Genetic studies of an Erwinia species isolated from Asian pears in Japan
Studies were carried out in USA to compare genomic and plasmid DNAs extracted from Erwinia strains isolated on Asian pears (Pyrus pyrifolia) in Japan, from E. pyrifoliae strains isolated on P. pyrifolia in South Korea, and from E. amylovora strains isolated on fruit trees and Rubus in various countries. Amplified fragment length polymorphism (AFLP) and comparison of sequences were used to differentiate the strains included in this study (4 Erwinia strains from Japan, 4 strains of E. pyrifoliae, 15 strains of E. amylovora). These genetic comparisons showed that the Erwinia pathogen found on pear in Japan is closely related to E. pyrifoliae and that both of these pathogens are distinct from E. amylovora (EPPO A2 list). However, it is noted that further studies should be done on a wider number of strains and that other techniques (i.e. total DNA-DNA homology) should be used to establish whether the pathogen found in Japan is E. pyrifoliae or a new species.
EPPO notes:
1) It can be recalled that Erwinia strains were reported to cause bacterial shoot blight in Hokkaido some years ago, and that since then the Japanese authorities have always denied the presence of E. amylovora on their territory.
2) E. pyrifoliae was formerly on the EPPO Alert List because it was reported in 1998 as a new bacterium of P. pyrifolia. But, as in 1999 and 2000 it could not be isolated again in the previously affected orchards and as no new information was available, it was decided in 2003 that a sufficient Alert had been given.
3) As a general remark, it could be underlined that up-to-date information is lacking on the extent and severity of both Asian pear blight in South Korea and bacterial shoot blight in Hokkaido in Japan, as well on their host range (in particular on the susceptibility of European pears, P. communis). But if it appeared that these diseases were causing damage to crops, the risk posed by the pathogen(s) involved might need to be reassessed.
Sources
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Maxson-Stein, K.; McGhee, G.C.; Smith, J.J.; Jones, A.L.; Sundin, G.W. (2003) Genetic analysis of a pathogenic Erwinia sp. isolated from pear in Japan.
Phytopathology, 93(11), 1393-1399.
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