Deciphering drought tolerance in cotton genotypes through integrated morpho-physiological and biochemical markers at flowering stage

Drought stress is one of the major abiotic factors that severely limits global cotton yield by disrupting essential morpho-physiological and biochemical functions. In this study, forty genetically diverse cotton genotypes were evaluated under three irrigation levels: control (100% field capacity), moderate (60% FC), and severe drought (40% FC), during the flowering stage in a controlled glasshouse environment. Increasing drought intensity led to a gradual decline in growth and physiological attributes. Severe stress reduced shoot and root lengths by 61% and 52%, respectively, compared with the control. Similarly, the photosynthetic rate and relative water content decreased by 60% and 32%. Conversely, stress-induced biochemical responses intensified, with proline content rising by 57% and superoxide dismutase activity increasing 2.3-fold under severe drought, reflecting enhanced osmotic adjustment and antioxidant defense. Principal Component Analysis (PCA) helps to identify the variability patterns among all the analyzed traits, while Pearson correlation analysis and heatmap analysis are useful for evaluating the positive and negative relationships between the studied attributes and for visualizing the clustering patterns of the cotton accessions. In addition, the multi-trait genotype-ideotype distance index (MGIDI) identified genotypes G₂ (IR-14), G₈ (N-221), G₉ (N-444), G₁₇ (FH-154), G₂₀ (FH-492), and G₂₅ (FH-540) as highly drought-tolerant. These genotypes maintained superior photosynthetic efficiency, antioxidant activity, and osmolyte accumulation under stress. The combined assessment of morpho-physiological and biochemical traits effectively distinguished drought-resilient genotypes, offering valuable guidance for breeding programs targeting enhanced cotton productivity in arid and water-deficient regions.