Lotus glaber is naturalized in the Salado (River Basin) Province of Buenos Aires, Argentina. A significant area of this region is represented by saline and alkaline lowlands which limit the colonization by L. glaber. The incorporation of tolerant species with forage value would enhance the productive area of cattle establishment of the region. According to Miñón et al.(1990) the natural populations of L. glaber are excluded from the alkaline low soils by edaphic limitations. Nevertheless, in the "Pampa Deprimida" the presence of the species has been registered in soils within a wide range of pH and salt concentrations, (Montes, 1988). This suggests the existence of variability in the regional germplasm for tolerance of the adverse conditions of the alkaline low soils.

The germination of two varieties of L. corniculatus has been evaluated in a range from 0.25 to 8 bars of osmotic pressure and no significant differences between varieties were found in germination (Woods and Mc Donald, 1971). Significant differences between alfalfa seed lots of the same germplasm were determined by differences in the age of the seeds, (Smith and Dobrenz, 1987). After 5 cycles of mass selection in alfalfa, a significant advance has been attained in tolerance to salinity during germination in a range from -1.00 to -1.60 Mpa in NaCl solutions (Allen et al., 1985).

The objective of this experience was to evaluate the germination of two improved populations in a wide range of saline concentrations.

Materials and methods
Scarified seed from two improved populations of L. glaber, LH1 and Tresur Chajá, was used. The saline treatments consisted in different NaCL concentrations: 0 (control), 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 and 22 mM. Seeds were placed on filter paper, saturated with water or NaCl solutions, in Petri dishes, (50 per dish). Each treatment was replicated four times in a completely randomized experimental design. The germination conditions were darkness at 21 ± 1ºC. Seeds were considered germinated when the radicle was 0.2 cm in length. The germinated seeds were counted and removed every day during 7 days. The percentage of accumulated germination was determined. In order to evaluated the effects of saline treatments on viability of the non germinated seeds, they were washed and transferred to Petri dishes with distilled water on the seventh day.

Data (arcsin transformed) were analyzed using analysis of variance and treatment means were compared using Tukey test at a = 0.05 and a = 0.01.

Results
The behavior of accumulative germination, at the evaluated saline concentrations, did not show significant differences between populations at a =0.05 and a =0.01.

Concentrations lower than 12 mM did not affect germination of evaluated materials, (Fig.1).

Figure 1. The accumulative germination percentage of seeds of two inbred populations, LH1(x) and cv. Tresur Chajá (+) of L. glaber in a range of NaCl concentrations (mM). The arcsin transformed (^_____) and untransformed (-----) values are presented. Vertical bars represent the least significant difference (Tukey test, a = 0.01) to arcsin transformed data.

From 12 mM on, accumulated germination of both populations was reduced significantly (P<0.01) compared to the control (distilled water). More than 50% of the seeds showed tolerance up to 12 mM. From the 14 mM and up to 22 mM a group of tolerant seeds gradually lower than 30%, was observed. Seeds that did not germinate after 7 days in different NaCl solutions were washed and transferred to distilled water, showed viability affected in an increasing grade according with the rise of saline concentration, (Fig.2).

Figure 2. Germination of seeds affected by NaCl solutions, washed and transferred to distilled water. Vertical bar represent the least significant difference (Tukey test, a = 0.05) cv. Los Hornos (x) and cv. Tresur Chajá (+) of L. glaber.

This effect of toxicity of NaCl affected differently the evaluated populations. LH1 population was least affected than cv. Tresur Chajá (P<0.01) at 14 mM and (P<0.05) at 16 mM. Tresur Chajá population showed more stable behavior in general, and favorable (P<0.05) at 20 mM. Although differences between populations were not found in relation to grade of inhibition of germination in salinity conditions, results suggest the existence of variability within populations. Differences found between populations with respect to toxicity by NaCl could be associated to different mechanisms of tolerance.

References
Allen S.G., A.K. Dobrenz, M.H. Schonhorst and J.E. Stoner (1985). Heritability of NaCl tolerance in germinating alfalfa seeds. Agronomy Journal, 77: 99-101.
Miñón D.P., G.H. Sevilla, L. Montes and O. Fernandez (1990). Lotus tenuis: Leguminosa forrajera para la Pampa Deprimida. Boletín Técnico Estación Experimental Agropecuaria Balcarce Nº 98:8.
Montes L. (1988). Lotus tenuis. Revista Argentina de Producción Animal, 8: 367-376.
Smith S.E. and A.K. Dobrenz (1987). Seed age and salt tolerance at germination in alfalfa. Crop Science 27: 1053-1056.
Woods L.E. and H.A. MacDonald (1971). The effects of temperature and osmotic moisture stress on the germination of Lotus corniculatus. Journal of Experimental Botany 22: 575-585.

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