First Report of Black Rot on Arugula Caused by Xanthomonas campestris pv. campestris in Argentina.

During the fall of 2005, arugula (Eruca sativa Mill.) plants grown in experimental field plots in Buenos Aires, Argentina presented V-shaped necrotic lesions on leaf margins and blackened veins with broad yellow halos, followed by leaf necrosis. At flowering, 96% of the plants were affected with 27% of the leaves with symptoms. Yellow, round, mucoid, convex, bacterial colonies were isolated from several leaves on yeast dextrose chalk agar. Two strains were further studied. Xanthomonas campestris pv. campestris Xcc8004 was used as a control. Strains were gram negative, rod shaped, strictly aerobic, catalase-positive, oxidase and urease-negative, hydrolyzed starch, gelatine and aesculin, and did not reduce nitrate (2). Pathogenicity was tested by spraying 10 3-week-old arugula plants with either a bacterial suspension (10 CFU/ml) or sterile water. Plants were placed in plastic bags for 72 h after inoculation. All inoculated plants showed necrotic lesions enlarging from the margin of the leaves 7 days after inoculation. No lesions were observed on control plants. On the basis of biochemical characterization (2) and genomic fingerprints generated by BOX-PCR (1), the pathogen was identified as X. campestris pv. campestris. To our knowledge, this is the first report of X. campestris pv. campestris causing black rot on arugula in Argentina. References: (1) J. L. Rademaker et al. Int. J. Syst. Evol. Microbiol. 50:665, 2000. (2) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2001.