Carbon Isotope Discrimination, Ash, and Canopy Temperature in Three Wheatgrass Species

Soil water is the main factor influencing forage production in the semiarid Northern Great Plains. Developing germplasm that uses limited water more efficiently would benefit forage production for hay and livestock grazing. Development of selection criteria suited to screeniing large breeding populations for water‐use efficiency (WUE) are needed to enhance this effort. This study evaluated carbon isotope discrimination (Δ), tissue ash concentration, and canopy temperature of populations of diploid crested wheatgrass ( Agropyron cristatum L.), tetrapioid crested wheatgrass [A. desertorum (Fisch. ex. Link) Schult.], and western wheatgrass [ Pascopyrum smithii (Rybd.) Love] to determine the utility of using ash concentration and canopy temperaturea s alternative criteria to Δ for selecting plants with high WUE. Tissue ash concentration, canopy temperature, and Δ were measured on half‐sib families from genetically broad‐based populations of each species across two field growing seasons. Sufficient genetic variation was present for Δ and ash concentration among families within each species to suggest possible use of these traits as criteria for selecting plants with higher WUE. Differences in canopy temperature among families were present only in 1994. Correlations between ash and Δ were greatest for tetraploid crested wheatgrass and least for western wheatgrass. Correlation of canopy temperature with Δ was significant for tetraploid crested wheatgrass both years and for diploid crested wheatgrass in 1993, but neither year for western wheatgrass. Ash concentration and Δ were moderately heritable in all three grass populations, indicating that both traits are under genetic control and could likely be altered through breeding. Using ash and canopy temperature as criteria for selecting plants with greater WUE would provide a relatively low‐cost, simple approach to develop cultivars with improved WUE.