Typical symptoms of fire blight, caused by Erwinia amylovora, were observed in late June of 1998 on Crataegus monogyna Jacq. (hawthorn) and Pyrus pyraster Burgsd. (syn. P. caucasia, wild or thorny pear) in the region of Plovdiv. Symptoms observed on hawthorn were shepherd's-crook shoots, necrotic flowers and fruitlets, and dried amber ooze droplets. On thorny pear, only infected shoots were detected. Isolation on King's B medium (2 days, 26°C) resulted in the appearance of whitish, glistening, rounded colonies. Based on their cultural characteristics, positive hypersensitive response (HR) on tobacco leaves, successful laboratory inoculations of hosts' shoots and pear fruitlets, positive serological reaction (slide agglutination), and target-specific polymerase chain reaction (PCR; 23S rDNA), the isolates from both species were placed in the E. amylovora group. The bacterium has also been isolated by the first author from Cydonia oblonga, Pyrus communis, Mespilus germanica, and Malus sylvestris within the 5-year period of 1989-1993 (1). To our knowledge this is the first official report of fire blight on C. monogyna and P. pyraster in Bulgaria.
Reference: (1) S. G. Bobev. 1995. Pages 121--126 in: Jubilee Scientific Session, Higher Agricultural Institute of Plovdiv, vol. 3, bk. 1. (In Bulgarian.)