TROPICAL ÏAMS AND THEIR POTENTIAL Part 1. Dioscorea esculenta

Agriculture Handbook No. 457

r

I' .. "O

tn -^

tp

Agricultural Research Service UNITED STATES DEPARTMENT OF AGRICULTURE in cooperation with U.S. Agency for International Development This publication reports research involving pesticides. It does not contain recommendations for their use, nor does it imply that the uses dis- cussed here have been registered. All uses of pesti- cides must be registered by appropriate State and/ or Federal agencies before they can be recom- mended.

rOLLOW TH« UAMb ' « |. MWiatir t> eUHnmC

CAUTION: Pesticides can be injurious to hu- mans, domestic animals, beneficial insects, desir- able plants, and fish or other wildlife—if they are not handled or applied properly. Use all pesticides selectively and carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide containers.

Washington, D.C. Issued April 1974 PREFACE The feeding of future generations requires a knowledge of the individual crop plants of the world and their poten- tials. Crops can be recommended for use in particular re- gions only on the basis of potential yield, the costs of pro- duction, the food and feed value of the crop, and the way the crop can be processed or otherwise used. For most of the major food crops of the world, a body of information is already available. However, tropical roots and tubers, which are widely used as staple foods, have been largely neglected. Only in recent years has an awareness been growing of the potential of these crops to supply large amounts of food in relatively small amounts of space. Yams are the second most important tropical root, or tuber, crop. The annual production, perhaps 25 million tons, places them second in importance to cassava. But yams are better food than cassava, and while they are usually thought to be more difficult to grow, under some conditions yams outproduce cassava. Yams fill an important role in the diet of many areas of the Tropics—a role that can increase in im- portance. That role and its potential are not, however, well understood. The yam is not a single species. Perhaps 60 species have edible tubers; of these about 10 species can be considered crop plants. The literature concerning these species is wide- spread but fragmentary. This is the first of several Agricul- ture Handbooks in which the major species of yams are individually treated in order to bring the investigator as well as the agriculturalist up to date with respect to the status of these important plants. This is part of a research effort cosponsored by the Agricultural Research Service of the U.S. Department of Agriculture and the U.S. Agency for International Development to introduce, evaluate, and dis- tribute better yam varieties. CONTENTS Page Preface * iii Introduction 1 History and origin 1 Geographic distribution 1 Botany 2 Classification 2 Morphology 2 Cytology 7 Varieties — * 7 Wild varieties 7 New Guinea varieties 7 Varietal characteristics ^ 8 Culture 8 Environmental requirements ^ 8 Land preparation 9 Planting 10 Fertilization 11 Staking • 11 Pests and diseases • 11 Harvesting 12 Storage and marketing 14 Cooking 15 Composition 16 Potential uses 16 Literature cited 18 TROPICAL YAMS AND THEIR POTENTIAL Part 1. Dioscorai esculenlu

By FRANKLIN W. MARTIN, plant geneticist. Federal Experiment Station, South- em Region, Agricultural Research' Service, U,S, Department of Agriculture, Mayaguez, P,R, INTRODUCTION ter of origin). However, the spe- cies is so ancient that few wild Of the many edible yams found forms are known. Burkill {8} de- in the Tropics, the lesser yam, scribes several wild varieties from Dioscorea esculenta (Lour.) New Guinea and the Philippine Burk., ranks third in production Islands and suggests this as the and utilization. Only the West Af- center of origin of the species. rican yam, D, rotundata Poir., and Feral forms evidently occur on the Asian greater yam, D. alata some islands of the Pacific and in L., are more widely used. D. escu- India. Ting and Chi (9) mention lenta is widely distributed and accounts of cultivation of this spe- well known throughout the Trop- cies in China in the second and ics, but it is best known and most third centuries A.D. and maintain used near its origin, Indochina, that it was an especially impor- and in adjacent islands, including tant staple food in southern Papua New Guinea and those of China from the 2d to the 11th the Pacific Ocean. Some of the century. Burkill (^) summarizes characteristics of this yam recom- the distribution and nomenclature mend it for wider planting, but it of this species from India through also has several severe disadvan- Southeast Asia to the islands of tages, which might limit its po- the Pacific. There is little doubt tential as a commercial crop. On of its use for hundreds of years the other hand, recent collecting there. The species has also reached efforts suggest that the best the small islands of the Pacific, forms of this species have only where it is widely used, but has now been obtained and that the never become a staple (2), potential is greater than had pre- viously been realized. Geographic Distribution The lesser yam is widely dis- History and Origin tributed throughout the tropical Vavilov (10)^ considers that D, world, but it is little known or esculenta was domesticated in used except in southeastern Asia. Burma or Indochina (Indian cen- Many forms can be seen in New 1 Italic numbers in parentheses refer Guinea. All of the collections ob- to items in "Literature Cited," p. 18. tained in West Africa appear to

