This study aims to characterize plant growth-promoting rhizobacteria (PGPR) in sunflowers growing in different locations at North West of Iran.Materials and methods: Sunflower plants were collected from different regions of West Azarbaijan, and rhizospheric bacterial strains were isolated and screened for PGP traits. Identification and characterization of the PGPR were conducted based on 16s rDNA sequences and phenotypic analysis, the strains clustered for genetic diversity by rep-PCR method.Results:Among the 80 bacterial isolates, 20 showed PGP traits and were selected for other potentials. All the selected isolates produced indole-3-acetic acid at the rate of 9.2–33.7 mg/ml. In addition, 13, 15, 12, and 16 were positive for phosphate solubilization, siderephore, hydrogen cyanide, and ammonia production, respectively. The results from a subsequent pot experiment indicated that PGPRs distinctly increased sunflower shoot and root length, shoot and root fresh weight, as well as shoot and root dry weight. Based on 16S rDNA sequences and biochemical and physiological characteristics, 20 PGPRs were identified as Pseudomonasfluorescens (five isolates), Pseudomonas aeruginosa(four isolates), Pseudomonas geniculata(one isolate), Bacillus subtilis(four isolates),Bacillus pumilus(two isolates),Stenotrophomonas maltophilia(two isolates), andBrevibacterium frigoritolerans(two isolates). In rep-PCR, PGPR isolates were differentiated into seven clusters (A–G) at 65% similarity level. These results demonstrated the existence of a considerable species richness and genetic diversity among PGPRs isolated from different regions of North West of Iran.Conclusions:To the best of our knowledge, this is first report for the identification and characterization ofB. frigoritoleransas PGPR in sunflower plants.
