Fungal pathogens of yams (Dioscorea rotundata Poir.) during storage in Nigeria

Abstract

Fungal pathogens responsible for yam losses during storage were investigated. One hundred and fifty yam tuber samples showing rot symptoms were collected from three agroecological zones representing the yam belt of Nigeria to identify the associated fungal pathogens. The 17 fungal isolates obtained from the infected tubers were Nattrassia mangiferae, Fusarium oxysporum, Fusarium verticillium, Fusarium semitectum, Fusarium chlamydosporum, Fusarium solani, Fusarium dimenrum, Penicillium oxalicum, Rhizoctonia solani, Aspergillus niger, Aspergillus flavus, Lasidiodiplodia theobromae, Setosphaeria rostrata, Colletotrichum gloeosporioides, Trichoderma longibrachiatum Rhizopus stolonifer and Sclerotium rolfsii. Aspergillus niger was the most predominant species in all the agroecological zones. On artificial inoculation, all the 17 fungal species were found to be pathogenic on healthy-looking yam tubers of the variety TDr 93-31 but none of the fungal isolates could initiate rot symptoms on unwounded healthy-looking yam tubers however, results showed that there were significant differences (P < 0.05) in virulence among pathogens from different agroecological zones when inoculated into healthy tubers of TDr 93-31. Rots caused by Lasidiodiplodia theobromae and Aspergillus niger were more severe on yams when inoculated and stored for 14 days. The isolation of more than one type of fungi from a particular tuber suggests the possibility of multiple infections and the cumulative effects of these fungi interactions may cause rapid and extensive rotting of tubers.