Antimicrobial Effects of Four Plant Extracts against Post Harvest Spoilage Fungi of Yam (Dioscorea rotundata Poir)

This study investigated the effects of plant extract on fungal pathogens responsible for yam rot in storage. Among the eight fungal pathogens isolated from yams with symptoms of post-harvest rot, the inhibitory effects of four plant materials on four of these organisms (Fusarium solani, Aspergillus niger, Botryodiplodia theobromae and Rhizopus stolonifer) with the highest prevalence were examined. Phytochemicals test of these plant materials showed the presence of alkaloid, flavonoid, glycosides, saponin and tannins at different quantities. The pathogenicity test revealed that all the organisms tested were pathogenic on healthy yam tubers with Aspergillus niger being the most pathogenic. All the plant extracts inhibited the growth of the test organisms at varying degrees. The degree of inhibition was dependent on concentration of extract, extraction medium and the test organism. The highest inhibitory values were obtained from ethanol extracts of Moringa oleifera and Azadirachta indica at 7.5% and 10.0% concentration each, while Gongronema latifolium and Xylopia aethiopicum gave lower inhibitory values. This suggests that Moringa oleifera and Azadirachta indica are good bio killers and their biological active ingredients can be exploited for the control of yam rot.