diseased plants, and the second, or seed, tuber is not produced or 

 is too small to use. The vigor of the disease-free materials probably 

 assures their preferential selection. 



Storability, closely related to dormancy duration, is also high- 

 ly important in a select cultivar. Keeping quality during long 

 storage is desirable, but germination should occur readily after 

 planting. Storability is highly related to resistance to insects and 

 fungi and is a trait that is normally recognized by farmers. 



It is very difficult to get a clear picture of superior cultivars - 

 in West Africa. In the sparse literature, nevertheless, certain 

 cultivars are frequently mentioned. Since in most cases cultivars 

 have not been tested in more than limited areas, it is very difficult 

 to compare cultivars from different countries. Some better 

 cultivars mentioned in the literature or known to the authors are 

 listed in table 3. 



From a collection of over 200 cultivars of D. rotundata and 

 D. cayenensis at the Mayagiiez Institute of Tropical Agriculture, 

 12 outstanding varieties were selected (table 4). Free seed pieces 

 are available in January and February for shipment to tropical 

 regions where they might be of use. An important characteristic 

 of all these cultivars is that they resist virus. (See 'Test Control.") 

 While not immune, they develop heavy vegetative cover and yield 

 well. In spite of susceptibility to virus, roguing and seed-tuber 

 selection can result in symptom-free plants. 



CULTURE 



Environmental Requirements 



The African yams are found most often in forests, where 

 they are adapted to climbing trees in search of sunlight. Cultivars 



Table 3. — Some of the better Dioscorea rotundata and D. cayen- 

 ensis cultivars of the Tropics 



Source 



and 

 cultivar 



Brazil: *Cara de Costa 



Ghana: Tuna' 



Guadeloupe: 'Grosse 



Caille Corrosol' 



Ivory Coast : 



'Akandu' 



'Gnan' 



'Krengle' 



'Lopka' 



'N'Detre' 



Number of 

 harvests 



Source 



and 

 cultivar 



Number of 

 harvests 



Jamaica: 'Negro' 2 



Nigeria: 



'Aure' 1 



'Boki' 1 



'Guinea Blanco' 2 



'Igangan' 1 



'Imowe' 2 



'Ounmodo' 2 



'Olo' 1 



15 



