Efficacy of Extracts of Some Plants against Post Harvest Fungal Deterioration of Cassava Root (Manihot esculenta Crantz) in Nigeria

Abstract

Fungitoxic potentials of Piper guineense, Ocimum graticimum, Casia alata, and Tagetes erecta extracts in the management of postharvest fungal deterioration of cassava root were investigated. Pathogenicity tests revealed Aspergillus niger, and Trichodderma viride as causal organisms of root rot of cassava which utilized the substrate for their growth and development. A. niger was found to be more virulent having the highest rot incidence of 75% followed by T. viride which depicted a lower pathogenic effect with rot incidence of 33.3%. The result of the inhibitory potentials of the water and ethanolic extracts of P. guineense, O. graticimum, C. alata, and T. erecta against the two fungal pathogens showed significant differences (p≤0.5) in their rates of fungitoxicity on A. niger, and T. viride. The ethanolic extract of T. erecta gave the highest mean inhibitory effect of 63.8% on A. niger while the least mean growth inhibition of 9.20% was recorded by water extract of P. guineense on T. viride. The results of in vivo test of the plant extracts applied before and after inoculation with spore suspension of test fungi indicated high significant effect on the rot incidence and severity. Piper guineense water extract was less effective in controlling the development and spread of the pathogens during pathogenesis hence the highest percentage disease incidence and severity when it was applied after the inoculation with spore suspension of A. niger. The lowest incidence of rot was recorded with water and ethanol extracts of T. erecta applied before inoculation of T. viride. A. niger showed a stronger resistance to the plant extracts than T. viride in the control of cassava root rot in storage.