Water-Use Efficiency Is Negatively Correlated with Leaf Epidermal Conductance in Cotton (Gossypium spp.)

Water-use efficiency (WUE) may be a useful trait for improving productivity of cotton (Gossypium spp.) under certain water-limited conditions, but it is difficult to measure in the field or in large controlled-environment screening studies. Recently, an easily measured trait, the epidermal conductance of dark-adapted leaves (g(dark)), was shown to be predictive of whole-plant WUE in soybean [Glycine max (L.) Merr.]. Here, a greenhouse experiment was conducted using 22 cotton race stocks, converted lines, and commercial varieties to determine if the relationship between WUE and g(dark) previously observed in soybean also exists in cotton. A secondary objective was to determine if genotypic differences in WUE and g(dark) in cotton were constitutive in nature, or if they differed between water replete and drought conditions. There was significant genotypic variation for both WUE and g(dark), and in both cases the lack of a treatment x genotype interaction indicated that the trait was constitutive. The relationship between WUE and g(dark) (r = -0.75, P < 0.0001) was very similar to that reported previously for soybean. Understanding the mechanistic link between g(dark) and WUE may provide further insight into the physiological basis of genotypic differences in WUE.