In-vitro and In-vivo Antimicrobial Potency of Selected Plant Extracts Against Postharvest Rot-Causing Pathogens of Stored Yam Tubers

Potency of Piper guineense Linn., Zingiber officinale Rosc., Azadirachta indica A. Juss., Carica papaya Lam. and Nicotiana tabacum Linn. againt in vitro control of Curvularia eragrostide and in vivo inhibitions of rot-causing microorganisms in storage were studied. Rotted Ogoja and Ghini white yam tubers were picked from yam farmers at various locations at Lafia, Nigeria. Rot-causing organisms from Ghini and Ogoja that were isolated for a period of four months included Botryodiplodia theobromae, Aspergillus flavus, A. niger, Fusarium moniliforme, Colletotrichum sp, F. oxysporum, C. eragrostide and Penicillium purpurogenum. Pathogenicity test confirmed all the isolated fungi as rot causing organisms. Result showed that Z. officinale, P. guineense, A. indica, C. papaya and N. tabacum exhibited more antifungal properties against C. eragrostide at 60 g/L and 90 g/L than at 30 g/L. Results further confirmed that Z. officinale, P. guineense, A. indica and mancozeb were more efficacious in vitro. In vivo test using the most potent extracts; Z. officinale, P. guineense and A. indica and mancozeb revealed that the selected plant extracts were effective against postharvest pathogens of yam. Mean decay reduction index (DRI) of more than 0.6 indicated that the extracts and the chemical inhibited the growth of the rot causing organisms by more than 60% throughout the five months storage period. It is therefore recommended that extracts from these plants could be formulated at appropriate concentrations and used to inhibit the growth of postharvest pathogens of yam tubers because of their cheapness, ease to purchase and environmental friendliness.