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 <i>NHX7.1</i> and <i>NCL1</i> 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 <i>Tritipyrum</i> lines, derived from the cross of <i>Triticum aestivum</i> cv. Xinong 6028 and <i>Thinopyrum ponticum</i> 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.