Fungitoxic Potentials of Extracts of Plant Origin against Fugal Root Rot of Cassava (Manihot esculenta Crantz) in Storage

Abstract

Investigations were carried out on the use of the water and ethanolic extracts of Piper guineense, Ocimum graticimum, Casia alata, and Tagetes erecta in the management of postharvest deterioration of cassava root caused by Aspergillus flavus and Rhizopus stolonifer. Water and ethanolic extracts of the plant materials had significant differences (p≤0.5) in their rates of fungitoxicity on the pathogenic organisms. Water and ethanol extracts of C. alata and T. erecta respectively at 50% concentration gave the same highest radial growth inhibition of 80.20% on A. flavus in vitro  followed by ethanol extracts of C. alata, O. graticimum, and P. guineense. The ethanolic extract of T. erecta at 50% concentration gave the highest inhibitory effect of 53.50% on R. stolonifer followed by ethanol extracts of C. alata, O. graticimum, and P. guineense whereas the least growth inhibition of 0.17% was recorded by aqueous extract of P. guineense on R. stolonifer.  In vivo test of the plant extracts applied before and after inoculation with spore suspension (1x105 spores/ml of distilled water) of test fungi showed significant reduction in root rot incidence and severity.  The lowest incidence and severity of cassava root rot of 16.5% and 1.45 respectively were recorded with T. erecta ethanol extracts applied before inoculation of A. flavus indicating that the extracts of the plant materials could be better used as protectant than eradicant in the control of post harvest fungal deterioration of cassava root. R. stolonifer showed stronger resistance to the extracts of the plant materials than A. flavus during pathogenesis in vivo.