During spring 1999, lettuce (Lactuca sativa) plants grown at Oltu in the eastern Anatolia region of Turkey were observed with numerous lesions typical of bacterial leaf spot. Lesions on leaves were irregular, small, pale green to black, water-soaked, and 2 to 5 mm in diameter. Coalescing lesions sometimes caused defoliation of older leaves. Isolations made from diseased leaves on yeast dextrose carbonate agar yielded nearly pure cultures of a yellow pigmented bacterium typical of a xanthomonad. Five bacterial strains were purified and used for further tests. The strains reacted positively with a Xanthomonas-specific monoclonal antibody, X1, in indirect enzyme-linked immunosorbent assays (1). Fatty acid analysis identified the strains as X. campestris pv. vitians (proposed name X. axonopodis pv. vitians), with greatest similarity indices of 29 to 71% (2). Pathogenicity of strains was confirmed on 5-week-old lettuce plants (cv. Darkland) sprayed with bacterial suspensions containing 108 CFU/ml of sterile water. Inoculated and sterile water-sprayed control plants were covered with polyethylene bags for 48 h at 25°C, after which bags were removed and plants were maintained in the greenhouse. Water-soaked spots similar to those in the field were observed on inoculated plants within 5 to 7 days. No symptoms developed on control plants. The bacterium was reisolated from inoculated plants and identified as X. campestris pv. vitians. This is the first report of bacterial leaf spot of lettuce in Turkey.
References: (1) A. M. Alvarez et al. Phytopathology 84:1449, 1994. (2) Vauterin et al. Int. J. Syst. Bact. 45:472, 1995.
