Evaluating of Stress Tolerant Bean-Nodulating Rhizobium Strains on Growth and Symbiotic Efficiency of Bean

There are many scientific reports about the detrimental effect of environmental stresses on Rhizobium-legume symbiosis. Selection of some strains with high efficiency and tolerance to environmental stresses is the most commonly acceptable solution for that problem. In order to investigate the effects of inoculation of stress tolerant bean-nodulating Rhizobium strains on growth characteristics of bean and symbiotic efficiency, a greenhouse experiment was conducted with 29 strains of Rhizobium, one level of nitrogen (N=200 kg/ha) and a control treatment in a completely randomized design with three replications. Selected strains provided by the microbial collection of Soil and Water Research Institute. Plants were maintained up to 50% flowering and then harvested. Dry and wet weight of shoot, root and symbiosis efficiency were measured. The results showed that there was a significant difference in shoot dry weight and based on the results of this part, 4 strains (CCSM-B01171, CCSM-B01172, CCSM-B01186 and CCSM-B01210) were selected as strains with high efficiency in nitrogen fixation. Two more strains were also selected CSM-B01232 and CCSM-B01233 strains (type International strains) for next experiments. Tolerance of Selected Stains (totally 6 strains) to four environmental stress including pH in three levels (5, 7, 9), salinity in four levels (0.97, 4, 8 and 12 dS/m), drought in five levels (0, -0.05, -0.25, -0.9 and -3.4 MPa) and temperature in three levels (29, 37 and 42 °C) were assessed in the culture medium. Based on the results, CCSM-B01172, CCSM-B01171 and CCSM_B01232 strains had the highest tolerance to pH. CCSM-B01210 strain was resistant to drought. CCSM-B01186 strain had the highest tolerance to temperature and salinity environmental stress and recommended for further research.