Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/30/2007
Publication Date: 6/30/2008
Citation: Johnson, R.C., Hopkins, A.A., Evans, M.A. 2008. Carbon Isotope Discrimination, Selection Response, and Forage Production of Tall Fescue in Contrasting Environments. Crop Science 48:10481054. Interpretive Summary: Carbon isotope discrimination (') may be a way to breed crops for improved water use efficiency. In tall fescue, and important forage grass, we found that differences in high and low ' selections made on spaced plants were maintained in solid seed plots in contrasting environments of Pullman WA and Ardmore OK. It was also found that selection for low ' may increase forage production in some environments but not consistently. As such, we recommend one cycle of selection for ' would likely be most efficient and would also be relatively inexpensive. The data shows that this could be done on spaced plants with the expectation of similar ' in solid seeds stands. We further recommend that selection not be carried out under high drought stress, as differences in dehydration avoidance mechanisms may mask genetic differences in '.
Technical Abstract: Carbon isotope discrimination (') usually correlates with the dry matter to transpiration ratio (water use efficiency) in C3 species, but its heritability and relationship to forage production is less clear. In a four year study of tall fescue (Festuca arundinacea Schreb.) at Pullman, WA and Ardmore, OK we determined, 1) if ' differences in divergently selected populations made on single plants were maintained in solid seeded plots, and, 2) how ' in selected populations and a set of four cultivars were related to forage production, leaf N, C, and the C:N ratio. Differences in ' for low and high ' populations selected on spaced plants were maintained in solid seeded plots at both Pullman and Ardmore. At Pullman, the low ' selection had higher production than the high ' selection with the base population intermediate. That pattern was observed at Ardmore in one of six total cuttings. Leaf N, C, and C:N were not consistently related to forage production. Across cuttings, ' was negatively correlated with forage production at Ardmore (r = -0.26**) and positively correlated with production at Pullman (r= 0.71**). But partial correlations of ' with forage production, controlling for cutting effects, were not significant. Partial correlation between ' and forage production on the selected and base populations was significant (r= -0.36*, n=32) at Pullman, but not at Ardmore. The data show selection for low ' may improve forage production, but not consistently. For breeding tall fescue, one cycle of phenotypic selection in advanced material is recommended.