sign in sign up
<<
Home , Dioscorea, Dioscorea alata, Dioscorea esculenta, Oxalis tuberosa, Root, Tacca leontopetaloides

Origin, Evolution, and Early Dispersal of and Crops Jorge Leon1 Tropical root and tuber crops have been domesticated in Southeast Asia, west-central , and tropical Latin America (including the high ). The crops belong to different families. Species of the one genus () were domesticated independently in each of the three regions. Species of Colocasia and Xanthosoma (family Araceae) and Pachyrrhizus and Pueraria (family Leguminosae) were domesticated in separate regions. Many of these crops have restricted areas of distribution due to physiological requirements and are becoming relict crops. and are ancient crops, and even today support groups of people who gather them from wild . Poisonous, acrid, or bitter qualities were found in the most important crops by early man, who learned how to remove or destroy these undesirable qualities. Most of the root and tuber crops are polyploids, and most of them are vegetatively propagated. Fertility traits are therefore of special importance in their evolution under cultivation, but there is no evidence that clonal propagation has led to sterility. Information on their evolution is extremely scarce as cultural sources, archaeological, linguistic, and historic information is scanty and unevenly distributed. On biological sources, compara­ tive , metaphase cytology, and hybridization have given some important clues, but there is still very little information available on the evolution of these species. Root and tuber crops dispersed slowly between Southeast Asia and Africa. After the seventeenth century a very active interchange occurred especially with the American crops. Since then, there has been a continuous replacement of crop species, especially in Africa. The sweet , of American origin, was found in when the Europeans arrived, but no satisfactory explanation of how it got to has ever been made. Root and tuber crops are thought to be of tion" with cereals. In vegetative propagation ancient origin, and are often regarded as relics primitive farmers apply simple husbandry, but of primitive . This concept is based the same is true when they grow crops. On on the important role these crops play in exist­ the other hand, some vegetative crops, such as ing primitive societies, and on the rudimentary potatoes, have reached an advanced stage of husbandry they require, particularly vegetative production and technology, comparable to propagation. These crops are easily adapted in many other crops. The view persists, however, the less-advanced agricultural systems because that vegetative propagation represents a low of their high yields, resistance and earliness, stage of progress, and a distinguished cyto­ and in the dietary pattern by their bulk and geneticist in his interpretation of history taste qualities. (Darlington 1969), points to "the fatal abun­ Since the last century, geographers and an­ dance of tropical root crops imported from thropologists have contrasted root and tuber Asia and America" as one of the main factors production, which includes other clonally in the decline of Africa. propagated crops such as bananas, , The contrasting of agricultural systems , with seed agriculture. Vegetative based on the differences between seed and propagation, developed in tropical regions, is clonal propagation is a simplification of a assumed to be a static system, whereas seed problem that is too complex to be reduced to agriculture is associated with the development the duality of planting materials. of more advanced societies. Geographers and historians are tempted to associate "civiliza- The Basic Materials Roots and tubers are storage organs that are IPrograma de Germoplasma, CATIE, Turrial­ developed in many families of plants, probably ba, Costa Rica. as a result of selective pressures in environ- 20 LEON: ORIGIN, EVOLUTION, AND DISPERSAL 21 ments with varying amounts of rain. The on crop evolution - comparative taxonomy, storage organs permit the accumulation of nu­ cytological analysis especially at metaphase, trients elaborated by the aerial parts of the and experimental hybridization - have been . By growing underground, they maintain applied to some of the root and tuber crops. the with minimal loss. Once the tem­ However, as a whole, the information avail­ porary or foilage have dried, new able, with the possible exception of potatoes, develop from the storage organs. By is very poor and scattered. harvesting roots and tubers before the plants Comparative taxonomy aims to establish the have flowered, man has interrupted this pro­ relationships among existing taxa with the cul­ cess, and has thus kept the plants in a kind of tivated species. The definition of their taxo­ permanent juvenile stage. nomic position permits the identification of Although storage organs may vary in their putative parents and the delimitation, within phylogeny and structure, the nature of their the genus, of the cluster of species more storage tissues is common. These organs are closely associated with the cultivated taxa. The large masses of parenchyma that contain traditional methods of taxonomy do not work mainly and grains. The paren­ well with root and tuber species. Often foliage chyma is intimately connected with the vascu­ is difficult to accommodate in lar system, which permits easy transport from sheets; are bulky, fleshy, and frequently and to the storage organs. Frequently, there are absent; root and tubers too difficult to preserve. poisonous, bitter, or acrid substances in the In some genera, like Xanthosoma, the taxo­ storage tissues, which present an obstacle to the nomic status is extremely unsatisfactory; the utilization of roots and tubers. However, these abundant synonymy in the aroids and yams is, substances are a deterrent to animals and there­ in part, a result of studies based on herbarium fore play an important role in the survival of materials. As in other crops, the identification plants growing in natural conditions. The of a wild population closely related to the cul­ quantity of these materials (e.g. raphides or tivated species, raises the question of whether it glucosides) varies considerably within the is an ancestor of the cultivated type or a feral or same species, a trait that is mainly determined weedy form. In , an aboriginal species by inherent factors. has been described (Brucher 1962), but this The storage organs may be roots or stems. could be only a wild variety. A hexaploid popu­ In roots, such as , the storage tissues lation of Ipomoea from , has been con­ may derive from a normal cambium, or as in sidered as an ancestor species (Nishiyama the from tertiary cambiums that 1971) or a weedy variety of the sweet potato develop around vascular elements. Storage (Martin et al. 1974). stems a:re of different kinds (e.g. , Cytological studies are interrelated with tubers, and ), and as in roots, the storage taxonomy and both have helped to solve some tissues may derive from different types of problems. But it is surprising how little is cambium. In most of the root and tuber crops, known in this field. Of some of the cultivated storage organs are more than species there is no information even on chro­ sinks. They are also reproductive organs, and mosome number. On the other hand, some of this double function has been of foremost im­ the root tuber crops offer technical problems portance in their propagation by man. such as chromosome size and high number, The common classification of crops by the which make it difficult to detect possible link­ utilization of certain organs results in artificial ages or identification points. groupings. Thus, temperate species utilized for There is a trend to attribute to interspecific their roots or stems (, beets) are con­ hybridization the origin of most cultivated sidered as vegetables, whereas tuber crops plants, especially if they are polyploids. In yielding essential oils (ginger) are included roots and tubers, sweet potatoes (Nishiyama among the . The present discussion is et a1. 1975), African yams (Ayensu and Cour­ limited to tropical and subtropical species used sey 1972), common potatoes (Dodds 1965), mainly for their starch content as energy and others have been assigned such origin, (Table 1). and putative parents have been suggested for some of them. Genome identification lends Factors in Evolution some support to this contention, but it is very The usual sources of biological information difficult to obtain definitive evidence from 22 TROPICAL ROOT CROPS SYMPOSIUM Table 1. Tropical and subtropical species used mainly for their starch content as energy foods.

