Physiological and molecular responses of bread wheat and its wild relative species to drought stress

Drought stress is a major abiotic factor limiting wheat productivity and threatening global food security. Understanding the mechanisms underlying drought tolerance in wheat and its wild relatives offers critical insights for breeding more tolerant cultivars. In this study, we investigated the physiological, biochemical, and molecular responses of bread wheat (Triticum aestivum L.) and three of its wild relatives-Aegilops tauschii (genome DD), Ae. speltoides (genome BB), and T. urartu (genome AA)-under varying drought stress conditions to evaluate their adaptive strategies.

Physiological and biochemical parameters assessed included photosynthetic pigments [chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl T), and carotenoids (CAR)], stomatal conductance (SC), net photosynthesis rate (Pn), maximum primary and quantum yield of PSII photochemistry (Fv/Fo and Fv/Fm), relative water content (RWC), the activity of antioxidative enzymes [guaiacol peroxidases (GPX), catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD)], and shoot dry matter (SDM). Additionally, the relative expression levels of three dehydrin (DHN ) genes (DHN5, DHN13, and DHN15) were analyzed across species. Analysis of variance (ANOVA) revealed that drought treatments had highly significant effects on all measured traits (except GPX) and the relative expression of DHN genes. Moreover, the main effect of species was significant for all traits except Chl b, Fv/Fm, RWC, Fv/Fo, CAT, APX, and SDM. The moderate drought (MD) stress led to reductions in the mean values of CAR content, Pn, FV/Fm, Fv/Fo, SC, RWC, and SDM, while other traits showed on increase relative to the control. Under severe drought (SD) treatment, a general decline in physiological traits and SDM was observed, accompanied by elevated biochemical activity and DHN gene expression. Notably, a strong correlation was identified between SOD activity and DHN gene expression under both drought treatments.

Among the species studied, Ae. speltoides and Ae. tauschii demonstrated the most pronounced resilience to drought stress, underscoring their superior adaptability under water-limited conditions. Their ability to maintain physiological integrity and enhance antioxidative enzyme activity suggests a promising genetic reservoir for improving drought tolerance in cultivated wheat. These findings highlight the importance of exploring wild germplasm to identify novel genes and alleles associated with drought tolerance, with potential implications for wheat breeding programs aimed at improving sustainability and productivity under climate stress.