Submitted to: Fire Blight International Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 5/21/2010
Publication Date: 8/12/2010
Citation: Carey, A., Pusey, P.L., Loper, J.E., Stockwell, V. 2010. Plasmid content of isolates of Erwinia amylovora from orchards in Washington and Oregon in the USA. 12th International Workshop on Fire Blight. p.92. Interpretive Summary:
Technical Abstract: Washington (WA) and Oregon (OR) represent a major pome fruit production region of the United States, and streptomycin-resistant isolates of the fire blight pathogen Erwinia amylovora are common in orchards in this region. We examined the plasmid content of a collection of more than 200 isolates of E. amylovora representing the major pome fruit-growing regions of WA and OR with RFLP and PCR assays. Ninety-seven percent of strains harbored the plasmid pEA29, which is known to be present in nearly all strains of E. amylovora, but ~3% of the isolates lacked pEA29. The isolates lacking pEA29 were obtained from a few orchards in central WA and one in Northeast OR. To our knowledge, this is the first report of E. amylovora lacking pEA29 in the United States. The RFLP patterns of plasmids isolated from ~60% of E. amylovora strains were identical to one another and reflect the pattern associated with pEA29 alone; 40% of the isolates also had another plasmid, pEU30. There was no correlation between resistance to streptomycin and plasmid content among isolates. None of the strains tested carried the streptomycin-resistance genes strA-strB, so resistance to streptomycin likely was due to spontaneous mutations in the genome of E. amylovora. The pathogen population within an orchard was not homogeneous in plasmid content. These results indicate that plasmid acquisition and propagation in populations of E. amylovora in orchards in the Northwestern United States is more common than previously assumed.