Conidial production, virulence, and stress tolerance of Beauveria bassiana conidia after successive in vitro subculturing

The effect of successive subculturing of Beauveria bassiana under different in vitro nutritional conditions was evaluated on vegetative growth, conidial production, virulence, tolerance to UV radiation and heat tolerance. Potato dextrose agar (PDA) and a medium based on adult Alphitobius diaperinus (MAD) were used. The fungus was inoculated on the insects, isolated, and subcultured 17 times on the different media. After subculturing, the fungus was again inoculated on the insects, and it was then re-isolated. Successive subculturing and nutritional conditions influenced fungus quality. MAD favored maintenance of vegetative growth and conidial production on culture medium and on rice after a greater number of successive subcultures than PDA. Furthermore, a decrease in conidial production in MAD was less pronounced than in conidia from the PDA medium. Conidia cultured on MAD maintained virulence after 17 successive subcultures. Conidia cultured on PDA retained initial thermotolerance levels. Conidial viability decreased after UV irradiation, but this decrease was unaffected by successive subculturing on PDA and MAD. Virulence, conidial production, and temperature tolerance, which were reduced after successive in vitro subculture, were restored with fungus passage through the host.