Water use efficiency The differences between genotypes in the way they use water to form yield (the water use efficiency, or WUE) are related to growth potential more than differences in actual water use. Hence, genotypes that yield poorly, but use similar amounts of water to other more high yielding genotypes, essentially waste water. Breeders would like to eliminate these types from their advanced breeding pool. Carbon isotope discrimination ratio (CID) was inversely related to WUE, but the correlation was not as strong as that observed in previous experiments. Data from a lysimeter experiment designed to measure water use efficiency more accurately than in field experiments were not reliable because plants became too stressed during unusually hot weather in July. However, much was learned about how to do these types of experiments. Secondary traits Traits that are associated with drought tolerance and water use efficiency, but are easier and cheaper to measure, could be useful selection criteria in breeding programmes. We studied a number of morphological and physiological traits that have shown promise in previous studies. New ways of measuring stomatal conductance and specific leaf weight were 2 investigated, and improvements in techniques were made. We field-tested and calibrated a new viscous flow porometer, which should be a useful tool for assaying transpiration capacity, as measurements can be made rapidly on a large number of plants.
Outcomes / Key Message For Growers And Industry
Conclusions These experiments fulfilled the objectives of confirming the ranking of an extended and more diverse set of genotypes than had previously been examined. These genotypes will be useful tools in on-going studies. The relationships between secondary traits and water use efficiency were further elucidated, but the strength of the correlations are not yet strong enough to warrant their immediate use by breeders as indirect selection criteria for drought tolerance or water use efficiency. We have discovered extensive genotypic variation for carbon isotope discrimination ratio, and this trait could be directly applied in breeding programmes for water use efficiency.