CARBON-ISOTOPE DISCRIMINATION, ASH, AND CANOPY TEMPERATURE IN 3 WHEATGRASS SPECIES

Soil water is the main factor influencing forage production in the sem iarid Northern Great Plains. Developing germplasm that uses limited wa ter more efficiently would benefit forage production for hay and lives tock grazing. Development of selection criteria suited to screening la rge breeding populations for water-use efficiency (WUE) are needed to enhance this effort. This study evaluated carbon isotope discriminatio n (Delta), tissue ash concentration, and canopy temperature of populat ions of diploid crested wheatgrass (Agropyron cristatum L.), tetraploi d crested wheatgrass [A. desertorum (Fisch. ex. Link) Schult.], and we stern wheatgrass [Pascopyrum smithii (Rybd.) Love] to determine the ut ility of using ash concentration and canopy temperature as alternative criteria to Delta for selecting plants with high WUE. Tissue ash conc entration, canopy temperature, and Delta were measured on half-sib fam ilies from genetically broad-based populations of each species across two field growing seasons. Sufficient genetic variation was present fo r Delta and ash concentration among families within each species to su ggest possible use of these traits as criteria for selecting plants wi th higher WUE. Differences in canopy temperature among families were p resent only in 1994. Correlations between ash and Delta were greatest for tetraploid crested wheatgrass and least for western wheatgrass. Co rrelation of canopy temperature with Delta was significant for tetrapl oid crested wheatgrass both years and for diploid crested wheatgrass i n 1993, but neither year for western wheatgrass. Ash concentration and Delta were moderately heritable in all three grass populations, indic ating that both traits are under genetic control and could likely be a ltered through breeding. Using ash and canopy temperature as criteria for selecting plants with greater WUE would provide a relatively low-c ost, simple approach to develop cultivars with improved WUE.