Tolerance Against Combined Drought and Heat Stresses in Wheat Landraces of Omani Origin: Morphological, Physiological, Biochemical, and Grain Yield Assessment

Drought and heat are major abiotic stresses threatening the sustainability of global wheat production. The landraces are tolerant to abiotic stresses and can serve as valuable genetic resources in breeding programs aimed at developing stress-tolerant genotypes. In this study, wheat landraces of Omani origin were evaluated for morphological, physiological, biochemical, and yield responses under combined drought and heat stresses. In this study, four popular Omani wheat landraces, Sarraya, Waleedi, Missani, and Cooley, and an exotic genotype TW1509 were evaluated for tolerance against combined drought and heat stresses. The wheat landraces were exposed to drought (35% water holding capacity (WHC)), heat (37/29 ± 1°C), and combined drought and heat stress. Drought and heat stresses caused a significant reduction in plant growth, water relations, chlorophyll fluorescence, gas exchange, grain-filling enzymes, grain yield, and related traits, whereas a significant increase was observed in malondialdehyde, leaf trehalose, free proline, and glycinebetaine contents. The effect of combined drought and heat stress was additive. The Omani wheat landrace Cooley had the lowest relative stress-induced decrease in grain yield and related traits. This was due to higher leaf trehalose, free proline and glycinebetaine contents, and activities of antioxidant enzymes, which enabled this landrace to sustain carbon assimilation and grain development under stress. Although wheat genotype TW1509 experienced a higher relative reduction in grain yield under stress conditions compared to Omani wheat landrace Cooley, its grain yield remained the highest under non-stress and stress conditions due to its small stature, relatively less reduction in leaf area, gas change attributes, photosystem-II efficiency, and grain-filling enzymes. The Omani landrace Cooley was excellent in performance based on physiological and biochemical attributes under individual and combined drought and heat stress and may be used in breeding programs aimed at developing high-yielding and stress-tolerant wheat genotypes.