Screening Of Salt Tolerant Rhizobium Strains In Alfalfa

Salt stress is a major abiotic stress that severely affects crop growth and yield.Alfalfa(Medicago sativa L.)is an important leguminous forage,which inoculated with rhizobia not only allows biological nitrogen fixation but also increases plant stress resistance.In order to screen out the best rhizobia strains that match with different varieties of alfalfa under salt stress,Sinorhizobium meliloti and alfalfa are used as materials for this study.We measured the absorbance values of 10 rhizobium species and analyzed the various physiological indicators of three species of alfalfa(Ladak+,Victorian and Zhongmu No.1)under salt stress.The main results are as follow:(1)We measured the absorbance at 600 nm of rhizobia for 48 h under different Na Cl concentrations by liquid culture method,the results showed that all of the 10 strains could grow at 0-2.0% Na Cl concentration and none of the 10 strains grew at 3.5-4.0% Na Cl concentration,we also found that 7 strains(except for ACCC17562,ACCC17569 and ACCC17659)could grow at 2.5% Na Cl concentration,there are 2 strains(ACCC17754 and ACCC17763)that can grow at 3.0% Na Cl concentration.(2)By measuring the growth characteristics indicators,physiological indicators and photosynthetic characteristics of alfalfa,we found that not all alfalfa inoculated rhizobia outperformed the uninoculated rhizobia in plants growth performance.Compared with the non-inoculated rhizobium alfalfa,the three varieties of alfalfa inoculated with 10 rhizobia can increase the yield to some extent under salt stress,the Ladak+ inoculated with rhizobia could increase the yield by 0.79 g per plant,Victoria inoculated with Rhizobia could increase the yield by 1.64 g and Zhongmu No.1 inoculated with Rhizobia could increase the yield by 0.81 g per plant;Alfalfa inoculated with some rhizobia could reduce the salt stress on plant cell membrane damage,reduce water loss and plant mortality;Alfalfa inoculated with some rhizobia could improve their own photosynthetic rate(Pn),transpiration rate(Tr)and stomatal conductance(Gs).According to the data of 10 isolated rhizobia,growth characteristics,physiological indexes and photosynthetic characteristics of three species of alfalfa under salt stress,we found that the salt tolerance of the vitro rhizobia and the symbiont formed by the rhizobia and alfalfa were not exactly the same,the above-ground biomass was used to represent the symbiotic effects of alfalfa and rhizobia because the best values of different plant indexes of three species of alfalfa point to different rhizobia,the results indicated that the strain(ACCC17726)had better symbiotic relationship with Ladak+,the strain(ACCC17741)showed better symbiotic relationship with Victorian and Zhongmu No.1 under salt stress.