An outbreak of bacterial leaf spot disease, caused by Xanthomonas axonopodis pv. Vitians, on lettuce in the mediterranean region of turkey

In the winter of 2002, lettuce plants (Lactuca sativa cv. Tasna, cv. Arapsaci, and cv. Yedikule) from different commercial fields near Adana, Eastern Mediterranean Region of Turkey, had symptoms similar to those caused by Xanthomonas axonopodis pv. vitians (Xav) (Brown) Dye. Leaves of the infected plants were water-soaked, black and with angular lesions. When the lesions coalesced, defoliation of older leaves and large necrotic areas were observed. Nearly all plants in a 100 decares-field were infected. Disease incidence was approximately 100%. The dead area was papery in texture. Heavily affected lettuce plants were unmarketable. Bacteria consistently isolated from leaf spots formed mucoid and yellow colored colonies on yeast dextrose calcium carbonate agar (YDC). Eleven bacterial strains were purified and used for further studies. The strains were gram negative, oxidase negative and catalase positive. Fatty acid analysis identified the strains as Xav with similarity indices of 71 to 89 %. A reference strain of Xav (LMG 938) and all test strains reacted positively with Xanthomonas-specific monoclonal antibodies X1, X11, Xv 5, 6, 8 and 10, but not with MAbs Xv1, 15, 21, 30 in indirect enzyme-linked immunosorbent assays. Pathogenicity of the strains was confirmed on 4 week-old lettuce plants (cv. Yedikule) by spray inoculating with 108 cfu/ml suspension of bacteria. Saline was used as negative controls. Inoculated plants and water-sprayed controls were covered with polyethylene bags for 24 hours in a climate room at 25oC, 70% relative humidity and 16-hour per day light period. Bags were removed and plants maintained in the climate room to observe symptoms. Bacterial leaf spots developed on inoculated plants in seven days, and leaf lesions similar to those observed in the fields. No symptoms developed on negative control plants. The bacterium was re-isolated from the inoculated plants and characterized as identical to the reference strain. This is the first report of the observation of Xav in the Mediterranean region of Turkey