In Argentina over the past years there was a strong increase of agricultural production displacing livestock into marginal areas, affected by temporary flooding, salinity, alkalinity and temporary droughts. Salinity and droughts negatively affect the growth, biomass production and seed yield of crops. Tall fescue (Festuca arundinacea Schreb. var arundinacea) is a valuable perennial grass that grows spontaneously on the roadsides of the humid Pampas region. The aim of this study was to determine phenotypic and genetic parameters of nine populations collected on the ecological niche boundaries, and 30 half sib families (HS) growing under salinity and drought conditions. Five experiments were conducted on field, greenhouse and laboratory conditions. An important phenotypic and molecular variability between and within collected populations were detected in experiments 1 and 2, and could be associated to the species evolutive expansion to restricted environments. The salinity experiment showed HS initial growth reduction under hydroponics conditions, with different responses depending on each family and treatment; at 250 mM NaCl an important heritability was expressed by the families. The drought experiment affected the families´ initial growth, and narrow sense heritability was low probably because of moderate drought stress. The Relative Tolerance Index (ITPSA) was an important variable to select tolerant and susceptible half-sib families. The molecular characterization of tolerant and susceptible HS allowed the detection of 12 alleles with significant effects, which would indicate association between both stresses. The present thesis provides information and germplasm to be used in future breeding programs in order to obtained salt and drought-tolerant tall fescue cultivars.