P-010 - Prevalence and genetic diversity of Pseudomonas syringae pv. aptata in table beet and Swiss chard seed production in Washington State

Pseudomonas syringae pv. aptata (Psa) is a seedborne and seed transmitted pathogen that causes bacterial leaf spot (BLS) of table beet and Swiss chard. BLS has gained greater economic importance in beet and chard seed production due to the rising demand for seed to plant the expanding acreage of baby leaf beet and chard crops. In surveys to assess the prevalence and genetic diversity of Psa in beet and chard seed crops in western Washington, BLS was present in 72% of the beet and chard seed crops surveyed in 2020 but absent in all crops surveyed in 2021 and 2023. Pathogenicity tests on beet and chard seedlings demonstrated variation in virulence among Psa isolates from the beet and chard crops surveyed, with some isolates more virulent on beet than chard. Multilocus sequence analysis (MLSA) and whole genome sequence (WGS) analysis revealed the Psa isolates are diverse genetically. Neither MLSA nor WGS-based phylogeny differentiated pathogenic Psa isolates from non-pathogenic isolates of P. syringae obtained in the survey, nor isolates pathogenic on beet and chard from those pathogenic on beet only. Effector analysis provided insights into potential virulence factors associated with pathogenicity, and identifed core T3SSE such as AvrE, HopM1, and HopAA1-1, which may contribute to host infection. Clustering of pathogenic and non-pathogenic isolates within the same phylogroup subclades, along with high levels of genetic connectivity, highlight the complexity of P. syringae populations associated with beet and chard, and the potential role of recombination in their evolution.