Pseudomonas syringae is a member of the Gammaproteobacteria and comprises strains isolated from dozens of cultivated, ornamental, and wild plants. According to the current taxonomy, isolates are grouped into 50 pathovars based on the plant host from which they were isolated. The diseases that P. syringae strains cause range from foliar spot diseases to blights, stripes, and cankers. Bacteria are transmitted mainly by rain and wind, can survive for periods of time on leaf surfaces as epiphytes without causing disease, and thenenter leaves either through natural openings like stomata or through wounds and finally reach high population densities in the intercellular plant spaces and cause visible disease symptoms. Recently, P. syringae isolates have been found in clouds, rain, snow, and river epilithion, suggesting that these environments are important inoculum sources. The P. syringae complex can be defined as oxidase-and arginine dihydrolase-negative fluorescent pseudomonads which induce a hypersensitive reaction in tobacco plants. A collection of Pseudomonas syringae isolates was established between 2008 and 2010 from diseased organs sampled from 15 almond, plum, apricot, peach, sour and sweet cherry orchards in Khorasan razavi. The 216 isolates were selected to be investigate in this study. The phytotoxin, siderophore and classical microbiology tests, as well as the genetical methods REP-, ERIC- and BOX-PCR, enabled identification to be made of 189 isolates as P. syringae pv. syringae (Pss) and 27 isolates as unclassified P. syringae. The rep- PCR methods, particularly BOX-PCR, proved that all strains are P. syringae pv. syringae and there was no P. syringae pv. morspronurum among isolates. Combined genetic results confirmed high diversity in the pv. syringae. In the pv. syringae, homogeneous genetic groups conconsistently found on the same hosts (almond and apricot, cherries, plum and peach) were observed. Pathogenicity on host was sometimes variable among Pss isolates from the same genetic group. In the BOX analyses, many TLP-producing Pss isolates nonpathogenic to host and the TLP-non-producing Pss isolates were classified differently. Pseudomonas syringae isolates that differed from known fruit pathogens were observed in almond, sour cherry and apricot orchards in Mashhad.

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