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Streptomycin Resistance and Copper Tolerance Among Strains of Pseudomonas cichorii in Celery Seedbeds. KEN POHRONEZNY, University of Florida, IFAS, Everglades Research and Education Center, Belle Glade 33430. MARK L. SOMMERFELD, A. Duda & Sons, Belle Glade; and RICHARD N. RAID, IFAS, Everglades Research and Education Center, Belle Glade. Plant Dis. 78:150-153. Accepted for publication 15 October 1993. Copyight 1994 The American Phytopathological Society. DOI: 10.1094/PD-78-0150.

Strains of Pseudomonas cichorii were isolated from celery plants exhibiting symptoms of bacterial blight at four seedbed sites in Florida. In 1991, 70% of 87 isolated strains were resistant to 200 ?g/ml of streptomycin in vitro. In 1992, 32% of 106 strains were streptomycin-resistant. Most of the reduction in streptomycin resistance in 1992 was accounted for by a reversal from 100% to 0% resistance among strains collected from one seedbed site. Strains were also assayed for tolerance to 0.64 mM CuSO4. In 1991, 32% of the strains were classified as sensitive (growth 0-30% of that on controls), 44% as moderately tolerant (growth >30 to <60% of that on controls), and 25% as highly tolerant (growth > 60% of that on controls). In 1992, 36% were sensitive, 27% were moderately tolerant, and 37% were highly tolerant. When exposed to 1.2 g/L of a commercial copper hydroxide bactericide for 4 hr in the laboratory, populations of tolerant strains were reduced from 108 to only 106 cfu/ml. In contrast, populations of sensitive strains were typically less than 100 cfu/ml. Strains identified as copper-tolerant became more sensitive as cryogenic storage time increased. After 10 mo of storage, 103-104 cells survived exposure to copper hydroxide. Phenotypic expression of copper tolerance (107 cfu/ml) could be retrieved by growing cultures from cryogenic storage on media containing a sublethal dose of copper (0.32 mM CuSO4).