1 AGRICULTURE HANDBOOK 457, U.S. DEPT. OF AGRICULTURE be similar or closely related. At Morphology least three distinct races have D. esculenta is a thorny, climb- been collected in the Caribbean. ing vine, seldom more than 3 The floras of most tropical coun- meters high (fig. 1). The stems tries mention the lesser yam, but are thin (1- to 3-millimeter di- it is seldom seen except in home ameter) and thorny to glabrous. gardens. The yam is common to They twist to the left in climbing. many islands of the South Pacific, The leaves are alternate (or oc- but appears to have been recently casionally subopposite at the base introduced on the eastern side. of the stem) and orbicular, but with an acuminate apex and cor- BOTANY date base (fig. 2). The leaves are Classification slightly rugose and finely pubes- Z). esculenta (Lour.) Burk. has cent. The petioles are thickened at also been named D, aculeata L. their proximal end and are armed and Oncus esculenta Lour. It is with four sharp prickles. The often called the lesser yam, the po- roots of Z>. esculenta often bear tato yam, or the Chinese yam. All thorns, which may impede depre- of these common names are de- dations by burrowing animals and ficient in that they do not reflect wild pigs. These thorns, arising the unique characteristics of the only from the fibrous roots and species. not from tuber-bearing stolons, D. esculenta belongs to the sec- may be very fine and sharp. Flow- tion Combilium, a monotypic sec- ers are rarely seen on cultivated tion with no close affinities to any forms of this strictly dioecious other cultivated species. In com- species. On the presence or ab- mon with other yams, the lesser sence of thorns, two botanical va- yam belongs to the family Dio- rieties of the species have been scoreaceae, of v^hioh-Dioscorea is distinguished, varietas spinosa the principal genus. The family is (Roxb.) Prain & Burk. and va- usually classified among the mon- rietas fasiculata (Roxb.) Prain ocotyledons, although some evi- & Burk. This distinction is artifi- dence of a second cotyledon has cial, for all degrees of thorniness been found. The family is charac- can be found. The less thorny va- terized by rhizomes, usually re- rieties have presumably been se- duced to a nodeless structure. lected and. represent the most Male and female flowers, usually evolved forms of the species. on separate plants, are small and The tubers superficially appear usually inconspicuous, although to be tuberized roots, but are the inferior ovary inay become swellings of stolons arising from quite prominent after fertiliza- the crown of the plant (fig. 3). tion. The floral pattern is based on The stolons vary in length from sets of three. 5 to about 50 centimeters. The TROPICAL YAMS AND THEIR POTENTIAL, PART 1

FIGURE 1.—Mature vines of Dioscorea esculenta. length i^ a varietal characteristic. Spindle shapes (such as those of Each stolon bears only one termi- the sweetpotato) are not uncom- nal tuber. About 4 to 20 tubers mon. The tubers of better varie- are borne by each plant. The num- ties are seldom branched, but in ber of tubers increases with favor- some primitive varieties branch- able growth conditions, but is also ing is common (fig. 4). In a few related to the variety. The tubers varieties the tuberizing stolons vary in diameter from the size of grow upward, giving the tuber a a stolon to 20 centimeters in ex- crescent shape. The shape of the ceptional cases. In the Caribbean, tuber is strongly affected by the tubers average 8 to 10 centimeters soil and by stones or debris in the in length, with a diameter of 2.5 soil. Regular shapes occur in soft, to 5 centimeters and a weight of loamy soil. 100 to 200 grams. Small tubers, The surface of the tuber is useful as seed, are common. Very smooth, with few to many adven- large tubers (as in the case of titious, fibrous roots. A few de- New Guinea varieties) reach 3 pressions appear like the eyes of kilograms. a potato. These are not the sites of The tuber is usually shaped like preformed buds, but are local a potato, although it is propor- growth irregularities caused by tionally longer and narrower. minor injuries to the tuber. The 4 AGRICULTURE HANDBOOK 457, U.S. DEFF. OF AGRICUI-TURE

