Abstract: Tomato gray mold caused by Botrytis cinerea is one of the most widespread and destructive tomato diseases globally. The long-term application of chemical pesticides for controlling tomato gray mold in agricultural production leads to pesticide residue problems, while the use of beneficial microorganisms serves as an ideal green control strategy. In our previous research, the biocontrol strain Pseudomonas protegens FD6 was identified to exhibit strong antagonistic activity against B. cinerea in vitro, whereas the antifungal activity of its sterile filtrate was relatively weak. To improve the antifungal activity of fermentation products of P. protegens FD6 against B. cinerea, King's B(KB) medium was adopted as the basal medium in this study. Through single-factor and response surface methodology experiments, the optimal fermentation medium formulation for FD6 was determined to be 0.5% glycerin, 1.98% arginine, 0.15% dipotassium hydrogen phosphate, and 0.15% magnesium sulfate heptahydrate. The optimal culture conditions were determined as pH 6.97, fermentation temperature of 24.12 ℃ and fermentation time of 60 h. The inhibition rate of the optimized FD6 sterile filtrate against B. cinerea reached 95.12%, which was nearly twice that before optimization. Furthermore, quantitative detection of the main active antifungal components in the optimized FD6 fermentation broth revealed a significant increase in siderophore production. In conclusion, optimizing fermentation conditions effectively enhances the antagonistic activity of P. protegens FD6 against B. cinerea, which provides a theoretical reference for the development and application of green and efficient biological pesticides for tomato gray mold control in agricultural production.

Key words: Botrytis cinerea, Pseudomonas protegens, fermentation optimization, antifungal activity, secondary metabolite