Argentina has 2.5 million hectares considered marginal for agriculture, with salinity problems that limit productivity. Among the adapted species, Thinopyrum ponticum is one of the perennial grasses worth mentioning because of its adaptation to lowland and salty soils. On soils with low osmotic potentials, available water is reduced, and toxicity due to ion concentration arises. Salt tolerance is genetically determined and its improvement is similar to any other character in that requires genetic variability and evaluation methods to identify superior genotypes. Due to the essentially low-intensity livestock production in Argentina, and the soil limitations in marginal environments, the characterisation and evaluation of germplasm is important in order to have a higher genetic diversity. The knowledge of parameters, procedures and methodologies for the evaluation of genetic diversity would help to plan future collection efforts aiming to add divergent populations. The objectives of this work, were to characterise T. ponticum germination under saline stress in ten naturalised populations through the Relative Index of salt Tolerance (RIT) (Pearen et al., 1997) and to quantify population diversity through the Shannon-Wiener index (H)( Pielou, 1969)