Abstract: In recent years, cucumber bacterial soft rot caused by Pectobacterium brasiliense (Pbr) occurred severely and was difficult to control. In this study, the control effect in greenhouse was used to screen the biocontrol agent strain suitable for field applications. The diluted plating method was used to separate and purify rhizosphere bacteria of healthy cucumber plants collected from severely diseased plots. Six antagonistic strains of Pbr were screened by the double-layer culture method. The result of spray infection method indicated that the disease incidence of cucumber inoculated with strain ZF390 was significant reduced and the control efficacy was 77.94%. Meanwhile, ZF390 exhibited significant and broad inhibition spectrum against eight pathogenic bacteria. The strain ZF390 was identified as Paenibacillus peoriae based on morphological traits, physiological and biochemical characteristics and multilocus sequence analysis. The fermentation process of strain ZF390 was optimized by single factor test, and the concentration of the fermentation broth was 10⁴ times up to 2.94×10⁹ CFU/mL. In summary, the strain ZF390 is an effective biocontrol strain against cucumber bacterial soft rot and has the potential for further development into biocontrol formulations.

Key words: cucumber bacterial soft rot, Paenibacillus peoriae, biocontrol, fermentation