Genetic mapping and physiological characterization of water-use efficiency in barley (Hordeum vulgare L.) on the Canadian Prairies

Temporal or seasonal water deficit is one of the major factors limiting crop yield on the Canadian Prairies. Empirical knowledge suggests that carbon isotope discrimination (Delta13C), through its negative relationship with water-use efficiency (WUE), is a good index for selecting crop varieties with stable yield in some rain-fed environments. Identification of quantitative trait loci (QTL) and linked markers for leaf Delta13C will help select genotypes with improved WUE in breeding programs. This thesis research investigated the genetic and physiological determinants of Delta 13C variation in Canadian spring barley (Hordeum vulgare L.) and used two recombinant inbred line (RIL) mapping populations, including 200 RILs of W89001002003 x I60049 (six-row type) and 127 RILs of Merit x H93174006 (two-row type) to identify QTLs and their linked molecular markers for the trait.;The parental lines used to produce the mapping populations and several of the RILs maintained consistent ranking of leaf Delta13C across years and in different experiments. The broad-sense heritability of leaf Delta13C was 0.8, suggesting stability of this trait under the environments studied. Leaf Delta13C was positively correlated with stomatal conductance (gs) in both greenhouse and field experiments, suggesting that gs caused most of the variation in leaf Delta13C. Low leaf Delta 13C genotypes such as 'CDC Cowboy' and RIL '147' achieved high WUE and yield by maintaining a high photosynthesis rate at a low gs, which suggests that it is possible to select low Delta13C genotypes that can maintain high yield under low moisture conditions.;Using two mapping populations and phenotypic data for leaf Delta 13C and agronomic traits collected from 4 different field environments, a total of 12 (six-row population) and 5 (two-row population) QTLs for leaf Delta 13C were detected. A transgressive segregation pattern for leaf Delta 13C was observed among RILs. For the six-row RILs, a major QTL for leaf Delta13C co-located with several agronomic traits on chromosome 3H near SSR marker Bmag606 (9.3, 9.4 and 10.7 cM interval) was identified across environments. This marker when validated may be useful in breeding programs for improving WUE and yield stability of barley on the Canadian Prairies.