently, at CIP a stable method can obtain high survival and high plant recovery rate in most genotypes of native potato (90%) tried on to date. Satisfactory results were also obtained in a verification trial by cryo-laboratories of CIAT, IITA and Bioversity International. This is a costly conservation system because it can only be established with an adjoining tissue culture laboratory. The direct costs are the technician cost, laboratory space, cryo-equipment, cryo-storage tanks and LN (which could be expensive in developing countries). The protocols are tedious and involve many treatment 12 Tropical and Subtropical Root and Tuber Crops 277 steps. Technicians have to be very accurate in chemical preparation, formulation, treatment and incubation time in each step, and thus the introduction of a complete collection will take many years. Presently, CIP has only more than 1,000 of its 4,235-accession native potato collection in its cryo-genebank after 7 years of work. However, once in LN the maintenance cost is low comparing with the other conservation methods. On the whole cryo-genebank could be said in a pilot stage. The long-term survival and recovery rates have not been fully evaluated. The genetic stability of an accession subjected to intense cryo- stresses at pre-freezing, storage and thawing treatments has not been studied in details. There is no safe duplicate (blackbox) system in place as that for seed crops at Svalbard, Norway. The international clonal crop genebanking community’s proposal to use cryo-genebank to keep the base collections and in vitro slow-growth method the working collections in order to reduce cost could not be implemented until the above issues are fully resolved. Seed genebank: The seed of most RTC both cultivated and related wild species are orthodox seed which mean that they can be stored at low seed moisture content of around 5% (wet weight basis) at −20°C for long period. In the case of potato it is about 30–40 years. At CIP, all the duplicates of the native potato cultivars were converted to seed using bulked pollen pollination within an accession for the tetraploids before they were eliminated from the field and in vitro collection. All the related wild species of potato are conserved as seed populations using bulked pollen pollination in greenhouse with 20–25 plants at CIP based on findings of del Rio and Bamberg (2003). Similarly, wild relatives of sweet potato are kept this way. These are the seed lots that are being deposited at Svalbard vault for safe duplication. The seed banking management processes are similar to that for seed crops. In situ and on-farm conservation: In recent years in situ and on-farm methods are applied for both CWR and cultivated species. The Global Plan of Action (GPA) on Plant Genetic Resources for Food and Agriculture (FAO 1996) states the need to promote in situ conservation of CWR and wild plants for food production. Recently, a manual on in situ conservation focusing on CWR was published (Hunter and Heywood 2011). Collections maintained ex situ can be said to be in a static state in evolution. In situ conservation provides the needed interaction for the changing environments and agricultural systems to act on the genetics of the accessions and the introgression of CWR to the cultivated forms. This may be the most cost effective and feasible way for managing large diversity of CWR with limited information on their geographical distribution and reproductive biology to efficiently collect and maintain them in ex situ collections. The model of Nature Conservancy (http:// www.nature.org/) to procure lands with endemic targeted species has proven to be effective in some countries. Biosphere reserves and heritage sites for the conservation of traditional cultures and crops are being declared and implemented. Community-based natural resources management and community conserved areas such as the Potato Park are increasingly promoted. Public awareness in the value of these different models is an important message to get through. At CIP, in the last 15 years, a dynamic conservation strategy linking the well established ex situ collection with in situ/on-farm conservation activities by the 278 D. Tay Andean farming communities has been developed and the in situ-ex situ complementary has proven its benefits in the case of native potato conservation. In the project, the ex situ accessions under custodianship at CIP collected some 20–40 years ago are returned back to their respective original farming communities from where they were collected. In the recent 10 years (1998–2008) 3,608 samples of 1,250 accessions (out of 4,235 accessions) have been returned back to 41 communities using