Detection of Streptomycin-Resistant Pseudomonas syringae pv. papulans in Michigan Apple Orchards. A. L. Jones, Department of Botany and Plant Pathology and Pesticide Research Center, Michigan State University, East Lansing 48824-1312. J. L. Norelli, and G. R. Ehret. Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456-0462, and Department of Botany and Plant Pathology, Michigan State University, East Lansing 48824-1312. Plant Dis. 75:529-531. Accepted for publication 3 December 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0529.

Streptomycin-resistant Pseudomonas syringae pv. papulans was recovered from blister spot lesions on fruit of the cultivar Mutsu collected from 12 of 17 apple (Malus domestica) orchards in Michigan in 1989. Resistant, but not sensitive, bacteria grew on King’s medium B amended with 100 µg of streptomycin·ml^–1. A 500-base pair DNA probe (SMP3) that is specific for the streptomycin-resistance gene in strain Psp36 of P. s. papulans hybridized with 238 of 275 streptomycin-resistant, but none of 122 streptomycin-sensitive, strains of P. s. papulans from Michigan orchards. Hybridization occurred with plasmids of several different sizes and not solely with the 108-kb plasmid associated with streptomycin resistance in New York State. DNA from resistant strains isolated from one orchard did not hybridize with the probe, indicating that these strains contain a resistance system unrelated to that in strain Psp36.