Copper and Streptomycin Resistance in Strains of Pseudomonas syringae from Pacific Northwest Nurseries. Heather J. Scheck, Graduate Student, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902. Jay W. Pscheidt, Associate Professor, and Larry W. Moore, Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2902. Plant Dis. 80:1034-1039. Accepted for publication 21 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-1034.

Growers’ reports of disease-control failures following the application of copper and streptomycin bactericides led to collecting and testing strains of Pseudomonas syringae for resistance to copper and streptomycin. A comparison of strains isolated from 25 species of diseased woody plants in the Willamette Valley, Oregon, in 1992 and 1993 was made with strains collected in 1982 and 1983 from 30 diseased woody plant species in Oregon and Washington. On differential media supplemented with copper sulfate or streptomycin sulfate, the growth of 467 isolates recovered in 1992 and 1993 was determined. Twenty-four percent of the isolates were found to be copper-resistant (Cur) and streptomycin-sensitive (Sms), 6% were CusSmr, 24% were CurSmr, and 46% were CusSms at the concentrations tested. Of 192 strains isolated in 1982 and 1983, 25% were CurSms, 7% were CusSmr, none were CurSmr, and 68% were CusSms. In DNA colony hybridizations with digoxigenin-labeled probes, the copABCD probe from P. syringae pv. tomato hybridized with 10% of the Cur strains isolated in 1992 and 1993, and the copJ probe from P. syringae pv. syringae hybridized with a different 6% of the Cu’ strains isolated in 1992 and 1993. Neither probe hybridized with any Cur strains isolated in 1982 and 1983. A DNA probe encoding the streptomycin resistance determinant strA-strB from P. syringae pv. syringae hybridized with 98% of the strains that grew on King’s medium B with 100 µg of streptomycin sulfate per ml (KBS) and 4% of the strains that did not. This is the first report of copABCD, copj, and strA-strB homologues in strains of P. syringae from Pacific Northwest nurseries. The emergence of strains resistant to both copper and streptomycin shows that growers need to explore new methods to control Pseudomonas diseases.