Alteration in Physiological, Biochemical and Yield Traits by Combined Salinity and Heat Stress and Mechanism of Stress Tolerance of Wheat Genotype
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Abstract
Heat and salinity stress, both individually and combined, significantly reduce wheat yield in tropical and subtropical areas. The flag leaf of wheat, during its terminal growth phase, plays a crucial role in assimilate partitioning and stress tolerance. However, little is known about their combined effects on the crop. This study aimed to explore the effects of individual and combined heat and salt stress on water relations, membrane stability index, photosynthetic pigments, antioxidant defense mechanism, osmolytes accumulation, and yield attributes in flag leaf of bread wheat. Two independent experiments were conducted at the seedling stage. The second experiment was conducted under natural environmental condition (in pots). Experimental treatments comprised of control (timely sowing on the soil of EC 0.25), salt stress alone (timely sowing on soil of EC 7.4), terminal heat stress alone (late sowing on the soil of EC 0.25) and combined salt stress + terminal heat stress (late sowing on soil of EC 7.4). Salt and heat stress posed significant reduction (p0.05) in physiological parameters, along with activating SOD and proline accumulation thus ultimately reducing yield. Here, the combined stress appeared more detrimental then the individual stress due to the hypo-additive interaction between the two stresses. A unique tolerance mechanism was revealed by some wheat genotypes by their ability to maintain comparatively high WUE, chlorophyll a and b content, MSI and higher induction of antioxidant defence system (SOD, APX), osmolyte concentration (proline) and ultimately yield (harvest index and yield per plant) then the susceptible genotypes. These findings will be critical in future studies aimed at improving wheat stress tolerance by fully understanding the genetic pathways behind the physiological and biochemical effects related to combined heat and salt exposure on the wheat flag leaf.