Irrigation systems as reservoirs of diverse and pathogenic Pseudomonas syringae strains endangering crop health

• P. syringae complex in irrigation systems poses a significant threat to crop health • Globally distributed P. syringae haplotypes identified in the Danube-Tisa-Danube Hydrosystem • dPCR method optimized for efficient quantification of P. syringae complex in water • Highly specific primers and probes developed for precise detection of phylogroup 2 Pseudomonas syringae ( Psy ) is a widely distributed bacterial species complex primarily recognized as a foliar pathogen but also inhabits diverse environments, including water habitats, where strains closely related to agricultural pathogens have been identified . The connection between Psy -caused epidemics and its potential presence in nearby irrigation systems remains underexplored. This study comprehensively examined the Psy complex in the Danube-Tisa-Danube Hydrosystem (DTD) in Serbia, assessing its abundance, phylogenetic diversity, and pathogenic potential. To reduce the reliance on the time-consuming steps of isolation and identification, we developed novel high-specific primers and probes for precise detection of strains belonging to phylogroup 2 within Psy complex. Our results demonstrated that dPCR, coupled with highly specific and sensitive primers, outperformed both traditional plating and qPCR in detecting the Psy complex and phylogroup 2 in irrigation waters, making Psy diagnostics more effective. Phylogenetic analysis indicated high strain diversity within the DTD, identifying phylogroups 1, 2, 7, 12, and 13 and haplotypes linked to strains previously encountered in epidemics on sugar beet in Serbia. Notably, 66.67% of the isolates from the DTD were capable of inducing disease. Phylogroup 2 isolates displayed a broad host range, suggesting that the dissemination of Psy from DTD through irrigation, poses a substantial threat to crop health and agricultural productivity.