Monocotyledoneae Agavaceae Cordyline terminalis Ti, palm lily Araceae A/ocasia , biga, birah Amorphophallus Suran, elephant Colocasia Cyrtosperma Xal1lhosoma Cannaceae Canna edulis Achira Cyperaceae Cyperus esculentus Eleocharis /uberosus Water Dioscorea (12 species) Yam Marantaceae arundinacea Arrowroot Calathea alluia Lairen Taccacaeae leolltopeta/oides Pia, Polynesian arrowroot Zingiberaceae Curcuma angustifolia Curcuma zeodoaria Dicotyledoneae Basellaceae Ullucus tuberosum Ulluco Compositae Polymnia sOllchifolia Yacon Convolvulaceae Ipomoea batatas Sweet potato Cruciferae Lepidium meyenii Maca Euphorbiaceae Manihot escu/enta Cassava Labiatae Plectran/hus esculelllus Kafir potato, dazo So/enos/em 011 ro/undifolius Hausa potato S/achys sieboldii Leguminosae Pachyrrhizus (spp.) Ahipa Psyphocarpus tetragonolobus SigariIla Pueraria lobata Sphenostylis s/enocarpa Oxiladaceae /uberosa Oca Solanaceae So/anum /uberosum Potato Tropaeolaceae Tropaeoleum /uberosum Mashua Urn belliferae Arracacia xall/horrhiza hybridization work. Often the terms "nobiliza­ of somatic mutation in the evolution of these tion" or "ennoblement" are applied to root and crops. However, hybridization in these crops is tuber crops, meaning improvement by primi­ a potential force of considerable value for tive agriculturists. These terms imply a planned further improvement (Abraham et al. 1964). hybridization, as in cane breeding, which is not the case in root and tuber crops. On the other hand, information obtained from hybridization aimed at crop improvement is As expected in cultivated crops, a good num­ rather incidental to crop evolution. ber of root and tuber crops have different As a main force in evolution, the impact of ploidy levels. The early cytological studies on recombination is possibly less evident now than potatoes led to the separation of the numerous in the past. Under original conditions, root and included in Solanum tuberosum into tuber species were closer to their primitive al­ several species (Juzepczuk 1937), or into one lies and hybridization may have been more species formed by five groups and two hybrids frequent. But as man moved them to new en­ with other species (Dodds 1962). The culti­ vironments, not only did the possibility for vated diploids have been derived either from further crossing and segregation decrease, but wild diploids, again with no total agreement the mechanisms of seed setting and sexual re­ on the identification of the ancestors, or from a production were affected. The practice of vege­ primitive complex in which many diploid tative propagation helped to reduce the im­ species may have taken part (Ugent 1970). portance of segregation and increased the role The tetraploids may have arisen through aHo- LEON: ORIGIN, EVOLUTION, AND DISPERSAL 23 polyploid or doubling of diploids (Simmonds the second process is more likely to have 1976); the triploids as hybrids of tetraploids occurred. Other species showing different levels and diploids; and a pentaploid group from of ploidy are: Maranta arundinacea, tetra­ crosses between a triploid (unreduced gametes) ploid; Canna edulis, triploid; Ullucus tuber­ and a tetraploid (Ugent 1970). osus, triploid; , hexaploid; Perhaps the group of root and tuber crops in Tropaeoleum tuberosum, hexaploid. On the which polyploid is most complex is Dioscorea, other hand, the cultivated Xanthosoma (X = but here again the studies have been scarce and 13) are diploids, 2n = 36 (Plucknett 1976). isolated. In D. aiata, a survey of chromosome Cassava, 2n = 36, has been considered as a numbers in Indian cultivars has established a diploid (Magoon 1967) and as a tetraploid series of 2n = 30, 40, 50, 70 for different (J ennings 1976). In the Euphorbiaceae, X = clones that do not show phenotypical differ­ 9 is found in M anihot and allied genera, and ences (Sharma and Deepesh 1956). Also poly­ the presence of three nucleolar chromosomes somaty has been detected in this species, and and some chromosome duplication at pachy­ this could be a possible source of new types tene, suggest that cassava is possibly a seg­ through vegetative propagation. In D. ­ mental allotetraploid (Magoon et al. 1969; i/era, there are morphological differences in Jennings 1976). the cultivated types of Africa and Asia, the There are several questions to consider in former being considered by some authorities as relation to polyploidy. For example, does it a distinct species. Cytological counts tend to have any significance, as in other crops, on the support such differences. The African size and quality of the useful parts of the have 2n = 36, 40, 54, 60 with a basic number plants. The information is meagre, except on lenta, 2n = 40, 90, 100; D. cayenensis 2n = potatoes, and in this crop it is masked by long 40, 60, 80, 100 with a basic number of 20 selection, environmental conditions, and crop (Martin 1974). Other polyploids are D. escu­ protection. There is no information, for in­ ienta, 2n = 40, 90, 100; D. cayennensis 2n = stance, of any correlation in size of tubers and 140; D. opposita 2n = 40; D. penthaplylla 2n ploidy in the series mentioned = 140. However, Coursey (1976) points out above. that in Dioscorea polyploidy is not restricted to In triploids of Canna edulis, the starch con­ cultivated species only. tent is almost three times higher than in the In taro, a general survey of its variability is diploid, but there is no information on yield badly needed, as it is one of the most ancient (Mukerjee and Khoshoo 1971). On the other of the root and tuber crops and one of the most hand, induced polyploids in cassava, assuming widely spread. Two basic chromosome num­ that it is a diploid, are not superior in yield to bers have been recorded in taro, X = 12 and diploids. In Ipomoea, wild hexaploids do not X = 14. Clones with 2n = 24 and 2n = 48 show any root thickening, and therefore, the are reported from , while clones with 2n domestication character may result from pro­ = 28 and 2n = 42 are found from India to cesses other than polyploidy. in one direction, and to Timor, New It is well known that most polyploids have a Caledonia, and in the other. But wide adaptability to new conditions. In culti­ east of 180·, that is in most of Polynesia, all vated polyploids, this characteristic aided by clones show 2n = 28 (Yen and Wheeler 1968). cultural practices, especially crop protection, The most interesting example of polyploidy is a key factor in their success and expansion. in root and tuber crops is the sweet potato, a Finally, an important aspect is to consider hexaploid, 2n = 90, which could be derived, the possible relationships between polyploidy as has been proved experimentally, in two and vegetative propagation. Through the latter, ways: (1) by the multiplication of a diploid a not fully balanced allopolyploid, for instance, (I. leucantha), or (2) by the duplication of a could be multiplied and meiotic irregularities triploid resulting from the crossing of a diploid or gene-determined sterility bypassed. Such (I. leucantha) and a tetraploid (I. littoralis). polyploids may spread, through clonal propa­ The resulting hexaploid, I. trifida, is considered gation, in a way that would be difficult through a primitive form of I. batatas (Nishiyama seed reproduction. 1971). As two of the three genomes in the sweet potato show more with each Fertility and Vegetative Propagation other than with the third (Magoon et aI. 1970), Vegetative propagation is necessary in most 24 TROPICAL ROOT CROPS SYMPOSIUM root and tuber crops because of their ineffi­ seed production in taro (reports from Papua ciency in producing seed, a result of natural and , Raratonga, ) could be cultural factors. Among the natural factors are due to harvesting practices. In yams, seed set­ incompatibility, dichogamy, abnormal seed ting is often limited by harvesting practices, but and development, seed dormancy, and with some African species the constraints for pests and diseases attacking flowers and . sexual reproduction include a large number of Cultural factors are equally important. First, male clones, imperfect seed, and dormancy man has taken clonal crops to regions where periods. In potatoes, seed reproduction and fac­ environmental conditions do not favour seed tors conditioning low setting are well known, setting. Second, plants are harvested when the but even hybrids of induced haploids can set storage organs have reached maturity, which seeds under special conditions of temperature occurs in most cases well before ini­ and air moisture (Subramanyan et al. 1972). tiation. Third, man, by copying the same type All the Andean tubers produce abundant seeds. (clone) in millions of individuals may have In oca (Oxalis tuberosa), however, seeds are increased the possibilities, if a natural trait extremely scarce in field conditions, but if pro­ limiting fertility is present, to extend it into tected from wind and frost, which produce large popUlations. abcission of the , seed setting is It has been stated often, especially by non­ normal (Alandia 1967). In arracacia, seeds are biologists, that continuous vegetative reproduc­ produced the second year but as the root ma­ tion leads to sterility. Sauer (1952) stated that tures in 8-14 months, flowers and seeds are cassava reproduction by cuttings has been car­ rarely seen. ried out for so long that it has lost completely Vegetative propagation as a cultural practice its ability to set seeds. Vegetative propagation is very important in the evolution of root and in itself cannot lead to sterility although, as tuber crops. In modern