Carbon isotope discrimination of two-rowed and six-rowed barley genotypes under irrigated and non-irrigated field conditions

Abstract

Carbon isotope discrimination (Δ) has been widely used to estimate the water-use efficiency (WUE) of C3 cereals including barley (Hordeum vulgare L.). Genetic lines of barley belong to two phenotypic classes for ear morphology, either two-rowed or six-rowed, a simply inherited trait. We tested the value of Δ as a predictor of grain yield and WUE for these two types of barley under different conditions of water availability. We also investigated if differences in plant morphology and yield parameters between these two types resulted in different carbon dynamics and different Δ values for grain, awn and flag leaf. We conducted field experiments for 3 consecutive years with genetic lines of both ear types in northern Utah and southeastern Idaho under irrigated and non-irrigated conditions, including two line-source sprinkler experiments. Correlations between grain yield and Δ values of flag leaf, awn and grain were stronger in combined analyses across ear types than in analyses within two-rowed (2R) and six-rowed (6R) types. Nevertheless, we found that Δ of mature awns and grains were a good predictor of yield for both barley types under low to moderate water stress. However, Δ was not a reliable predictor for barley yield under severe water stress. Pearson's correlations were used to test associations between Δ values and several yield parameters (heading date, above-ground dry matter, harvest index, grain mass per fertile tiller). Our data indicated that among the field-grown genetic lines tested, the two types of barley differed in Δ values for grain, awn and flag leaf. Values of Δ for 2R barley were usually lower, suggesting higher WUE, than those for 6R types. Fundamental differences in sink size or grain mass per fertile tiller between 2R and 6R cultivars probably have important consequences on carbon/water metabolism at the whole tiller level.