Occurrence of black rot caused by Xanthomonas campestris pv. campestris on ornamental kale in Italy

In March 2000, V-shaped yellow lesions were observed at the leaf margins of ornamental kale (Brassica oleracea subsp. acephala) grown as borders in public gardens in Perugia (Italy). The lesions, only found on basal leaves, sometimes reached the main leaf vein, and the veins in the lesions appeared black. From diseased leaves we consistently isolated smooth, yellow, raised bacterial colonies on nutrient agar. For pathogenicity tests, ornamental kale plants (cv. Sekito) were watercongested by placing them in clear polyethylene bags 12h before inoculation, then airbrush sprayed with bacterial suspensions of six isolates (108 cfu ml-1) and kept in a greenhouse at 18-25°C, at 50-75% relative humidity, with natural lighting. The plants were covered with polyethylene bags for the first 24 h. About 10 days after the inoculation, typical symptoms resembling the natural ones were observed. The bacterium was consistently re-isolated from these plants. All the bacterial isolates were gram-negative, aerobic, catalase-positive, and oxidase- and urease-negative. They hydrolyzed esculin, gelatin, casein and starch, grew at 35°C, produced acid from arabinose, glucose, and mannose and produced hydrogen sulfide from cysteine. Based on these biochemical, physiological, nutritional and pathogenicity tests, it was concluded that the bacterial isolates from ornamental kale belonged to Xanthomonas campestris pv. campestris (Pammel) Dowson. This appears to be the first report of black rot on ornamental kale, caused by X. campestris pv. campestris, in Italy. The disease was previously described in the U.S.A.