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First Report of Fire Blight Disease on Blackberry in Turkey

During 2008 and 2009, a new disease on blackberry (Rubus fruticosus cv. Chester) causing leaf and shoot blight and cankers with brown discoloration of necrotic tissues on mature branches was observed in Isparta and Konya provinces of Turkey. Disease incidence was estimated to be 4% for the two years. Isolations were made from lesions on leaves and shoots on nutrient sucrose agar (NSA) medium. Bacteria consistently isolated from the diseased tissues were identified on the basis of biochemical, physiological (2), and molecular tests (1). Eleven representative bacterial strains were gram-negative, rod-shaped, mucoid, fermentative, yellow-orange on Miller and Scroth (MS) medium, positive for levan formation and acetoin production, no growth at 36°C, positive for gelatin hydrolysis, and negative for esculin hydrolysis, indole, urease, catalase, oxidase, arginine dehydrolase, reduction of nitrate, acid production from lactose, and inositol. Two reference strains of Erwinia amylovora (EaP28 and NCPPB 2791) obtained from the culture collection unit of Selcuk University were used as positive controls. All strains induced a hypersensitive response in tobacco (Nicotiana tobaccum cv White Burley) 24 h after inoculation with a 10⁸ CFU/ml bacterial suspension in water. All strains were identified as E. amylovora using the species-specific primers set A/B (1), which amplified a 1-kb DNA fragment in PCR, and fatty acid methyl ester (FAME) profiles determined by Sherlock Microbial Identification System software (TSBA 6 v. 6.00; Microbial ID, Newark, DE) with similarity indices ranging from of 79 to 99%. Pathogenicity was confirmed by injecting bacterial suspensions (10⁸ CFU/ml^–1) in sterile distilled water into the shoot tips of 2-year-old R. fruticosus cv. Chester and the first blighting symptoms were observed on leaves within 3 days and also 10 days later after inoculation on shoots. Sterile distilled water was used as a negative control. No symptoms were observed on control plants. All tests were repeated three times. The bacterium was reisolated from inoculated plants and identified as. E. amylovora. To our knowledge, this is the first report of E. amylovora on blackberry in Turkey. Phytosanitary measures are needed to prevent any further spread of the bacterium to new blackberry areas.

References: (1) S. Bereswill et al. App. Environ. Microbiol. 58:3522, 1992. (2) A. L. Jones and K. Geider. Lab. Guide for Identification of Plant Pathological Bacteria, 40, 2001.