Increased levels of greenhouse gases in the atmosphere and associated climatic variability is primarily responsible for inducing heat waves, flooding and drought stress. Among these, water scarcity is a major limitation to crop productivity. Water stress can severely reduce crop yield and both the severity and duration of the stress are critical. Water availability is a key driver for sustainable cotton production and its limitations can adversely affect physiological and biochemical processes of plants, leading towards lint yield reduction. Adaptation of crop husbandry techniques suitable for cotton crop requires a sound understanding of environmental factors, influencing cotton lint yield and fiber quality. Various defense mechanisms e.g. maintenance of membrane stability, carbon fixation rate, hormone regulation, generation of antioxidants and induction of stress proteins have been found play a vital role in plant survival under moisture stress. Plant molecular breeding plays a functional role to ascertain superior genes for important traits and can offer breeder ready markers for developing ideotypes. This review highlights drought-induced damage to cotton plants at structural, physiological and molecular levels. It also discusses the opportunities for increasing drought tolerance in cotton either through modern gene editing technology like clustered regularly interspaced short palindromic repeat (CRISPR/Cas9), zinc finger nuclease, molecular breeding as well as through crop management, such as use of appropriate fertilization, growth regulator application and soil amendments.

Limitations of soil water and nitrogen (N) are factors which cause a substantial reduction in cotton (Gossypium hirsutum L.) yield, especially in an arid environment. Suitable management decisions like irrigation method and nitrogen fertilization are the key yield improvement technologies in cotton production systems. Therefore, we hypothesized that optimal water-N supply can increase cotton plant biomass accumulation by maintaining leaf photosynthetic capacity and improving root growth. An outdoor polyvinyl chloride (PVC) tube study was conducted to investigate the effects of two water-N application depths, i.e., 20 cm (H₂₀) or 40 cm (H₄₀) from soil surface and four water-N combinations [deficit irrigation (W₅₅) and no N (N₀) (W₅₅N₀), W₅₅ and moderate N (N₁) (W₅₅N₁), moderate irrigation (W₇₅) and N₀ (W₇₅N₀), W₇₅N₁] on the roots growth, leaf photosynthetic traits and dry mass accumulation of cotton crops. H₂₀W₅₅N₁ combination increased total dry mass production by 29–82% and reproductive organs biomass by 47–101% compared with other counterparts. Root protective enzyme and nitrate reductase (NR) activity, potential quantum yield of photosystem (PS) II (F_v/F_m), PSII quantum yield in the light [Y(II)] and electron transport rate of PSII were significantly higher in H₂₀W₅₅N₁ prior to 82 days after emergence. Root NR activity and protective enzyme were significantly correlated with chlorophyll, F_v/F_m, Y(II) and stomatal conductance. Hence, shallow irrigation (20 cm) with moderate irrigation and N-fertilization application could increase cotton root NR activity and protective enzyme leading to enhance light capture and photochemical energy conversion of PSII before the full flowering stage. This enhanced photoassimilate to reproductive organs.

There is a need to optimize water-nitrogen (N) application to increase seed cotton yield and water use efficiency of field grown cotton under mulch drip irrigation system. This study evaluated the effect of the four water regimes (moderate drip irrigation from the third-leaf to the boll-opening stage (W1), deficit drip irrigation from the third-leaf to the flowering stage and sufficient drip irrigation thereafter (W2), pre-sowing and moderate drip irrigation from third-leaf to the boll-opening stage (W3), pre-sowing and deficit drip irrigation from the third-leaf to the flowering stage and sufficient drip irrigation thereafter (W4). Two N dressing ratios (7:3 (N1), 2:8 (N2) under N rate of 520 kg ha-1) on morphological and physiological traits of roots, cotton yield and water use efficiency and analyzed the relationship between root distribution and dry matter. Investigations have shown a strong correlation between root activity and water consumption in the 40-120 cm soil layer. The W3 and especially W4 treatments significantly increased root length density (RLD), root volume density (RVD), root mass density (RMD), and root activity in the 40-120 cm soil layers. RLD, RVD, RMD and root activity in the 0-40 cm soil layers at 70 days after planting (DAP) were 13.1%, 13.3%, 20.8% and 10.8% lower in N2 relative to N1, respectively. However, root activity in the 40-120 cm soil layers at 140 DAP was 31.6% higher in N2 than that in N1. Total RMD, RLD and root activity in the 40-120 cm soil profile were significantly and positively correlated with shoot dry weight. RLD and root activity in the 40-120 cm soil layer was highest in W4N2 treatments. Therefore increased water consumption in the deep soil layers resulted in increased shoot dry weight, seed cotton yield and water use efficiency. Our data will help in the future research planning of water-N management for optimal cotton yield and high water use efficiency.