CHARACTERIZATION OF PATHOGENIC BACTERIA FROM KOREA AND JAPAN CAUSING ASIAN PEAR BLIGHT

Pathogenic bacteria isolated from necrotic Nashi pear trees in Korea and Japan were compared for their molecular properties with the fire blight pathogen Erwinia amylovora. These included PCR assays, PFGE analysis and alignment of corresponding DNA sequences at the nucleotide or amino acid level. In all cases, divergences were observed to E. amylovora, but many similarities between the Erwinia strains from Japan and E. pyrifoliae from Korea. These results confirm E. pyrifoliae as a species different from E. amylovora and imply that the Erwinia strains from Japan are not closely related to the fire blight pathogen. In virulence assays with plants the pathogen from Korea is mostly restricted to pear fruit trees for symptom formation. Apple and other fire blight host plants seem to be barely or not at all affected by the pathogen. Successful isolations of E. pyrifoliae strains were achieved in 1995 to 1998, but not anymore in 1999, 2000 and 2001, when disease events may have been low in Korean orchards. No recent data about Asian pear blight have been released from Japan.