Integrated physiological performance and <i>Nax1</i> -mediated sodium exclusion reveal mechanisms of salinity tolerance in spring wheat ( <i>Triticum aestivum</i> L.)

Abstract Soil salinity is a rapidly intensifying abiotic stress that significantly limits wheat productivity, particularly in coastal and irrigated agroecosystems. Although sodium (Na + ) ion exclusion has been recognized as a key tolerance mechanism, the integration of physiological performance with Nax1 -mediated molecular regulation among regionally adapted wheat genotypes remains insufficiently characterized. The present study aimed to dissect salinity tolerance by combining hydroponic phenotyping, multivariate trait analysis, molecular marker profiling, and quantitative expression analysis of the Na + ion transporter gene Nax1 . Seventeen spring wheat genotypes were evaluated under four salinity levels (0.0, 10, 12, and 14 dS m⁻¹). Germination and survival rate, shoot and root growth, and biomass accumulation were measured. Principal component analysis (PCA) and hierarchical clustering were performed to classify genotypes, while SSR (simple sequence repeat) and Nax -linked markers assessed genetic diversity. Relative Nax1 expression was quantified using qRT-PCR (quantitative real-time polymerase chain reaction). Salinity significantly reduced germination, survival, elongation, and biomass, with strong genotype-dependent variation. Multivariate analyses clearly separated tolerant and sensitive genotypes, with biomass retention and survival contributing most to total variation. Marker analysis revealed moderate genetic polymorphism. Notably, tolerant genotypes exhibited 3-6-fold induction of Nax1 under severe salinity, positively correlating with biomass maintenance. These findings demonstrate that salinity tolerance in wheat is associated with coordinated physiological resilience and enhanced Nax1 -mediated Na⁺ ion exclusion, thereby advancing mechanistic understanding and supporting molecular-assisted breeding for salt-affected environments.