Salt tolerance identification, screening and salt tolerance index evaluation of wheat-Thinopyrum intermedium radiation mutagenesis germplasm at germination and seedling stage

Saline-alkali land is widespread in China and poses a significant limitation to crop growth. Screening for salt-tolerant crop varieties is a key strategy to enhance the utilization of saline-alkali soils. In this study, 40 radiation-induced wheat-<italic>Thinopyrum intermedium</italic> lines, three conventional wheat varieties, and the wheat-<italic>Th. intermedium</italic> disomic addition line SN6306 were used as experimental materials. Chinese Spring (CS) was used as a salt-sensitive control, and Shanrong 3 (SR3) served as a salt-tolerant control. Phenotypic traits were comprehensively analyzed under hydroponic conditions, and the optimal salt treatment concentrations for both germination and seedling stages were determined. Using multivariate statistical analysis, salt tolerance of the 44 experimental materials was evaluated at the seedling and germination stages. Based on the results, the materials were classified into four salt tolerance levels: five highly salt-tolerant lines (e.g., A275, A051), thirty-one moderately salt-tolerant lines (e.g., A079, A262), seven salt-sensitive lines (e.g., A140, A284), with CS identified as highly sensitive. A stepwise regression model was established using the salt tolerance scores and the relative salt tolerance coefficients of physiological and biomass indices: <italic>D</italic>-value = 0.033-0.050×K⁺-S+0.002×Na⁺-R+0.237×K⁺-R+0.176×GP+0.139×GR-0.005×PC+0.197×SFW+0.088×WCS-0.110×RDW+0.242×SL+0.019×MRL (<italic>R</italic>²= 0.999). Significant indicators for identifying salt-tolerant wheat included potassium ion content in shoots and roots, sodium ion content in roots, germination potential and rate, proline content, seedling fresh weight, water content, root dry weight, seedling height, and maximum root length. This study established a reliable regression model for evaluating wheat salt tolerance and identified both salt-tolerant and salt-sensitive lines, providing valuable genetic resources for further research on the molecular mechanisms of salt tolerance and for breeding salt-tolerant wheat varieties.