Optimization of Biphasic Fermentation Conditions for Beauveria bassiana TaBb2405 and Its Pathogenicity against Tuta absoluta

Purpose The aim of this study was to optimize the biphasic fermentation process of Beauveria bassiana TaBb2405, increase conidial yield, and evaluate its pathogenicity against Tuta absoluta, thereby providing a theoretical basis for the biological control of T. absoluta.

Methods Single-factor experiments and response surface methodology were employed to optimize liquid fermentation conditions. Solid-state substrates were screened, and the inoculum amount and moisture content were optimized. The virulence of the obtained conidia against third-instar T. absoluta larvae was determined using the immersion method.

Results The optimal liquid fermentation conditions were as follows: maltose 40 g, yeast extract 15 g, KCl 2 g, temperature 28 ℃, fermentation time 4 d, inoculum amount 2%, and initial pH 8.0. Under these conditions, the blastospore density reached 1.92×10⁸ CFU/mL. Corn flour was identified as the optimal solid-state substrate, and the highest conidial yield was achieved at an inoculum amount of 20% and a moisture content of 55%. The virulence assay results showed that the median lethal concentration of the conidial suspension against third-instar larvae of T. absoluta was 7.35×10⁵ CFU/mL, and the median lethal time at a density of 1×10⁸ CFU/mL was 3.01 d.

Conclusion The optimized biphasic fermentation process achieves efficient proliferation of blastospores and high yield of conidia. The resulting conidia exhibit strong virulence against T. absoluta, providing a theoretical basis for the industrial production of B. bassiana formulations and the green control of this pest.