Potential use of Iranian rhizobial strains as plant growth-promoting rhizobacteria (PGPR) and effects of selected strains on growth characteristics of wheat, corn and alfalfa

Abstract Many agricultural researches have been performed to improve soil productivity. Nitrogen (N) and Phosphorus (P) are essential elements which are utilized by the plants in large amounts. Phosphorus can be provided by applying chemical fertilizers. Microorganisms convert insoluble phosphate to the soluble form and some bacteria such as rhizobacteria play an important role in this process. This research was designed to determine the plant growth promoting (PGP) abilities, especially phosphate solubilization, of different isolates of indigenous rhizobia and their effect on growth characteristics of wheat, corn and alfalfa. 446 isolates belonging to different species of rhizobia were examined regarding inorganic and organic P solubilization, siderophore, auxin (IAA and homologes), 1-aminocyclopropane-1-carboxylate (ACC) - deaminase and hydrogen cyanide (HCN) production. It was found that 7% of the strains could produce HCN, 86% siderophores and 74% IAA and 44% were able to solubilize phosphorus. 8 rhizobial isolates were found as superior plant growth promoting rhizobacterial (PGPR) strains. Green house experiments using these strains evaluated the promoting effects of different strains on legume (alfalfa) and non-legume (wheat and corn) plants. Total biomass to the above mentioned plants was determined and the amount of N, P and iron (Fe) in shoots were also measured. The results were analyzed by the RCBD contrast method using SAS software V6.12. In conclusion, the green house experiment showed that P1B2 and a mixture of 4 plant growth stimulating rhizobacterial strains are the best suited as growth promoting inoculants.