Abstract:
Erwinia amylovora is a plant pathogenic bacterium that causes the destructive disease fire blight of apple and pear. We examined the plasmid content of a collection of 305 isolates of E. amylovora from Washington and Oregon with PCR assays and RFLP. Nearly all isolates of E. amylovora carried plasmid pEA29, which is not found in other species of bacteria, but 4% of the isolates from this region lacked pEA29. The plasmid pEU30, previously reported in pathogen strains from western states in the USA, was detected in 28% of isolates. The RFLP patterns of plasmid preparations from a third of isolates from an epidemic in Washington in 1988 had altered RFLP patterns, possibly due to the presence of plasmid(s) in addition to pEA29 or pEU30. Considering all samples, the majority of isolates in this region was typical of E. amylovora and harbored only pEA29. Nonetheless, many of the pathogen isolates had altered plasmid content, indicating that plasmid acquisition and propagation in populations of E. amylovora in orchards in the Northwestern USA is more common than previously assumed.
