Phylogeny, chitinase activity, and pathogenicity of Beauveria, Metarhizium and Lecanicillium species against cowpea aphid, Aphis craccivora Koch

Abstract

Cowpea aphid, Aphis craccivora Koch is a serious insect pest of cowpea distributed in almost all states of India and its management is essential to increase the quality and quantity of cowpea yield. This study sought to characterize the indigenous isolates of fungal entomopathogens, Beauveria bassiana, Metarhizium pingshaense, M. guizhouense, and Lecanicillium muscarium, using molecular phylogeny and evaluate their pathogenicity against A. craccivora under greenhouse conditions and compare their extracellular chitinase activity. Thirty isolates of fungal entomopathogens were collected from semi-natural and agricultural habitats. Molecular phylogeny of these isolates using partial nuclear sequences, Bloc and MzIGS3, and mitochondrial sequence, nad1, resolved four species. Screening of the isolates against A. craccivora using a single concentration of 1 × 106 conidia/ml revealed that all isolates were pathogenic, with mortality of aphids ranging from 16.67 to 100%. Bioassays of the highly pathogenic isolates of B. bassiana, M. pingshaense, and L. muscarium against A. craccivora revealed low LC50 value of L. muscarium isolate GKVK 03_11 (1.4 × 105 conidia/ml) under greenhouse conditions. Comparison of the extracellular chitinase activity of these isolates detected high chitinase activity of GKVK 03_11 isolate (0.621 U/ml). Study results suggest the biocontrol potential of indigenous L. muscarium isolate for the management of A. craccivora and the possible role of chitinase enzyme in the virulence of fungal entomopathogens.