First report of Bacillus velezensisJK-F2 for the biological control of crown gall in kiwifruit

A highly pathogenic bacterium, Agrobacterium Fabacearum, causes crown gall in kiwifruit plants leads to serious damage resulting in huge economic losses. In this study, we aimed to screen antagonistic bacterial biocontrol agents against crown gall disease of kiwifruit plants. A total of 225 bacterial strains were isolated from kiwifruit plant rhizosphere soil. Among these, strain JK-F2 exhibited good biocontrol effects in the form of antagonistic activity against A. Fabacearum in vitro. Based on morphological, physiological, and biochemical features and 16S rRNA and gyrAgenes, the strain JK-F2 was identified as Bacillus velezensis. The zone of inhibition of strain JK-F2 was 22.84 ± 0.21 mm when the plate was covered with A. Fabacearum. In pot tests with artificial inoculation of A. Fabacearumto kiwifruit plants, the application of strain JK-F2 ahead of pathogen inoculation significantly reduced the incidence of crown gall by 26.67%, and the control efficiency was 71.96%. In field experiments, the inoculation of strain JK-F2 by root irrigation reduced the average growth rate of galls by 17.95–43.15%. The undiluted strain JK-F2 was more effective than the diluted strain in controlling crown gall by reducing the growth rate of galls, with a biocontrol effect of 68.07%. In this study, strain JK-F2, with good biocontrol application value, was isolated and identified. It is a promising candidate for the biocontrol of crown gall in kiwi plants.