Relatedness of proteolytic potency and virulence in entomopathogenic fungus Beauveria bassiana isolates

Entomopathogenic fungi produce a variety of degrading enzymes, including proteases, chitinases and lipases, to facilitate their entry through the massive barriers of insect cuticle. Isolates of the entomopathogenic fungi vary considerably in their proteolytic activity and virulence. The proteolytic activity of different isolates has been hypothesized to reflect their virulence toward the host. In this study, we evaluated the virulence and proteolytic activity of 17 Beauveria bassiana sensu lato isolates collected from different geographical regions in Iran. The selective medium D0C2 was used for isolating B. bassiana from soil samples. Casein substrate was used for protease assay. Total mortalities caused by different B. bassiana isolates through the dipping method, ranged from 25 to 60% with the highest and lowest rates for isolates BA and MITE, respectively. Our results revealed a wide variation in both proteolytic activity and virulence among the studied isolates. Additionally, we found a strong positive correlation between the proteolytic activity on Casein substrate and virulence of the isolates against the Khapra beetle, Trogoderma granarium. This finding will facilitate the screening and selection process of virulent fungal isolates as efficient agents for use in biological control programs of insect pests.