Based on the analysis of the results of previous studies, a review of theoretical and practical data is devoted to the study of salt tolerance and genetic determination of this trait in nodule bacteria Sinorhizobium meliloti - alfalfa symbionts. A collection of natural isolates of the nodule bacterium Sinorhizobium meliloti from nodules of wild species of alfalfa (Medicago polymorpha) and alfalfa plant of the Taisiya varieties were used. The degree of resistance of these strains to salinity and which of them fix nitrogen more efficiently under salinization conditions was discussed, and the effect of different levels of salinity on the growth of seeds of alfalfa cultivar (Taisiya) was studied.