Potato bacterial wilt caused by Ralstonia solanacearum is one of the predominant diseases encountered worldwide. It has been determined that both biovars 2A and 2T, race 3 of R. solanacearum is the causal agent of bacterial wilt in Iran . Despite distribution of Biovar 2A in main potato growing areas, Biovar 2T is limited to Khuzestan province with warm climate. Therefore, a better characterization of their ecological and pathological behaviors would facilitate to manage their control. For this purpose, 15 Iranian strains of biovar 2 race 3 of R. solanacearum consisted of eight biovar 2A isolated from Isfahan and 7 biovar 2T isolated from Khuzestan, were subjected to compare in detail for morphological, molecular, biochemical characteristics and pathogenicity circumstances under different climatic conditions. All strains of biovar 2A were developed in TZC medium with irregular, highly fluidal, creamy-white with pink center colonies and produced melanin pigments in the culture, while colonies of strains 2T were small, less fluidal, round-shaped, containing deep red color with a thin white margin without melanin production The strains conformed closely to the established set of biochemical and physiological tests for biotype 2 of R. solanacearum . Strains belong to biovar 2T utilized ribose and tryptophane, while 2A strains did not use these compounds. In PCR reactions with specific primers sets PS759f/760r and RS1F/R, all of the strains yielded characteristic products . PCR-RFLP analysis of these products with Alu I, Rsa I and Taq I endonucleases resulted fragments with similar sizes among the strains supporting further their identity as R. solanacearum. Comparative analysis of the strains based on BOX-IR and ERIC-PCR fingerprinting separated strains biovar 2A and biovars 2T into two distinct subgroups which was compatible with their morphological and biochemical characterization results. Infiltration of bacterial suspensions of biovar 2T strains in tobacco leaves, induced a rapid localized necrotic response (within 24 to 48 h) characteristic of the hypersensitive response (HR), while strains biovar 2A elicited a yellowish discoloration and weaker necrosis at the same time. To evaluate the pathogenicity of strains, two isolates representing biovars 2A and 2T were inoculated in six potato cultivars (Agria, Arinda, Marfona, Labida, Ramus and Sante), tomato, eggplant and petunia plants at the third internode from the apex. After inoculation, the pots were arranged in a randomized complete design and then potato plants placed in two different cold (31-25°C) and warm (39-45°C) greenhouse conditions. The aggressiveness of strains was evaluated by appearance of wilting
