Erwinia pyrifoliae, an Erwinia species different from Erwinia amylovora, causes a necrotic disease of Asian pear trees

Bacteria from necrotic branches of Asian pear trees (Pyrus pyrifolia) in Ko rea were consistently isolated as white colonies on nutrient agar and forme d mucoid, slightly yellow colonies on a minimal medium with topper sulphate . Isolates with this colony morphology were studied in a series of microbio logical, molecular and pathological tests. Most isolates allowed the verifi cation of Koch's postulate on P. pyrifolia seedlings and on slices from imm ature pear (Pyrus communis) fruits and were also positive in hypersensitivi ty tests on tobacco leaves. They showed characteristics common to species i n the genus Erwinia, but were different from Erwinia amylovora, the agent o f fire blight. A relationship between the novel pathogen and E. amylovora w as found in microbiological and serological tests. Both organisms had simil ar but not identical protein patterns in 2-D gel electrophoresis, and in gr owth morphology the new pathogen produced colonies on MM2 Cu medium that we re mucoid and slightly yellow, compared with the clearly yellow colonies of E. amylovora. No similarity was found in the plasmid profiles, and consequ ently no PCR signal was obtained with primers from the E, amylovora plasmid pEA29. REP-PCR also produced bands differing for the two organisms.