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The symbiotic efficiency of each of 30 alfalfa (16 Medicago sativa and 14 M. varia) cuhivars inoculated with 7 Rhizobium meliloti strains was studied in three field experiments. Two-factor analysis of variance of the obtained date demonstrated that the green mass yield and nitrogen accumulation depend on genotypes of both partners. The total contribution of plant and bacterial genotypes to the variation of green mass yield increased from 0-17% in the first year of alfalfa growth to 40-78% in the third year. The effect of the genotypic variability of the symbiotic partners was higher for N accumulation than for the green mass. There was a negative correlation between plant mass and N accumulation in the uninoculated plants with the relative (%) deviations of these parameters in the inoculated plants. In the experiments conducted in the Tashkent region the efficiency of the "alfalfa -R. meliloti" symbiosis was higher than in the experiment conducted in the Tureen region.