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Disease Detection and Losses

Pectolytic Xanthomonads in Mixed Infections with Pseudomonas syringae pv. syringae, P. syringae pv. tomato, and Xanthomonas campestris pv. vesicatoria in Tomato and Pepper Transplants. R. D. Gitaitis, Associate professor, Department of Plant Pathology, University of Georgia, Coastal Plain Experiment Station, Tifton 31793; M. J. Sasser(2), R. W. Beaver(3), T. B. McInnes(4), and R. E. Stall(5). (2)Professor, Department of Plant Sciences, University of Delaware, Newark 19711; (3)Research coordinator II, Mycotoxin Analysis Research Center, Tifton, GA 31793; (4)Former graduate research assistant, Department of Plant Pathology, University of Georgia, Athens 30602; (5)Professor, Department of Plant Pathology, University of Florida, Gainesville 32611. Phytopathology 77:611-615. Accepted for publication 10 October 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-611.

Gram-negative, yellow, aerobic, cellulolytic, rod-shaped bacteria were originally isolated in mixed culture along with other phytopathogenic bacteria from tomato and pepper transplants, or in pure culture from pecan and weeds. Based on fatty acid composition, presence of xanthomonadin pigment, and standard bacteriological characteristics of the bacteria, the unknown strains were identified as xanthomonads. However, all strains differed from endemic strains of Xanthomonas campestris pv. vesicatoria because they typically displayed strong starch hydrolysis, pectolytic activity on crystal violet pectate medium and did not elicit a hypersensitive response in tobacco. When atomized onto tomato and pepper foliage, the pectolytic xanthomonads failed to induce disease; however, they produced restricted necrotic areas in association with wounds produced by the Carborundum-rub method of inoculation. In addition, soft-rot symptoms were induced in 82% of tomato fruits and 38% of pepper fruits when 20 μl of a dilute inoculum suspension (5 × 10³ cfu per milliliter) was placed in wounds. Approximately 20% of the test strains were lysed by bacteriophages that were originally developed for X. campestris pv. campestris. Fatty acid profiles of the pectolytic xanthomonads had a high similarity to known profiles of X. campestris pv. raphani. Except for two strains from pecan that caused black rot, the test strains only produced localized necrosis in association with wounds when inoculated onto cabbage and radish.