Salicylic acid seed priming improves tolerance to salinity, iron deficiency and their combined effect in two ecotypes of Alfalfa

•Unprimed alfalfa seeds produced seedlings that showed reduced photosynthetic assimilation, chlorophyll concentration, stomatal conductance and ionic uptake under salinity and iron (Fe) deficiency. These effects were additive when both salinity and low Fe were combined. The extent of these effects was dependent on the alfalfa ecotype, tissue, and the stress applied.•Under the studied saline condition, Gabes ecotype showed relative tolerance by maintaining tissue hydration, growth, photosynthetic assimilation, chlorophyll biosynthesis and nutrient uptake.•Alfalfa seeds pretreated with 100 μM of salicylic acid (SA) produced seedlings that showed tolerance to Fe deficiency and the combined stress of both salinity and Fe deficiency by maintaining plant growth as via reducing the chlorosis index and increasing roots acidification and Fe uptake.•Priming seeds with SA could be used as a mitigating strategy against the harmful effects of salinity and Fe deficiency in alfalfa and potentially other crops. The aim of this work was to investigate the role of salicylic acid (SA) seed priming on plant growth, chlorophyll content, photosynthesis and ionic composition in two ecotypes of Medicago sativa (Gabes and Presmenti) when subjected to salinity (75 mM) and iron deficiency (1 μM) either separately or combined. Our results showed that under unprimed conditions, salinity and iron (Fe) deficiency reduced shoot and root growth, photosynthetic and transpiration rates, chlorophyll concentration, stomatal conductance and ionic uptake. The reduction in all of these parameters was additive in the combined treatment with salinity and low Fe supply. This reduction depended on the ecotype, the tissue and the stress applied. However, under saline conditions, the Gabes ecotype showed tolerance by maintaining tissue hydration, growth, photosynthetic assimilation, chlorophyll biosynthesis and nutrient uptake, compared to the control. While priming seeds with 100 μM SA had the best positive impact on all studied physiological parameters under different stresses, and especially under the combined treatment, a 500 μM concentration had no effect. We conclude that the effect of seed priming with SA is dose-dependent and may vary depending on ecotypes and stress.