Multi-Index Evaluation of Saline–Alkali Tolerance in Oat (Avena sativa L.) Germplasm Accessions at the Seedling Stage

Saline–alkali stress is a major abiotic constraint limiting crop production worldwide. To address the lack of a systematic evaluation system for oat seedling saline–alkali tolerance adapted to soda saline–alkali soil in the Hetao Plain, 80 oat accessions with diverse genetic backgrounds were used as materials in this study. Seedlings were subjected to stress induced by a 75 mM composite saline–alkali solution (NaCl:Na2SO4:NaHCO3:Na2CO3 = 1:9:9:1), which simulates the typical salt composition of local soda saline–alkali soils. Six seedling-stage traits, including seedling emergence rate, chlorophyll content, relative electrolyte leakage, malondialdehyde content, free proline content, and soluble sugar content, were determined, and the saline–alkali tolerance coefficient of each trait was calculated. Principal component analysis, the subordinate function method, and hierarchical cluster analysis were integrated to construct a comprehensive evaluation system for saline–alkali tolerance. The results showed that the coefficients of variation of all tested traits ranged from 21.15% to 113.66%, indicating abundant genotypic variation among different germplasms. Three principal components with eigenvalues greater than 1 were extracted, with a cumulative contribution rate of 65.79%; these components mainly reflected cell membrane status, osmotic substance accumulation, and growth performance, respectively. The comprehensive evaluation value (D-value) ranged from 0.290 to 0.884, and stepwise regression analysis identified soluble sugar, relative electrolyte leakage, and proline as core screening indicators. Combined with hierarchical cluster analysis, the 80 oat germplasms were classified into five saline–alkali tolerance grades, and significant differences in key traits were observed among grades. Germplasms with high saline–alkali tolerance performed outstandingly in maintaining membrane integrity and accumulating osmotic substances. This study established a practical multi-index comprehensive evaluation system for seedling-stage saline–alkali tolerance in oats adapted to soda saline–alkali environments and identified three candidate tolerant germplasm resources. These results provide technical methods and preliminary candidate materials for oat saline–alkali tolerance breeding and saline–alkali land utilization in the Hetao Plain, while the tolerance performance of the selected germplasms still needs to be verified under multi-concentration stress and field conditions.