P-011 - Using PopCOGenT to group pathogens within the Pseudomonas syringae species complex and generate hypotheses about host range

The Pseudomonas syringae species complex (PSSC) is comprised of at least 20 closely related bacterial species, with some further divided into pathovars based on host range. Host specificity and authenticity of pathovars within species remains unresolved because some pathovars of P. syringae sensu lato belong to other species in the PSSC and reciprocal host range testing is needed. In this study we used Populations as Clusters Of Gene Transfer (PopCOGenT) to estimate genetic exchange among members of the PSSC, which we hypothesized will help predict host range and prioritize reciprocal host range testing. We investigated genetic exchange within P. syringae sensu stricto because of the broad host range of pathogens in this species, including P. syringae pv. aptata strains pathogenic on chenopods or cucurbits. Within this species, five exchanging populations of pathogens and nonpathogens were identified. The P. syringae pv. aptata pathotype strain and several strains isolated from watermelon belonged to the same population as one of the two genotypes representing the most aggressive pathogens on beet and chard. P. syringae pvs. atrofaciens, dysoxyli, lapsa, papulans and syringae also belong to one of the five populations. The type strains of the 20 species within the PSSC were not estimated to have exchanged genetic material across species, further supporting that the PSSC is comprised of multiple distinct species. This study serves as the first use of PopCOGenT to begin disentangling the pathovar system used in P. syringae.