Characterization of potential plant growth-promoting rhizobacteria isolated from sunflower (Helianthus annuus L.) in Iran.

PURPOSE

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 sun flower 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 Pseudomonas fluorescens (five isolates), Pseudomonas aeruginosa (four isolates), Pseudomonas geniculata (one isolate), Bacillus subtilis (four isolates), Bacillus pumilus (two isolates), Stenotrophomonas maltophilia (two isolates), and Brevibacterium 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 of B. frigoritolerans as PGPR in sunflower plants.