Screening of salt-tolerant alfalfa germplasm and study of salt-tolerance mechanism.

key messageScreening of salt-tolerant alfalfa varieties, identification of key genes and verification of gene function. Screening and breeding salt-tolerant alfalfa varieties is crucial for the development and utilization of saline-alkali land. This study employed a comprehensive evaluation system to examine the response of various alfalfa germplasms to different salt concentrations during the germination and seedling stages. The classification of germplasms was achieved by integrating salt tolerance indicators across both phases, identifying the highly salt-tolerant cultivar 'Pegasus' and the salt-sensitive cultivar 'Fort'. Transcriptome analysis revealed significant differences in gene expression between 'Pegasus' and 'Fort' under salt stress conditions. This identified 24 key candidate genes associated with alfalfa salt tolerance. Further analysis showed that the differential pathways between the tolerant and sensitive varieties involved metabolism and ion transport. The selected differential gene, MsELIP, was heterologously expressed in Arabidopsis. Compared to wild-type plants, the germination rate, main root length, chlorophyll content, and antioxidant capacity of the overexpression lines increased significantly under salt stress conditions. These findings provide germplasm resources for breeding salt-tolerant alfalfa and a theoretical foundation for elucidating the molecular mechanisms of salt tolerance in alfalfa.