Abstract: This study aims to screen biocontrol strains that produce exopolysaccharides (EPS) and induce resistance against cucumber bacterial angular leaf spot, evaluate their potential for inducing disease resistance, and provide excellent strain resources for the development of microbial agents. LB-aniline blue plates combined with a string test were used to qualitatively screen EPS-producing bacteria. High-yielding EPS strains were further selected by measuring EPS production, and their efficacy against cucumber bacterial angular leaf spot was evaluated in pot experiments. The selected strain was identified by multi-gene sequence analysis, and its direct antagonistic activity was tested using the dual-culture method. After root drenching with EPS, the control efficacy was determined, and several defense-related indicators in cucumber leaves, including defense enzyme activities, chlorophyll, total phenolics, flavonoids, and malondialdehyde (MDA) content, were analyzed. The results showed that strain ZF535 was obtained, with an EPS yield of 1.67 g/L and a pot control efficacy of 58.75%. It was identified as Peribacillus simplex and exhibited no direct inhibitory antibacterial activity. pot experiments showed that EPS from P. simplex ZF535 achieved 60.43% control efficacy against cucumber bacterial angular leaf spot, significantly increased the activities of defense-related enzymes, raised the levels of chlorophyll, total phenolics and flavonoids, induced callose deposition, and reduced MDA accumulation in cucumber leaves. These results indicate that strain ZF535 has the potential to induce plant resistance and represents a promising biocontrol resource for future development.

Key words: Peribacillus simplex, angular leaf spot of cucumber, extracellular polysaccharides, induced resistance