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CROP PHYSIOLOGY & METABOLISM

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

^a Dep. Crop and Soil Sciences, Univ. of Georgia, Athens, GA 30602
^b Dep. Plant Agriculture, Univ. of Guelph, Guelph, ON Canada, N1G 2W1. This research was funded in part by state and Hatch funds allocated to the Georgia Agricultural Experiment Station, and by a grant from the USDA-NRI Plant Responses to the Environment program

^* Corresponding author (hjearl{at}uoguelph.ca).

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.

Abbreviations: c_i, leaf internal gas phase CO₂ concentration • DAP, days after planting • DM, dry matter • g_dark, dark-adapted leaf epidermal conductance • QTL, quantitative trait loci • RSWC, relative soil water content • WUE, water-use efficiency • WUE_L, leaf-level water-use efficiency