agriculture, it permits mentioned above, it may increase the fre­ the multiplication of superior and uniform ma­ quency in a population of a trait favouring terials in large monoclonal plantings. This sterility, or has an indirect effect as it permits leads to a continuous replacement of cuItivars the cultivation in environments unfavourable when superior clones become available, with for seed setting. However, some recent work in consequent losses in germ plasm. In addition, Nigeria shows that seed production is higher monoclonal plantings may be wiped out in yams coming from seed-producing plants quickly by diseases or pests. Vegetative propa­ than those obtained from tubers of continuous gation materials may become sinks of viruses clonal propagation (Sadik and Obereke 1975). and mycoplasma, and are subject to physio­ This could be due to the nature of the samples logical degeneration also requiring clonal re­ studied, but is worth further study. Some ex­ placement. Under systems of primitive agricul­ perimental work in cassava (Jennings 1963) ture the effect of changes in planting materials showing different degrees of male and female is of less importance, as the standard practice sterility in hybrids and backcrosses may be is to plant several clones in the same plot, partly due to the different materials used and to mixed or separated. Frequently the planting environmental effects. material is the edible part, and in time of As was said before, all root and tuber crops scarcity or famine the "seed" has to be eaten. set seed. Reluctant clones are found, but ex­ This double utilization made it possible for the perimental work shows that it may be possible Polynesians and possibly Incas to propagate as to promote the formation of viable seed by crops what they had brought as for their changing environmental conditions or manipu­ long sea journeys. lating the flowering process. In cassava, flower As a whole, vegetative propagation, espe­ induction has been obtained by moving plants cially in monoclonal plantings, is an important to higher altitudes (above 1000 m in Java, restriction in increasing variability. In species Costa Rica, etc.) or in areas with special of imperfect evolution, sexual reproduction is climatic conditions, such as the coast of central a second best choice in their reproductive , where most of the clones set seed regu­ system (Martin 1967). larly. In sweet potato, seed setting is reported from many countries (Yen 1974), often out­ The Role of Mutation side its natural area (e.g. the Philippines and Papua New Guinea). The scarcity of records of In root and tuber crops, evolution through Lf~ON: ORIGIN, EVOLUTION, AND DISPERSAL 25 chromosome or gene recombinations is limited of the up to insertion of the , often by the predominance of vegetative propaga­ blotched), or the branching in the corms of tion. Therefore, somatic mutation plays a very Xanthosoma and Colocosia, could also be at­ important role. However, any new type has tributed to somatic mutations. Colour changes to be carefully evaluated before determining due to mutation were mentioned above in roots if it is a mutation or a chance seedling. of the sweet potato and a characteristic feature There is no survey of somatic mutations in of somatic mutation, sector colouring, is root and tuber crops to determine mutation found in the petioles of many taro and Alocasia rates. In primitive populations of sweet potato, clones. Quite common are chimeras affecting changes in the skin colour of the root - from colour or structure of the outer layers in tubers white or cream to orange or - have and corms. In potatoes and Ullucus, been recorded roughly at 1:1000 (Yen 1974). coming out of areas of different colour give In more reduced samples of improved clones, rise to different clones. In potatoes, it is com­ mutation rates vary from 0 to 2.9% (Hern­ mon to find purple areas in white tubers. In andez et al. 1964). The frequency of mutation Ullucus, there is a group of clones with tubers may give an indication of the age of the crop, either completely yellow or magenta or with although it is mainly determined by the num­ large areas of both colours. In this crop, as in ber of individuals. Because mutations change potatoes, russeting is common and types with only certain characters, the original popula­ this kind of skin are recognized as different tion could be recognized. The mutants form clones. It is very likely that the ornamental "groups of varieties" (e.g. in taro and other cassava has a similar origin. As mutation rate tuber crops). Within a mutant population not is a function of popUlation size, it is quite likely all the individuals are alike (e.g. potatoes). that in the relict crops so common among root Some may produce subclones that differ in im­ and tubers, this force is decreasing its effects portant characters such as yield and resistance and therefore reducing crop diversity. to disease. Somatic mutation is probably the most im­ The same mutation may appear in different portant factor in the evolution of root and places, and this is one of the reasons for the tuber crops under cultivation. It is probably high number of repetitions in collections. How­ easier to find a bud mutation than a chance ever, two mutations phenotypically alike may seedling. However, gene and chromosome be different in their physiological responses. mutation, although less well-documented and Most mutations do not have any agricultural with far less chances of occurring, may have value and in an advanced system of agricul­ contributed considerably to the diversity of ture, where uniformity is highly desirable, they these crops, especially when they were grown are immediately eliminated. But in primitive under more natural conditions and seed setting systems of agriculture, farmers like to main­ was more frequent. tain as many types as possible, as a kind of agricultural asset. It is likely that the "magic Domestication gardens" of the taro growers of Polynesia are collections of aberrant clones. A similar situa­ The process of domestication in root and tion occurs in the mixed agricultural system in tuber crops, including potatoes, has not been the Andes. Primitive farmers have learned by widely studied. Domestication of grain crops experience that some of these new types may in arid lands has been studied, but the results show special resistance and become an im­ are of little value in explaining root and tuber portant resource when the common clones are domestication. The archeological evidence has wiped out by disease and pests. considerable limitations. Evidence depends on Somatic mutations affecting the whole plant preserved plant materials, from which we can are known in few cases. Brachytic types are determine the structure of the organs and en­ found in cassava and sweet potato and the main vironmental conditions. However, because of difference between wild and cultivated Ullucus the fleshy tissues of roots and tubers, they are is internode length. easily destroyed by fungi, , and in­ Several instances are known in sweet potato sects. As well, most grow in wet regions and in which a normal produces others the materials preserved are very scarce and with of different shape (Yen 1974). irregularly distributed. The presence of plant Characters like the "piko" in taro (a deep cut remains in dry areas, like the coast of Peru, 26 TROPICAL ROOT CROPS SYMPOSIUM provides secondary clues often of great im­ Polynesians also learned to prepare a taro portance, as in the case of the sweet potato, mash ("poi"), which was more nutritious and but not the fundamental information on orig­ easier to keep than the fresh product. The inal places and processes. Even less helpful is extraction of glucosides in cassava required the the indirect evidence derived from tools and development of special techniques and tools. pottery. Historical evidence is most important The planting and cultivation practices and but, like archeology, it provides an irregular tools are less complicated than those used in picture. Africa has been the foremost meet­ preparing the crop for meals. The stick ing place of root and tubers, however its early of the yam gatherers can be easily transformed written history is very fragmentary. A similar into a planting tool. In a very simple situation occurs in southeast Asia and tropical instrument was developed to cut the upper part America. of the taro to obtain propagation material Plant domestication was initiated to answer (Buck 1964). Evidently early man learned the needs of primitive man for food, clothing, simple cultural practices, such as providing body painting, medicines, and . It could support for yams and piling earth on the base have been carried out in areas where materials of the plants to supply better and looser for domestication were abundant but also to the growing tubers. The processes of under the pressure of scarcity (Harlan and domestication of roots and tubers, particularly Zohary 1966). The common concept that plant the development of practices and instruments domestication led to the establishment of sed­ for their preparation as food, were far more entary human communities is open to some difficult than for or grains. Also in select­ questioning. Burkill (1960) suggested that ing less poisonous or acrid clones and develop­ fishing people, who were rather sedentary, ing cultural practices, primitive man showed after a period of gathering may have started such ingenuity that Burkill (1951) said they domestication and cultivation of yams. How­ must have "already