Assessment of the Biocontrol Potential of Bacillus velezensis WL–23 against Kiwifruit Canker Caused by Pseudomonas syringae pv. actinidiae

Kiwifruit canker disease, caused by Pseudomonas syringae pv. actinidiae (Psa), is the main threat to kiwifruit production worldwide. Currently, there is no safe and effective disease prevention method; therefore, biological control technologies are being explored for Psa. In this study, Bacillus velezensis WL–23 was isolated from the leaf microbial community of kiwifruit and used to control kiwifruit cankers. Indoor confrontation experiments showed that both WL–23 and its aseptic filtrate had excellent inhibitory activity against the main fungal and bacterial pathogens of kiwifruit. Changes in OD(600), relative conductivity, alkaline proteinase, and nucleic acid content were recorded during Psa growth after treatment with the aseptic filtrate, showing that Psa proliferation was inhibited and the integrity of the cell membrane was destroyed; this was further verified using scanning electron microscopy and transmission electron microscopy. In vivo, WL–23 promoted plant growth, increased plant antioxidant enzyme activity, and reduced canker incidence. Therefore, WL–23 is expected to become a biological control agent due to its great potential to contribute to sustainable agriculture.