Cruciferous Weeds as Sources of Inoculum ofXanthomonas campestrisin Black Rot of Crucifers

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Abstract
Cruciferous weeds were studied as a potential source of inoculum of X. campestris, the causal agent of black rot of crucifers. Four transplant farms in southern Georgia [USA] and 19 sites in the seed production areas of California [USA] were surveyed; cruciferous weeds were widespread in both states. In Georgia, black rot was found on Brassica campestris, Lepidium virginicum, Coronopus didymus and Raphanus sativus. In California, black rot was found on B. campestris, B. nigra, B. geniculata, R. sativus and Cardaria pubescens. Three of the 7 sites in California where black rot was found in weeds were associated with a cultivated crop of crucifers. Field plot data in Georgia showed that X. campestris was dissseminated up to 12 m from infected weeds to cabbage. These results may explain the unusually high levels of black rot found in transplant and seed fields in the last 10 yr. More attention should be paid to controlling cruciferous weeds in transplant and seed production fields.