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The culture of pasture legumes is of special interest for the world’s agriculture because it results in the production of high value protein accompanied by improvement of soil fertility, since they undergo symbioses with dinitrogen-fixing bacteria. Alfalfa is the most important forage crop for the and and semi-arid areas, where increased salinity of irrigated fields is one of the major constraints that limit crop productivity. Recently, using in vitro selection, we obtained alfalfa genotypes with increased tolerance to PEG 6000, an agent that mimics drought. Here, we present studies on salt tolerance with adult plants of these alfalfa genotypes grown either on nitrate or diazotrophically at various non-lethal salt concentrations. Growth parameters and parameters related to nodule physiology and development have been analysed. All R lines had a higher salt tolerance than their explant source genotype (T I) in germination and growth on nitrate-containing medium. Under diazotrophic growth conditions, R I and R3 were with higher relative salt tolerance than T1. Nodule biomass was depressed at high salt concentrations in all genotypes. This growth decline went in pair with changes in carbohydrate partitioning and in the hormonal balance. (C) 2003 Elsevier Ireland Ltd. All rights reserved.