PN-3433 FIGURE 2.—Leaves of five Dioscorea species. Left to right, top to bottom: D. esculenta, D. rotundata, D. trífida, D. bulbifera, and D. alata. thin bark is easily torn and may varies from pure white to dark be marked with thin longitudinal cream or pale yellow. The raw cracks, which seldom extend be- flesh of a few varieties may irri- yond the cortex. These fissures, tate human skin. When the tuber when extensive, can lead to fungal is cut, gum oozes from the surface. infections of the tuber. The cor- This may be sticky and stringy. tex of the yam is thin (less than The surface may oxidize and turn 1 millimeter) and usually white. brown within a few minutes. The Types with a pink or purple cor- tendency to oxidize is associated tex have been described. with variety, with size and age of The flesh (parenchymatous tuber, and with region (proximal tissue) of the tuber is crisp and portions oxidize most rapidly). uniformly fine grained. The color The tubers always contain fibers, TROPICAL YAMS AND THEIR POTENTIAL, PART 1

PN-3434 FIGURE 3.—Clump of lesser yams on long stolons. Fibrous root system is seen above. (One-fourth actual size.) 6 AGRICULTURE HANDBOOK 457, U.S. DEPT. OF AGRICULTURE

PN-3435 FIGURE 4.—Unusual tuber shapes of the lesser yam. TROPICAL YAMS AND THEIR POTENTIAL, PART 1 but these may be soft and incon- again. A further possibility exists spicuous. in ridding the plants of viruses. The starch of the tuber is very Probably all plants carry at least fine. Larger particles avera^ge one virus that they tolerate very about 0.50 to 0.60 microns in di- well. Since this virus appears to ameter. In addition, there are be peculiar to yams, once virus- many very fine starch grains. The free stocks are produced, it should tuber contains 10 to 24 percent be easy to maintain them in iso- starch, and the proportion of amy- lated plantings. Hill selection for lose in the starch varies from 9 tuber shape and for root-free tu- to 16 percent. Thus, the starch is bers has not been effective. much finer than that of cassava, sweetpotato, and most other yams, VARIETIES but the amylose content is quite Wild Varieties low. Most common forms of D. escu- lenta are cultivated varieties. Cytology Wild varieties have been de- Only a few chromosome counts scribed, but these appear to be of the lesser yam have been re- mostly cultivated types that have ported. The West African form of been abandoned. Nevertheless, a D, esculenta has 40 chromosomes few wild varieties have been (7). This is a common tetraploid found in Malaysia, New Guinea, number in the genus. Raghavan and the Philippine Islands, and (8) reports counts of 90 and 100. these differ from the cultivated Thus, highly polyploid races exist. and the feral types in having more Because of the normal lack of vigorous foliage, larger leaves, flowering, breeding the lesser yam longer stolons, and more fibrous is not practical. Experience sug- tuber flesh. Although these races gests that rapid improvement can tend to be more thorny, thorniness be achieved through introduction is also related to other factors, and selection of varieties. This such as the age of the plant and possibility has not been systemati- its size and condition. The shape cally explored. Within varieties, of the tuber is a varietal charac- hill selection appears to be bene- teristic. The wild types tend to be ficial, especially during early roundish or somewhat flattened generations. By selection of bet- and lobed. ter hills, diseased and pest-ridden plants are gradually eliminated, New Guinea Varieties and thus cleaner stocks are pro- Varieties are more numerous duced. Unless selection is contin- and varied in New Guinea than ued, varietal stocks can decline in any other area. In the Maprik 8 AGRICULTURE HANDBOOK 467, U.S. DEPT. OF AGRICULTURE area southwest of Wewak, Papua foliage to leaf-spot diseases, ex- New Guinea, about 80 varieties pression of virus symptoms, tend- are distinguished by the local peo- ency to flower, and sex of plant. ple. However, some characteris- Among the characteristics de- tics, such as relation to family, sired in a good variety are rela- may not be valid, and perhaps as tively large and uniform tubers, few as 30 actual varieties exist. compact tuber clusters, and few High-yielding varieties that re- adventitious roots on the tubers. quire long growing seasons, with The tubers of the varieties seen in large tubers that store well, are the Caribbean are usually too the most common. Finer, im- small for convenient handling, proved varieties that mature ear- but are produced in suitable clus- lier, have better eating qualities, ters (fig. 5). More widespread in- but yield less, are also known. troduction and testing of newly New Guinea cultivars have been collected varieties is desirable. collected by the author and will The few varietal names current be released after evaluation to in the Caribbean area and Africa other investigators. have little utility because of their local nature. Varietal names in Varietal Characteristics India, Indochina, Indonesia, and The following tuber character- Papua New Guinea are seldom istics distinguish varieties of D. widespread or well known and are es

