PJB-2026-68
Biocontrol efficacy of Bacillus marisflavi XJ-04 against watermelon sclerotiniosis caused by Sclerotinia sclerotiorum
Lingyue Zhu
Abstract
Watermelon sclerotiniosis is increasingly severe under expanded cultivation and continuous cropping, and this study aimed to isolate the causal pathogen and evaluate a rhizosphere-derived bacterial antagonist for biological control. S. sclerotiorum (Lib.) de Bary was isolated from diseased watermelon stems and vines as strain LY24 and identified by morphological characteristics and molecular analysis; the optimal growth conditions for LY24 were mannitol (carbon source), tryptone (nitrogen source), NaCl, pH 9, 25 °C, and complete darkness. Forty rhizosphere soil samples were collected from watermelon-growing areas in Changchun (including Jiutai District), and 300 bacterial isolates were obtained and screened using a dual-culture (plate confrontation) assay. Strain XJ-04 exhibited strong antagonism against S. sclerotiorum, with a 5.21 mm inhibition zone and a 70.12% inhibition rate, and was identified as B. marisflavi based on morphological and molecular evidence; its physiological and biochemical characteristics were assessed by Gram staining and standard biochemical tests. Fermentation medium was optimized using an orthogonal design combined with response surface methodology, and the optimal formulation (sucrose 21.08 g/L, fine bran 9.17 g/L, K₂HPO₄·3H₂O 9.77 g/L, pH 9) increased inhibition to 77.78% (71.75% before optimization); the optimal fermentation conditions were 100 mL working volume, 30 °C, and 3 days. The fermentation broth maintained stable antifungal activity after treatments involving temperature, pH, storage time, and light, indicating that B. marisflavi XJ-04 is a promising biocontrol candidate for watermelon sclerotiniosis.
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