clean virus indexed tubers. In return the communities of the Potato Park in Cusco, the most progressive field site, through trust established in the engagement and collaboration, have solicited CIP to safeguard their landraces that are not yet conserved in CIP ex situ genebank. This dynamic in situ-ex-situ conservation strategy is being implemented in the last 10 years as the ‘Ruta Condor’ project in the repatriation of clean native potato cultivars back to their respective original owner communities and guide them in the establishment and maintenance of communal genebanks of native potato. Micro-centers of native potato diversity are established using the passport information of the 17,000 accessions collected by CIP and they are the priority sites of the project. However, in situ conservation activities should be treated as complementary and not a substitution to the well established ex situ conservation strategies and collections. 12.4 Quality of RTC Collections The quality of a collection is equivalent to how useful it is. The factors determine this include the following: • Good representation of the crop genepool covering primary, secondary and also to some extent tertiary genepool; • Accurate passport and genetic identity of all accessions; • Good characterization and evaluation information; • Well documented with user friendly searchable database; and • Cleaned of quarantined pathogen for safe distribution. The RTC collections of the CGIAR centers (CIAT, CIP and IITA), the South Pacific Commission (SPC) and some major national collections are to large extent representative of the primary genepool for cassava, potato, sweet potato and yams, but lesser extent for taro and aroids, and ARTCs. Upon the completion of the implementation of the global crop conservation strategies by the Global Crop Diversity Trust, CG centers and national genetic resources programs in the coming years the primary genepool of RTC should be well in place. The recently initiated CWR collection and utilization project – ‘Adapting agriculture to climate change: New global search to save endangered crop wild relatives’ of the GCDT and Kew Gardens will increase the representation of cassava, potato, sweet potato and yams secondary genepool (http://www.eurekalert.org/pub_releases/2010-12/bc-aat120610.php). The quality and accuracy of passport information are fundamental relating to genepool assessment, the management of the genetic integrity at accession level and 12 Tropical and Subtropical Root and Tuber Crops 279 taxonomic treatment. New acquisitions have to ensure the best accompanying information are acquired. In RTC a collection is subjected to frequent yearly regeneration both in the field and in vitro genebank and a systematic genetic identity verification program has to be in place to correct any mechanical mix-up of accessions. This program is not well developed in most RTC genebanks. Together with good characterization and evaluation information and a good collection catalog (hard copy and online) the utilization of a collection will be greatly enhanced. Proven crop descriptors are available for all the major RTC. A user-friendly computerized software package for managing a collection accession information and genebanking management information is essential. In CIP genebank, a custom-built software package is used together with a wireless barcode system for its in vitro, seed and field genebanks since 2004. Minimum uses of pens and pencils have eliminated handwriting mistakes completely. The barcode system has been introduced to other CGIAR centers through the World Bank Global Public Goods Project II (http://www.sgrp.cgiar.org/?q=gpg2). Safe movement of clonal germplasm around the world should be a vital concern of any genebank to prevent the spread of quarantine diseases to new areas in the world. FAO and IPGRI have published guidelines for the main clonal crops including that for RTC (http://typo3.fao.org/fileadmin/templates/agphome/documents/PGR/PubPGR/ FAOIPGRI_list.pdf). At CIP accessions qualified for international distribution have to have a health status (HS) level of 2, i.e. HS2. To obtain this level of cleanliness, a potato accession has to be cleaned through meristem culture and thermotherapy and indexed for some 30 known viruses and potato spindle-tuber viroid, and any detected bacteria and phytoplasma, and for a sweet potato accession for 10 known viruses and bacteria. The process involves meristem culture, micropropagation, ELISA and DASELISA tests, thermotherapy and greenhouse diagnostic tests. They are all held together with the wireless barcoding system in real-time. Standardized ‘best practice’ protocols were developed and documented