graduated in ." ever it may have been a different process for Out of simple management practices, man each species, and it is extremely important not evolved more complex systems of agriculture. to generalize. In southeast Asia, terracing was developed for Some domestication characteristics common taro cultivation, which eventually was adapted in root and tuber crops are: (1) large size of for rice production. In the Andes, the most edible parts; (2) earliness; (3) low content of complex system was developed to cultivate poisonous or acrid substances; (4) attractive tubers and other crops, including terracing, shape and colour; (5) shallow underground fertilization, , and food storage. This growth; (6) sugar content. Other characteris­ development was far superior to any agricul­ tics, such as resistance to disease, may come in tural system in western or elsewhere in more advanced stages of agriculture. The size the world in the fifteenth century. of the useful parts, like the corms of aroids, and the shape and colour (e.g. Andean tubers) Geographical Origin may have attracted the attention of gatherers. and Early Dispersal In the transition from gathering to cultivation, thc main obstacle was the presence of bitter or Root and tuber crops were domesticated in­ poisonous substances in the edible parts. The dependently in three regions: ( 1) southeast discovery of techniques to eliminate these sub­ Asia and its geographic continuation - the stances played a decisive role in domestica­ Sunda Islands, Papua New Guinea, Oceania; (2) tion. The processes differed according to Africa - ; (3) Tropical America. species. One special technique was washing the A few species were domesticated in southern roots or tubers for many hours to remove and Japan. The three regions were active poisonous principles. In the Andes this method centres of domestication of animals as well. permitted the use of bitter types of potatoes, Agricultural systems were developed independ­ mashuas (Tropaeo/um) , and oca (Oxalis). ently but they have many common features This also led to the preparation of "chuno," a because of similar environments. Prior to the dry mass easier to store and transport than the 1500s there were no exchanges of materials and whole tubers. Roasting or washing methods techniques between the Old and the New were developed in Polynesia to remove the Worlds. The sweet potato was the only known acrid substances from the stems of aroids. The root crop in tropical America and Oceania. LEON: ORIGIN, EVOLUTION, AND DISPERSAL 27 Southeast Asia Mongoloid, came in successive waves from dif­ ferent regions. They mixed together and the The Indo-Malayan region, the land between resulting population, to which the names of the Deccan peninsula and the South China Sea, Indo-Malays or Malays have been applied, was could be considered as a primary agricultural possibly the group that started plant domestica­ hearth because of its domestication of plants tion. Burkill (1953) says it is likely that root and animals, the development of systems of and tubers were the first domesticated crops in agriculture typical to the region, and the in­ this area. vention or changes in the utilization of plant As was stated earlier, the development of materials for food and other uses. The region more efficient techniques in food preparation is limited by natural barriers to the north (the may have been as important in domestication Himalayas but in its northeast corner is open as the development of crop husbandry. Yams towards China) and to the west (the Indian gathered in India and Malaya are roasted or Desert). The rest of the region is surrounded cooked. The removal of poisonous substances by water. The larger Sunda Islands and Papua or acrid materials in yams and aroids is done New Guinea could be considered as a natural by pounding, washing, and heating. Thus, continuation of the region. The Indian section through a combination of simple practices and comprises mainly the coastal areas of the tools, it was possible in this region to start an Deccan peninsula. In Indochina, the relief is agricultural system based on the production of quite complex, and is determined mainly by tuber crops. The region is extremely rich in three major mountain ranges, which run from other foods, especially fruits - mangoes, northwest to southeast with narrow valleys , rambutan and others - which grow and alluvial plains in between. Its western side, wild in the forests. Fish and wild animals sup­ towards the Bay of Bengal, from the foot of plied the necessary . The later domesti­ the Himalayas to the tip of Malaysia and cation of rice in the region started a new pat­ farther on to Sumatra, Java, and , is a tern of agriculture. "tropical rainy" area (over 2000 mm per year). The most important expansion of root and Towards the centre, there are large areas with tubcr crops from the Southeast Asian region "tropical rainy" or "wet and dry" climates with was eastward, carried out by a mixed group, savannas and open forests. The vegetation is the proto-Malays, which moved from the con­ one of the richest in the world and decreases tinent first to the Great Sunda Islands and then in number of species from west to east. The to Papua New Guinea, about 3000 years ago. conditions in the region are not favourable for The first cxpansion occurred about 2000 years the preservation of plant remains, and arche­ ago with the settlement of Polynesia when the ological surveys have been sporadic. Malays from Samoa and reached the There were five racial groups in this region Marquesas to the east, Tokelau to the north, belonging to the N egrito stock who, up to this and the Ellice islands to the northeast. Pre­ century, lived only by gathering roots and viously, had been settled by other tubers. These were the Andamanese in the immigrants from the Sunda and Philippine Andaman Islands; the Semang in North islands. The second expansion occurred before Malaya; the Kadar and the Chenchu in the 500 AD when the Polynesians starting from Western Ghats in India, and the Veddas in Sri the Marquesas reached the extremes of the Lanka (Burkill 1953; Coon 1974). Polynesian triangle (i.e. Hawaii, Easter Is­ The gathering practices of these groups give land, New Zealand). There are no written a picture of how man lived before agriculture. records before 1500, and linguistic and archeo­ Even today, small groups of food gatherers in logical evidence is not strong enough to sup­ this region collect yams and aroids which are port the view that in Oceania there was a pre­ abundant in the rain forest. Because of their re­ and post-Polynesian stage in agriculture. duced numbers and the availability of other Towards the west, the expansion of crops food sources, they have survived in the same was prevented by the dry and desert areas in areas for many centuries. northeast India. Only one species (Colocasia The Negrito stock settled in the region some esculenta) may have followed a land route, 25 000 years ago, but was pushed eastwards by either through Syria or by the Sabean Lane to other immigrants and is represented today only Egypt. by enclaves. The new arrivals, Australoid and To the northeast, taro and some yams 28 TROPICAL ROOT CROPS SYMPOSIUM moved into the subtropical areas of China and seems to have originated in India. It has spread from there to Japan. eastward in recent times, but is not found in From the background of roots and tubers, Polynesia (Yen and Wheeler 1968). new crops and techniques were developed in It reached China and the Lower Yangtze Southeast Asia and Malaysia, thus creating a valley and is mentioned in literature towards large agricultural complex. Rice was the main 100 BC. From China it moved into Japan. The crop on the continent and the large islands, introduction into the Philippines came possibly alone with bananas, sugar cane, through the Sunda Islands. and many other minor crops. The oldest arche­ The spread of C. esculenta to the west is ological date for rice in India is 4300 BC. By poorly documented. It reached Egypt around that time other cereals such as and 100 AD, either through Syria (and there is sorghum had been introduced and were al­ some linguistic support for this, Tackholm and ready in cultivation (Rao 1974). Dar 1950), or through the Sabean Lane, since it is found in Yemen from where it may have Aroids originated. From Egypt, it went through North Alocasia macrorrhiza (A. indica). This is a Africa to Morocco and then to Spain and very primitive crop, possibly domesticated in Portugal. It spread also from Egypt to Italy India (Assam, Bengal), or in Indochina; in and to Cyprus, where it is an old and im­ India other species (e.g. A. cucullata) are cul­ portant crop. tivated and wild Alocasia is used as food. Its When, where and by whom Southeast Asian large trunk contains a fine starch, but because crops were transported to Africa is still open of the high content, it must be cut and to question. Indians or Indonesians settled baked on hot stones, or boiled. In Java and south of Ethiopia around 500 AD, leaving in­ Tonga some cultivars are used only for their struments and practices, like certain types of leaves. Alocasia spread only to the east to­ boats along the coast of Zanj and the lakes, wards and Polynesia. It is of some and they brought in their crop plants from importance in Tonga and Samoa and to all of Malaysia. Madagascar is culturally linked with Micronesia, especially the , Indonesia, and many of the words for crops and was introduced into in the last like Tacca, , taro, are the same in the century