PN-M36 FIGURE 5.—A large, compact clump of tubers of the lesser yam. (One-third actual size.) without interruption. In such a plants and are produced anew case, when vigorous new growth each year before the dry season. is resumed, the tubers gradually Land Preparation wither. Only when the tubers are Yams are usually planted in in- cut free from the plant do they dividual hills or high ridges to germinate independently and pro- provide drainage and increase duce new plants. Thus, the tubers aeration of the soil. In addition, serve as a food reserve for the yams can be harvested much 10 AGRICULTURE HANDBOOK 457, U.S. DEPT. OF AGRICULTURE easier from ridges than from flat ground, holes, or trenches. If the soil is particularly heavy, subsoil plowing may be desirable. Planting The time of planting the lesser yam is somewhat more flexible than with other yams because of the capacity of the plants to grow almost year round. For practical purposes, however, time of plant- ing is usually adjusted to conform to the beginning of the rainy sea- son. Since the growing season is long, it is desirable to plant as soon as weather conditions are favorable. The possibility of ex- tending the season of this yam by off-season planting needs study. Late planting has been shown in one study to reduce yields (6). D. esculenta can be propagated from stem cuttings (fig. 6). Each cutting consists of a single leaf, PN-3437 the attached node, and a short FIGURE 6.—Single leaf stem cutting of length of each internode. Placed D. esculenta with newly produced in mist spray, the cuttings quick- roots. ly root, and small vines are form- ed. The technique is most useful bers of 50 to 75 grams are best. when rapid propagation is de- Larger seed tubers suitable for sired from a small amount of ma- consumption do not yield propor- terial. tionately more. At this rate and Normally, whole tubers are used with spacing of 100 centimeters for planting. At time of harvest between rows and 30 centimeters there are always many tubers that between plants, the amount of are too small for convenient house- planting material needed per hec- hold use. These tubers can be used tare is about 2,080 kilograms. for planting the next crop. How- Tubers are planted with a short ever, yields are closely related to hoe 8 to 12 centimeters below the seed-tuber size (table 1). Small surface of the ground. Atrazine, seed tubers yield more per gram a preemergence herbicide, has but less per plant than large tu- been used experimentally at 3 bers. As a practical guide, seed tu- kilograms per hectare in Trinidad TROPICAL YAMS AND THEIR POTENTIAL, PART 1 11

