Comparison of Salt Tolerant Alfalfa (Medicago sativa) Genotypes: Seed Germination, Emergence, and Dry Matter Yield and Mineral Composition of Mature Plants.

Alfalfa (Medicago sativa L.) is an important forage crop of California which supports the large dairy industry. The objective of this research was to determine the relative salt tolerance of 19 new alfalfa varieties in terms of seed germination (Phase 1), emergence (Phase 2) and mature plant response (Phase 3).  As the salinity (EC_w) of the incubation solution increased, the germination percentage of most varieties decreased steadily with no threshold for germination loss. Salinities above 8dS/m (EC_w) substantially reduced alfalfa emergence.

For mature plants, the relative yield (RY) for shoots and for root+ crown dry matter yield decreased significantly when the EC_w was > 5 dS/m.  The most tolerant varieties had a RY for shoot dry weight of 39.5 to 84.1% at 10 dS/m EC_w; whereas for sensitive varieties, RY for shoots was only 0.5 to 2.3% at this salinity level. Shoot biomass was more sensitive to salinity than was root biomass, consequently the shoot / root + crown biomass ratio decreased with salinity. For most varieties, Na⁺ and Cl^- concentrations in shoots (and roots + crowns) steadily increased (and K⁺ decreased) as salinity increased. However, the most tolerant varieties exhibited relatively little increase in Na⁺ and Cl^- (and decrease in K⁺) in shoot tissue, indicating that toxic ion exclusion and K⁺ discrimination (over Na⁺) are key tolerance mechanisms in these alfalfa varieties.