into operation manuals. ISO accreditation: With the fundamentals mentioned above at CIP the ISO 17025 accreditation documentation was put together consisting of the following components: • General organization and policies • Quality system and related documents both internal and external • Workflows (19 under ISO accreditation) and operational procedures (41 under ISO accreditation) of all the processes • Records and forms used and auditing reports both internal and external • Tools and views CIP became the first genebank in the world to be accredited with this standard from February 2008 to date. The maintenance of the accreditation required programmed internal and yearly external auditing on staff competency, staff succession plan (shadow-training) and staff training plan at all levels, equipment calibration and monitoring plan and implementation documentation, equipment renewal plan, consumable procurement and proper storage procedures, suppliers plan, laboratory and greenhouse procedures, quality control and monitoring procedures, validation 280 D. Tay testing with both within and outside reputable laboratories, information documentation and backup plan and procedures, germplasm acquisition and distribution procedures, quarantine procedures, etc. All non-conformities and observations have to be corrected and a corrective procedure in place and documented to prevent a repeat occurrence. All these mean additional costs. However, the benefits are many and the single most important benefit is that all the best practices are actually implemented exactly as they should be in the documentation. If not, ‘best practices’ could exist only on paper and not being implemented as should be. Decentralized conservation and distribution strategy: As mentioned above RTC (clonal) collections are expensive to conserve. Two components of a clonal genebank, the ‘blackbox’ and safe distribution, are particularly challenging relating to their short regeneration and replacement cycle and the quarantine related delay in shipment. A strategy to duplicate sub-collections in different regions of the world for conservation and distribution will take away these two difficulties. In a situation like this a duplicated subset will act as the ‘blackbox’ for that subset. When the whole collection is completely duplicated as subsets in different regions of the world there is no more need for a ‘blackbox’. When a subset is in a region with similar quarantine risks the distribution of these germplasm will be facilitated in clearing the regional quarantine requirements. The selection of an appropriate subset for a particular region will enhance the effectiveness of this strategy. This strategy will call for a good global real-time database system. Core collection: It is a subset of 10% of a collection that represents the total diversity of the whole collection (Brown 1989). A core collection could be formulated with the use of passport data in combination with molecular and morphological data, ecological adaptation data, evaluation data, nutritional chemistry data, and from breeding aspect combining ability data, and genomic and other omics data. Core collections could vary according to focus on particular traits or regions. The formulation of these fine-tune cores will need evaluation data from multi-location trials. A comprehensive core should include the wild relative species so as to include both the primary and secondary genepools. In the case of RTC, core should exclude closely related clones such as mutated variants and sister lines which could be common because many of the clones could have in cultivation for hundreds of years. The purpose of a core collection is to provide a tool in the management of a large collection. A core is a scientific starting point for the evaluation of a specific trait because germplasm evaluation is a tedious and costly process and a core allows effort to concentrate on the most diverse set of the whole collection. Additionally, because the maintenance of RTC collections is very costly a strategy to put all the accessions of a collection in cryopreservation and only to maintain the core as active collection and this will reduce the maintenance cost significantly. Securing the funds for the conservation of RTC: The Global Crop Diversity Trust and CGIAR Consortium in 2010 jointly did a detailed costing study on the conservation component of all CGIAR center’s crop genebanks. Based on this study, the funds for RTC conservation at CIAT, CIP and IITA in 2011 have been allocated and commitment to further this funding into future years is under consideration. The present funding plan is the sharing of responsibility between the GCDT endowment 12 Tropical and Subtropical Root and Tuber Crops 281 long-term grant and the CGIAR allocation to each center. As the GCDT endowment grows, the GCDT long-term grant will increase and the CGIAR contribution will decrease until a stage that GCDT will fund the whole conservation operation. 