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Streptomycin Resistance of Pseudomonas syringae pv. papulans in Apple Orchards and Its Association with a Conjugative Plasmid. Thomas J. Burr, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456-0462; John L. Norelli(2), Barbara Katz(3), Wayne F. Wilcox(4), and Stephen A. Hoying(5). (2)(3)(4)Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456-0462; (5)Cornell Cooperative Extension, P.O. Box 217, Alton, NY 14413. Phytopathology 78:410-413. Accepted for publication 1 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-410.

Pseudomonas syringae pv. papulans strains resistant to streptomycin were isolated from blister spot lesions in 10 of 22 western New York apple orchards. The growth of a streptomycin-sensitive strain was inhibited by 2.5 μg of streptomycin per milliliter of culture medium. Resistant strains grew on medium containing 100 μg/ml but not on medium containing 250 μg/ml. There was a significant association between the number of streptomycin sprays applied in orchards in 1985 and the detection of streptomycin-resistant strains of P. s. pv. papulans. Streptomycin-resistant strains were isolated from dormant buds and from fruit lesions the year after initial detection of resistance. A 68-megadalton (MDa) plasmid was present in streptomycin-resistant field strains of P. s. pv. papulans but was not observed in streptomycin-sensitive field strains. Streptomycin resistance was transferred from streptomycin-resistant donor strains Psp 34 and Psp 36 to streptomycin-sensitive recipient strains after matings on nitrocellulose membranes at frequencies of 4.7 x 10-3 and 2.0 x 10-2 per recipient cell, respectively. Transconjugants contained the plasmids of recipient strains plus the 68-MDa plasmid of the donor strain. The 68-MDa plasmid of Psp 36 was designated pCPP501. Transfer of streptomycin resistance from donor strain Psp 33 occurred at the much lower frequency of 2.0 10-6 per recipient cell and resulted in more complex changes in the plasmid content of transconjugants.

Additional keywords: blister spot.