as cattle feed. two areas. The Malay sailors may have reached Amorphophallus campanulatus. This plant the coast of Africa with the favourable winds is found from India to Polynesia but with no during the monsoon season. Propagation clues as to the area of domestication. It is an material of roots and tuber crops, brought in ancient plant, low-yielding, and difficult to these trips, may have remained viable for prepare for eating, with the result that it is weeks and very likely were established in being grown less and less. It is cultivated from Africa after many failures. Taro, bananas, India to Malaysia, and in Java as a backyard greater and lesser yams, and sugar cane were crop (Sastrapradja 1970). In Polynesia, it adopted by the Bantu people and other tribes grows wild and is occasionally gathered, but is on the continent. Either by the geographic unknown in Micronesia (Barrau 1962). spread of the former ethnic group, or through Colocasia esculenta. This species is found diffusion into different tribes, these crops wild from India to Southeast Asia, and has reached central Africa and later on west Africa. spread throughout the tropical world and to Taro was already in cultivation in Gambia and the fringes of the temperate regions. San Thome around 1500 (Mauny 1953). Towards the east, the plant was spread by Taro was taken from west Africa to tropical the Malayans and Polynesians to all the islands America, probably in the early 1500s. How­ of Oceania, including Hawaii, Easter Island, ever, it is difficult to establish its arrival because and New Zealand. In this vast area, some early descriptions confuse it with Xanthosoma. hundreds of clones are known, but there is no By the end of the 18th century it had spread complete survey of its diversity. From chromo­ from the Caribbean to Brazil, and early in this some counts, it has been established that there century to the southern coast of the United are two types, 2n = 28 and 2n = 42, with the States. Again, very little is known of its diver­ former the predominant type from India to sity in this area. Superior clones, called Japan and Polynesia. Type 2n = 42 occurs in "dasheen," are recent introductions but the India, New Zealand, and the Philippines and native Xanthosoma, being more productive LEON: ORIGIN, EVOLUTION, AND DISPERSAL 29 and resistant, has prevented the expansion of India and . Before the arrival of the Colocasia esculenta in the American tropics. Europeans, it had spread from Southeast Asia Cyrtosperma chamissonis. This aroid was to the Philippines and into Oceania but not not domesticated on the continent since it is not beyond Tahiti, and north to China, where it is cultivated in India and Malaysia. Its range ex­ mentioned in the literature around 200 and 300 tends from Indonesia to the north side of New AD. It was taken by the Portuguese, along with Guinea; in Melanesia, the Solomons and , D. alata, around the Cape to west Africa. By but not in ; in Polynesia, in the selection, superior clones with larger and fewer central part as far as the Marquesas, but not tubers and less thorny stems have been ob­ in Hawaii or Southeast Polynesia; throughout tained in Southeast Asia and Oceania. Recent Micronesia, as it grows well in the low atolls collections suggest that this species has a (Barrau 1962). greater potential than previously realized (Martin 1974b). Yams (Dioscorea) Dioscorea bulbi/era was independently do­ Six species of Dioscorea were domesticated mesticated in the region, and the Asiatic clones in this region: D. alata, the "greater yam," show morphological and cytological differ­ originated in the area occupied by Burma and ences from the African cultivars. It is found China where the rivers Irrawaddy, Salween, from India to north (only wild types and Mekong ran closely and parallel to each on this continent) and all over Oceania. Asiatic other (Burkill 1951). This is a mountainous clones have recently been introduced to tropi­ area with alternate seasons. Two wild species, cal America (Martin 1974a). closely allied to D. alata, and many primitive extends from west India, cultivars are found here. These yams grow where it is sporadically cultivated, to Malaysia large rhiznmes deep in the soil to survive the and Papua New Guinea. In Java it is planted as dry season, and this characteristic may have a minor crop. The cultivated types are often as attracted the attention of man since early times. poisonous as the wild plants. The greater yam was taken first to the Sunda Dioscorea nummularia is a relict crop, found Islands, to the east, quite possibly only as from the Philippines to Borneo, Celebes and clones with shallow-growing tubers. Many Papua New Guinea and Tahiti, but is not culti­ mutants were concentrated or appeared in vated in Java, Sumatra, or New Caledonia. these islands, differing in tuber shape and size, grows wild in India, and in other characteristics, and this area has southern China (to 22°N), Philippines, In­ the highest diversity of the species. It spread donesia, and all over Oceania; cultivated types also to the Philippines and to all parts of have been selected in separate localities in Oceania, including New Zealand. Toward the Malaysia and Oceania. west, it extended to west India, stopped by the Great Indian Desert. It spread toward Africa, Other minor root and tuber crops maybe taking the same route as taro, banana, originating in this region and other Southeast Asian crops. It spread to East Africa and Madagascar, and later to Cordyline terminalis is found wild in South­ central and west Africa. In the latter region, east Asia, Australia, and most of Oceania; a however, it did not become important because clone with green foliage extensively planted there were already native yams under cultiva­ for the fleshy roots that contain levulose tion. An historical expansion took place after (Ezumah 1970). Curcuma augusti/olia is 1500, when the Portuguese brought it to the planted in 'south India as a source of starch, west coast of Africa. It became the main food "East Indian arrowroot," and C. zeodaria, used in the slave ships and was marketed widely as for the same purpose, is cultivated mainly in "Lisbon yams," especially from San Thome. north India and Sri Lanka (Kundu 1967). With the slaves, the greater yam arrived quite Tacca leontopetalcides is planted sporadically early, around 1530, in the Caribbean and from Southeast Asia, Philippines to eastern Brazil, but in the New World its expansion was Polynesia as a source of starch, the "Tahiti checked again by the African yams. arrowroot." It was possibly domesticated by , the "lesser yam," was Polynesians, who developed several ways of possibly domesticated in the same area as D. preparing it for food or starch, but it is now alata. Wild types have been reported from losing importance. It was taken by Malays to 30 TROPICAL ROOT CROPS SYMPOSIUM Madagascar but it is likely that the African the Malays or Indians. Among the root and cultivars found from west Africa to Ethiopia tubers, Plectranthus tuberosus was introduced may have an independent domestication. It has to India and Indonesia. Perhaps the two cul­ not improved as has the Malaysian crop. tivated species of Psophocarpus, if they are Pueraria thunbergiana (P. Zobata) is cultivated African, followed the same route. in the highlands of Papua New Guinea for its From tropical America the introductions are fleshy roots. Psophocarpus tetragonaZobus is more recent and important: cassava, sweet cultivated from India to Polynesia, especially potato X anthosoma, and potatoes have dras­ in Burma, for the fleshy, sweetish roots. Its tically changed the agricultural systems and origin is unknown, though it could be traced to food habits in west and east Africa. The Africa. The recent interest in this crop is due to Guinean yams were taken very early to the the protein value of the seeds. It is widely Antilles and the coast of Brazil, during the planted as a vegetable for its green pods. slave trade, and are now the most important yams in the region. Root and tuber crops in the Far East Several species have been domesticated in Yams China or Japan but they have not spread much The main contribution of Africa in root and outside this region. In the last decades in tuber crops is the domestication of the Guinean China, both native and introduced root and yams Dioscorea cayenensis and D. rotundata. tuber crops have had a large expansion in area These have been considered one species with and production. These far eastern species in­ D. rotundata as a subspecies of D. cayenensis, clude: Dioscorea opposita, the "China yam," but the recent trend is to keep them apart, is possibly derived from D. japonica; Amor­ partially based on anatomical characters phophallus rivieri, or "bonjac," is found in (Coursey 1967). The Guinean yams are Japan, China, and possibly Vietnam. Its origin especially important in West Africa, and were is possibly south China, with quite a complex probablY domesticated in this area 5000 BP. utilization in Japan; EZeocharis duZcis, the (Coursey 1976; Ayensu and Coursey 1972). "water chestnut," is assumed to be the culti­ Dioscorea cayenensis, the "yellow yam," vated form of E. tuberosa, a wild species widely which is less important than the white yam, is a distributed in the Asiatic tropics; Sagittaria polyploid of unknown origin, although it may sagitti/olia is cultivated mainly in China for its derive from D. minutiflora or other closely re­ tubers, and was introduced by the Chinese to lated species. It grows wild throughout West Polynesia and Stachys