Fire blight, caused by the bacterium Erwinia amylovora, is a serious disease of apples (Malus spp.) and pears (Pyrus spp.) but can also infect many ornamental species in the Rosaceae family. In the summers of 2009 and 2010, leaf and shoot blight and reddish colored cankers were observed on firethorn (Pyracantha coccinea) and brown discolored leaves and necrotic stem lesions on mountain ash (Sorbus sp.) both from the landscape areas of Konya province. Investigation of these symptoms showed that in an 85-ha area, disease incidence was estimated at 1.5% and 1% on firethorn and mountain ash, respectively. Bacteria were consistently isolated from both leaf and lesions onto nutrient sucrose agar medium. Nine representative bacterial colonies from firethorn isolations and six from mountain ash isolations purified and characterized as gram-negative, rod-shaped, mucoid, fermentative, yellow-orange on Miller & Scroth medium, positive for levan formation and acetoin production, no growth at 36°C, positive for gelatin and esculin hydrolysis, and negative for indole, urease, oxidase, arginine dehydrolase, reduction of nitrate, and acid production from lactose and inositol (2). Two reference strains of E. amylovora (EaP28 and NCPPB 2791) obtained from culture collection at Selcuk University, Department of Plant Protection, Konya, Turkey, were used as positive controls. All strains induced a hypersensitive response in tobacco (Nicotiana tobaccum cv. White Burley) and produced ooze when stab inoculated on immature pear fruits. In addition, all strains and the references were identified as E. amylovora on the basis of a 1-kb DNA fragment amplification with a species-specific primer set, A/B (1) in PCR. Pathogenicity tests were performed by injecting a bacterial suspension (108 CFU ml–1) into the shoot tips of 3-year-old firethorn and mountain ash seedlings, resulting in leaf and shoot blight symptoms observed 10 to 15 days after inoculation. No symptoms were observed on control plants treated with sterile water. E. amylovora was positively reisolated from leaf and shoot lesions from the inoculated seedlings and identified as described above. To our knowledge, this is the first report of E. amylovora on P. coccinea and Sorbus sp. in Turkey.
References: (1) S. Bereswill et al. Appl. Environ. Microbiol. 58:3522, 1992 (2) A. L. Jones and K. Geider. Page 40 in: Laboratory Guide for Identification of Plant Pathogenic Bacteria, 2001.