Genetic control of tolerance to salinity in Medicago truncatula

Among abiotic stresses salinity is considered as a serious problem affecting plant functions especially growth and yield. In order to study the genetic control of salt stress in the model legume Medicago truncatula, two experiments were performed. The first experiment was conducted to study the effect of salt stress on some morpho-physiological parameters in M. truncatula genotypes and to determine the eventual use of some traits as tolerance criteria. Genotypes including A17, TN1.11, DZA315.16, A20, TN1.12 and F83005.5 are selected through a sequenced lines collection (http://www1.montpellierinra.fr/BRC-MTR/mauguio/mauguio.php) which are originated from different Mediterranean countries. Genotypes were studied under 6 salinity treatments (0, 30, 60, 90,120 and 150 mM NaCl) in a factorial design based on randomized complete blocks with three replications. Analysis of variance show significant differences among genotypes, salinity levels and interaction between genotypes and salt treatments for most of studied traits. “DZA315.16” genotype presents the highest main effect values for morphological traits whereas”TN1.11” has low values. Vertically projected leaf area (LA); show the highest variability through all studied salt concentrations. The best concentration to find differences between parental lines is 90 to 120 mM Nacl. A segregating population of recombinant inbred lines (100 RILs) of M.truncatula derived from a cross between TN1.11 and Jemalong-A17 was used for the second experiment. RILs were developed by single-seed descent until F6 generation at the INP-ENSAT, France. The experiment was undertaken to determine the genetic variability and to identify QTLs controlling several traits related to plant growth and physiology, in the population of recombinant inbred lines (RILs). Analyses of variance showed a large genetic variation and transgressive segregation for the traits studied. The difference between the mean of RILs and the mean of their parents was not significant for all of the traits in both conditions, showing that the RILs used in our experiment are representative of the possible recombinant lines from the cross TN1.11 x A17. A total of 21 QTLs were detected under control and 19 QTLs were identified under 100mM salt stress conditions. The percentage of total phenotypic variance explained by the QTLs ranged from 4.60% to 23.01%. Some of the QTLs were specific for one condition, demonstrating that the genetic control of a traits differed under control and salt stress conditions. Some others are non-specific and control a trait in both conditions. Overlapping QTLs for different traits were also observed. The results provide important information for further functional analysis of salt tolerance in M. truncatul