Abstract Plant pathogenic strains of Pseudomonas syringae (Psy) spp. have been detected in nonagricultural habitats, including those associated with the water cycle. Their presence in aquatic systems allows dissemination over long distances, especially with irrigation practices. In May 2021, we sampled 15 sites along the Danube River Basin in Serbia to gain insight into P. syringae abundance and diversity. We identified 79 Psy strains using Psy-specific primers, and a partial sequence of the citrate synthase (cts) house-keeping gene has served for phylogenetic diversity assessments. Phenotypic diversity determination included characterizing features linked with survival and pathogenic lifestyle. The ice nucleation activity, pectinolytic activity, swimming and swarming assays, and hypersensitive reaction on plants were tested. Psy was detected at ten of 15 sites examined at abundance ranging from 1.0 × 102 to 1.2 × 104 CFU/L. We discovered the presence of four phylogroups, with phylogroup 2 being the most abundant, followed by phylogroups 7, 9, and 13. The hypersensitive reaction was induced by 68.63% of the isolates from the collection. A partial sequence comparison of the cts gene showed 100% similarity between isolates from cherry plants epidemics in Serbia caused by Psy and isolates from the Danube River. Our results suggest that the Danube River, extensively used for irrigation of agricultural fields, harbors diverse strains of Psy, which possess various features that could lead to potential disease outbreaks on crops. This study represents the first in-depth analysis of Psy abundance and diversity in the Danube River Basin. It sets the ground for future pre-epidemic studies and seasonal monitoring of Psy population dynamics.
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