Identification of fungi causing decay of water yam (Dioscorea alata L.) tuber setts in natural soil and composts. (142)
Keywords:Yam, Dioscorea alata, Tuber sett rotting, Fusarium solani, Pythium, Geotrichum, Organic substrate
AbstractA survey of fungi on water yam (Dioscorea alata L.) tuber fragments was conducted to identify those inducing rotting of setts in soil and composts. Fungi detected after incubation of tuber fragments in an autoclaved ferrallitic soil were Gliocladium sp., Fusarium oxysporum, F. solani, Penicillium oxalicum and Trichoderma harzianum. In natural ferrallitic soil, F. solani was detected with higher frequency on tuber fragments. In both natural ferrallitic and vertisol soil, small pieces of tuber flesh were primarily invaded by F. solani with 84 and 100 % of colonization, respectively. In the ferrallitic soil, these flesh fragments were also contaminated by F. oxysporum (2 % of colonization), and by Pythium sp. and Geotrichum candidum. Tuber setts that were planted in a natural ferrallitic soil, in a sand-“bagasse/vinasses/filtermud” compost (SC) mixture, suppressive to Pythium but conducive to F. solani or in a “vegetable mould” substrate (Biogwa® [BG]) were diversely affected by decay. No germination of setts occurred in the SC mixture and within 10 days, they all were completely invaded and rotted by F. solani. Twenty eight days after planting, 42 and 100 % of setts sprouted in the ferrallitic soil and the BG substrate, respectively. Our results indicate that F. solani may be an important rotting agent of water yam setts if it is present in natural soil and compost. Some indications on the management of these setts are also discussed.