Effect of extracts of Thevetia peruviana (Pers.) K.Schum on development of Phytophthora megakarya causal agent of black pod disease of cocoa

Abstract

Objective: The in vitro and in vivo effects of seed extracts of Thevetia peruviana (Apocynaceae) on the growth and the germination of spores of Phytophthora megakarya causal agent of black pod of cocoa was evaluated.
Methodology and results: Five extracts obtained by soxhlet apparatus (extracts of hexane, ethyl acetate, acetone, methanol and aqueous extract) were used. One fungicide (Ridomil ® gold plus) served as control reference. Five strains of P. megakarya (Mbal 121, Ngoke 111, Nom121, Mbal 212, njo111) were tested. Three concentrations of extracts (6.25, 12.5 and 25 =l/ml) and one concentration of fungicide were used in V8 medium. Detached fruit bioassay was performed. Spores of five strains of P. megakarya were inhibited by methanolic and acetonic extracts of T. peruviana with an inhibition percentage ranging from 99-100 %. Thus, the smallest concentration of extract is capable of acting on the germination of spores of the fungi. Only hexane extract did not inhibit the growth of strains. Methanol extract reduced the growth from 60 to 100% at 25 =l/ml. The detached fruits bioassays demonstrated the effectiveness of extracts on plant tissue when inoculated with P. megakarya zoospores.
Conclusion and application of findings: Statistical analysis shows that methanol and acetone extracts are as effective as the tested fungicide on the growth and germination of zoospores, aqueous extract are effective as Ridomil ® on growth on the black pod disease of cocoa. These extracts could be used in the integrated pest management strategy of the plant pathogens tested.

Keywords. Phytophthora megakarya; Thevetia peruviana; extract; biocontrol; black pod disease.