An Integrated Method for Evaluation of Salt Tolerance in a Tall Wheatgrass Breeding Program

Tall wheatgrass, a perennial forage grass renowned for its salt-alkali tolerance, has recently been proposed as a key species for planting in coastal saline-alkaline lands to establish a "Coastal Grass Belt". Highly salt-tolerant and high-yielding varieties are essential to achieve this objective. To enhance breeding efficiency, a method integrating seed germination, seedling emergence, and seedling growth was established to evaluate salt tolerance in tall wheatgrass. Germination tests revealed that under 250 mM NaCl, 150 mM Na₂SO₄, 150 mM NaHCO₃, or 100 mM Na₂CO₃, the relative seed germination rates were 31.5%, 65.4%, 68.2%, and 32.6%, respectively, compared to the non-stress condition. Germination tests can use 250 mM NaCl and 100 mM Na₂CO₃ to assess tall wheatgrass tolerance to neutral and sodic salt stress, respectively. In addition, 250 mM NaCl or saline water with EC_w = 6.6 dS m^-1 resulted in relative seedling emergence rates of 52% and 59.8%, respectively, compared to the non-stress condition. Seedling hydroponic culture demonstrated that exposure to 300 mM NaCl resulted in relative total dry weight, shoot dry weight, and root dry weight of 38.2%, 35.7% and 50%, respectively, compared to the non-stress condition. Salt-response genes exhibited differential expression in tall wheatgrass under long-term and short-term salt stress. Interestingly, the expression levels of NHX7.1 and NCL1 were significantly higher in salt-tolerant lines compared to salt-sensitive lines. Based on an integrated evaluation of seed germination, seedling emergence, and seedling growth, five out of the 28 tall wheatgrass lines were identified as salt-tolerant. Additionally, two Tritipyrum lines, derived from the cross of Triticum aestivum cv. Xinong 6028 and Thinopyrum ponticum line Zhongyan 1, were found to inherit salt tolerance from tall wheatgrass. Collectively, this work provided an integrated method for salt tolerance testing in a tall wheatgrass breeding program.