Genetic and environmental components were analysed in 32 Argentinian populations of Bromus catharticus. The research was based on 39 vegetative and reproductive characters. Constancy (r c ) and heritability (h 2 ) ratios were calculated. ANOVAS showed differences between populations for 14 traits, most of them reproductive. Total phenotypic variation was mostly due to the environmental component. Microfloral attributes showed the highest values of r c and h 2 . The traits average length of the spikelets (LS), average number of florets per spikelet (NFS), and lemma length (LL), which simultaneously reach r c values higher than 1 and h 2 values higher than 0.60, could be considered useful in systematic studies. Leaf, stem, and some reproductive characters, linked to propagule production, had plastic responses. However, traits associated with size and shape of propagules and spikelets remained constant. Results suggest that a double strategy is operating: plasticity in some traits (to give greater adaptability), and constancy in other traits related to species stability that are of systematic significance.

Native species show adaptive traits that are difficult to find in introduced species. The Pampas region in Argentina is a valuable nature reserve of grasses and Paspalum dilatatum Poir. is one of the most important grasses found there. Based on ploidy level and on morphological traits, five biotypes of P. dilatatum have been described. Two of them were included in this study: a tetraploid biotype with sexual reproduction and a pentaploid biotype with apomictic reproduction. We analyzed the genetic diversity in eight native populations from the Salado basin, Argentina, using both quantitative traits and molecular data (RAPD) with these aims: to obtain information of the degree of phenotypic variation in that area, to know which the pattern of distribution of this variation is and to look for association between molecular markers with populational or biotypic differentiation. Cluster analysis based on morphological data grouped the individuals of the different populations by ploidy level. Molecular markers showed the inverse situation because individuals were grouped by geographic origin as opposed to biotype. Moreover, since RAPD did not discriminate between biotypes with sexual or apomictic reproduction, they are probably not associated with mating system. The results let us conclude that polygenic traits such as LP, LBSR, NRT and NSP can discriminate between biotypes and molecular markers such as bands 12, 40, 19 and 46 can be used to discriminate among populations, probably because they detect neutral variation.

Thirteen different inbred lines in relation to the type of grain and life cycles were characterized by testing for osmotic stress associated with salinity. The identification of tolerant genotypes would be an effective strategy to overcome the saline stress. Osmotic stress reduces immediately the expansion of the roots and young leaves which determine a reduction in the size of the plant. A completely randomized design was adopted to test seedlings under controlled conditions of light and temperature. Two treatments were used: 0 mM NaCl (as control) and 100 mM NaCl. After 15 days of complete salinization, the seedlings were harvested and several morphological traits were measured. The morphological traits of growth were leaf growth (Ar1, Ar2, Ar3 and Ar4), dry masses of shoot and root (SDM and RDM, respectively). Also, traits associated with water economy were registered: leaf water loss (LWL) and relative water content (RWC). The morphological traits were expressed in relative terms, while the traits associated with the economy of water were expressed in absolute terms. Uni and multivariate techniques were applied to identify genotypes with divergent behaviors to osmotic stress tolerance. Also, a Tolerance Index was employed to identify superior genotypes. Four clusters were obtained after applying a Cluster Analysis and Principal Component Analysis (PCA). The genotypes were compared to each other with a test of DMS. The results obtained with different statistical techniques converged. Some variables presented a differential weight classification of genotypes. The morphological traits like RDM, SDM, Ar3, Ar4 and Ar5 were the most discriminating. Tolerance Index allowed to classify genotypes, thus SC2 and AD3 lines were that reached highest value of the index and therefore would be tolerant lines, while AF3 and LP3 had a low index and were seen as sensible.

Our objective was to evaluate the combining ability among cultivars of forage species, commonly sown in temperate regions of Argentina using a short rotation system. Three genetically diverse cultivars of prairie brome grass (Bromus catharticus, cv Copetona, cv Ñandú and cv Tango), a white clover cultivar (Trifolium repens, cv Lucero) and a red clover cultivar (T. pratense, cv Tropero) were evaluated. A randomized complete block design experiment was established in 2005. The treatments included five monocultures and ten binary mixtures. The experiment was harvested 6 times over an 18-month period. Cumulative dry matter yield (kg·ha -1 ) was calculated as the sum of the six individual harvests. Diallel analysis provided estimates of the general combining ability (GCA) and specific combining ability (SCA). Red clover in monoculture and mixtures produced the highest yields, with significant positive GCA effects (P < 0.01). Lucero white clover, and Copetona and Tango prairie grasses had significant negative GCA effects (P < 0.05). In mixtures, red clover with each of the three grass cultivars and white clover with Tango had significant and outstanding SCA effects (P < 0.01). Grass/grass mixtures and the legume/legume mixture showed non-significant SCA effects, while the grass/legume mixtures generally had higher yield than either component sown as a monoculture (P < 0.01). Given the short-term nature of this study, we must limit our inference to short-term pastures (<2 years). Under these conditions, red clover had the best combination with prairie brome grass.

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