Genetic and phenotypic characterization of bacterial strains isolated in Japan that resemble Erwinia rhapontici and E. persicinus

The taxonomic identity of Japanese isolates of bacteria with physiological and biochemical characteristics similar to Erwinia rhapontici or E. persicinus was clarified using genetic analyses, pathogenicity tests and phenotypic characterization. In a phylogenetic analysis based on 16S rRNA and housekeeping genes gyrB, rpoD, and recA, the strains formed two independent clusters, one for E. rhapontici and another for E. persicinus, each including the type strain. The E. rhapontici cluster had three subclusters: pink-pigmented strains isolated in Japan, the type strain, and nonpigmented strains isolated from wasabi. rep-PCR banding patterns confirmed this grouping. The ability to cause rot on plants and the rot severity depended on the strain, though virulence of E. rhapontici strains isolated in Japan tended to be relatively weaker than that of the others. Pink pigment formation by E. rhapontici and E. persicinus strains was abundant on onion, Welsh onion and garlic, but E. rhapontici strains isolated from wasabi did not produce pink pigment on any plants or media tested. Thus, the unknown strains from Japan that produced pink pigment were E. rhapontici or E. persicinus. Despite being nonpigmented, E. rhapontici strains from wasabi were genetically closely related to pink-pigmented E. rhapontici strains. Based on the rpoD sequence, two specific primer sets were newly designed to discriminate E. rhapontici and E. persicinus.