First Record of Bacterial Blight Caused by Pseudomonas syringae pv. syringae on Pyracantha coccinea and an Amelanchier sp. in Bulgaria.

During the spring and summer months of 2004 and 2005, sporadic damage on individual shrubs of Pyracantha coccinea and an Amelanchier sp. were observed at two locations in the region of Plovdiv, Bulgaria. Symptoms initially were expressed as blossom blight and subsequently expanded to the shoots and branches, forming cankers on the supplying wood. In both years, a fluorescent gram-negative bacterium was isolated from diseased tissues onto King's B medium. The bacterial strains were levan positive and oxidase and arginine dihydrolase negative. They were able to induce a typical hypersensitive response on tobacco plants (cv. Samsun), but failed to rot potato slices. Pathogenicity of the strains was confirmed by puncture-inoculating detached shoots from both hosts and immature cherry and pear fruits with a bacterial suspension (10⁸ CFU/ml, 50 μl per wound, and 3 replicates). Controls were punctured with sterile water. The inoculated plant material was maintained at room temperature (22 to 25°C) in plastic pots and covered with polyethylene bags for the first 48 h after inoculation. The inoculated and control subjects were kept under the same conditions as before inoculation. Except for the controls, slowly expanding but well defined necrotic lesions around the inoculation points were observed within the next 5 to 7 days. Bacteria reisolated from symptomatic tissue were identical to the initial cultures. On the basis of the symptoms and results from all laboratory tests, the bacterium was considered to be Pseudomonas syringae pv. syringae (1). PCR amplification of the 752-bp syrB fragment (2) confirmed the identification. To our knowledge, this is the first occurrence of P. syringae pv. syringae on Pyracantha coccinea and an Amelanchier sp. in Bulgaria, and most probably, this pathogen will play a more significant role within the rosaceous group because of a rising number of the cultivated ornamental species. References: (1) N. W. Schaad et al., eds. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2001. (2) K. N. Sorensen et al. Appl. Environ. Microbiol. 64:226, 1998.