Genomic and phenotypic diversity of Pseudomonas syringae populations associated with table grapevine in southern Italy

Table grape production represents a major agricultural sector in Apulia (southern Italy). This study investigated the occurrence, diversity, and genomic characteristics of Pseudomonas syringae (Ps) populations associated with symptomatic grapevines in 12 vineyards surveyed during the 2019, 2021, and 2025 growing seasons. Typical symptoms included leaf spots surrounded by chlorotic halos, marginal leaf necrosis, shoot lesions, and bunch necrosis. Fifteen isolates were recovered and identified as Ps through 16S rDNA sequencing. Pathogenicity assays performed on grapevine leaves, shoots, and berries confirmed their ability to reproduce disease symptoms and fulfill Koch’s postulates. Phenotypic characterization revealed variability in carbon source utilization, with some isolates able to metabolize tartrate but not lactate. These isolates were classified as atypical compared to the reference P. syringae pv. syringae (Pss) strain. Whole-genome sequencing further supported the distinction between typical and atypical isolates. Comparative genomic analyses showed that the atypical strains form a separate cluster and are genetically divergent from the Pss lineage. These findings suggest the presence of a previously unrecognized Ps pathovar associated with grapevine, characterized by distinct virulence, fitness, and resistance traits. The results provide new insights into the epidemiology and evolution of grapevine-associated Pseudomonas populations and support the development of new integrated disease management strategies.