Effects of different bacterial strains isolated from alfalfa roots and synthetic microbial communities on alfalfa seed germination

Probiotic microbiota in roots can enhance nutrient uptake and stress tolerance, thereby improving plant growth.Objective To identify elite microbial resources from alfalfa roots.Methods We used eight functional bacterial strains isolated from the roots of Medicago sativa var. ‘Caoyuan No. 3’ and eight synthetic microbial communities (synthetic microbial communities, SynComs) composed of different strains for seed soaking treatments under 0, 200, and 250 mmol/L NaCl stress conditions. The germination potential (rate), radicle (embryonic shoot) length, and seed fresh weight were measured, and the effectiveness of the bacterial strains and SynComs in improving stress tolerance and growth was comprehensively evaluated via the membership function method. The effects of strains isolated from roots on alfalfa seed germination were thus evaluated.Results Under non-saline conditions, seed soaking had no significant impact on alfalfa seed germination. However, under salt stress, seed soaking significantly enhanced seed germination. Under 200 mmol/L and 250 mmol/L NaCl stress, MS8 was the most effective strain in promoting seed germination. Compared with the control treated with sterile water, MS8 treatment improved the germination potential by 76.67%. Compared with the control, the seeds treated with SynCom 1 exhibited increases of 113.04% to 405.41% in germination rate, significant increases of 47.87% to 56.67% in radicle length, significant increases of 19.13% to 24.01% in embryonic shoot length, and significant rises of 157.64% to 1 300.00% in fresh seed weight.Conclusion Under 200 mmol/L and 250 mmol/L NaCl stress, SynCom 1 was the most effective synthetic microbial community in enhancing seed germination, outperforming strain MS8. This study provides a theoretical foundation and technical support for the subsequent development of efficient functional bacterial agents to enhance the salt tolerance of alfalfa.