TABLE 1.—Yield of lesser yams as plications, except in the latter half related to size of seed tubers of its growth cycle when it is de- sirable to increase tuber rather Seed-tuber Yield per plant than vegetative growth. On the size No. of other hand, potassium is needed tubers Grams (grains) especially during tuberization. 15 20 400 Phosphorus is removed very ef- 30 26 540 ficiently from the soil by yams 45 29 590 and seldom is a limiting factor in 60 31 660 growth. 75 32 680 90 34 710 In Trinidad, the following ferti- 105 35 735 lization schedule has been recom- 120 36^ 750 mended for the lesser yam (Ï): apply either 200 kilograms am- monium sulfate per hectare 3 after planting for weed control. months after planting or 400 kilo- Later weed control is managed by grams compound fertilizer high in direct spraying of weeds with potassium (11:11:13) per hectare paraquat at 3 liters per hectare. 6 to 8 weeks after planting. How- Before atrazine and paraquat can ever, local trials with fertilizer be used commercially in the pro- are always desirable. duction of yams, however, they must^be approved by local juris- Staking dictions. The plants of the lesser yam climb by twining and need some Fertilization kind of climbing support for max- The question of mineral fertili- imum growth. Any stake that per- zation of yams needs further in- mits growth up to about 2 meters vestigation. After planting, the is probably adequate. Living initial growth of the yam is sus- plants used as supports compete tained principally by the tuber. excessively with the yams and re- Six or eight weeks later the prin- duce yields. Although some va- cipal sustenance is drawn from rieties of yams can produce ade- the soil. Thus, fertilization is most quate yields without staking, less- effective if given when needed. er yam tubers from unstaked Nevertheless, application at this plants seldom reach an adequate time is more costly and less pre- size. Poor yield is closely associ- cise. A compromise may be to ated in this case with poor vine de- bury the fertilizer under the ridge velopment. before planting, where it can be reached by the roots of the grow- Pests and Diseases ing plant. One advantage of the lesser yam Generally the lesser yam re- is its relative freedom from pests sponds positively to nitrogen ap- and diseases. The foliage often 12 AGRICULTURE HANDBOOK 457, U.S. DEPT. OF AGRICULTURE has virus symptoms, but virus is Harvesting probably always present and is Studies are lacking to suggest tolerated (fig. 7). Methods are the limits of the lesser yam har- needed to test for the presence of vest season. Harvesting 10 months virus and to eliminate it from se- after planting is probably real- lected varieties. Coursey (5) has istic. Without doubt some yams listed some of the common dis- can be harvested earlier, although eases of yam. Leaf spots, of such the tubers may be immature. Since significance in the culture of D. the foliage of the lesser yam often alata, are seldom a problem with does not die back, harvest may be D. esculenta. Stem dieback, often delayed until or even after spring seen in D. rotundata, does not af- growth begins. fect D. esculenta. Because of the very succulent On the other hand, nematodes and fragile nature of the tubers, can severely affect production extreme care must be taken to re- of the lesser yam. Root-knot nema- move the tubers from the ground. todes (Meloidogyne) can be par- This is normally done with hand ticularly destructive (fig. 8). The tools, but commercial potato-dig- lesions associated with this pest ging devices can be used also. are large and often infected by These may damage the tubers if other organisms. The, best protec- not carefully used. Tubers must tion against nematodes is avoid- be cut from the crown and may ance of soils that may be con- then be washed and dried. Dam- taminated and selection of nema- aged tubers should be processed tode-free tubers for replanting. or used up as rapidly as possible.

PN-3438 FIGURE 7.—Normal lesser yam leaf (left) and two leaves affected by mosaic virus disease. TROPICAL YAMS AND THEIR POTENTIAL, PART 1 13

/K

1

PN-3439 FIGURE 8.—External and internal lesions in lesser yam tubers, associated with nematode damage. 14 AGRICULTURE HANDBOOK 457, Ü.S. DEPT. OF AGRICULTURE

The yams can be sorted best in harvest®! yams with wood ashes. the field and packed into con- This treatment probably impedes tainers that permit maximum fungal growth by both chemical aeration. and physical means. Individual tubers of D, escu- Uninjured yams may be stored lenta of more than 1 kilogram for satisfactory periods. Four have been reported. The majority months is generally mentioned as of the tubers of the Caribbean va- the maximum storage life, but sat- rieties, however, weigh several isfactoiy storage of up to 8 hundred grams, somewhat less months has been reported. In than an average potato. Yields of New Guinea storage life is closely 25 to 45 metric tons per hectare related to variety and ranges from have been reported. These yields 5-6 to 12-14 months. Larger tu- compare favorably with those of bers store better than small tu- other yam species and of any other bers. During storage, respiration root or tuber crop. Maximum continues, and loss of dry matter yields at the Federal Experiment and water occurs. Thus, the small Station, Mayaguez, P.R,, of 55 tubers shrivel. Sugars are re- metric tons per hectare were ob- leased, and sweetness increases. tained with seed yams of 135 Changes in flavor, unacceptable grams planted in hills spaced at to some persons, occur. Stored tu- 60 by 60 centimeters. Some of the bers usually sprout (fig. 9), es- larger tubered varieties from New pecially under somewhat moist Guinea would probably outyield conditions. These sprouts rapidly any of the varieties tested so far. reduce the weight and quality of the stored tuber. Tubers stored as STORAGE AND long as 9 months have been germi- MARKETING nated satisfactorily. Reports on storage behavior Appropriate temperatures for are contradictory, probably be- storage have not been investi- cause the lesser yam is easily dam- gated. Most yams are subject to aged during harvest, and once injury by cool (15^ C or less) damaged, subject to rapid rotting. temperatures. Short-term storage Under favorable, dry conditions, in the household refrigerator is superficial scrapes and clean practical. wounds can be healed, but when The lesser yam is normally ventilation is poor and the tubers grown for home use or is marketed are kept damp, fungal growths in small quantities or under limit- rapidly destroy the tubers. An ar- ing conditions. Except under rested fungal development is limited circumstances, it cannot much more rare in this than in be considered an item of com- other species. A common practice merce. Even in New Guinea, mar- in Puerto Rico is to treat newly keting is managed chiefly on a TROPICAL YAMS AND THEIR POTENTIAL, PART 1 15

