Phenotypic and genetic characterization of Erwinia rhapontici isolated from diseased Asian pear fruit trees

In 1995, a serious necrotic disease appeared in Asian pear trees in the orchards of Chuncheon, South Korea. Large numbers of bacterial samples were collected, and the causative microorganism was identified as a novel pathogen, Erwinia pyrifoliae. Among the samples, four bacterial isolates with atypical characteristics were further analyzed through biochemical tests and 16S rRNA gene sequence analysis. By phenotypic and genetic analysis these isolates were identified as E. rhapontici. Phylogenetic analysis using 16S rRNA sequence data revealed that E. rhapontici forms a discrete clade with high bootstrap value close to the E. amylovora group. Pathogenicity tests on leaves of tobacco plants (Nicotiana tabacum) elicited hypersensitivity responses, but artificial inoculations on immature fruits and shoots of Asian pear (Pyrus pyrifolia) did not show any necrotic symptoms. The developed primers showed no cross reactivity when tested against other phytopathogens and were able to detect E. rhapontici from mixed culture and in planta.