breeding of better cultivars, it might be possible to increase the 

 content of vitamins, total protein, and sulfur-containing amino 

 acids to enhance the food value of these yams. 



POTENTIAL USE 



It is still unclear whether the relatively limited distribution of 

 D. rotundata and D. cayenensis outside West Africa is associated 

 with particular characteristics of these species or with the com- 

 petition of other species. Surely, D. alata is an easier species to 

 grow: the African species are not lazy man's food. But it is also 

 highly probable that the limited use of African yams is associated 

 with a lack of introduction and distribution. Probably haphazard 

 distribution by casual visitors accounts for the principal distribu- 

 tion achieved. Most introductions probably died out, and it is 

 surprising, therefore, to find superior standard cultivars in Puerto 

 Rico, Jamaica, and Brazil. 



The D. rotundata and D. cayenensis germplasm in Africa is 

 so diverse that it is extremely difficult to select a few really 

 superior varieties. Trials will be necessary in many regions. 

 Since yam growing is closely associated with customs and culture, 

 one cannot expect that the favorite variety of one region will 

 automatically gain acceptance in another. 



Preliminary experience in the introduction and distribution 

 of African yam varieties suggests that most, if not all, are af- 

 fected by mosaic virus. It is still uncertain whether this disease 

 is a hazard for other yam species, but it appears to be widely 

 distributed already. As attempts are made to utilize the African 

 yams in new areas, it will be necessary to watch the virus situation 

 carefully. If current attempts to rid varieties of virus through 

 meristem culture are successful, introduction should be safe and 

 profitable. 



In West Africa the culture of yams is still highly viable even 

 though cassava, rice, and cocoyams compete with and have dis- 

 placed yams to a great extent. While it is impossible to think of 

 West Africa without yams, they may play a smaller role if acre- 

 ages continue to decrease. This trend is regrettable, for the West 

 African yams are a food resource meriting preservation and 

 development. 



Because the evolution of yams has not been guided by princi- 

 ples of plant breeding, the potential for rapid advancement by 

 breeding has not yet been demonstrated. It has been assumed 

 that conventional breeding was impossible because of lack of 

 flowering and fertility. The development of freely flowering, 

 fertile populations and the ease of production of countless seed- 

 lings suggest that for the first time an important species can 

 be improved by modern techniques (28). 



34 



