Faculty: Biosences
Department: Botany


Chikwendu, A. E.
Okigbo, R. N.
Amadi, J. E.


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, Occimum gratissimum, Azadirachta indica, Cymbopogon citratus, Carica papaya and Citrus sinensis were tested in combination for their synergistic effect against six different fungi responsible for post-harvest rot of yam. Seven extract combinations were obtained. 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 forin vitro screening of plant extracts against rot inducing fungal organisms. Botryodiplodia theobromae, Rhizopus stolonifer and Fusarium solani had the highest percentages of occurrence with frequencies of 30%, 26% and 16% respectively. Five of the test fungi caused rot in healthy yam tubers, with Botryodiplodia theobromae being the most virulent while Penicillium spp was not pathogenic. 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 most virulent 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. Quantitative and qualitative phytochemical test were conducted using different standard procedures; this showed the presence of phytate, flavonoid, alkaloid, saponin, tannins, oxalate and phenol. The quantities of phytochemicals in these plant materials ranged from 0.08% and 14.9%, the mixture of Orange/Neem contained more alkaloid, tannins and oxalate than other mixtures, with values of 6.19 %, 14.9% and 8.67% respectively. With respect to the synergistic activity between the plants materials combined in this study, all the combinations showed great synergism against the test organisms. Therefore, due to the emergence of multifungicides-resistant pathogens, control of rot induced pathogens with organic substances combinations, using two or more plant materials is vital and paramount. This is because synergistic interactions can potentially increase efficacy, prevent the emergence of resistance, and provide broader-spectrum of activity than the use of single plant material. 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 Vernonia amygdalina, Azadirachta indica, Occimum gratissimum Cymbopogon citratus, Carica papaya and Citrus sinensis showed potential synergy on organisms responsible for yam rot, hence they are recommended for the control of rot inducing microbial organisms.