Abstract: Clubroot disease of cruciferous plants caused by Plasmodiophora brassicae Woronin occurred severely and was difficult to control. In this study, a biocontrol agent ZF72 was screened by using dual-culture assay against Fusarium oxysporum and Phytophthora capsica. Control efficacy of ZF72 against clubroot disease in pot experiment was 74.6%. The strain ZF72 was identified as Bacillus velezensis based on morphological characteristics, physiological and biochemical analysis, as well as 16S rDNA, gyrBand atpDphylogenetic analysis. The fermentation of strain ZF72 was optimized by single factor test. An optimum medium composition was as followings: sorbitol 3 g/L, bran 8 g/L, CaCl₂ 1 g/L, and MgCl₂·6H₂O 3 g/L. The optimum fermentation conditions were as followings: temperature 28℃, pH 6.0, loading volume 50 mL/250 mL, rotating speed 180 r/min, and inoculation amount 1% (v/v). Treatment with strain ZF72 significantly reduced the incidence of clubroot disease of Chinese cabbage, with a control efficacy of 63.8% in field experiment, which provides new microbial resources for biological control of clubroot disease of crucifers.

Key words: clubroot of crucifers, Bacillus velezensis, biocontrol