12.5 Future Challenges and Possibilities Increasing utilization of the Genetic Resources: The utilization of the genetic resources for crop improvement is lagging behind conservation effort and this is a challenge. For example, only an estimated 5.6% of CIP in trust Native Potato collection has been used in CIP breeding program in the last four decades by CIP breeders. The low usage is partly attributed to the limited ‘good quality’ evaluation information available on this collection (Tables 12.7 and 12.8) and also the bias toward using known clones already described, improved and/or proven for making crosses. The use of the CWR is even less. The publication of the CIP wild potato catalog in 2009 (Salas et al. 2009) has not seen an increase in the request for this group of germplasm. In fact there are only a few breeding programs in the world with pre-breeding activities looking at enhancing the use of these wild genepool. The recent publication of the potato genome (The Potato Genome Sequencing Consortium 2011) may provide the genetic information and knowledge to pace the utilization of this broader genepool in the native potatoes and the wild relatives. The use of the sweet potato collection is even less as compared to potato. On the other hand, their direct use may be quite impressive. In the case of the native potato, the collection at CIP has been extensively used in the repatriation program at CIP in the ‘Ruta Condor’ project. In the recent past 10 years, 30% (1,250 accessions) of the collection of 4,235 accessions have been returned to their original communities (41 farming communities) in the Andes. The key breeding objectives for cassava, potato, sweet potato and yams identified in the 2011 CGIAR Research Program proposal on root and tuber crops and banana (CRP3.4 or CRP-RTB) is shown in Table 12.9. This means increasing germplasm evaluation efforts both in genotyping and phenotyping the collections to look for new novel genes for abiotic and biotic traits to be bred into the existing cultivars. Equally important is the use of new genepools of both landraces and CWR to widen the gene base of RTC. For example, innovative ideas proposed include durable resistance to major diseases, earliness in tuberization in potato, role of mycorrhizal fungi in mineral nutrition in different yams accessions, etc. The ‘chuno’ (traditional freeze-dried potato) factor – facing climate change for native potato in the Andes: Rosegrant (2009) using modeling on crop growth and other factors on climate change indicated by 2050 severe negative impacts on yield and production for all root and tuber crops and thus sharp price increases. Climate change in the Andes is real. The high mountain glaciers are shrinking (Thompson et al. 2011) and the winter-month snow caps are disappearing in many high tropical mountains. Growing seasons in the Andean highlands are experiencing more and more frequent adverse weather conditions. There are increasing 282 D. Tay Table 12.7 Evaluation summary for the in trust potato collection maintained at CIP in 2011 Number of accessions Biotic/abiotic stresses and traits evaluated Fungi Bacteria Viruses Nematodes Insects Environmental stress Other desirable traits Total Reaction to late blight leaf Reaction to late blight tuber Reaction to pink rot Reaction to scab Reaction to wart Reaction to smut Reaction to Fusarium Reaction to Phoma blight Reaction to charcoal rot Reaction to potato soft rot Resistance to black leg Reaction to PVX Reaction to PVY Reaction to PLRV Reaction to PVS Reaction to cyst nematode race pa2 Reaction to cyst nematode race pa3 Reaction to cyst nematode in Cusco Reaction to golden nematode Reaction to root-knot nematode Reaction to potato tuber moth Reaction to Andean potato weevil Reaction to frost Reaction to hail Dry matter content Protein content Tuber dormancy Evaluated With useful genesa 700 318 1,334 546 855 199 59 440 40 464 77 2,092 0 3,196 3,068 1,339 1,333 737 660 1,376 2,011 574 43 10 938 273 1,605 142 218 4 41 62 2 0 277 8 34 4 19 0 3 0 148 180 72 87 570 142 59 9 3 408b 36c 167d 24,287 2,695 Evaluations at CIP using material from native and landrace potato a Includes highly resistant, resistant, moderately resistant, highly tolerant and tolerance cultivars b Percentage of dry matter content in freshly harvested tuber >24% c Percentage protein content >10% d Tuber dormancy about 6 months drought and hail