Agronomic, Physiological, and Biochemical Responses of Durum Wheat Genotypes to Drought Stress

Introduction: Drought is a major limitation to cereal production, particularly at the vegetative stage when canopy establishment and photosynthetic capacity determine the trajectory of yield formation. Physiological resilience under water deficit depends on pigment stability, antioxidant defenses, osmotic adjustment, and membrane integrity. This study aimed to (i) compare the responses of six durum wheat cultivars to controlled drought at the vegetative stage, (ii) identify reliable morphological and physiological indicators for early screening, and (iii) determine each genotype’s position along the tolerance–susceptibility spectrum using multivariate analyses.
Materials and methods: Six cultivars (Arya, Behrang, Dena, Deh-Dasht, Shabrang, and Karkheh) were obtained from the Seed and Plant Improvement Institute. Seeds were surface-sterilized and sown in 15-cm pots containing an equal mixture of soil, sand, and well-decomposed farmyard manure. Plants were grown in a greenhouse, and drought stress was imposed from the 4–6-leaf stage by maintaining pots at 50% field capacity until heading; control plants were well-watered. Measured traits included flag-leaf length and width, stem diameter, tiller number per plant, plant height, fresh and dry biomass, chlorophyll a, chlorophyll b, total chlorophyll, carotenoids, electrolyte leakage, hydrogen peroxide (Hâ‚‚Oâ‚‚), malondialdehyde (MDA), guaiacol peroxidase (GPX), catalase (CAT), proline, and total phenolic content (TPC).
Results: Analysis of variance indicated that drought and genotype effects were significant (p < 0.01) for almost all traits. In mean comparisons, Behrang maintained the highest biomass under both regimes. Shabrang sustained biomass under drought and had the tallest plants in both environments. The highest tiller number occurred in Karkheh (control) and Behrang (drought). Stem diameter peaked in Dena under control and in Shabrang under drought conditions. Behrang showed the highest levels of photosynthetic pigments under control conditions; under drought, Behrang and Shabrang retained the highest pigment levels. For osmotic adjustment, proline was maximum in Deh-Dasht (control) and Behrang (drought), whereas the largest relative increases were observed in Shabrang and Dena. The greatest TPC increases under stress occurred in Dena, Deh-Dasht, and Shabrang, respectively. Antioxidant enzymes responded strongly to stress: GPX peaked in Behrang and Shabrang under drought, and CAT exhibited the largest relative increases in Shabrang, Dena, and Behrang. Oxidative-damage indicators differentiated genotypes: Arya showed the highest increases in oxidative indices, while Shabrang and Behrang showed the lowest. Principal component analysis (PCA) explained ≈approximately 74% of the variance of the data under control conditions and ≈approximately 76% under drought conditions. In both environments, pigments and biomass loaded strongly and positively on PC1, whereas oxidative-damage indices loaded oppositely; under drought, proline and the examined antioxidant enzymes also aligned with PC1 (drought tolerance). In this ordination space, Behrang and Shabrang aligned with the tolerance component, Arya and Deh-Dasht aligned with the sensitivity component, Karkheh occupied an intermediate–tolerant position, and Dena combined larger leaf dimensions and higher TPC with intermediate-to-sensitive membrane stability.
Conclusion: Convergent evidence across analyses indicates that Behrang and Shabrang are leading candidates for breeding and early-stage screening under water deficit. The proposed selection panel comprises: (a) stability of photosynthetic pigments, (b) biomass maintenance, (c) proline accumulation and high activities of antioxidant enzymes (CAT and GPX), and (d) low levels of oxidative-damage indices (electrolyte leakage, Hâ‚‚Oâ‚‚, and MDA). Karkheh is a complementary parent with stable antioxidant metrics; Dena combines favorable leaf architecture and higher phenolics but requires attention to membrane stability; Arya and Deh-Dasht serve as sensitive checks. Applying these indices at the vegetative stage can accelerate the identification of drought-tolerant parents and streamline selection process.