Abstract
Water is the most important resource in plant growth and is a major limiting factor in sugarcane productivity worldwide. Improving water use efficiency (WUE) can increase sugarcane productivity relative to available water resources by increasing photosynthetic capacity relative to transpiration and stomatal conductance instead of decreasing stomatal conductance. Leaf carbon stable isotopic composition (δ 13 C leaf ) can serve as a proxy for intrinsic WUE (WUE i ) because WUE i and δ 13 C leaf are theoretically related through the link between intracellular and ambient CO 2 concentrations ( C i / C a ) and leaf CO 2 discrimination (Δ 13 C leaf ). In this study we surveyed 55 sugarcane genotypes for WUE i , leaf WUE (WUE leaf ), C i / C a , and δ 13 C leaf by gas exchange measurements and stable isotope analysis. We hypothesized that significant genotypic variation was found in WUE i , WUE leaf , and δ 13 C leaf within the sugarcane population in Louisiana. We also hypothesized that both WUE i and δ 13 C leaf and Δ 13 C leaf and C i / C a were correlated and that δ 13 C leaf could be used as a proxy for WUE i in sugarcane. Here WUE i and WUE leaf had a genetic effect and were controlled mostly by water loss (stomatal conductance or transpiration). WUE i , WUE leaf , C i / C a , and δ 13 C leaf were correlated, but δ 13 C leaf was not correlated with the component traits of WUE i (photosynthetic rate and stomatal conductance). δ 13 C leaf shows promise as a proxy for WUE i to at least be able to select the tails of the distribution, but the relationship between WUE i and δ 13 C leaf may not be sufficiently strong to select WUE at a finer scale.