Virulent and copper-tolerant population of pseudomonads associated with bacterial blight and canker of highbush blueberry

Pseudomonas syringae complex (Psc) is an economically significant endemic bacterial pathogen in highbush blueberry (Vaccinium corymbosum), causing bacterial blight that results in significant yield losses. Information on the phenotypic diversity of the Psc complex is critical to implement tools and practices for managing this bacterial disease. This study evaluated the virulence diversity and copper tolerance of diverse isolates of Psc collected from multiple blueberry cultivars, fields, and locations of British Columbia during 2017–2020. Virulence diversity of the pathogen population was assessed by inoculating the pathogen on detached leaves of the bacterial blight susceptible cultivar ‘Draper’. Final disease severity (FDS) and relative area under the disease progress curve (rAUDPC) values were used as variables to categorize the virulent groups of the pathogen population. Of the 60 isolates tested, 45 were pathogenic. About 40% of the pathogenic isolates were highly virulent, predominantly belonging to phylogenomic species P. syringae and P. viridiflava, and many of these isolates were isolated from fields in Delta, Surrey, and Vancouver Island. Isolates from ‘Draper’ and ‘Aurora’ cultivars exhibited the highest virulence. Copper sensitivity assays revealed that 98% of isolates (n = 92) were tolerant to copper sulphate, as these isolates grew at 250 mg L−1. Interestingly, 73% of tested isolates grew at 500 mg L−1 Cu. The co-occurrence of highly virulent and copper-tolerant pseudomonads poses a significant challenge for disease management. Further genomic studies are warranted to elucidate the genetic basis of virulence and copper tolerance in pseudomonads affecting blueberry.