Abstract
Land salinity is one of the major abiotic constraints that affect negatively crop production worldwide. Medicago genus, mostly composed by annual species, is of a real interest in improving soil fertility and maintaining pastures for livestock. We assessed adaptive traits for salt tolerance in 40 contrasted populations belonging to 6 Medicago species. In a common site, trial was performed in saline and non-saline soils where functional and fitness traits were recorded. Only M. ciliaris populations survived in the saline soil, highlighting the negative effect of even low salt levels at plant lift. ANOVA and PCA revealed that lifting rate, length branch at flowering time and total pod number might be involved in salt tolerance. The response to salt stress of Medicago was further studied by analyzing germination kinetics of 37 populations under five ranges of NaCl concentrations from 0 to 200 mM, during 7days. Kaplan-Meier survivor curves and Cox PH models indicated that time to 50% germination, germinability and germination synchrony are affected by the increase of salts. The risk of non-germinated seeds depends on species, populations and NaCl concentrations. Altogether, these results show that both salt level and exposition duration affect the phenotypical traits. Local adaptation may partly explain the patterns of salt tolerance. M. ciliaris is the most tolerant species, with a relatively high level of intraspecific variability for most studied traits.