In May 2018, blossom necrosis on pear (Pyrus communis L.) was found in pear trees in several orchards of Hamadan province in Iran. UnlikeErwinia amylovora that causes flower necrosis, immature fruit rot, shoot recurvature, profuse bacterial ooze and cankers on pome fruit, the symptoms were observedonlyonblossomsof pear trees and did not progress to other parts of the trees. Fireblight caused byE. amylovorawas not found at the same time in this region. Nine bacterial isolates were obtained on nutrient agar (NA) from infected blossoms that were surface-disinfected in 70% ethanol for 30 s. The isolates were Gram-negative, facultatively anaerobic, formed levan from sucrose, and oxidase, urease, arginine dihydrolase and nitrate reduction negative, and catalase positive. They caused hypersensitivity reaction on gera-nium. They produced acid from arabinose, and raffinose, but not from D-arabitol. Isolates were deposited in the Culture Collection of the Bu-Ali Sina University of Iran with the following numbers: YMAP1, YMAP2, YMAP3, YMAP4, YMAP5, YMAP6, YMAP7, YMAP8, and YMAP9. DNA was extracted from a representative iso-late (YMAP7) by the alkali lysis method and the 16S rRNA and atpDregions were partially sequenced using fD1/rP2, and ATP D 01-F/ATP D 02-R primers, respectively (Moradi Amirabad and Khodakaramian 2017). Sequences were aligned and compared with those deposited in GenBank. Sequences of the 16S rRNA (ac-cession No. MK990155), andatpD(MK994523) of iso-late YMAP7 showed 100% identity with those of refer-ence strain E. piriflorinigransCFBP 5882. In order to confirm Koch’s postulates, artificial inoculations were carried out with the representative strains (YMAP1, YMAP7, and YMAP9) on immature pear fruits, detached pear shoots, and detached pear blossoms as described by Roselló et al. (2006), but necrosis symptoms were reproduced only on pear blossoms in pear. The same bacterial strains were reisolated from artificially infected blossoms as confirmed by phenotypic
