Improving salt stress responses of the symbiosis in alfalfa using salt-tolerant cultivar and rhizobial strain

•Alfalfa inoculated with salt-tolerant rhizobial strain Rm1521 maintained higher water content under salt stress than with A2.•Pinitol, sucrose and starch were much more abundant in nodules inoculated with salt-tolerant strain Rm1521 than with A2.•Strain Rm1521 increases the sink strength toward nodules to maintain nodule activity under salt stress.•Combining salt-tolerant alfalfa cultivars and rhizobial strains is an effective strategy to improve alfalfa productivity under salinity.