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

Abstract

Bacteria from necrotic branches of Asian pear trees (Pyrus pyrifolia) in Korea were consistently isolated as white colonies on nutrient agar and formed mucoid, slightly yellow colonies on a minimal medium with copper sulphate. Isolates with this colony morphology were studied in a series of microbiological, molecular and pathological tests. Most isolates allowed the verification of Koch's postulate on P. pyrifolia seedlings and on slices from immature pear (Pyrus communis) fruits and were also positive in hypersensitivity tests on tobacco leaves. They showed characteristics common to species in the genus Erwinia, but were different from Erwinia amylovora, the agent of fire blight. A relationship between the novel pathogen and E. amylovora was found in microbiological and serological tests. Both organisms had similar but not identical protein patterns in 2‐D gel electrophoresis, and in growth morphology the new pathogen produced colonies on MM2 Cu medium that were mucoid and slightly yellow, compared with the clearly yellow colonies of E. amylovora. No similarity was found in the plasmid profiles, and consequently no PCR signal was obtained with primers from the E. amylovora plasmid pEA29. REP‐PCR also produced bands differing for the two organisms.

Molecular comparison of pathogenic bacteria from pear trees in Japan and the fire blight pathogen Erwinia amylovora

“…Recently, a bacterial pathogen, Erwinia pyrifoliae, was characterized as a novel Erwinia species that also causes necrotic symptoms on Asian pears Rhim et al, 1999). The Asian pear pathogen was first detected in orchards near Chuncheon, South Korea, and has not been reported to occur in other countries.…”

“…Isolates from Japanese orchards described by Beer et al (1996) and Kim et al (1996) were characterized for molecular properties and were found to differ from Erwinia amylovora, but to be related to Erwinia pyrifoliae, the novel species causing Asian pear blight Rhim et al, 1999).…”

Molecular Characterization of Natural Erwinia pyrifoliae Strains Deficient in Hypersensitive Response

“…A bacterial disease similar to fire blight was observed on Nashi pear trees (Pyrus pyrifolia) in South Korea, caused by the novel species Erwinia pyrifoliae (16). The pathogen was consistently isolated from orchards in the area of Chuncheon from 1995 to 1998 and identified on semiselective agar plates and by PCR (15,16).…”

“…The pathogen was consistently isolated from orchards in the area of Chuncheon from 1995 to 1998 and identified on semiselective agar plates and by PCR (15,16). E. pyrifoliae is restricted mainly to pear and is highly related to pear-pathogenic Erwinia strains from Japan (14).…”

“…In 1997, necrotic tissue from a Nashi pear tree was obtained from Korea and extracted for isolation of the causative pathogen. White colonies on LuriaBertani (LB) agar (with 50 g of cycloheximide/ml to avoid fungal growth) were assayed for the mucoid, yellowish colony morphology typical of E. pyrifoliae on MM2Cu agar as described before (13,15,16). The isolates were further assayed on LB plates with 5% sucrose and on MM1Cu agar as described for identification of E. amylovora (3).…”