sieboZdii, which is re­ Africa, and was probably domesticated in the ferred to in the Chinese literature of the four­ Guinea coastal area, spreading through the teenth century, is also grown in Japan. It was Guinean region in areas of high rainfall. Thorn­ introduced into Europe at the end of the nine­ less clones have been introduced into tropical teenth century and became quite popular in America. . Dioscorea rotundata, the "white yam," is supposed to be a hybrid between D. cayenensis Africa and D. praehensilis (Ayensu and Coursey 1972). It is more widely adapted to moisture In Africa, more than in any other continent, conditions, and its cultivation is most intense we see a full range in the gradual transition in Nigeria. It has spread from Senegal to south in utilization of root and tuber crops, from Ethiopia, including parts of the savanna area, gathering of wild materials to well-established and to Uganda, Angola, and Northern Rho­ cropping systems. The African root and tuber desia. It is also cultivated in the Comores and crops were domesticated south of the Sahara, Madagascar. The primitive types have thorny some in the savanna region, others in the roots which provide good protection, but Guinean forest. Africa is also the meeting point through selection of mutants, thornless clones for Asian and American roots and tubers, and have been established and were taken to tropi­ nowhere else has there been such drastic re­ cal America during the slave trade where it placements in these crops. Among the Asian has become the most important yam. roots and tubers, taro (CoZocasia esculenta) The following yams are of lesser importance. was the first. Dioscorea bulbi/era, which was mentioned be­ Several African crops were taken to Asia by fore, is found in Southeast Asia and Polynesia. LEON: ORIGIN, EVOLUTION, AND DISPERSAL 31 There are differences between the Asian and found from tropical Africa to Papua New the African clones, the latter being less ad­ Guinea. vanced in their domestication. Some clones do Sphenostylis stenocarpa, one of the "yam not produce underground tubers. It grows beans," of African origin possibly from roughly between looN and to 1 ODS lat through­ Ethiopia, is cultivated in east Africa and the out west Africa and from the Nile valley near Guinea area for its spindle-shaped tubers and the Ethiopian border to Southern Rhodesia. dry seeds. The clones in tropical America seem to belong to the African group. is cultivated particularly in the border of the yel­ (T. involucrata, T. pinnatifida) low yam plots, and is found wild through This species is found wild from Senegal to Africa from 15°N to 15°S (Ayensu and Cour­ East Africa and also in Southeast Asia and sey 1972). Other species cultivated are D. Oceania. In Africa it is seldom cultivated. The abyssinica, D. colocasiifolia, D. hirtiflora, D. tubers require careful preparation to remove praehensilis, D. quartininiana, and D. san­ the toxic prinCiples; in some places they are sibarensis. In Madagascar a number of local used as a source of starch. species (D. antaly, D. ovinala, D.soso, the latter with very sweet tubers) have been domesticated Tropical America but their cultivation is being reduced by cas­ sava and sweet potato. The three most important root and tuber crops - potatoes, cassava, sweet potato­ The African tuberous Labiatae come from Tropical America. Other crops, like Xanthosoma, are of high potential value and In the mint family (Labiatae) the formation several minor crops offer limited possibilities of tubers is not uncommon, as was mentioned due to their physiological requirements. under Stachys sieboldii. Two African species The American root and tuber crops have have been domesticated. One was taken some two main areas of domestication - the high centuries ago to India and Indonesia, and has Andes and the lowlands in northern South become a regular crop in these countries America, and a secondary area, Middle Amer­ (Chevalier 1905). ica. The Andean crops include potatoes, oca Plectranthus esculentus (Coleus dazo, C. (Oxalis tuberosa) , mashua (Tropaeolum tu­ esculentus, C. langouassiensis, C. floribundus) , berosum) , ulluco (Ullucus tuberosum) , and the "Kafir potato" is native to west and central maca (Lepidium meyeni) that were domesti­ Africa, though its origin and variability are un­ cated in the Peruvian-Bolivian altiplano, above known. The plant produces many elongated 300 m, and two crops native to the northern tubers, arising from the central stem. section of the Andes (Le. ), at lower Solenostemon rotundifolius (Coleus dysin­ elevations (1000-2500 m), arracacha (Arra­ tericus, C. rotundifolius, C. coppini, Plectran­ cacia xanthorrhiza) and yacon (Polymnia thus tuberosus, P. ternatus), the "Hausa po­ sonchifolia). In the Andes, other root and tato" is cultivated in west and central Africa to tuber crops were early introduced from lower Transvaal and Madagascar. The plant pro­ areas and became an important part of the duces spheric to ovoid tubers, dark red and agricultural complex: sweet potato, achira white. It is an old introQ.uction to India (Canna .edulis), ahipa (Pachyrrhizus sp). ("koorkan"), Malaysia, Indonesia, and recently The second source of root and tuber crops to the Philippines. is the lowlands of northern South America in­ cluding the Antilles, an area of very imprecise Tuberous Leguminosae limits, in which Xanthosoma spp., arrowroot Two species of possible African origin, (Maranta arundinacea) , lairen (Calathea al­ Psophocarpus palustris and P. tetragonolobus, louia), Pachyrrhizus tuberosus, and possibly are cultivated widely in tropical Africa and cassava and sweet potato were domesticated. Asia for their fleshy, sweet roots and for the Middle America, which is so rich in native green pods. The second species, by far the crops, has contributed few and unimportant most important, is intensively cultivated in crops: jicama (Pachyrrizus erosus) is the most Burma for its tuberous roots. The origin of outstanding and has spread to Asia and these species is unknown. Psophocarpus is Oceania. In pre-Colombian times and even to- 32 TROPICAL ROOT CROPS SYMPOSIUM day in remote localities, some plants are Mayan agriculture is still open to discussion gathered for their tubers or corms: Bomarea (Bronson 1966; Cowgill 1971), but it is un­ edulis, Dalechampia spp., some beans (Phase­ likely that cassava could have been a very olus) , Tigridia pavonia, and Dahlia spp. The important food source in the conditions of last two species are now grown as ornamentals Yucatan and Peten. All this may point to a but were once used for their corms and fleshy South American domestication and the fact roots respectively. Sechium edule is planted for that its spread towards the north was restricted its though it also yields edible roots. The to the sweet varieties. On the other hand, early introduction of cassava and sweet potato Humboldt suggested that the sweet types may to Middle America probably prevented the have been domesticated first and that later on domestication and expansion of the local tuber man learned how to utilize the bitter varieties. crops. Cassava was introduced early to Africa by the Portuguese. The first published report by Cassava Barre and Thevet is dated 1558 (Mauny 1953). Cassava (Manihot esculenta) , known only Further spread inside Africa was determined under cultivation, is a complex of clones show­ by its adoption first as a vegetable and later as ing the widest morphological diversity in the a source in the Kingdom of Congo, which Paraguay - South Brazil area. Clusters of was an advanced state that influenced the rest closely-related species to cassava are located in of tropical Africa. The spread apparently was both North and South America (Rogers and rather slow, but was favoured by the resistance Fleming 1973), but no wild species have been of cassava to locusts (Jones 1959). suggested as a possible ancestor. The time and Cassava was introduced to India and South­ place of domestication are unknown. The most east Asia late in the nineteenth century. important trait for the use of cassava as a food is the HCN content in the roots, which has a Sweet potato wide range from high (bitter ) to very Sweet potato (Ipomoea halalas) was the low (sweet cassavas). There is a clear correla­ only food crop common to Tropical America tion in the geographic distribution of the two and Polynesia before the Discovery. As such, it kinds: sweet cassavas occur in the western side has raised a long discussion on which of the of South America, Central America - Mexico, two regions is its place of origin and on how while bitter clones are planted mainly in the its early dispersal occurred (Yen 1974). The eastern side of South America and the Antilles, recent discovery in coastal Peru of sweet potato with an overlapping area in between (Renvoize tubers dating from 10 000 BP (Engel 1970) 1972). Archeological evidence is very scarce. settles the question of the origin, as this date by The remains of cassava leaves have been iden­ far antedates any agricultural development in tified in caves in Mexico dated 2500 BP, and Polynesia. However, it should be considered tubers in coastal Peru from about the same age. that, like all other plants cultivated in the Indirect evidence, such as the presence in early coastal region of Peru, sweet potato was in­ times of grinding stones in Colombia and troduced from elsewhere, possibly from the assumed to be used for grinding north, the coastal area of Ecuador and Colom­ cassava roots, is not very convincing. It is also bia, where close wild types have been found assumed that cassava flour was an important (Martin et al. 1974), or from across the Andes, article of commerce in northern South America like Canna edulis and other crops. in the second and third millenia BC (Jennings At the arrival of the Europeans, the sweet 1976). What is clear is that cassava was more potato was known in all Tropical America, intensively used in South America than in with an important area of diversity around the Middle America. In the former area, the Caribbean. Oviedo, writing in 1530, reports artefacts for the preparation of flour were far that several varieties he had seen in the early more developed, and other uses, such as the days of the Conquest were already disappear­ utilization of leaves as vegetables or for the ing. preparation of sauces, are typical of South The spread of the sweet potato to the Old America. Archeological information, such as World was quite rapid; it was introduced in representations in ceramics and early historical Spain, after several failures, as living plants information, gives additional support to a more before 1550. It is not known how it reached intensive use in South America. Its role in the Africa, whether from Spain or from tropical LEON: ORIGIN, EVOLUTION, AND DISPERSAL 33

