Physiological characterization of recombinant inbred lines of barley with contrasting levels of carbon isotope discrimination

Carbon isotope discrimination (Delta C-13) in C-3 plants used as an indirect measure of water-use efficiency (WUE) provides a tool for selecting crops with high WUE under dry environments. We evaluated the physiology and Delta C-13 of a set of 8 F-5 recombinant inbred lines (RILs) with contrasting levels of leaf Delta C-13 derived from two parents, 'W89001002003' (low Delta C-13) and 'I60049' (high Delta C-13) of six-row barley (Hordeum vulgare L.) in a greenhouse and under field conditions in three locations (Lacombe, Vegreville and Castor). In the greenhouse experiment, seven days of water deficit was imposed at the stem elongation stage followed by re-watering to pre-deficit level. A significant negative relationship between WUE and leaf Delta C-13 was observed. Under water-deficit conditions, both photosynthetic rate (A) and stomatal conductance (g (s) ) were significantly reduced with a strong positive correlation (r = 0.89) between the two, and the variation in g (s) was proportionally greater than A. The low leaf-Delta C-13 RIL '147' maintained the highest A and g (s) among ten genotypes (RILs and parents) under water-deficit conditions. Leaf Delta C-13 was positively correlated with biomass and grain yield in the field trials. Multivariate analysis of leaf Delta C-13, harvest index and plant height discriminated genotypes into three clusters: drought sensitive, drought tolerant and an intermediate type. The study suggests that it is possible to select low Delta C-13 lines such as RIL '147', which is able to maintain or produce high yields under low moisture conditions on the Canadian Prairies.