Screening Aegilops tauschii accessions for salinity tolerance at the seedling stage using multi-trait-based indices

Genetic diversity provides a critical foundation for the development of stress-resilient crops. Aegilops tauschii , the diploid progenitor and D‑genome donor of bread wheat ( Triticum aestivum L.), is an important source of genetic variation for wheat improvement, including the enhancement of salinity tolerance. Despite its breeding potential, the physiological basis of salinity adaptation in Ae. tauschii and the extent to which these responses vary among geographically distinct populations remain insufficiently resolved. In this study, geographically diverse Ae. tauschii accessions collected from Iran, Turkey, Tajikistan, Turkmenistan, and Afghanistan were evaluated under control conditions without NaCl and under salinity stress imposed with 200 mM NaCl. Plant growth, ion accumulation, photosynthetic performance, and a range of physiological traits associated with stress responses were characterized. The salinity treatment significantly affected multiple traits, resulting in reductions in shoot and root dry weight, shoot K⁺ concentration, root and shoot K⁺/Na⁺ ratios, relative chlorophyll content, membrane stability index, stomatal conductance, net photosynthetic rate, maximum quantum efficiency of photosystem II, and maximum photochemical performance. Conversely, the salinity treatment increased root Na⁺ and K⁺ accumulation and initial fluorescence compared with the respective control conditions. To identify genotypes exhibiting superior and balanced performance across multiple traits, multi-trait selection was performed using the multi-trait genotype–ideotype distance index (MGIDI) and the factor analysis and ideotype-design approach based on best linear unbiased prediction (FAI-BLUP). Iranian and Turkish accessions generally had the best performance under salinity, as observed by better biomass retention, preservation of photosynthetic activity, and maintenance of membrane stability. In contrast, several Afghan accessions exhibited comparatively favorable photochemical responses. The combined analysis indicated clear geographic differentiation in the physiological responses of Ae. tauschii to salinity stress and demonstrated that superior salinity tolerance was associated with the coordinated maintenance of several physiological processes rather than a single trait response. Seven Iranian accessions (26, 37, 38, 39, 40, 42, and 44) were consistently identified as the highest-performing genotypes across the analytical approaches. These accessions constitute promising sources of salinity-adaptive variation for wheat pre-breeding and may serve as priority donors for the targeted introgression of potentially beneficial D-genome alleles into cultivated wheat. The breeding value of these accessions should be further assessed through field-based evaluation and genomic characterization before their deployment in wheat improvement programmes.