Analysis of NaCl Stress Response in Tunisian and Reference Lines of Medicago truncatula

We analyzed the effects of NaCl stress on nine lines of Medicago truncatula, including four lines from southern Tunisia, three from the north, and two references lines. Plants were cultivated in two treatments (0 and 45 mM NaCl) for a period of 45 days. At harvest, we measured seven quantitative traits of the shoot and root growth. The analysis of variance showed that responses of lines to NaCl stress depended on the effects of line, treatment, and their interaction. Treatment had the largest effect. All measured traits showed high broad-sense heritability (H(2)) under both treatments. While the leaf area was the less affected trait, the length of stems was the most affected regarding the sensitivity index (SI) parameter. Estimated SI for total plant biomass showed that TN13.11 and TN11.0 were the most contrasting lines with the lowest and the highest values, respectively. Established correlations between measured traits and the hierarchical cluster relationships among lines depended on the treatment effect. The site-of-origin environmental factor that influenced more the response of lines to NaCl stress was the relative humidity.