Abstract
Salinity stress severely impacts wheat productivity and grain quality. This study investigated the effects of application of plant growth promoting substances (non-primed control (NP), hydropriming (HP), combined priming (1 mM silicon + 250 mg L(- 1) thiourea) (SiP + TUP), combined TU priming (250 mg L(- 1) thiourea) + Si foliar application (1 mM silicon) (TUP + SiF), combined TU foliar application (250 mg L(- 1) thiourea) + Si priming (1 mM silicon) (TUF + SiP) on salt tolerance and grain quality of two wheat cultivars (salt-tolerant Barzegar and salt-sensitive Amin) under three salinity levels (0.5, 4 and 10 dS m(- 1)). The experiment used a completely randomized factorial design with three replications under greenhouse conditions. Salinity reduced grain yield by 42-60% (more severely in Amin), decreased ash content, moisture, carbohydrates, fiber, and gluten, while increasing grain hardness and protein. The combined TUP + SiF treatment significantly mitigated these effects, particularly in Barzegar, restoring 10.5-39.0% of yield versus 34.4-50.0% in Amin. Mechanistically, the treatment: (1) enhanced K(+)/Na(+) ratio (1.7-2.2-fold) via upregulation of transporters, (2) reduced oxidative damage (MDA decreased by 33.8-60.9%) through boosted antioxidant enzymes (SOD 12-14%, POD 33%, APX 25-26%, CAT 55-94%), and (3) improved grain quality by increasing gluten (8.8-9.8%) and carbohydrates (6.7-7.5%) while reducing hardness and protein. Silicon's role in epidermal silica deposition reduced Na(+) uptake, while thiourea's thiol group directly scavenged ROS. Cultivar differences revealed Barzegar's superior ion homeostasis and antioxidant capacity. The TUP + SiF combination effectively counters salinity impacts through synergistic physiological mechanisms, with greater efficacy in tolerant cultivar. These findings provide practical strategies for wheat cultivation in saline soils, though cultivar-specific optimization may enhance results.