Phytochemical characterization of sub-fractions of Thevetia peruviana, Azadirachta indica and their antifungal efficacy on Pythium myriotylum, the causal agent of cocoyam root rot disease (Xanthosoma sagittifolium L. Schott)

Abstract

Pythium myriotylum is a telluric Oomycete, the causal agent of cocoyam root rot disease. In Cameroon, it can cause crop losses of up to 100% without sanitary measures. The aim of this study was to evaluate the antifungal efficacy of bioactive compounds from Thevetia peruviana (yellow oleander) and Azadirachta indica (neem) sub-fractions obtained by GC/MS against P. myriotylum. The antifungal activities of crude extracts (2%; 1%; 0.5% (m/v)) of T. peruviana and A. indica (2% and 0.5% (m/v)) in water, methanol and acetone were evaluated. The sub-fractions resulting from the roughing of the most active fractions by VLC (Vacum Liquid column) were characterized by GC/MS and their minimum inhibitory concentrations (MIC) were determined, as well as their mode of action on P. myriotylum. The results obtained show that GC/MS analysis identified many compounds with antifungal activities such as Oxime-, methoxy-phenyl, Hexadecanoic acid, methyl ester; 9,12-Octadecadienoic acid, methyl ester, (E,E); 7-Octadecenoic acid, methyl ester; 9-Octadecenoic acid, methyl ester, (E); Methyl stearate, Phenol, 2,2’-methylenebis[6-(1,1-dimethylethyl)-4-methyl. All fractions derived from crude extracts significantly reduced the growth of P. myriotylum compared with the negative control, with the highest inhibition rates obtained with the aqueous ethyl acetate phase fractions (87.77% and 100% for T. peruviana and A. indica, respectively). The most active sub-fractions F1 of VLC2 and F4 of VLC1 inhibited the pathogen’s protein synthesis. The lowest MICs were obtained with sub-fractions F1 of A. indica and F4 of T. peruviana (0.166% and 0.0837%). T. peruviana and A. indica can be considered as potential substitutes for chemical control.