Characterization and genetic diversity of pseudomonads population from highbush blueberry in western Canada

Bacterial blight (causal agent Pseudomonas syringae complex, Psc) is an endemic and economically important disease of northern highbush blueberry production in Canada and the Pacific Northwest of the USA. To date, there is no comprehensive survey of the disease in the region and detailed characterization of associated pathogens from Pacific western Canada. Therefore, we did comprehensive disease survey and characterization of associated pseudomonads population using pathogen morphology, biochemical tests, and molecular characterization. We isolated 380 strains of pseudomonads from symptomatic plants from 32 research and commercial fields in 10 diverse geographic locations in British Columbia. We used P. syringae specific (Psy) primers and identified 197 Psy-PCR positive isolates out of 380. We further sequenced Psy-PCR positive isolates of pseudomonads using four housekeeping genes and identified four phylogenomic species: P. syringae (40%), Pseudomonas avellanae (29%), Pseudomonas viridiflava (20%), and phylogenomic species A (7%). P. avellanae and P. viridiflava are new phylogenomic species of Psc causing bacterial blight in highbush blueberry. We found some patterns among geographical locations and highbush blueberry varieties in the frequency distribution of isolates of these phylogenomic species. Genetic fingerprinting with rep-PCR assays identified a very high genetic diversity of pseudomonads populations among geographical locations, varieties, and phylogenomic species. Biochemical characterization (LOPAT- levan, oxidase, pectolytic activity, arginine dihydrolase, and tobacco hypersensitivity) revealed that the vast majority of isolates were Pseudomonas Group Ia. Findings of this study provide insight into the population biology of pseudomonads infecting highbush blueberry, provide information for disease diagnosis, and exploit disease management options, including identifying sources of disease resistance. KEY POINTS: • High prevalence of bacterial blight caused by P. syringae complex (Psc) in highbush blueberry in Pacific western Canada • We report two new phylogenomic species of Psc, P. viridiflava and P. avellanae, that cause bacterial blight and canker disease in highbush blueberry • The genetic diversity of the population of Psc was very high.