Aetiology of yam (Dioscorea rotundata) tuber rots held in traditional stores in Nigeria: importance of Fusarium spp. and yam beetle.

The extent and causes of yam (Dioscorea rotundata) tuber rots were investigated in Igalaland, Nigeria. Rots were found to be associated with prior physical damage in almost all cases. Numerous fungal species were isolated from the infected lesions of which Fusarium spp. predominated, not Botrydiplodia theobromae as previously reported in other studies. None of the fungi was able to infect undamaged yams in laboratory experiments. The damage was caused by both biotic and abiotic factors of which the yam beetle (Heteroligus meles) was the largest single cause. There were significant differences in the frequency with which different varieties of yam were attacked by H. meles and found to be infected with Fusarium spp. In an independent survey of farmers' experience of yam rots, varieties that scored well correlated with apparent resistance to the beetle and Fusarium spp. These studies highlight the importance of yam beetle infestation and the need to have independent methods for varietal authentication.