Paper Details

Abstract

Watermelon sclerotiniose has become increasingly severe under conditions of expanded cultivation and continuous cropping. This study aimed to isolate the causal pathogen and evaluate a rhizosphere-derived bacterial antagonist for biological control. Strain LY24, isolated from diseased watermelon stems and vines, was identified as S. sclerotiorum (Lib.) de Bary, through morphological and molecular analyses. Strain LY24 exhibited optimal growth under the following conditions: mannitol as the carbon source, tryptone as the nitrogen source, supplementation of NaCl, pH 9, a temperature of 25°C, and complete darkness. Forty rhizosphere soil samples were collected from watermelon-growing areas in Changchun (including Jiutai District), yielding 300 bacterial isolates. These isolates were 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. Based on morphological and molecular evidence, combined with Gram staining and standard biochemical tests, strain XJ-04 was identified as B. marisflavi. The fermentation medium was optimized using an orthogonal design combined with response surface methodology. The optimal formulation (sucrose 21.08 g/L, fine bran 9.17 g/L, K₂HPO₄·3H₂O 9.77 g/L, pH 9) increased the inhibition rate to 77.78%, compared to 71.75% before optimization. The optimal fermentation conditions were 100 mL working volume, 30°C, and a 3-day incubation period. The fermentation broth demonstrated stable antifungal activity after treatments involving temperature, pH, storage time, and light conditions. These results indicated that B. marisflavi XJ-04 may be a promising biocontrol candidate for watermelon sclerotiniose

To Cite This Article