Sorbus sp. - New host of Erwinia amylovora in Serbia

Abstract

In 1989 Erwinia amylovora was confirmed to be a pathogen of pear and quince in Serbia. Subsequently, apple, firethorn, hawthorn, Mespilus spp., Cotoneaster horisontalis and Cheanomeles spp. were confirmed as hosts of the pathogen. During the summer 2005, fire blight symptoms were observed on Sorbus spp. for the first time in the south-eastern Serbia, near Nis. Disease symptoms included leaf and shoot blight and cankers with purple-brown colouration of necrotic tissue on mature branches. The diseased tissue was macerated and the suspension was streaked on nutrient sucrose agar (NAS) and King's medium B. Typical light grey, levan-positive colonies developed on NAS medium after two day incubation at 25°C. Colonies on King's medium B were white and nonfluorescent. The results of physiological and biochemical tests of the bacterium were as follows: gram negative, oxidative and fermentative metabolism of glucose; oxidase negative, gelatin hydrolysis positive, aesculin hydrolysis negative and acid produced from most carbon sources. In pathogenicity tests, all isolates induced HR in tobacco leaves and necrosis on artificially inoculated pear fruits followed by appearence of bacterial ooze. After inoculation of petioles and shoots of the host plant (Sorbus spp.) initial symptoms were dark green, watersoaked, eliptical spots on inoculated tissues. Leaf and shoot blight resembling the natural infection appeared five to six days after inoculation. The investigated strains reacted positively with antisera specific to E. amylovora in DASI ELISA test. Identity of isolated strains also was confirmed by polymerase chain reaction (PCR). According to the biochemical and physiological characteristics, pathogenicity tests, results of PCR analyses and ELISA test, strains isolated from Sorbus spp. plants were identified as E. amylovora. This is the first report of E. amylovora on Sorbus spp. plants in Serbia.