Common bacterial blight has become more prevalent in many bean-growing areas of Iran . To gain insight into the nature of these outbreaks, it is essential to understand the pathogenic variation and genetic diversity among strains of the disease causal agent, Xanthomonas axonopodis pv. phaseoli (Xap) dispread across the country. For this reason, strains of Xap isolated from beans growing sites in Lorestan, Markazi, Isfahan , Charmahal –Bakhteyari and Zanjan provinces were initially characterized according to their colony morphology, biochemical and serological properties. The isolates those were confirmed as Xap were further characterized by polymerase chain reaction (PCR) using species specific primer pair X4c/X4e which leads to the amplification of a ~730 bp DNA fragment. The generated fragment from different strains was digested with restriction endonuclease Rsa I, Taq I, Hae III and Sau 96I. In this PCR-RFLP assay, Identical DNA patterns produced by strains originating from different locations confirmed their homogeneity. With exception of Xapf isolate, the specific primer pair Xf 1 / Xf 2 , did not amplify any fragment from Xap isolates. A PCR-based fingerprinting method with markers BOX-PCR and ERIC-PCR (rep-PCR method) primers were used for genotypic characterization of Xap isolates and reference strains Xcpf. Based upon data from rep-PCR analysis, the polymorphism rate among Xap isolates was determined 15.79% and 19% for BOX-PCR and ERIC markers, respectively. Genetic similarity between Xapf and Xap isolates was in a range 38% through 46%. The rep-PCR fingerprinting readily distinguished Xapf isolate from those of Xap isolates, however despite a limited genomic differences among isolates, the overall level of polymorphism within Xap isolates collected from different locations in Iran was low, confirming their close relationship. In order to investigate pathogenicity variation and tobacco hypersensitivity reaction among the isolates, suspension of Xap and Xapf strains were inoculated on pinto bean cv. CFO 6 and tobacco ( Nicotiana tobacum cv. samsun ). Based on evaluating of pathogenicity severity and hypersensitivity reaction, the isolates grouped as virulent and moderately virulent. However, the data did not reveal a relationship between genetic diversity and virulence differences of isolates. Since Pathogenicity of strains can be an important param
