The aim of this investigation was introducing native alfalfa growth promoting bacteria that have the ability to simultaneous mitigation of imazethapyr stress and stimulation of plant growth. In the first study the native rhizospheric bacteria were isolated from alfalfa field and screened based on their ability in terms of nitrogen fixation, phosphate and potassium solubilization, auxin production, lipase, protease and cellulose enzymes production and tolerance to imazethapyr. According to the results of the first study, three bacterial species named Serratia rubidaea (A), Pseudomonas putida (B) and Serratia sp.(C) were found to have the most plant growth promoting potential. In the second study, the effects of seed and soil inoculation by the selected bacteria and also by Sinorhizobium meliloti (R) as a symbiont of alfalfa on the growth and yield of alfalfa (Hamedani cultivar) was investigated in a pot experiment. The experiment was performed outdoors as factorial based on a randomized complete block design with three replications,. having 16 treatments including control (non-inoculated), single, double, triple and quadruple species inoculation and two level of herbicide (zero and one liter per hectare as the recommended dose for field application). The bacterial inoculum was prepared by adding 100 µl bacterial suspension (109 CFU/ml) into 20 ml nutrient broth and the seeds were immersed in it just before sowing. The second inoculation was performed one month later through irrigation. The result of the pot experiment revealed that all treatments except BC, BCR, ABCR and CR increased plant growth, the concentration of photosynthetic pigments, bacterial population and antioxidant enzyme activity under both presence and absence of herbicide while the most effective treatments were ABR, AB and AR. Herbicide application decreased plant growth but the reductions were in most cases lower under bacterial treatments. In the third study, based on the results of the pot experiment, the best 11 treatments were selected regarding their abilities in terms of herbicide tolerance and alfalfa growth promotion. Treatments were eva‎luated in a factorial field experiment based on randomized complete block design with three replication. Seed inoculation and the second inoculation were done as applied in pot experiment. The results indicated that all bacterial treatments increased plant growth, photosynthetic pigments, microbial population and antioxidant enzyme activity but decreased neutral detergent fiber (NDF) and acid detergent fiber (ADF) under both presence and absence of herbicide. ABR and AR treatments had the best effectiveness on plant growth properties.. Herbicide treatment reduced growth parameters and NDF and ADF contents. In conclusion, it can be stated that eva‎luated rhizospheric bacteria could mitigate herbicide stress in parallel to promoting plant growth. These findings may, therefore, open new insights for development of biofertilizers that can be applied under herbicide stress.

مرتضي زاهدي

حسن كريم مجني , حسين معتمدي

جهانگير خواجه علي , پرويز احسان زاده , غلامعباس اكبري