Biocontrol Efficacy and Genomic Basis of Endophytic Bacteria Against Xanthomonas campestris pv. campestris in Cabbage

Xanthomonas campestris pv. campestris (Xcc) is the causal agent of black rot, one of the most destructive bacterial diseases on crucifer crops, resulting in yield losses of up to 90%. The aim of this study was to identify novel endophytic bacteria from cabbages with potential biocontrol agents against Xcc. A total of sixty-five isolates were evaluated for plant growth-promoting characters and antagonistic activity, from which ten were selected for in planta assays and subsequently validated under field conditions. Pseudomonas synxantha BR25/2 consistently demonstrated the highest efficacy, reducing disease severity by 81.12% in in planta trials and 33.5% in field trials, thereby comparing to copper-based control measures. Additionally, Pseudomonas synxantha BR25/2 significantly enhanced yield parameters, including a 31.8% increase in head weight under field conditions. Whole-genome sequencing identified biosynthetic gene clusters, including siderophores, phenazines, and non-ribosomal peptide synthetases, notably a coronatine-like NRPS and a fengycin-like betalactone, suggesting an extensive antimicrobial potential of metabolites. This represents the first report of P. synxantha exhibiting control over Xcc. For commercial application, large-scale fermentation and encapsulation techniques are recommended to overcome shelf-life challenges, providing a sustainable microbial solution for crucifer production.