Résumé
In order to assess the effect of salinity constraint on some agro-physiological and biochemical traits in Medicago sativa L., four Alfalfa populations (Tafilalet 1, Tafilalet 2, Demnate and Tata), originated from mountains and oasis of Morocco, were tested. The plants were grown under greenhouse conditions in pots filled with sand and peat under three salt treatments (0, 100 and 200 mM NaCl). Thereafter, plants were harvested 45 days after salt treatment and some agro-physiological and biochemical parameters related to salt tolerance, such as plant biomass, water content, membrane permeability, nutrients contents, nitrate reductase and acid phosphatase activities, were measured. Results showed that increase in NaCl concentration gradually reduced plant biomass, which displayed significant differences among the tested populations. Thus, Tata population appeared to be the most tolerant population to salinity, Tafilalet 1 population was the least tolerant one, while Tafilalet 2 and Demnate displayed moderate salinity tolerance. Variations in plant growth were associated with changes in physiological and biochemical parameters. Indeed, salinity caused a decrease in relative water content, perturbation of membrane permeability, and nutrients concentrations. Results also showed that salinity inhibited nitrate reductase activity in leaves of all tested populations, but acid phosphatase activity was increased in both leaves and roots of stressed plants. Salt tolerance of alfalfa populations was associated with high inorganic ion accumulation and the maintenance of membrane integrity and an adequate level in terms of nitrate reductase and acid phosphatase activities.