Heritabilities of Water-Use Efficiency Traits and Correlations with Agronomic Traits in Water-Stressed Alfalfa
Inadequate supplies of surface water limit forage production in the southern Great Plains and western United States. Alfalfa (Medicago sativa L.) production in this region may benefit from improvements in water-use efficiency (WUE), the amount of forage and root biomass produced per unit of water transpired. If benefits from improved WUE are to be realized, correlations between important agronomic traits and key physiological traits associated with WUE must be determined under water-limited conditions. This study characterized genetic correlations among C isotope discrimination (Δ), canopy temperature, ash concentration, dry-matter yield, forage maturity, and leaf-to-stem ratio (LSR) in alfalfa grown under water-stressed field conditions. Heritabilities of the traits on a progeny mean basis were also determined. Thirty semidormant half-sib families were evaluated in seeded plots that were irrigated every 30 d during 2 yr near Las Cruces, NM. Carbon isotope discrimination was negatively correlated with canopy temperature and ash content. An increase in dry-matter yield was associated with higher Δ, lower canopy temperatures, low ash concentration, taller shoots, earlier maturity, and reduced LSR. Carbon isotope discrimination, ash concentration, and yield were moderately heritable (h2 = 0.4–0.56) indicating that these traits could be altered through breeding and selection. The positive relationship between Δ and shoot yield suggests that germplasms should be evaluated for both Δ and yield when characterizing alfalfa for high WUE to minimize potential yield reductions that may result from selection based only on Δ. Moderate correlations between Δ and canopy temperature or ash content indicated that neither trait provided highly reliable estimates of Δ in water-stressed alfalfa.
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