TROPICAL YAMS 



AND THEIR POTENTIAL 

 Part 4. Dioscorea rotundata 

 and Dioscorea cayenensis 



By Franklin W. Martin and Sidki Sadiri 



INTRODUCTION 



Although other yam species have been introduced in Africa, 

 in West Africa the word **y^rn" is almost synonymous with 

 Dioscorea rotundata (L.) Poir., the African white yam. There, this 

 species is associated with millennia of cultivation and probably 

 with the origins of agriculture itself. It is an old staple food, 

 but a crop that has suffered from the encroachment of rice, 

 cassava, and cocoyams. Nevertheless, it remains the starchy food 

 of choice and certainly the prestige food to be served to guests. 

 Dioscorea alata L. might be more widespread and might outyield 

 D. rotundata, but D. rotundata is usually enthusiastically pre- 

 ferred. 



Although D, cayenensis Lam. is a sister species of D. rotun- 

 data, they can be easily distinguished. The two species have 

 apparently hybridized frequently, and intermediate forms impede 

 exact classification. Therefore, this second most important African 

 species is also considered here. The evidence for one versus two 

 species will be considered, but the reader should be aware that 

 the problem has not been resolved to everyone^s satisfaction. The 

 names themselves are often used interchangeably. 



With the decline in the use of yams throughout the Tropics, 

 including West Africa, it is particularly appropriate to consider 

 the virtues and weaknesses of these two species, to see what their 

 potential is. 



Domestication 



In the forests of West Africa, in particular from the Ivory 

 Coast to Cameroon, D, rotundata and D. cayenensis were domesti- 

 cated. The exact process of domestication is not recorded, but it 



1 Plant geneticist, Mayagiiez Institute of Tropical Agriculture, Agricultural 

 Research Service, U-S". Department of Agriculture, Mayagiiez, P.R., and 

 plant physiologist. International Institute of Tropical Agriculture, P.M.B. 

 5320, Ibadan, Nigeria. 



1 



