Development of Biphasic Culture System for an Entomopathogenic Fungus Beauveria bassiana PfBb Strain and Its Virulence on a Defoliating Moth Phauda flammans (Walker).

Abstract

Beauveria bassiana PfBb is a new strain with high host specificity to the target pest Phauda flammans. We conducted a series of experiments to optimize the biphasic fermentation system of B. bassiana PfBb by screening the medium compositions and fermentation environmental conditions in both liquid and solid fermentations. In the liquid fermentation, glucose and yeast extract with a C:N ratio of 17:1 were the optimal carbon and nitrogen sources, respectively, for B. bassiana PfBb mycelium growth and blastospore production, and liquid fermentation with an inoculation concentration of 1 × 10⁸/mL and an inoculum content of 50 mL conidial suspension, at 180 rpm/min rotation speed, pH 7 and 26 °C, favored mycelium growth. However, additional trace elements did not significantly improve liquid fermentation. In the solid fermentation, wheat bran and chaff at a ratio of 8:2 were identified as the best substrates that facilitated B. bassiana PfBb sporulation and conidial germination, and optimal substrates with 20% inoculum content, 50% water content, and 3-day fermentation in darkness had the highest conidia yield. The resulting conidia, stored at -20, 4, and 20 °C for one year, did not significantly change the water content, and with prolonged storage duration, conidial germination was significantly higher at -20 and 4 °C. Moreover, conidia stored at 4 °C for one year maintained its validity and virulence, which were toxic to all instar larvae of P. flammans. Our results provide essential support for the commercial production of B. bassiana PfBb-based biopesticides.