Bioassay and enzymatic comparison of six entomopathogenic fungal isolates for virulence or toxicity against green peach aphids Myzus persicae

Abstract

Myzus persicae is an economically important pest infecting more than 40 families of crops throughout the world. Six entomopathogenic fungal isolates, three each of Beauveria bassiana and Verticillium lecanii, were screened for pathogenicity test against the M. persicae to select high virulent isolate with the most suitable application and to determine the role of individual enzyme in its virulence. Two treatments that is, conidial shower (190±23 conidia/mm²) and filtrate (3 ml filtrate per treatment from six days liquid broth culture of 1.0x10⁸ conidia ml^-1) were conducted for virulence or toxicity test and a comparison was made between treatments and among fungal isolates against the target pest. The percent mortality rates of filtrate at each day, after inoculation was found higher as compared to percent mortality of conidial showering. V. lecanii 3 showed highest virulence or toxicity against the target pest treated either with conidial (80.70%) or filtrate (88.36%) application while B. bassiana 70 and B. bassiana 76 showed high toxicity (77.14 and 80.86%, respectively) in filtrate application at 6^th day of incubation. The aphidicial activities of the fungal isolates were evaluated by correlating the enzymes (Chitinase, protease and lipase) activities with enzymes production. On the basis of enzymatic activities, lipase was assumed to participate more in the total virulence or pathogenicity as compared to protease and chitinase while protease was assumed to participate more than chitinase. The pathogenicity test reveals the selection, effective application of most virulent isolate and the role of individual enzyme to develop an alternative control agent against M. persicae.

Keywords: Beauveria bassiana, filtrate, conidia, enzymes, Verticillium lecanii