In vitro Control of Phytophthora colocasiae Causing Leaf Blight of Taro (Colocasia esculenta (L.) Schott.) With Selected Botanical Extracts

Background and Objective: Leaf blight incited by Phytophthora colocasiae has been a major challenge impacting on yield and commercialization of taro (Colocasia esculenta (L.) Schott) in Nigeria since 2009.This study evaluated in vitro, the efficacy of selected plant extracts against the causal pathogen.Materials and Methods: Four botanical extracts: Azadirachta indica A. Juss.Eucalyptus camaldulensis Dehn, Senna alata L. and Tithonia diversifolia (Hemsley) A. Gray were tested in vitro for their fungi toxic effects on radial growth and mycelia dry weight of the pathogen at 5, 10 and 20 mg/mL of each extract.Ridomil (0.67 mg/mL) and zero treatment were set along tests and treatments were replicated thrice in a Completely Randomized Design.Data were subjected to analysis of variance at a 95% confidence interval using the SPSS package and significant differences among means were compared using Duncan's Multiple Range Test (DMRT).Results: All the extracts exhibited significantly varying degrees of inhibition in the radial growth and mycelia dry weight tests.Percentage inhibition increased as the concentration increased.Azadirachta indica and S. alata extracts at 20 mg/mL inhibit 100 and 97.13% radial growth, respectively and were significantly (p<0.05)superior to 40.00 and 31.81%caused by T. diversifolia and E. camaldulensis, respectively.Complete (100%) inhibition of mycelia dry weight was obtained with S. alata and T. diversifolia extracts at all the selected concentrations while A. indica and E. camaldulensis showed high inhibition at some concentrations.Conclusion: These extracts have strong inhibitory effects against P. colocasiae and are comparable to the synthetic fungicide Ridomil, therefore, their exploration in the management of TLB is strongly advocated.