Biocontrol Potential, Plant Growth-Promotion, and Genomic Insights of Pseudomonas koreensis CHHM-1 Against Bacterial Canker in Actinidia arguta.

In 2019, bacterial canker caused by Pseudomonas syringae pv. actinidiae was first identified in Actinidia arguta. This disease has led to significant yield reduction, plant mortality, and substantial economic losses in A. arguta cultivation. Its emergence poses a novel challenge to the sustainable global production of kiwifruit. Currently available treatments for bacterial canker caused by P. syringae pv. actinidiae are scarce. Moreover, the environmental toxicity of copper-based compounds and emerging antibiotic resistance issues necessitate the development of eco-friendly control strategies. Disease management strategies based on biocontrol bacteria have shown broad application prospects. In this study, the isolate CHHM-1 with significant antagonistic activity against P. syringae pv. actinidiae was isolated from the rhizosphere soil of healthy A. arguta. It was identified as Pseudomonas koreensis through 16S rRNA gene and whole-genome sequencing. Genomic analysis revealed that the isolate CHHM-1 harbors various genes related to biocontrol, plant growth promotion, and antibiotic resistance, suggesting strong environmental adaptability and functional potential. Furthermore, the strain exhibited multiple plant growth-promoting traits, such as nitrogen fixation, phosphate solubilization, siderophore production, and synthesis of indole-3-acetic acid (IAA). In vitro antagonism assays confirmed the strong antagonistic activity of the isolate CHHM-1 against P. syringae pv. actinidiae. A dual-culture plate assay showed an average inhibition zone of 4.36 cm, while preventive application on plants significantly reduced lesion length to 1.3 mm (vs. 6.2 mm control) in shoots and lesion area to 10% (vs. 80% control) in leaf discs. Further antibacterial tests revealed that its inhibitory mechanism is attributed to secreted antimicrobial substances. These findings provide a promising candidate for developing novel biopesticides to combat P. syringae pv. actinidiae variants, reduce chemical dependency, and foster sustainable A. arguta production.