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Relationship of Incidence of Seedborne Xanthomonas campestris to Black Rot of Crucifers. N. W. Schaad, Associate Professor, Department of Plant Pathology, University of Georgia, Georgia Experiment Station, Experiment, GA 30212. W. R. Sitterly, Professor, Clemson University, Vegetable Truck Station, Charleston, SC 29407; and H. Humaydan, Research Plant Pathologist, Joseph Harris Seed Company, Rochester, NY 14624. Plant Dis. 64:91-92. Accepted for publication 21 March 1979. Copyright 1980 American Phytopathological Society. DOI: 10.1094/PD-64-91.

The relation of amounts of seedborne Xanthomonas campestris, determined by laboratory assays, to the incidence of black rot in the field was determined. Seeds infested naturally with X. campestris were mixed with healthy seeds, assayed for X. campestris, and seeded in a field in South Carolina. The pathogen was detected in laboratory assays in two of four samples with 0.01% infestation, whereas black rot developed in the field in three of four such samples. In 1976, field plots that initially contained 0.03, 0.07, and 0.14% infected plants resulted in high incidences of black rot. In 1977, the incidences of black rot were high in plots that initially contained 0.05% infected plants but not in plots that initially contained 0.01% infected plants. We conclude that laboratory assays can be used to detect levels of seed infestation that may or may not result in a high incidence of black rot in the field.