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Abstract

Eggplant Root rot, caused by Fusarium solani, is a prevalent and devastating disease. To expand the resources of high-quality antagonistic bacteria against F. solani, the bacteria strains were isolated from soil and screened via a dual-culture plate assay. Among the isolates, strain X-104 exhibited superior antagonistic activity, achieving an inhibition rate of 66.70%. The inhibitory effect was determined as the mycelial growth inhibition rate (%). Based on morphological characteristics and molecular analysis, the strain was identified as Bacillus stercoris. To maximize the antagonistic efficacy of strain X-104, the fermentation medium and culture conditions were systematically optimized. Through a sequential approach involving single-factor experiments, orthogonal tests, the composition of glucose 20.88 g/L and ammonium fluoride 13.66 g/L, ZnSO4·7H2O 10.74 g/L was finally determined. Modeling via Design Expert software predicted inhibition rate of 82.53%. The actual inhibition rate after validation was 85.42%, closely matching the predicted value. The optimal fermentation conditions were 100 mL (in a 250 mL conical flask), 32°C temperature and 12 h of fermentation. A low concentration of the fermentation broth (diluted 1:50 with water) promoted both seed germination and plant growth. Specifically, it significantly enhanced key agronomic traits in eggplants, including plant height, root length, stem diameter, and both fresh and dry weight. Furthermore, significant increase in germination potential and germination rate was observed.

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