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Bacterial Leaf Spot Diseases of Leafy Crucifers in Oklahoma Caused by Pathovars of Xanthomonas campestris

Fields of kale, spinach mustard, and turnip were severely damaged by bacterial leaf spots during 1994 to 1996. Symptoms included circular to angular necrotic lesions with yellow halos and water-soaking on the abaxial leaf surface. Yellow, mucoid strains isolated from leaf spots were identified as Xanthomonas campestris using Biolog. Four strains caused black lesions on stems of cabbage seedlings in an excised cotyledon assay, leaf spots and sunken dark lesions on petioles of spray-inoculated crucifers, and leaf spots on spray-inoculated tomato. These strains were classified as X. campestris pv. armoraciae. Most other strains from leafy crucifers and all strains from a cabbage field caused black rot in the cotyledon assay and in spray-inoculations. Many of these strains also caused leaf spots on collard and kale but not stem and petiole lesions. The strains causing black rot were classified as X. campestris pv. campestris. Cluster analysis of Biolog profiles yielded a small group that contained local strains of both pathovars, and a large group comprised of reference and local strains of each pathovar, and some local, nonpathogenic strains. Five fingerprint groups were identified by rep-polymerase chain reaction using the BOXA1R primer. Local and reference strains of each pathovar occurred in two of the groups. Two pathovars of X. campestris are involved in the leaf spot diseases. Both pathovars were recovered within several fields, and also were recovered along with Pseudomonas syringae pv. maculicola. This is the first report of Xanthomonas leaf spot caused by X. campestris pv. armoraciae in Oklahoma.