Selection for Water Use Efficiency Traits in a Cotton Breeding Program: Cultivar Differences

Water stress adversely affects both yield and fiber quality of cotton ( Gossypium hirsutum L.) and any improvement in components of water use efficiency (WUE) would be expected to partially reduce these adverse affects. Six field experiments in Australia and one in Texas using four Australian and three Texas cultivars determined genetic differences in physiological WUE parameters. Four of the experiments were grown under dryland conditions and three under irrigated conditions. Cultivar differences for net photosynthesis ( A ) were found in only 30% of comparisons, ratio of intercellular CO 2 concentration to ambient CO 2 concentration (C i /C a ) in 20%, and carbon isotope 13 C discrimination (Δ) in 69%. Cultivars Cascot 014 and Sicot 189 had significantly ( P ≤ 0.05) higher A than Siokra 1‐4 and Siokra L23 and these differences were consistent across experiments. A significant ( P ≤ 0.05) cultivar × experiment interaction suggests C i /C a would be an environment specific measure enabling confident distinction of cultivar differences. Tamcot Sphinx and Cascot 014 had significantly higher Δ ( P ≤ 0.001) than Siokra L23, with the ranking differing in only one irrigated experiment. Broad sense heritability estimates were 0.65, 0.68, and 0.56 for A , Δ, and lint yield, respectively. Cultivar variation for these physiological traits measured in single leaves of cotton, and related indirectly to plant WUE, indicate potential for genetic advancement through selection. Further studies to determine heritability of these physiological traits in segregating populations are needed to confirm their usefulness in a cotton‐breeding program.