storm frequency, raising temperature and followed by frost events in the growing season. Diseases like potato late blight and insect pests are moving up the Andean slopes and so the traditional native potato planting system. This means a reduction in arable cultivated area because of the conical effect of mountains and the infringement into the paramo and puna wetlands, the ‘water-tank’ of the Andes and Amazon. At the same time the soil becomes thinner and once the soil organic matter is exhausted its renewal is slow because of the low temperature and low rainfall in the winter months which are unfavorable for vegetation growth to build up new organic material. The reduced cultivated land and increasing 12 Tropical and Subtropical Root and Tuber Crops 283 Table 12.8 The key breeding objectives for cassava, potato, sweet potato and yams in the coming decades as indicated in the 2011 CGIAR Research Program for root and tuber Number of accessions Traits evaluated Evaluated With useful genesa Nematodes Reaction to root-knot nematode Reaction to brown ring out Insects Reaction to west sweet potato weevil Fungi Reaction to java black rot Reaction to foot rot Viruses Reaction to SPFMV virus Environmental stress Reaction to salinity Hot tropical climate adaptation Nutritive quality Dry matter content Storage root starch content Storage root beta carotene content Protein content Total 2,761 758 744 25 1,596 395 604 168 231 42 587 58 615 302 44 53 1,654 2,698 1,949 848 14,540 (>45%) 40b (>75%) 34c (>3) 125d (10%) 7c 1,855 a Including highly resistant, resistant, moderately resistant, highly tolerant and tolerance cultivars Percentage of dry matter content in freshly harvested tuber c Based on a dry weight basis d mg/100 g fresh weight b Table 12.9 Key breeding objectives for root crops (CRP3.4 or CRP-RTB) as prepared by Bioversity International, CIAT, CIP and IITA (Source: internal document) Crop Key breeding objectives Cassava Potato Sweetpotato Yam Yield, high dry matter, resistance to viruses such as cassava mosaic disease and cassava brown streak disease, compatibility with integrated pest management (IPM), tolerance to drought and low fertility, and low toxins, high-carotene, and fodder High stable tuber yield, durable resistance to diseases late blight (LB) and bacterial wilt, resistance to multiple viruses (potato virus Y, potato leafroll virus) and pests, adaptation to heat and drought, short vegetative cycle, tuber quality, and nutritional attributes Wide adaptation, stable tuber yield, high nutritious genotypes and high foliage production for animal feed High stable tuber yields, resistance nematodes, viruses, anthracnose, and scale insects, tuber quality, ease of harvest and long storage, suitability to cropping systems and markets, tolerance to abiotic stresses, and textural and nutritional attributes 284 D. Tay population mean that the traditional fallowing period is shortening and as the result reducing yield and depleting soil fertility. Many of the native potato are adapted to the long growing season of up to six months from October–November planting to March–May harvesting. With climate change the growing season could be reduced to less than four months in the future because of late rain and early frost events. This means that many of the traditional late varieties will not be able to tuberize or yield well and thus will be selected against and disappear. The early tuberizing cultivars will persist and at the same time those that can tolerate frost will be selected for. The most frost tolerance cultivars among the native potato are the bitter potato of S. x ajanhuiri, S. x juzepczukii and S. x curtilobum. When the effect of climate change becomes extreme serious at one stage only bitter potato will be able to survive the severe weather. All the ‘sweet’ potato will be swept off in situ in the Andes and only bitter potato will remain. This is the ‘chuno’ factor. Ex situ conservation will be the only home of most native potato. Potato breeding has to concentrate on abiotic stress tolerance especially against frost in combination with drought and heat adaptation and at the same time be able to resist the increasing occurrence of late blight, viruses and pests. Breeding at triploid and pentaploid level based on S. x juzepczukii and S. x curtilobum model (Schmiediche et al. 1982) should be revisited. S. x curtilobum has limited cultivar forms but they perform well in the altiplano. The increasing use of wild species with frost tolerance such as S. acaule, S. megistracolobum, S. commersonii and others as parents means that an understanding on the genetic of bitterness and a high throughput evaluation method should be in place so that frost