i ...

PN-3440 FIGURE 9.—Left: Multiple sprouting characteristic of lesser yam tubers in storage. Right: Normal sprouting. small settlement or village scale. When yams are peeled with a Tubers are frequently not sold for pótalo peeler the amount of fresh cash, but are traded. weight lost is only 5 percent or less. The peel is easily removed COOKING because of its thinness and the Because of their small size and smoothness of the yam. Tubers of smooth exterior, yams of D. escu- the lesser yam can be peeled ef- lenta can be cooked without peel- ficiently with electric potato-peel- ing. After boiling, the peel can be ing devices. easily removed before serving. When boiled, lesser yams erode When yams are baked, the skin excessively. The amount of erosion hardens and cannot be easily re- can be controlled by boiling for no moved. Opened, baked yams are more than 10 minutes. Boiled eaten with spoon or fork. The skin yams can be mashed. This ex- of the yam is too hard to eat either poses the fibers and makes it pos- boiled or baked. The presence of sible to sieve them out. Mashed peel affects the taste of the cooked yams often have a slightly gray product. color, which is not appetizing. 16 AGRICULTURE HANDBOOK 457, U.S. DEPT OF AGRICULTURE However^ this differs with varie- cut and give a slimey feel to the ties. Yams have a fine texture cut surf ace. The gums impede the and feel moist in the mouth. extraction of starch. Excess The lesser yam is well suited for amounts of water are necessary french fries and fried chips. Of in starch preparation to disperse common commercial fats, corn oil the gums and to let the starch pre- yields the best product. Lesser cipitate. On cooking the yam, the yams have rather bland flavors slimey, or mucilaginous, charac- that are not as attractive to many ter is lost. as the rich, distinctive flavors of Thé sugars present in quanti- D. alata and D. rotundata. Because ties sufficient to influence taste of their high sugar content, lesser are glucose and fructose. yams are not as satisfactory for making instant flakes as are other POTENTIAL USES yams. The chief potential use of the lesser yam is as a starchy food in COMPOSITION tropical diets, a role it already has In common with other yams, in some areas. Because of its fine, the chief nutrient of the lesser easily digested starch and its high yam is starch. As previously men- protein eontent, it should be pre- tioned, this makes up about 20 per- ferred to some other starchy sta- cent of the fresh weight of the ples. Some varieties low in sugar tuber. It is a fine-grained starch might be used for fried chips. The with relatively low amylose con- starch may have special applica- tent. tions in some processed foods. A second important ingrédient Flour prepared from dried slices is protein. Sufficient protein oc- of tuber is sufficiently glutinous curs in the lesser yam to be of to substitiate for part of the wheat some value in the diet. Average flour in conventional cookery. protein contents, for example, are The characteristics of the lesser four times that of cassava. The yam make it attractive for the amino acid balance, however, is home garden and suggest that it poor (table 2). Sulfur-bearing would be a profitable commercial amino acids, methionine and cys- crop. It yields well. Moreover, the tine, are especially low and limit- size and shape of the tubers of ing. Lysine and tyrosine contents some varieties would make mech- are somewhat low. Investigators anized planting and harvesting have reported low tryptophan con- possible. Because the lesser yam is tent. Thus, the protein quality is highly disease resistant, planta- not especially good. tions need little care. The princi- The protein of yams is in the pal defect of many varieties— form of water-dispersible gums. their susceptibility to rot and gen- These exude rapidly when a yam is erally poor storage characteristics TABLE 2.—Protein and amino acids in six cultivars of D. escalenta^

