AbstractIn experimental plantings in Corozal, Puerto Rico, anthracnose (Colletotrichum gloeosporioides) was first observed on susceptible Dioscorea alata cv. Florida yams in June 1982 and again in July 1983. By October of both years, incidence had reached 100% with foliar necrosis exceeding 60%. High negative correlations (r = -0.93**) were found between sever ity ratings from September to November and total tuber yield in both seasons. Higher and more stable yields of Guinea Blanco yam (D. rotundata) were associated with anthracnose resistance and higher yield potential. Florida yams interplanted with Guinea Blanco yams showed later occurrence and lower severity of anthracnose and higher and less variable yield of larger sized tubers than the same cultivar in monoculture. Interplantings showed notable stability in tuber numbers among years. Economic returns of mixed plantings always exceeded those of Florida monoculture. One to one interplanting of Florido and Guinea Blanco equaled or outgrossed Guinea Blanco in monoculture when Guinea Blanco was valued at $0.55/kg and Florida at $1.10 and $0.99/kg for the 1982 and 1983 seasons, respectively. Species mixtures appear valuable for stabilizing yam production by reducing anthracnose.
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