Biological indices of the entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae, and assessment of their virulence diversity

Biological indices such as conidial morphology, germination, and surface characteristics influence the virulence of an isolate. Therefore, the growth indices (vegetative growth, conidiogenesis, and germination), hydrophobicity property and Pr1 protease enzyme activity of three isolates of Beauveria bassiana (JS1, JS2 and KA75) and TT1 isolate of Metarhizium anisopliae evaluated. Also, the relationship between these indices and the virulence of the isolates on the last instar larvae of Galleria mellonella and fourth instar larvae of Ephestia kuehniella investigated. There was no significant difference in vegetative growth rate between B. bassiana isolates, but the highest rate (7.05 cm) was related to the TT1 isolate. JS2 isolate showed the highest conidial production (4.11×106 spores / ml) compared to the other isolates evaluated. All isolates showed germination above 80%, and the highest value (100%) was related to the TT1 isolate, which was statistically on par with the conidiogenesis of the KA75 isolate. The lowest hydrophobicity of the conidial surface was related to KA75 isolate, which was significantly different from other isolates. However, the highest percentage was related to TT1 isolate with 91.7%. Also, no differences were observed between the isolates in terms of Pr1 enzyme activity. Bioassays showed that TT1 and JS2 isolates had the highest virulence on the last instar larvae of G. mellonella and fourth instar larvae of E. kuehniella, respectively. Among the evaluated indices, the hydrophobicity and conidiogenesis of these two isolates were higher than the other isolates, which was directly related to their high virulence. Thus, the TT1 isolate of the M. anisopliae and the JS2 isolates of B. bassiana had greater bioefficiency than the other isolates and therefore, they will be more suitable for use in plant pest biological control programs.