America. A report that sweet potato was grown In spite of its importance, very little is in San Thome in 1520 seems doubtful (Mauny known on the domestication and early dis­ 1953). More reliable information shows that persal of the cultivated potato, but the com­ it was widely cultivated by the end of the seven­ plexity of its structure as a species shows that it teenth century in West Africa, and a century has a long history. The oldest tubers are dated later all over the tropical areas of the con­ 200 BP (Ochoa, personal ) and tinent. potatoes are represented in ceramics of the The introduction to Polynesia, as discussed third century Be. Although very little is known above, has not been properly explained. It of the domestication process, the early spread could have been accidentally transported in to Europe and other continents is fairly well one of the Peruvian rafts lost in the Central documented (Dodds 1966; Hawkes 1967). Pacific, which reached Polynesia where the Other root and tuber crops of the highlands crop was established by Indo-Americans and are: Oxalis tuberosa, or "Oca", of which no developed later on by Polynesians. It has been wild ancestors are known. It has a large num­ proposed also that the sweet potato may have ber of clones differing in size, colour, and shape been taken to Polynesia by one of the Spanish of the tuber, plant size, foliage colour, and expeditions that visited the area starting from heterostyly. Clones with bitter tubers are used Peru in the sixteenth century. It was taken to to prepare "chuno." The oca was introduced China in 1594 and after a famine in Fukien, it into Mexico during colonial times ("papa ex­ later became an important crop. Sweet potato tranjera"), into southern France, and last was introduced early to Japan from Okinawa century to New Zealand where it is called and cultivated and adopted in the southern "yam." Ullucus tuberosus has slimy tubers region up to 35°N. which are not as attractive as ocas, but they are consumed even in the large towns. Wild or Xanthosoma ancestor types grow in the highlands of Peru The identification of the species of X an tho­ and . Two main groups of clones are soma, cultivated for the corms, is still not clear. known: in the northern extreme of the range The "species" described vary between them­ (Colombia), with trailing branches and large, selves like the clones of taro which is now con­ red tubers; and in Peru and Bolivia, erect, short sidered to be one species. The genus is found branches, with multi-coloured tubers. The from Mexico to Brazil, but the cultivated ulluco was introduced into southern Europe "species" are centred around the Caribbean. but it is not planted. There is no information on the evolution of grows in the same area as oca. No wild rela­ this crop. It is superior to taro in yield, re­ tives are known, although some other South sistance to disease, adaptability, and taste, and American species are reported to form large therefore it is not surprising that this species is tubers. Two main groups of clones are known: replacing taro all over the tropics. Xanthosoma in Colombia, tubers are slim, white, with deep was introduced to Africa by the middle of the eyes from which emerge fine rootlets; and in last century, where the replacement is most Peru and Bolivia, the tubers do not have root­ active. lets and the predominant colours are yellow with purple lines or fine points. The mashua Tubers of the high Andes grows often at altitudes where only bitter A group of tuber crops was domesticated potatoes are produced. Lepidium meyeni pro­ in the high Andes, above 3000 m, where they duces a -like root, sweet, yellow or dark are now intensely cultivated (Leon 1964). The purple in the highlands of Peru, above 400 m. most important are the potatoes, which at pres­ It is a relict crop that is rapidly disappearing. ent are considered as one species, Solanum tuberosum, including: 0) two tetraploid groups, Other Andean root and tuber crops Tuberosum and Andigena; (ii) a triploid, At lower elevations in the Andes, between Chaucha; (iii) two diploids, Phureja and o and 3000 m, several root and tuber crops Stenotomum; (iv) two intersperific hybrids, X are grown: A rracacia xanthorrhiza. "Arra­ juzepozukii, triploid, a cross between S. tuber­ cacha" is especially important in Venezuela and osum X S. acaule, and X curtilobum, resulting Colombia; no wild types are known and it from S. tuberosum X juzepozukii (Ugent seems to be of ancient cultivation. Several 1970). clones are known to differ in shape and size of 34 TROPICAL ROOT CROPS SYMPOSIUM the roots, foliage, colour, etc. It has been in­ tuber crops, the roles of polyploidy, mutation, troduced into Middle America, Brazil, East and vegetative propagation give some clues to Africa, India; Canna edulis is possibly native the general process. Some outstanding research to the eastern part of the Andes, and was in sweet potatoes has established the possible brought to the coast of Peru where it has been transition stage of the wild diploids to a com­ cultivated since 4000 BP; diploid and triploid plex hexaploid, and has recognized wild popu­ types are known (Mukherjee and Khoshoo lations which may have had a role in the de­ 1971); cultivated in Australia ("Queensland velopment of the crop. But in sweet potato, and arrowroot"), Hawaii, India, Polynesia; Po­ even in the common potato, there is an appall­ lymnia sonchi/olia is cultivated from Vene­ ing ignorance as to how domestication traits zuela to , and according to Bukasov occurred. Today there are increasing doubts (1930) grows wild in Colombia. The tuberous among anthropologists and botanists about the roots are fleshy, contain sugar (10%), and capacity of primitive man to have carried out were used in colonial times on long sea trips; crop selection. Primitive farmers profited from introduced to southern Europe as a forage the presence of edible organs in certain species. crop; Pachyrrizus sp. are ancient crops in the However, it is quite difficult to explain how he Andes, probably introduced from the Ama­ could carryon the improvement of inherent zonian lowlands. traits without knowledge of the rules of ge­ netics and the help of permanent records. On Minor tropical American the other hand, primitive man exchanged root and tuber crops planting materials with his neighbours, and in The West Indian yam (Dioscorea tri/ida) is vegetative crops he introduced superior clones the only species of the genus domesticated in and thus eventually contributed to their hybrid­ the American tropics, although other species ization. At the same time, by moving crops to are gathered, particularly in Brazil. The species new areas, he restricted the possibilities of has the highest diversity in the area between the further crossing with the species of its native Guianas and Brazil and selected types are habitat. Man-made isolation has been, there­ planted in the Antilles. Its domestication was, fore, an important factor in the evolution of of course, independent of the Asiatic and crop species. Man has also executed an im­ African yams (Alexander and Coursey 1969). portant action in taking plants to new habitats. Arrowroot (Maranta arundinacea) was, This is seen more clearly in relation to the­ around the middle of the eighteenth century, selective impact of diseases and pests, such as used mainly to cure the wounds from poisoned the attack of cassava viruses in Africa. arrows, and also started to be used in the Roots and tubers are ancient crops and Antilles as a source of starch (the "St. Vincent primitive man independently domesticated arrowroot" - Stutervant 1969). species of the same genus (Dioscorea) or of Lairen (Calathea allouia) was intensively allied species (Colocasia and Xanthosoma, cultivated at the time of the Discovery in the Pachyrrhyzus and Pueraria) in different parts Great Antilles and the Continent. The ovoid of the world and at different times. Many of tubers are now used for food mainly in Vene­ these crops, due to physiological constraints or zuela. lack of acceptability, have not spread farther Several species of jicamas (Pachyrrhizus spp.) than their native habitat, and in fact many are cultivated in South America, and are par­ are now becoming relicts in old agricultural ticularly important in Mexico and Central systems. Their spread, particularly after the America. From Mexico the plants went, by the Discovery, has led to competition among them­ Acapulco-Manila connection, to the Philip­ selves and to the eventual replacement of some and subsequently spread to Southeast species, a process that continues today. Asia and Oceania. Plants of the same "species" Root and tuber crops are associated with offer such a variability in size, shape of leaves, primitive systems of agriculture. A duality has and tuberous roots that the specific limits are been established between seed agriculture, difficult to recognize. which is supposed to be a dynamic process characteristic of advanced communities, and vegetative propagation which is supposedly Conclusion maintained by more primitive communities. In considering the evolution of root and The fact is that in the tropics there is no such LEON: ORIGIN, EVOLUTION, AND DISPERSAL 35 difference, and root and tuber crops as the only Cowgill, U. M. Some comments on Manihot source of energy food are found only in a few subsistence and the ancient Maya. Southwest isolated communities. Grains and tubers are J. Anthr. 