obtained. Knowledge of the behavior of varieties when infected 

 with virus is essential in comparisons or descriptions of varieties. 

 Some varieties of Guadeloupe are described in table 1. 



CULTURE 



Environmental Requirements 



All yam species are limited by more or less rigid growth cycles 

 that represent evolutionary adaptations to specific ecological situa- 

 tions. The tuber is a protective structure that guarantees continu- 

 ance of the living plant during the adverse conditions of the dry 

 season. D. trifida was apparently domesticated in the equatorial or 

 subequatorial forest, where rainy seasons are long and day-length 

 changes minimal. The growth season of D. trifida, although 10 to 

 11 months in length, is not as closely related to annual cycles as is 

 the growth season of other species. 



In Guadeloupe, experience with varieties from the Guyanas 

 suggests that D. trifida tubers can be produced during two over- 

 lapping seasons, or even year round. The normal season begins 

 from February to April and ends in December or January. Selected 

 lines planted in October will mature in June. Suitable varieties for 

 this purpose are now being developed. Successful two-season or 

 year-round planting requires year-round rains or supplemental 

 irrigation. Although tolerant of heavy rainfall, D. trifida plants do 

 not tolerate flooding. Good drainage must be provided. 



Land Preparation and Planting 



Soil for D. trifida should be rich in organic material, or min- 

 eral fertilizer should be added. Little formal study of land-prepara- 

 tion methods has been made, and the techniques used for other 

 yam species can be used without modification. Mixture of manure 

 or other organic material into the soil followed by the formation of 

 hills or ridges is an effective technique for hand or machine. 

 Primitive methods include clearing of the forest, planting of the 

 principal crops (maize and cassava) , and intercalated plantings of 

 yams and other minor crops. Yams are not normally planted twice 

 in the same area. 



Best yields have been obtained when high levels of fertilizer 

 were applied to fields not previously planted to yam. Poor yields 

 inevitably follow when the soil is impoverished and when little or 

 no fertilizer is applied {1 ) . 



Trials done in Guadeloupe by Rouanet (20, 21), in lateritic 

 soil and under high rainfall, showed the benefit of applying about 

 200-250-150 kilograms nitrogen-phosphorus-potassium, compared 

 with an unfertilized or a manure treatment of 15 tons per hectare. 



15 



