Variation in water-use efficiency and its relation to carbon isotope ratio in cotton

Cotton (Gossypium spp.) is often exposed to drought, which adversely affects both yield and quality. Improved water-use efficiency (WUE = total dry matter produced or yield harvested / water used) is expected to reduce these adverse effects. Genetic variability in WUE and its association with photosynthetic rate and carbon isotope ratio (¹³C/¹²C) in cotton are reported in this paper. WUE of six cotton cultivars-G. hirsutum L., G. barbadense L, and an interspecific F₁ hybrid (G. hirsutum x G. barbadense, ISH), was examined under two irrigation regimes in two field trials. The greatest WUE was obtained by two G. hirsutum cultivars (2.55 g dry matter or 1.12 g seed-cotton L^-1 H₂O); the ISH obtained similar or somewhat lower values, and two G. barbadense cultivars and one G. hirsutum cultivar exhibited the lowest values (2.1 g dry matter or 0.8 to 0.85 g seed-cotton L^-1 H₂O). These results indicate that different cotton cultivars may have evolved different environmental adaptations that affect their WUE. Photosynthetic rate was correlated with WUE in only a few cases, emphasizing the limitation of this parameter as a basis for estimating crop WUE. Under both trials, WUE was positively correlated with carbon isotope ratio, indicating the potential of this technique as a selection criterion for improving cotton WUE.