Busson (6) reported that the tubers of D. dumetorum contain 

 9.9 percent protein. Among the essential amino acids, the content of 

 lysine was good and that of methionine poor. Oyenuga {16) reported 

 protein contents of 12.58 and 11.73 percent in D. dumetorum, valuable 

 amounts indeed. 



An indigestible residue called the "insoluble formic residue" was 

 described by Busson (6). It occurs as 12.9 percent of the dry matter of 

 the tuber in D. dumetorum, versus 6.9 percent of the tuber in D. alata. 



The poisons of D. dumetorum and D. hispida are alkaloids, the 

 most important of which is dioscorine, used in North America to stimu- 

 late the heart. The amount of alkaloids varies, but in the more poisonous 

 races of both species less than a normal portion of a cooked yam can kill. 

 D. dumetorum must be used as food only when poison-free races are 

 on hand or when carefully detoxified. D. hispida is even more dan- 

 gerous. It must be remembered that toxic races of D. dumetorum are 

 cultivated to discourage thieves in the yam patch. 



POTENTIAL USE 



The future of the minor yam species is difficult to assess. On the one 

 hand, it seems that each is declining in importance. Yams in general are 

 competing with other root crops, and changes in agriculture or land use 

 are eliminating wild and unusual varieties. The question is: Can these 

 yams serve better if we know them better? Because they are now so 

 widely scattered, it may now be impossible to assemble them to judge 

 their potential. 



On the other hand, experimentation with minor species in the 

 French West Indies has suggested that the minor yams may have 

 unrealized potential. The high yields and disease resistance in D. trans- 

 versa is a case in point. Disease resistance may be of increasing impor- 

 tance, for leaf spot disease of D. alata {Colletotrichum gloeosporioides 

 forma alatae) seems to be spreading. Recent progress with sexual 

 breeding of D. trifida (11) and D. rotundata (19) opens new approaches 

 to yam improvement. Success may follow with now infertile species, 

 and introgression with wild species will be developed in the next 10 

 years. Even though proper sexual crossing may not be achieved, we 

 are confident that by means of tissue culture and cell hybridization 

 the wide genetic background of minor species will contribute to new 

 utilization of yams. 



LITERATURE CITED 



(1) Bourret, D. 



1973. Etude ethnobotanique des dioscoreacees alimentaires. 135 pp. Thesis, 

 Faculte des Sciences de Paris. 



(2) Brown, R. 



1810. Prodomus florae Novae Hollandiae et Insulae Van Diemen, Dioscoreae, 



22 



