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

Purpose This study aimed to optimize the two-phase fermentation process of Beauveria bassiana TaBb2405, increase conidia yield, and evaluated 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 substrates were screened, and the inoculum ratio 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 volume 2%, and initial pH 8.0. Under these conditions, the blastospore concentration reached 1.92×10⁸ CFU/mL. Corn flour was identified as the optimal solid-state substrate, and the highest conidial yield achieved at an inoculum volume 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 conidial. The resulting conidia exhibit strong virulence against T. absoluta, providing a theoretical basis for the industrial production of B. bassiana formulations and the green management of this pest.