An Outbreak of Bacterial Spot of Lettuce in Florida Caused byXanthomonas campestrispv.vitians

A widespread and damaging outbreak of a leaf spot disease of lettuce occurred in the 1992-93 winter vegetable season in southern Florida. Individual leaf lesions were dark brown to black, water-soaked, and greasy in appearance. A yellow-pigmented bacterium was consistently isolated. All 1992-93 lettuce strains and reference strains produced symptoms in greenhouse test plants that were identical to those seen in the field. Disease reactions generally were more severe in cos and butterhead lettuce than in crisphead. Strains were gram-negative rods, and negative for glucose fermentation, nitrate reduction, urease production, and utilization of asparagine as a sole source of carbon and nitrogen. Aesculin was hydrolyzed, gelatin was liquefied, and proteolysis occurred in litmus milk. Cellular fatty acid profiles matched well to library database strains of Xanthomonas campestris pv. vitians.