Table 4. — Superior cultivars of D. rotundata selected 

 in Puerto Rico from a large collection 



Identification 

 number^ 



Recent 

 origin 



Name 







• • • VlUJlIlccl JJldHUU . 









1 f^AQ^ 





• • • IN eg I O . 



xouoyj 





■ • • Z^dL la, . 





Hn 



• • • JLL/ bell l/U . 



15665 



TCfliolfl NiP'pyia 



'Fele' 



15667 



Iwo, Nigeria 



. . . 'Boki'. 



15668 



Nigeria 



• • • Unknown. 



15680 



Umudike, Nigeria • ■ 



. . . 'Awada'. 



15711 



Nigeria 



. . . Unknown. 



15740 



Dahomey 



. . . 'Baniore Bagarou'. 



15770 



do 



. . . 'Kourokouragourouko'. 



1 In the collection of the Mayagiiez Institute of Tropical 

 Agriculture. 



are adjusted to climatic conditions reflecting their evolution in 

 distinct ecological zones. Dioscorea cayenensis requires a fairly 

 long rainy season, about 10 months each year. On the other hand, 

 most D. rotundata cultivars can be grown with far less rainfall. 

 Seven months of wet weather is often sufficient. 



In most of West Africa the dry period corresponds to the 

 latter months of the year, and both species produce and mature 

 their tubers before the dry season begins. However, in D. rotun- 

 data, tuberization begins months earlier, as little as 4 months 

 after planting. This capacity to tuberize at a very early stage may 

 be an adaptation to very short rainy seasons. Different cultivars 

 maturing at different times add some flexibility to the annual 

 cycle of planting and harvest, but the annual growth cycle of a 

 given cultivar is difficult to change. 



When a collection of cultivars is grown in any one region, 

 differences in growth patterns can be seen. In Puerto Rico the 

 shortest time to complete a growth cycle has been 8 months, in 

 the case of some cultivars of D. rotundata. When the normal 

 growth cycle terminates, the foliage dies back, and only the tuber 

 is left in the ground. This response, which is not well understood, 

 occurs whether or not moisture is limiting. As a general rule, 

 D. cayenensis cultivars mature very late — in Puerto Rico, about 

 11 months after planting. 



Differences in time to maturity are related to differences in 

 the length of the period of dormancy. Since the complete growth 

 cycle always equals 12 months, early maturation is related to long 

 storage life. Thus, storage life is short in D. cayenensis and 



16 



