Potential of Streptomyces rochei G-6 for Biocontrol of Cucumber Wilt Disease and Growth Enhancement

Cucumber wilt disease, caused by Fusarium oxysporum f. sp. cucumerinum (FOC), is a major threat to cucumber production, especially in greenhouses. This study used a fermentation product derived from a new strain of Streptomyces rochei (G-6) to investigate the potential for biocontrol of cucumber wilt disease and the effect on promoting cucumber growth. In the first experiment, the inhibitory effect of S. rochei G-6 fermentation product (SGFP) on FOC growth was evaluated, then the effect of SGFP on wilt incidence and severity, as well as cucumber growth, antioxidant system, and soil nutrient conversion capacity were investigated. The results showed that SGFP inhibited FOC growth by 85.3% in the antimicrobial experiment. In the potting experiment, the incidence rate in the FOC group reached 88.7%, but it was only 56.0% in the SGFP1 group and 64.7% in the SGFP2 group, indicating the efficient inhibitory effect of SGFP on cucumber wilt, with the biocontrol effect of SGFP1 being higher than that of SGFP2. In addition, the disease index decreased significantly (p < 0.05) in both SGFP treatments, which was significantly (p < 0.05) lower in the SGFP1 group than in the SGFP2 group, indicating that pre-treatment was better than post-treatment in reducing the disease severity. In addition, SGFP promoted the growth of cucumber seedlings, as indicated by indicators related to the growth of aboveground and underground parts. Furthermore, the activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) in the cucumber seedlings increased after SGFP treatment and the malondialdehyde level was decreased, indicating a reduction in oxidative stress. SGFP also improved the soil nutrient conversion capacity by increasing the activities of urease, phosphatase, and sucrase, which may enhance nutrient uptake by cucumber seedling. The findings of this study suggest that SGFP is an effective biocontrol agent against cucumber wilt and also promotes cucumber growth by regulating the antioxidant system and soil environment, and its application is a promising solution to reduce wilt incidence in cucumber production.