Abstract: The efficacy of Bacillus velezensis (T2), Bacillus subtilis (T3), and Bacillus megaterium (T4) against cucumber powdery mildew and their impacts on plant growth, yield, fruit quality, and the antioxidant system were evaluated through field trials, and three Bacillus treatments were compared to a chemical fungicide (T1) and an untreated control (CK). Results demonstrated that all three Bacillus treatments effectively suppressed powdery mildew and enhanced plant growth, yield, and fruit quality, with T2 exhibiting the most pronounced effects. In terms of disease control efficacy, T2 achieved a level close to that of the chemical fungicide T1 and significantly outperformed both T3 and T4. Regarding yield, T1 produced the highest yield, closely followed by T2. Both T1 and T2 yields were significantly greater than those of the other Bacillus treatments and CK. Similarly, T1 showed optimal plant growth performance across measured indicators, with T2 ranking second. Both T1 and T2 significantly exceeded T3 and T4, while all treatments surpassed CK. T2 treatment significantly enhanced key fruit quality parameters, including soluble protein, free amino acid, soluble sugar, and vitamin C content, compared to CK. Furthermore, T2 effectively increased photosynthetic capacity, significantly reduced membrane lipid peroxidation levels, and boosted antioxidant enzyme activity, demonstrating superior antioxidant performance relative to T3 and T4.

Key words: Bacillus velezensis, Bacillus subtilis, Bacillus megaterium, cucumber powdery mildew, green biocontrol efficacy, quality