Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/20/2005
Publication Date: 5/6/2005
Citation: Stiller, W.N., Read, J.J., Constable, G.A., Reid, P.E. 2005. Selection of water-use efficiency traits in a cotton breeding program: cultivar differences. Crop Science. 45:1107-1113. Interpretive Summary: Cotton breeders and physiologists are trying to develop new varieties which use limited water more efficiently. Because water use efficiency is difficult to measure in a large number of plants, scientists are measuring the composition of naturally occurring stable isotopes of carbon in leaf dry matter as an index of water use efficiency. Plants which use water more efficiently also take up more of the heavy isotope of carbon during photosynthesis, as compared to the normal isotope, and this ratio can be measured using a mass spectrometer. Carbon isotope composition should be a more reliable way of determining water use efficiency even when measured in different environments. The researchers measured photosynthesis, leaf carbon isotope composition and yield in four Australian and three Texas cotton varieties in four seasons and under both irrigated and non-irrigated conditions. They compared the repeatability of these measurements in order to determine the most reliable and consistent trait to select for when screening plants for water use efficiency. The variation in carbon isotope composition between cotton varieties observed in this research indicates that plant breeders could enhance water use efficiency by using this new selection method. Results also suggest the best time to sample cotton for carbon isotope composition is when plants are at the flowering stage.
Technical Abstract: Enhancing the water-use efficiency (WUE) in Upland cotton (Gossypium hirsutum L.) is expected to mitigate water stress effects on lint yield and fiber quality. Six field experiments in Australia and one in Texas using four Australian and three Texas cultivars were used to determine genetic difference in physiological WUE. Plants were rainfed in four experiments and irrigated in three experiments. Several traits were measured periodically in uppermost fully-expanded leaves, including net photosynthesis (Pn), the ratio of leaf intercellular CO2 to ambient CO2 concentration (Ci/Ca) during gas exchange, and stable C isotope discrimination in leaf dry matter (CID, an estimator of leaf Ci/Ca). Cultivar differences in Pmax were found in only 30% of the possible comparisons, Ci/Ca in 20%, and CID in 69%. Cultivars Cascot 014 and Sicot 189 had higher Pn than Siokra 1-4 and Siokra L23 and these differences were consistent across experiments. A significant cultivar by experiment interaction for Ci/Ca suggested measuring this trait would not consistently rank cultivars for physiological WUE. Tamcot Sphinx and Cascot 014 had higher CID than Siokra L23, but this ranking differed in one irrigated experiment. Broad sense heritability estimates of 0.56 for lint yield, 0.65 for Pn, and 0.68 for CID, indicate potential for genetic advancement through selection. Further studies will determine variability for yield and physiological WUE in segregating populations in order to confirm their usefulness in the Australian cotton breeding program.