Variation in Water‐Use Efficiency and Its Components in Wheat: I. Well‐Watered Pot Experiment

Abstract

Genetic variation exists for season‐long water‐use efficiency (WUE) among bread wheat (Triticum aestivum L.) cultivars. To facilitate the study of such variation, we define WUE and its components so that the contribution of each component trait to variation in WUE can be evaluated. Seven diverse bread wheat cultivars were grown in replicated glasshouse pot experiments under well‐watered conditions. Significant genotypic variation was observed for WUE (ratio of grain yield to water used), evapotranspiration efficiency (ETE, ratio of total dry matter to water used), and harvest index (HI, ratio of grain yield to total dry matter). Old tall cultivars, on average, had relatively higher ETE (3.95 vs. 2.67 g kg−1), but much lower HI (0.35 vs. 0.53) than modern semidwarf and dwarf cultivars. Cultivars with similar WUE showed different patterns of component traits. Evapotranspiration efficiency, and HI accounted for 59%, and 41%, respectively, of the genotypic variation in WUE. A path coefficient analysis revealed that ETE had a higher direct effect on WUE than did HI. However, their positive direct effects were counterbalanced by negative indirect effects via each other, because ETE and HI were negatively correlated. Carbon isotope discrimination showed a negative correlation with WUE (−0.62) and ETE (−0.84), but a positive correlation with HI (0.43). Days from planting to maturity, plant height, root dry matter, and shoot dry matter each had a positive correlation coefficient with ETE, but a negative correlation with HI.