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چکیده
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Pear (Pyrus L.) is one of the most widely grown crops in western Iran. Since 2010 an outbreak of a disease with symptoms similar to fire blight has been observed on pear trees in various locations of Kurdistan province. Initial flower symptoms include water-soaking, and rapidly shriveling, infected flowers which remained hanging on the trees. Immature fruits become water-soaked, turn brown and shrivel. Infected flowers and immature fruits were collected from different locations in the province. Small pieces (about one mm2) were excised from infected tissues, surface sterilized with 0.5% sodium hypochlorite solution followed by rinsing in sterile-distilled water (SDW). Each piece was macerated in 2-3 ml SDW, streaked onto nutrient agar sucrose or Eosin methylene blue agar media, and incubated at 27 to 29°C. After 48-72 h, single colonies were subcultured onto the same media and stored at 4ºC. In total, 74 bacteria were isolated from infected tissues. All isolates were gram-negative and rod-shaped. Based on other phenotypic properties, strains were grouped into three clusters at a similarity level of 65% (data not shown). Forty-one and 23 strains showed properties as expected for E. amylovora and Enterobacter sp., respectively. Other strains showed properties resembling Pantoea agglomerans. All strains identified as E. amylovora produced an expected DNA fragment of about 900 bp by PCR using primers PE29A and PE29B corresponding to plasmid pEA29 (1). The result was confirmed by using primers AMSbL and AMSbR derived from the ams region required for amylovoran synthesis of E. amylovora. E. amylovora strains produced an expected 1600 bp fragment (2). For the pathogenicity test a bacterial suspension was adjusted to approximately 1 × 107 CFU/ml from cell cultures grown in nutrient broth at 27°C for 48 h. Immature pear fruits sterilized with 70% ethanol and rinsed with SDW were injected with the bacterial suspension using a 25-gauge sterile needle. Fruits injected with ster
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