S23 - Session O5 - In-vitro control of storage spoilage fungi in export grade white yam (Dioscorea rotundata Poir.) using cocoa (Theobroma cacao L.) leaf extracts

Authors: Patrick Kumah *, Samuel Ampofo

Ghana exports large amounts of yam but there are constraints associated with its storage because of yam rot during and after the pre-export handling period. The predominant method of control is the use of synthetic pesticides, which could pose health hazard to consumers. Therefore, this study assessed the fungicidal potency of cocoa leaves (CL) in the control of fungal rot pathogens of white yam. Fresh cocoa leaves were collected, steam-blanched, dried, powdered and qualitatively analyzed. Polyphenolic compounds were extracted using standard methods. Crude aqueous CL extract was also prepared by cold maceration for 7 days. Fungi were isolated and identified from yams collected from marketplaces and exporters' warehouses. Agar well diffusion and broth micro dilution assays were used to determine the antimicrobial activities and minimum inhibitory concentrations(MICs) in vitro . The experimental design was factorially arranged in CRD . The results showed that among the extracts, the ethylacetate purified CL extract's inhibition zone (5.4mm) was significantly (p≤0.5) most effective followed by acetone purified CL extract (3.13mm). Crude aqueous CL extract showed no inhibition (0.0mm) against the four test fungi in the agar well diffusion assay. The most effective MICs extract was that of Mancozeb (as positive control) (2mg/ml) followed the ethylacetate purified CL extract (2.5mg/ml) and the least was crude aqueous CL extract (15mg/ml) in vitro . Cocoa leaf extracts, especially the ethylacetate purified CL extract, which showed similar potential to that of Mancozeb, could be an ideal alternative to synthetic pesticides in controlling rot-causing pathogens on export grade white yam.