Yam Die-back and its Principal Cause in the Yam Belt of Nigeria

A survey was conducted to determine the prevalence of yam (Dioscorea spp) foliar diseases across farmers` fields in the yam belt of Nigeria. Diseased leaf and vine samples were randomly collected from some fields during the survey. Isolations were made from the samples. Colletotrichum spp. were identified as the major pathogens associated with most yam dieback and necrosis symptoms observed. Other microorganisms isolated from the samples were: Botryodiplodia spp., Curvularia spp., Pestalotia spp. and Fusarium spp. Greenhouse artificial inoculations of D. alata (water yam) clones with these isolates singly and/or in combinations were made. Colletotrichum gloeosporioides reproduced typical symptoms of yam die-back and necrosis when inoculated alone. The predominance of Colletotrichum spp. from sample isolations and the reproduction of typical symptoms with C. gloeosporoides indicate that Colletotrichum is the main cause of yam dieback of D. alata. The disease should therefore be called "yam anthracnose", to avoid confusion in the literature arising from several symptomatic common names.