Variability salt stress response analysis of Tunisian natural populations of Medicago truncatula (Fabaceae) using salt response index (SRI) ratio

We evaluated the responses to salt stress of 106 Medicago truncatula lines from 11 Tunisian natural populations collected from areas that varied in soil composition, salinity and water availability. Five references lines were also included in this study. Plants were cultivated in two treatments (0 and 50 mM of NaCl) during a period of 60 days. At harvest, we measured 14 quantitative traits of the aerial and root growth to identify genotypic variability in salt response. Analysis of variance showed that, the response to salt lines within populations was dependent on the effects of treatment, population, line within population and their interaction with maximum value recorded for treatment (93.78%). This study also analyzed heritability of the salt response index (SRI), defined as the ratio between the observed values with and without salt treatment. SRI of most measured traits had high broad-sense heritability (H-2). Most of established correlations among SRI values of measured traits were positive. SRI means revealed that, Soliman and Bulla Regia are the most salt-tolerant populations. Based on Ward's estimated distance, all lines were classified into 4 clusters showing similarity and dissimilarity in response to salt stress. The eco-geographical factors that influence more the variation of SRI of measured traits among populations are assimilated P2O5, % organic matter and carbon and mean annual rainfall. Findings from this study will provide the basis for identifying and breeding of salt-tolerant lines in M. truncatula.