Integrative multivariate analysis of morphological, physiological, and biochemical responses of upland cotton to water deficit at the reproductive stage

Abstract

Drought is a major abiotic stress that severely limits cotton productivity by reducing growth, yield, and fiber quality. Understanding genotype-specific responses to reproductive-stage drought is essential for identifying reliable selection traits and improving drought resilience in cotton breeding programs. This study evaluated 54 cotton genotypes at the flowering stage under three irrigation regimes: well-watered conditions (80% FC), mild drought stress (60% FC), and severe drought stress (40% FC). Morphological traits (root and shoot biomass), physiological traits (photosynthetic rate, leaf water loss, and relative water content), and biochemical traits (proline, soluble sugars, amino acids, antioxidant enzyme activities, and reactive oxygen species) were assessed. Drought treatments were imposed for three consecutive weeks during flowering to investigate genotype responses to varying levels of water deficit. The experiment was conducted in a rain-out shelter using a factorial completely randomized design (CRD) with three replications for each genotype–treatment combination. Cotton accessions were grown in plastic containers. Significant genotype-dependent variation was observed across all drought treatments, with responses becoming more pronounced under severe stress. Two-way analysis of variance revealed that drought significantly affected all measured traits. Descriptive statistics and boxplot analyses further illustrated variations in trait performance among genotypes under different stress levels. Principal component analysis (PCA) revealed clear phenotypic divergence among genotypes and highlighted trait associations under contrasting water regimes. Heatmap analysis further confirmed genotype grouping patterns and their relationships with the evaluated traits. Moreover, MGIDI-based selection at 15% selection intensity identified G 33 (FH-901), G 50 (N-1048), G 53 (N-135), G 36 (FH-Super-Cotton), G 29 (FH-556), G 47 (MNH-1035), G 54 (N-135-BB-121/38), and G 41 (IUB-13) as drought-tolerant genotypes based on their lower MGIDI values and favorable performance. These genotypes exhibited superior performance, greater water retention, lower oxidative damage, and stronger antioxidant defense systems under water-deficit conditions. The findings provide valuable insights for cotton breeding programs aimed at developing drought-resilient cultivars and support sustainable cotton production in water-limited environments.