Cultivar Protein Alanine Valine Glycine Isoleucine Leucine Proline Threonine Serine Methionine g

15081 de Papa -- ^ 8.2 e,6 4.0 4.1 2.7 6.1 4.6 4.0 7.1 1.4 15090 de Pana 9.3 4.5 4.9 4.0 3,5 7.6 5.2 4.1 5.7 1.6 15473 Trinulenta 8.9 4.1 4.6 3.9 3.8 7.1 4.6 3.9 9.3 1.3 02 15215 Fasciculata 3.4 4.1 5.0 3.9 3.8 7.1 4.6 4.3 6.4 1.6 15213 Spindle 8.7 4.8 5.2 . 4.1 4.3 8.6 4.6 3.9 7.2 1.6 15214 Assam 7.9 5.3 5.1 4.5 4.0 8.8 4.9 4.0 6.0 1.8

Hydroxy- Phenyl- Aspartic Glutamic proline alanine acid acid Tyrosine Lysine Histidine Ar^nine Cystine

15081 de Papa 0.18 4.1 9.4 12.1 2,6 3.8 3.3 23.4 0.17 15090 de Pana .13 5.0 11.1 12.6 3.2 3.9 2.8 20.0 .16 15473 Trinulenta .20 4.6 9.6 11.6 2.8 3.9 3.2 21.1 .12 15215 Fasciculata .08 5.4 12.2 12.2 3.3 3.6 2.4 18.1 .18 > 15213 Spindle .12 5.9 12.5 13.2 3.0 4.Ö 2.8 13.7 .22 15214 Assam .„_ 6.0 13.6 13.8 2.7 3.8 2.7 13.0 .12

1 Values of amino acids are miligrams per 100 grams of yam, dry weight. Protein content is given in percent. 18 AGRICULTURE HANDBOOK 457, U.S. DEPT. OF AGRICULTURE —might be overcome by selection yams. Gard. Bull. (Sin- of varieties. gapore) 1: 159-165. (4) Before the potential af the 1951. Dioscoreaceae. Flora Ma- lesser yam can be fully evaluated, lesiana, Ser. I, Sperma- the available germ plasm will have tophyta 43: 293-335. to be more thoroughly studied. (5) COURSEY, D. G. Many new varieties, believed to 1967. Yams. An account of the nature, origins, cultiva- represent a cross section of the tion, and utilisation of existing variation, have been col- the useful members of lected. Some appear to combine the Dioscoreaceae. 230 the best features for which this pp. Longmans, London. species is noted and seem to be (6) ENYI, B. A. C. free of the serious defects of 1970. Yams in Africa. Proc. 2d Int. Symp. Trop. Root the small-tubered cultivars. These Crops I: 90-93. better cultivars indicate that the (7) MEIGE, J. lesser yam has been underrated 1954. Nombres chromosomigues and that it may yet play an im- et répartition géograph- portant role in a hungry world. ique de quelque plantes tropicales et äquatoriales. Rev. Cytol. Paris 15: 314- LITERATURE CITED 348. (8) RAGHAVEN, R. S. (1) ANONYMOUS. 1958. A chromosome survey of 1970. Introducing the "Chinese" Indian Dioscoreas. Proc. yam. Root Crop Pro- Indian Acad. Sei., Sect. B, gramme Bull. 1, 5 pp. 48: 59-63. University of the West (9) TING, Y., AND CHI, CHIN-WEN. Indies, St. Augustine, 1948. The Chinese sweet pota- Trinidad. to — Dioscorea esculenta (2) BARRAU, J. (Lour.) Burk. J. Agrie. 1956. Les ignames alimentaires Assoc. China 186: 23-33. des iles du Pacifique sud. (10) VAVILOV, N. I. J. Agrie. Trop. Bot. Appl. 1950. The origins, variations, 3(7-8): 385-401. immunity, and breeding (3) BURKILL, I. H. of cultivated plants. 1919. Yields of the lesser yam English ed. Chronica and of some African Botánica, Waltham, Mass.