pv. pv. nov., a Clonal Pathogen Causing an Emerging, Devastating Disease of the Ornamental Plant spp.

Commercial production of the ornamental plant dipladenia ( spp.) is threatened by dipladenia leaf and stem spot disease, caused by the bacterium . includes four pathovars of woody hosts differentiated by a characteristic host range in olive, oleander, ash, and broom plants. However, isolates from dipladenia have not been ascribed to any particular lineage or pathovar. Here we report that isolates from dipladenia represent a distinct, clonal lineage. First, dipladenia isolates display very similar plasmid profiles, including a plasmid encoding the gene for biosynthesis of indole-3-acetic acid. Second, multilocus sequence analysis and core genome single-nucleotide polymorphisms phylogenies showed a monophyletic origin for dipladenia isolates, which cluster with isolates from oleander (pathovar ) in a distinct clade well separated from other strains. Metabolic profiling and cross-pathogenicity tests in olive, oleander, ash, broom, and dipladenia clearly distinguished dipladenia isolates from the four pathovars. Comparative genomics of the draft genome sequence of the dipladenia strain Ph3 with the other four pathovars showed that Ph3 encodes very few strain-specific genes and a similar set of virulence genes to pv. , including its repertoire of type III secretion system effectors. However, hierarchical clustering based on the catalog of effectors and their allelic variants clearly separated Ph3 from pv. strains. Based on their distinctive pathogenicity profile, we propose a de novo pathovar for isolates from dipladenia, pv. pv. nov., for which strain Ph3 (CFBP 8832) has been designated as the pathotype strain.