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First Report of Copper-Tolerant Pseudomonas syringae pv. tomato in Virginia

Bacterial speck of tomato, caused by Pseudomonas syringae pv. tomato, is an important disease of fresh-market tomatoes along the Eastern Shore of Virginia. P. syringae pv. tomato was first identified in Northampton County on 17 May 1993, using the Biolog software program. During the spring of 1998, a field of tomato plants showed symptoms of bacterial speck. Three isolations on tryptic soy agar were made from symptomatic leaves and fruit tissues taken from young transplanted tomato plants, cv. Sunpride. The isolates were identified as P. syringae pv. tomato, using Biolog. A representative isolate was sent to the Pennsylvania Department of Agriculture, Plant Disease Diagnostic Laboratory, Harrisburg, for confirmation. The Virginia isolate was transferred to King's medium B, and identification of P. syringae pv. tomato was confirmed by fulfilling Koch's postulates, matching with the Biolog database, and testing for levan production (+), oxidase reaction (-), potato soft rot (-), arginine dihydrolase production (-), and tobacco hypersensitivity (+). In vitro growth inhibition of the 1998 Virginia P. syringae pv. tomato isolate required anhydrous cupric sulfate at 368 μg/ml compared with only 175 μg/ml for a known copper-sensitive 1998 Pennsylvania isolate. Therefore, the 1998 Virginia isolate was considered a copper-tolerant strain of P. syringae pv. tomato. For field evaluation, three copper treatments and two noncopper treatments were established in a randomized complete block design replicated four times. Treatments were initiated on 19 May and reapplied every 7 days for a total of 10 applications. Three disease ratings were taken every 7 days beginning on 30 June. For copper hydroxide (2.24 kg/ha; Kocide DF) plus mancozeb (2.24 kg/ha; Dithane); chlorothalonil (2.34 liters/ha; Bravo) plus copper salts of fatty and rosin acids (2.34 liters/ha; Tenncop); 2% maneb plus 66% copper sulfate (6.72 kg/ha; Cuprofix); and an untreated control, area under the disease progress curve (AUDPC) values were 319, 468, 478, and 438, respectively. There was no significant difference (P = 0.05) between the copper treatments and untreated control, confirming laboratory findings. In contrast, noncopper treatments of acibenzolar (21g/ha; Actigard), and acibenzolar (21 g/ha) plus mancozeb (2.24 kg/ha) (Actigard plus Dithane) were significantly different (P = 0.05) from the untreated control and copper treatments with AUDPC values of 116 and 160, respectively. This is the first report of copper-tolerant P. syringae pv. tomato in Virginia.