Anthracnose of water yam in Nigeria
1981
Nwankiti, O.A. (National Root Crops Research Institute, Umudike, Umuahia (Nigeria)) | Okpala, E.U. (University of Nigeria, Nsukka. Dept. of Crop Science)
Field symptoms of anthracnose of water yam (Dioscorea alata) in Nigeria are described. Isolation studies revealed that more than seven organisms, namely: Colletotrichum sp.; Botryodiplodia theobromae; Fusarium sp.; Pestalotiopsis sp.; Syncephalastrum racemosum; Scopulariopsis fusca; and Curvularia sp. are involved in the disease syndrome. Colletotrichum sp. is described. The conidia measure 15-30 x 3-5 um and enter the host through stomata and by direct cuticular penetration. Inoculation studies showed that Colletotrichum sp.; which was commonly isolated, could not produce serious infection in the absence of a second pathogen. Colletotrichum inoculated alone produced lesions measuring between 0.1 and 4 mm with few lesions per leaf, whereas Colletotrichum inoculated in combination with either Botryodiplodia or with both Botryodiplodia and Fusarium produced lesions measuring up to 20 mm, with many lesions per leaf. Infection was more serious on the lower than on the upper leaf surface, probably because of the absence of stomatal apertures on the upper leaf surfaces of D. alata. Greenhouse tests confirmed that tuber-borne, soil-borne and infected yam debris (vine, petiole, and leaf) inocula of the pathogens were important in the development of the anthracnose disease of water yam. Therefore, control of tuber-borne inoculum, disposal of infected debris, and careful handling of harvested tubers are an essential part of an integrated program for control of the anthracnose disease of D. alata.
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