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A total of twenty seven bacterial strains were isolated from cankerous tissues of apricot, nectarine, peach, plum, sour cherry and sweet cherry trees in Tehran province and identified as Pseudomonas syringae pv. syringae (Pss), the causal agent of the bacterial canker disease, on the basis of LOPAT (levan production, oxidase test, potato rot, arginine dihydrolase and tobacco hypersensitive reaction) and GATTa's (gelatin liquefaction, aesculin hydrolysis, tyrosinase activity and Na-tartrate utilization) group tests. Pss strains showed slight differences in morphology, phenotypic (biochemical and physiological) characteristics, serological properties, plasmid DNA and cellular protein profiles and antibiogram. They were divided into three distinct groups based on hippurate and formate utilization which was correlated with protein profile in SDS-PAGE (sodium dodecyl sulfatepolyacrylamide gel electrophoresis). The virulence of Pss was significantly associated with the degree of necrosis on immature sweet cherry fruits and the rate of in vitro syringomycin production.