27, 1971,51-63. integral parts of most agricultural systems in Darlington, C. D. The evolution of man and society. Allen and Unwin, London, 1969. which they have different not antagonistic Dodds, S. K. Classification of cultivated potatoes. roles. Perhaps the best answer to the academic In Carrel, D. S., ed., The potato and its wild problem of seed versus vegetative culture lies relatives. Renner, Texas, 1962. in the ceramics of the Trujillo valley in North­ The history and relationships of cultivated ern Peru. On one of these ceramics dating from potatoes. In Hutchinson, Sir J., ed., Essays on around 1500 BI> an Indian farmer is shown crop evolution. Cambridge, 123-141, 1965. holding, at the same level, a corn plant in one La evoluciol! de la patata cultivada. Endea­ hand and a cassava plant in the other. vour 25, 1966,83-88. Engel, F. Exploration of the Chilca canyon. Curr. Anthr. 11, 1970,55-58. Abraham, A., Panicker, P. K. S., and Mathew, Ezumah, H. Miscellaneous tuberolls crops of P. M. Polyploidy in relation to breeding in tuber Hawaii. Tropical root and tuber crops tomor­ crops. J. Ind. Bot. Soc. 43, 1964,278-282. row. 1,1970,166-171. Alandia, S. Producciol! de semi/la sexual en oca. Harlan, J. R., and Zohary, D. Distribution of wild Sayana,5, 1967, 12-15. and . Science, 153, 1966, 1074- Alexander, J., and Coursey, D. G. The origins of 1080. yam cultivation. In Ucko, P. J., and Dibley, Hawkes, J. G. The history of the potato. J. Roy. G. W., eds., The domestication and exploitation Hort. Soc. 42, 1967,207-224; 249-365. of plants and animals. 405-425, 1969. Hernandez, T. P. et aI. Frequency of somatic Ayensu, E. S., and Coursey, D. G. Guinea yams. mutations in several sweet potato varieties. Econ. Bot. 26,1972,301-318. Proc. Amer. Soc. Hort. Sc. 85, 1964, 430-433. Barrau, J. Les plantes alimentaires de I'Oceanie. Jennings, D. L. Variation in and Ann. Mus. Corn. Marseille Ser. F. 1955-61. fertility of cassava and the effect of interspecific 1962. crossing on fertility. Euphytica, 12, 1963, 69- Bronson, B. Roots and the subsistence of ancient 76. Mayas. Southwest. J. Anthr. 22, 1966.251-279. Cassava, Manihot esculenta (Ellphorhiaceae). Brucher, H. Vllllcus aborigeneous, spec. nov. die In Simmonds, N. W., ed., Evolution of crop wildform einer andinen kulturpf/.anze. Ber. plants. Longman, London, 81-84,1976. Deutsch. Bot. Ges. 80, 1967,376--381. Jones, W. O. Manioc in Africa. Stanford, Calif., Buck, P. H. (Te Rangi Hiroa). Arts and crafts 1959. of Hawaii. I. Food. B. P. Bishop Museum Spec. Juzepczuk, S. M. New species of the genus PubI. 45. Honolulu, 1964. Solanum in the group Tuberarium. Bull. Acc. Bukasov, S. M. The cultivated plants of Mexico, Sc. USSR, 2,1937,295-331. Guatemala and Colombia. Bull. AppI. Bot. Gen. Kundu, B. C. Some edible rhyzomatous and tuber­ PI. Br. SupI. 47, 1930. ous crops of India. Proc. Intern. Symp. Trap. Burkill, I. H. The rise and decline of the greater Root Crops, 1, 1967, 124-130. yam in the service of man. Adv. Sci. Lond. 7, Leon, J. Plantas alimenticias andinas. I1CA BoI. 1951,443-448. Tec. 6. Lima, 1964. Habits of man and the origins of the culti­ Magoon, M. L. Recent trends in cassava breeding vated plants in the Old World. Proc. Linn. Soc. in India. Proc. Intern. Symp. Root Crops. 1, Lond. 164, 1953, 12-42. 1967, 100-113. Organography and evolution of the Diosco­ Magoon, M. L. et aI. Cytomorphological studies reaceae, the family of yams. J. Linn. Soc. (Bot.) on induced polyploids of cassava. Gen. Iber. 21, 56, 1960,319-412. 1969, 1-47. Chevalier, A. Les vegetaux utiles de l' Afrique Magoon, M. L., Krishnan, R., and Vijaya, K. tropicale. I. Coleus. Depot des Publications, Cytological evidence on the origin of the sweet Paris, 1905. potato. Theor. AppI. Gen. 40, 1970, 360-366. Clark, J. D. The spread of food production in Martin, F. W. The sterility-incompatibility com­ sub-Saharan Africa. J. Afric. Hist. 3, 1962, plex of the sweet potato. Proc. Intern. Symp. 211-228. Trap. Root Crops, 1, 1967, 3-15. Coon, C. S. The hunting peoples. Penguin, London, Tropical yams and their potential. Part 1. 1974. Dioscorea esculenta. USDA. Agric. Handb. No. Coursey, D. G. Yams. Longman, London, 1967. 457, 1974a. Yams, Dioscorea spp. (Dioscoreaceae). In Tropical yams and their potential. Part 2. Simmonds, N. W., ed., Evolution of crop plants. . USDA. Agric. Handb. No. 70--74, 1976. 466,1974b. 36 TROPICAL ROOT CROPS SYMPOSIUM

Martin, F. W., Jones, A., and Ruberte, R. M. A improvement of yams, Dioscorea rotundata. wild Ipomoea species closely related to the Nature, 254, 1975, 134-135. sweet potato. Ec. Bot. 28, 1974,287-292. Sastrapradja, S. Inventory, evaluation and mainte­ Mauny, R. Notes historiques autour des princi­ nance of the genetic stocks at Bogor. Trop. pales plantes cultiVl!es d'Afrique occidentale. Root and Tuber Crops Tomorrow, 2, 1970, Bull. Inst. Franc. Afrique Noir 15, 1953, 684- 87-89. 730. Sauer, C. O. Agricultural origins and dispersals. Mukerjee, I., and Khoshoo, T. N. V. Genetic The American Geogr. Society, New York, 1952. evolutionary studies in starch yielding Canna Sharma, A. K., and de Deepesh, N. Polyploidy in edulis. Gen. Iber. 23, 1971,35-42. Dioscorea. Genetica, 28, 1956, 112-120. Nishiyama. I. Evolution and domestication of the Simmonds, N. W. Potatoes, Solanum tuberosum sweet potato. Bot. Mag. Tokyo, 84, 1971, 377- (Solanaceae). In Simmonds, N. W., ed., Evolu­ 387. tion of crop plants. Longmans, London, 279- 283, 1976. Nishiyama, I., Miyazaki, T., and Sakamoto, S. Stutervant, W. C. History and ethnography of Evolutionary autoploidy in the sweetpotato some West Indian . In Ucko, J. J., and (Ipomea batatas (L). Lam.) and its preogenitors. Dimsley, G. W., eds., The domestication of Euphytica 24, 1975, 197-208. plants and animals. Duckworth, London, 177- Plucknett, D. L. Edible aroids, A locasia, Colo­ 199, 1969. casia, Cyrtosperma, Xanthosoma (Araceae). In Subramanyan, K. N., Kishore, H., and Misra, P. Simmonds, N. W., ed., Evolution of crop plants. Hybridization of haploids of potato in the plains London, 10-12, 1976. of India. Curro Sci. 41, 1972,580. Rao, M. V. Crops of West Asia. Cereals. In Tackholm, V., and Dar, M. of Egypt. Vol. Hutchinson, Sir J., ed., Evolutionary studies in 2. Cairo, 1950. world crops. Cambridge, 1974. Ugent, D. The potato. Science, 170, 1970, 1161- Renvoize, B. S. The area of origin of Manihot 1166. esculenta as a crop plant - a review of the Yen, D. E. The sweet potato and Oceania. An evidence. Ec. Bot. 26, 1972,352-360. essay in . B. P. Bishop Museum Rogers, D. J., and Fleming, H. S. A monograph Bull, 236, Honolulu, 1974. of Manihot esculenta with an explanation of Yen, D. E., and Wheeler, J. M., The introduction the taxometric methods used. Ec. Bot. 27, 1973, of taro into the Pacific: the indications of the 3-113. chromosome numbers. Ethnology, 7, 1968, Sadik, S., and Obereke, O. U. A new approach to 259-267.

Giant Swamp Taro, a Little-Known Asian-Pacific Food Crop Donald L. Plucknete Cyrtosperma chamissonis (Schott) Merr., a member of the Araceae and probably native to Indonesia, has now spread eastward to become a minor crop in the Philippines, Papua New Guinea, and some Pacific Islands, but a major crop on coral atolls and low islands of the Pacific. A hydrophyte, and extremely hardy perennial, it grows in coastal marshes, natural swamps, and man-made swamp pits in conditions unsuitable for other staple crops. Yields vary, but 10-15 metric tons of the large edible corms per hectare per year have been produced. There is a great need to collect and evaluate cultivars now in use for salinity and flooding limits, short crop duration, superior food value and acceptance, and other factors, before they are lost through neglect.

Recently, interest in subsistence tropical benefited from this new emphasis on in­ food crops has increased. Root crops have digenous staple foods. Some roots crops, however, are so poorly known or understood that they continue to be lSoil and Water Management Division, Office neglected. Cyrtosperma chamissonis (SchoU) Agency for International Development, Washing­ College of , University of Merr., commonly called giant swamp taro, is of Agriculture, Technical Assistance Bureau, such a crop. The only cultivated member (if ton, D.C., USA 20523. (Permanent address: C. merkusii is a separate species, then there are Hawaii, Honolulu, Hawaii, USA 96822). two cultivated species) of a pantropic genus of