Evaluation of plant growth promoting characteristics of some Rhizobia isolated from soils of Iran

Plant Growth Promoting Rhizobacteria (PGPR) is referred to a heterogeneous group of beneficial rhizosphere bacteria that could enhance plant yield through one or more mechanisms. In this study, some of Plant Growth Promoting Characteristics such as solubilizing of insoluble inorganic phosphate, ability to production of ACC-deaminase enzyme and auxin were evaluated in 60 Rhizobia (belonged to the species Rhizobium leguminosarum biovar phaseoli, Rhizobium leguminosarum biovar viciae and Sinorhizobium meliloti) selected from Gene Bank, Department of Soil Science, Tehran University. Results showed that all isolates have the ability to produce auxin, ranging from 0.45 to 10.86 mg/l averaged by 2.76. Also, 25 isolates (41.6%) showed the ability to produce ACCtransaminase. The results of evaluation of solubilizing of insoluble inorganic phosphate in sperber solid media revealed 73% of strains was able to phosphate solubilizing and the ratio of halo diameter to colony diameter was ranging from 1.05 to 2.07 in 12 day after incubation. Also, in sperber liquid media the amounts were between 3.2-158.6 mg/l after 120h of incubation. There was a significant negative correlation (r= -0.906**) between solubilized Phosphorus and the final pH of the growth medium. In this study, isolates belonged to the species Sinorhizobium meliloti in all characteristics were powerful than the other isolates. So, it is suggested to select and prepare the inoculum superior isolates belonging to this species and to evaluate their effects for the promotion of quality yield of different agricultural crops, as a biologic alternative and environmental friendly.