tolerance non-bitter cultivars can be selected for. Late blight resistance is also important. Many of the native potato cultivars may have been in cultivation for hundreds of years. They should have some minor genes in order to endure the disease all these years. Breeding to accumulate for minor genes should be emphasized. An alternative model is the breeding of potato that can be irrigated with saline water. Accession CIP 703254 (OCH 2699), known as Darwin Potato, an escaped S. tuberosum, is said to grow right to the ocean in Low Bay on Guaitecas Island, Chile (Ochoa 1975) and probably survived in brackish water. The genetics is thus available. Similarly, specific scenarios on other RTC in Africa, Asia and Oceania, where most RTC systems exist, have to be identified, analyzed and mitigation measures proposed and tested. The ‘42-day super-quick’ potato – the ‘poultry farm’ potato concept: Growing enough food under decreasing arable land and climate change for the estimated 9.2 billion people in 2050 is the ultimate challenge. Poultry chicken is marketed in 42 days in the Peruvian poultry industry. This is the result of good poultry genetics and poultry farm management. At CIP there are elite bred lines that can be harvested in 70 days from planting to harvesting. The author believes that potato has the genetics for the development of a ‘42-day’ cultivar (the ‘super quick’ potato). Potato harvesting index could be as high as 85% (Reynaldo et al. 1986), i.e. excellent sink-source photosynthetic assimilates translocation system. Preliminary screening of some native potato accessions at CIP in 2011 showed the presence of very early tuberization 12 Tropical and Subtropical Root and Tuber Crops 285 in 45 days after planting and day-neutral for long photoperiodic growth. The large sinks for assimilates makes potato a crop for photosynthetic enhancement in response to enriched CO2 growing environment. Studies have shown that RTC are more responsive to elevated CO2 than other C3 crops (Miglietta et al. 1998). The ‘super quick’ potato will be growing in a ‘potato’ factory, a computerized environmental controlled greenhouse, using the accompanying plant management technologies including temperature and humidity controlled, hydroponic, quarantine controlled, 24-h day length with combination light waves to promote vegetative growth, tuber initiation and tuber bulking, CO2 enrichment management, etc. The assembling of all the required genetics into a ‘42-day super-quick’ potato is a multidisciplinary project. Germplasm evaluation to identify, understand and isolate all the required genetic components is the first step and then the assembling of these components through breeding and biotechnology. In parallel greenhouse technologies have to be designed and tested according to the ‘super quick’ potato. Sweet potato – the space age staple, vegetable and ‘food for the mind’: Sweet potato is a survival crop. It travelled across the vast Pacific from Latin America to New Guinea before Columbus. Many lives were sparse from starving to death during the Second War World in Far East and Southeast Asia. The orange-flesh cultivars have high beta-carotene and in Asia, the leaves are a high nutritious vegetable of equivalent to spinach. The author was the first to use the yellow and purple leaf accessions as ornamental plants at AVRDC – The World Vegetable Center’s genebank in 1985 and this concept was then taken to the world. Currently, sweet potato is an ornamental species in its own right. These three qualities of sweet potato have prompted the author’s recommendation of sweet potato as a crop for the International Space Station (http://www.nasa.gov/mission_pages/station/main/) when Texas A&M University was looking for crops that can be grown at low pressure in the space station for NASA. The tuber will be the ‘space’ staple, the young leaves the ‘space’ vegetable and the growing vines the garden of the space station providing nature greenness and morning glory purple flowers in the harsh metallic environment, the ‘food for the mind’. Sweet potato, a humble vine with a proven past, will have a great future – the ‘space age’ crop. 12.6 Conclusion RTC have had proven to be important survival crops in history, e.g. many lives survived on sweet potato in Asia and the Pacific during the Second World War and in recent years they are proving to be important local staple food not suffering to the fluctuation in prices as the grain commodity crops. They are the food security of many people in the tropics and subtropics. The genetic resources conservation of the major RTC is progressing as for other important crops. 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