Erwinia amylovora causing fire blight of pear in the Guilan province of Iran

Fire blight, caused by Erwinia amylovora, is one of the important bacterial diseases of pear trees. It causes blight of different organs of the tree (blossoms, shoots, leaves, fruits, and limbs) and production of exudates. During a survey of pear orchards in different areas of the Iranian province of Guilan (Astaneh, Ashrafieh, Lahijan, and Kiashahr) necrotic shoots and exudates were observed in apple and pear trees. Samples taken from infected tissues were crushed in peptone water and aliquots of 100 mu l of the extract were cultured on nutrient agar (NA) and LB containing cycloheximide (50 mu g ml(-1)). A rod-shaped, gram negative, facultative anaerobic bacterium was consistently isolated, which produced levan in sucrose media but not fluorescent pigment in King's B medium. All isolates induced hypersensitive reaction (HR) in tobacco and geranium leaves, were oxidase, nitrate, urease, and indole negative, could not rot potato tuber slices, produced H2S, and grew at 36 degrees C. The isolates could utilize citrate, arabinose, sorbitol, galactose, and trehalose as carbon source and their gelatin test was positive. Based on morphological, biochemical and physiological characters, and PCR amplification with specific primers, most bacterial isolates were identified as E. amylovora. Some isolates from spear orchards were identified as Pseudomonas syringae pv. syringae. This is the first report of the occurrence of E. amylovora on pear trees in the province of Guilan.