Ion-beam and gamma-ray irradiations induce thermotolerant mutants in the entomopathogenic fungus Metarhizium anisopliae s.l.

Entomopathogenic fungi, such as Metarhizium anisopliae (Metch.) Sorokin, are important agents for the biological control of insect pests. However, these fungi are not compatible with high temperatures. In this study, mutagenesis using ion beams or gamma rays was used to generate five potentially thermotolerant mutants from two wild-type isolates of M. anisopliae (two using ion beams and three using gamma rays). The mutant isolates had a higher upper thermal limit for vegetative growth compared to the wild types (by 2–3°C) and enhanced tolerance to wet–heat stress of 45°C for conidial germination. At 25°C and 30°C, most mutants were as virulent to maize weevil adults as the wild type, however, one mutant produced using ion beams almost lost virulence entirely. These results indicate that ion beams and gamma rays are useful tools for improving biological characteristics, such as thermotolerance, in entomopathogenic fungi, but that mutants must be carefully evaluated for unpredictable negative side effects.