Effects of Some Ethno Medicinal Plant Extracts on Botryodiplodia theobromae the Causal Organism of Yam (Dioscorea rotundata Poir) Rot

Post-harvest deterioration and rot caused by diverse microorganisms is the single most important factor militating against yam production in Nigeria. In an approach towards the development of ecofriendly antifungal compound in controlling yam rot, ethanol and aqueous extracts of six commonly available plants: Vernonia amygdalina, Ocimum gratissimum, Azadirachta indica, Cymbopogon citratus, Carica papaya and Citrus sinensis were tested in combination for their synergistic effect against Botryodiplodia theobromae. Four different extract concentrations (2.5%, 5.0%, 7.5% and 10%) were obtained from each extract mixture. Cold solvent extraction method was used for the extraction of plant materials while food poisoning technique was used for in vitro screening of plant extracts against rot inducing fungal organism. Botryodiplodia theobromae was tested to be pathogenic on healthy yam tubers with rot incidence of 80 mm. The synergistic effects of the combined extract varied with the plants combined, solvent of extraction, concentration of extract and test fungi. Ethanol extract showed greater effect in the inhibition of the entire organism than aqueous. All the extract combinations that had Neem as a component did better than other combinations in aqueous extracts. Inhibition of fungal growth was best observed at 7.5% and 10% extract concentrations. The highest inhibitory effect on the test organism (Botryodiplodia theobromae) was by the combination of Neem/Bitter leaf and Orange/Scent leaf, with values of 98.40±0.095% and 94.24±0.583% respectively for aqueous while the highest inhibition for ethanol extract was observed from Scent leaf/Bitter leaf and Pawpaw/Lemon, with values of 99.80±0.000% and 98.83±0.619% respectively these were significantly (P<0.05) better than other combinations. With respect to the synergistic activity between the plants materials combined in this study, all the combinations showed great synergism against the test organisms. This is likely to be a means of achieving pragmatic, effective control and prevention of food spoilage, since the development of new classes of antifungal agents is of paramount importance. The crude aqueous and ethanolic extracts of all the six plant extracts showed potential synergy on organisms responsible for yam rot, hence they are recommended for the control of rot inducing microbial organisms.