Abstract: 【Objective】Entomopathogenic fungus Beauveria bassiana has been widely applied as an important biocontrol agent for controlling many insect pests, while the poorly large-scale production technology of B. bassiana is one of the key issues which may consequently restrict its wide application. Study on the liquid fermentation process research of B. bassiana can improve the liquid fermentation of biomass, thereby providing high-quality fermentation broth for solid liquid fermentation stage and improving spore production of solid fermentation. The study may serve as a basis for the large-scale production technology of B. bassiana. 【Method】The liquid fermentation of B. bassiana is affected by several factors, such as temperature, volume of liquid, rotate speed, initial conidia concentration, pH and so on. Firstly, Plackett-Burman (PB) design was used to screen the main factors which affected the liquid fermentation. Secondly, the method of the steepest ascent path was applied to identify the central point of response surface and approach the optimal region. The climbing direction and the change range were determined by gradient direction of experimental value changes and the effect value of each factor, respectively. Lastly, the central composite design (CCD) was adopted to identify the optimal liquid fermentation concentration by setting up a multiple quadratic regression equation, analyzing and evaluating the correlations among these factors which affect the mycelium mass of B. bassiana SDDZ-9, one of the most virulent strains against western flower thrips (Frankliniella occidentalis. 【Result】Temperature, volume of liquid, rotate speed and initial conidia concentration were the main factors on mycelium mass. The change of pH within certain limits had less influence on this strain of liquid fermentation. Without considering pH, when the fermentation conditions of temperature, volume of liquid, rotate speed and initial concentration were 27.08℃, 49.72 mL/250 mL of triangular flask, 205.45 r/min, and 1.122×10⁷ conidia/mL, the maximum mycelium mass was produced after 48 h of fermentation. Using the culture conditions to produce conidia, the mycelium mass obtained was about 14.769 g·L^-1, which was consistent with the predicted biomass. After the solid state fermentation, the yield achieved about 20.16 g·kg^-1 and 1.84×10¹¹ conidia/g.【Conclusion】The spore production of B. bassiana could be significantly improved under optimized fermentation conditions. The results may provide reference for large-scale liquid fermentation of B. bassiana SDDZ-9.

Key words: Beauveria bassiana, response surface methodology, fermentation conditions, optimization