TROPICAL YAMS AND THEIR POTENTIAL 



Part 3. Dioscorea iilata 



By Franklin W. Martin, plant geneticist, Mayagiiez Institute of Tropical Agri- 

 culture,'^ Agricultural Research Service, U.S. Department of Agriculture, 

 Mayagiiez, P.R. 



INTRODUCTION 



For many people in the world 

 the word "y^i^/' or its translation, 

 refers to Dioscorea alata L., the 

 most widespread yam species. It 

 has been introduced to all parts of 

 the Tropics where growing condi- 

 tions are suitable, and it has fre- 

 quently gone wild and continued 

 to develop new variations. It has 

 become accepted in West Africa, 

 where it now sometimes competes 

 with two important native species, 

 D. rotundata Poir, and D. cayenen- 

 sis Lam. It is difficult to say 

 whether or not the total production 

 of D. alata surpasses that of its 

 chief rival, D. rotundata. Whereas 

 the latter is almost restricted to 

 West Africa, D. alata is so widely 

 distributed that it is impossible to 

 give an accurate estimate of pro- 

 duction, but it cannot be less than 

 10 million metric tons per year. Its 

 agronomic flexibility, widespread 

 occurrence, ready acceptance, and 

 high nutritive value suggest that 

 D. alata is the most important of 

 the cultivated species. Further- 

 more, it has great promise for the 

 future, especially when improved 

 varieties are distributed. Those 

 already discovered are among the 



1 Formerly, Federal Experiment Sta- 

 tion. 



best yams in the world — in flavor, 

 processing quality, production, 

 and agronomic characteristics. 



History and Origin 



In spite of its importance, the 

 little that has been written about 

 the origin of D. alata is mostly 

 speculation. That great numbers 

 of varieties are known from India 

 to the islands of the South Pacific, 

 many of which are quite local in 

 distribution, suggests that the 

 species was domesticated and 

 widely distributed very early. 

 Furthermore, the occurrence of 

 distinct but closely related vari- 

 eties on somewhat isolated islands 

 suggests that it has continued to 

 evolve in areas where it has been 

 introduced. 



De Candolle (8)^ hypothesized 

 an Indo-Malayan center of origin 

 for D. alata, based on the wide- 

 spread varieties found there. Bur- 

 kill (^), a superb student of the 

 yam, placed the origin of the spe- 

 cies in Southeast Asia and at- 

 tempted to trace its distribution 

 throughout the world and gradual 

 decline in importance as cassava, 

 sweetpotatoes, and potatoes dis- 

 placed it. The existence in Burma 



2 Italic numbers in parentheses refer 

 to items in "Literature Cited," page 38. 



1 



