Activity screening of plant growth promoting rhizobacteria isolated from alfalfa rhizosphere

Introduction: Some rhizobacteria by various mechanisms influence plant growth as they are called plant growth promoting rhizobacteria (PGPR). Scientists identified some PGPR characters involved in promoting plant growth, while all these characters are not able to study. The aim of this study was to evaluate PGP activities of bacterial isolates, (45 isolates belonged to rhizobium and 2 bacterial isolates belonged to Pseudomonas fluorescens), which were isolated from alfalfa (Medicago sativa) rhizosphere and root nodules grown around Zanjan. Materials and methods: These bacteria were isolated from alfalfa roots grown around Zinc industries in Zanjan province. After bacterial isolation and purification from root and soil samples, isolates were screened in vitro for plant growth promoting traits such as IAA (Indole Acetic Acid), ACC- deaminase (Amino Cyclopropan Carboxylate), HCN (Hydrogen Cyanide), siderophore, chitinase production and mineral and organic phosphate solubilization activities. Results: The results indicated that 43 bacterial isolates produced IAA (4.04- 4.95 μg/ml) and 15 isolates produced ACC- deaminase (0.23- 1.05 μg/ml). Only one isolate (Rm66) produced high amount of HCN. Qualitative siderophore production was observed in 9 isolates. None of the isolates produced chitinase. Solubilization of mineral phosphate was commonly detected in 19 isolates (4.33- 5.86 μg/ml), and 15 isolates solubilized organic phosphate (1.66- 144.28 μg/ml). Discussion and conclusion: This study shows that most of the bacterial strains which isolated from alfalfa cultivated lands had PGP activities and also a good potential to increase plant growth after inoculation with to seeds as eco- friendly fertilizers.