EVALUATION OF WHEAT (TRITICUM AESTIVUM. L) GENOTYPES FOR DROUGHT RESISTANCE THROUGH AGRONOMIC AND PHYSIOLOGICAL CHARACTERS

Drought stress represents a critical constraint to global wheat production, causing significant yield losses and threatening food security in arid and semi-arid regions. This study evaluates 50 diverse wheat genotypes for drought resistance through comprehensive analysis of 15 agronomic traits and 12 physiological parameters under controlled and field drought conditions across three growing seasons (2020-2023). Employing a split-plot design with three replications, genotypes were subjected to three water regimes: well-watered (80% field capacity), moderate drought (50% field capacity), and severe drought (30% field capacity). Results demonstrate that drought stress reduced grain yield by 35-72% across genotypes, with drought susceptibility index (DSI) values ranging from 0.38 to 1.65. Physiological characterization revealed that drought-resistant genotypes maintained 40-60% higher relative water content (RWC), exhibited 25-45% lower canopy temperature depression (CTD), and demonstrated 30-55% higher chlorophyll stability index (CSI) compared to susceptible genotypes under severe drought. Root architecture analysis showed that drought-tolerant genotypes developed 35-70% deeper root systems with 40-85% higher root dry weight, while maintaining 20-40% lower root-to-shoot ratio under stress conditions. Stomatal conductance decreased by 45-80% across genotypes under drought, but resistant lines maintained 25-50% higher photosynthetic rates through better water use efficiency (WUE) of 2.8-4.2 g/kg H₂O versus 1.2-2.4 g/kg H₂O for susceptible lines. Proline accumulation increased 3-8 fold under drought stress, with highest concentrations (18-25 μmol/g FW) observed in resistant genotypes. Multivariate analysis identified three principal components explaining 78.4% of total variation, with root traits, WUE, and RWC contributing most to drought resistance. Genotypic clustering revealed four distinct groups: highly resistant (8 genotypes), moderately resistant (15), moderately susceptible (18), and highly susceptible (9 genotypes). Genome-wide association study (GWAS) identified 12 significant marker-trait associations for drought resistance traits, explaining 8-22% of phenotypic variation. This study concludes that integrative evaluation combining agronomic performance with physiological mechanisms provides effective identification of drought-resistant wheat genotypes, with root architecture, water use efficiency, and osmotic adjustment emerging as key selection criteria for breeding programs targeting drought-prone environments.