Globally, increasing water and energy demand is expected to reach 6.9 trillion cubic meters by 2030, exceeding 40% of the available water supplies. Climate change and rising temperatures caused water shortages due to lesser and irregular rainfalls, leading to lower production of crops. The research to assess drought tolerance of Pima cotton (Gossypium barbadense. L) lines in Uzbekistan revealed the line, T-450 as the most promising for drought environments. The research, in a randomized complete block design (RCBD) in three replications with a factorial arrangement and two irrigation regimes (non-stress and water stress at the seedling stage), was conducted at the experimental field of the Institute of Genetics and Plant Experimental Biology, District Zangi-Ota, Tashkent Region, Uzbekistan. Nine Pima cotton lines, i.e., Сурхон-14 (control cultivar), Т-1, Т-5440, Т-2006, Т-10, Т-167, Т-5445, Т-450, and Т-663 with diverse agronomic characters, were selected for their potential yield during 2019, 2020, and 2021 cropping seasons under two different environments (optimal and water deficit condition). Drought indices revealed significant differences among lines, except the golden mean (GM). Results in the ranking method indicate that among the drought tolerance indices, mean productivity (MP), geometric mean productivity (GMP), stress tolerance index (STI), mean relative performance (MRP), relative efficiency index (REI), and relative drought index (RDY), show the most suitable indicators because of their high correlation with seed cotton yield. Cluster analysis and three-dimensional plots showed the cotton inbred lines with the highest tolerance to drought under both irrigation conditions. The first three principal components (PCs) explained 67.54% of total variation and the PC1 can be nominated as a potentially stable yield. The biplot diagram based on PCs and drought tolerance indices showed that MP, GMP, STI, MRP, REI, and YI were the best indices for screening the tolerant cotton inbred lines, such as, T-450.

Water scarcity during the flowering and ripening stages disrupts physiological processes in crop plants. The recent study on cotton genotypes and their F1 hybrids under two different water regimes (nonstress and stressed conditions) took place in 2018–2020 at the Institute of Genetics and Experimental Biology, Academy of Sciences, Tashkent, Uzbekistan. In optimum and controlled water regimes, the cotton genotypes received irrigation four times, using 4800-5000 m3/ha water. However, under stress conditions, the genotypes received only two irrigations, using 2800-3000 m3/ha water. Comparing the optimum water regime with the water stress conditions, chlorophyll ‘b’ in plant leaves decreased by 3.0% to 46.7% and 1.1% to 26.2% in the parental cultivars and their F1hybrids, respectively. With water deficit conditions, the carotenoid content increased from 8.5% to 39.1% and 2.1% to 44.2% in plant leaves of parental cultivars and their F1hybrids, respectively, compared with the optimal water condition, which indicates how cotton genotypes protect themselves from water scarcity by varying magnitudes of carotenoids in plant leaves. The use of decreased levels of chlorophyll ‘a’ and ‘b’ and increased levels of carotenoids aided the inhibition of oxidants during photooxidation under drought conditions. The F1 hybrids viz., Listopad × Farovon (62.2±0.9 g.), F1 Kupaysin x Elastik (55.8±1.2 g.), F1 Listopad × Kupaysin (55.7±0.2 g.) produced higher seed cotton yield, which might be due to their resistance to drought conditions, as well as heterosis. These promising populations proved suitable for developing drought-tolerant cotton genotypes in future breeding programs.