Parent-Progeny Relationships for Carbon Isotope Discrimination and Related Characters in Crested Wheatgrass

Improved cultivars of perennial grasses developed for natural resource conservation and forage production on semiarid rangelands of western North America must persist under extreme environmental stress and make efficient use of limited water resources. A close negative relationship has been documented between carbon isotope discrimination (Δ) and water use efficiency (WUE) in temperate ( C3) grasses, and preliminary evidence indicates that Δ would be a promising indirect selection criterion to improve WUE in crested wheatgrass, Agropyron cristatum (L.) Gaertner and Agropyron desertorum (Fisch. ex Link) Schultes, a widely used grass on semiarid rangelands. We determined the magnitude of genetic variability and parent-progeny relationships for Δ and the correlation of this attribute with forage yield in a genetically broad-based crested wheatgrass breeding population. Significant differences (P < 0.01) were found among clonal and progeny lines for Δ of the leaves and seeds. Broad-sense heritability values for leaf and seed Δ computed on a mean basis across two years exceeded 90%. Narrow-sense heritability for leaf Δ, based on parent-progeny regression analysis across two years, was 60%. Broad- and narrow-sense heritability values for dry matter yield (DMY) were substantially less than the corresponding values for Δ. The correlations between Δ and DMY were generally low and nonsignificant. These data confirm earlier, preliminary conclusions that selection for Δ to improve WUE would be a worthy breeding objective in crested wheatgrass and that genetic advances in Δ and DMY could be achieved concurrently.