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 souther n Great Plains and western United States. Alfalfa (Medicago sativa L.) prod uction in this region mag benefit from improvements in water-use efficiency (WUE), the amount of forage and root biomass produced per unit of,vater tr anspired. If benefits from improved WUE are to be realized, correlations be tween important agronomic traits and key physiological traits associated wi th WUE must he determined under water-limited conditions. This study charac terized genetic correlations among C isotope discrimination (Delta), canopy temperature, ash concentration, dry-matter yield, forage maturity, and lea f tu stem ratio (LSR) in alfalfa grown under water-stressed field condition s. Heritabilities of the traits on a progeny mean basis were also determine d. Thirty semidormant half-sib families were evaluated in seeded plots that Here irrigated every 30 d during 2 yr near Las Cruces, NM. Carbon isotope discrimination was negatively correlated with canopy temperature and ash co ntent. An increase in dry-matter yield was associated with higher Delta, lo wer canopy temperatures, low ash concentration, taller shoots, earlier matu rity, and reduced LSR, Carbon isotope discrimination, ash concentration. an d yield were moderately heritable (h(2) = 0.40-0.56) indicating that these traits could be altered through breeding and selection. The positive relati onship between Delta and shoot yield suggests that germplasms should he eva luated for both Delta and yield when characterizing alfalfa for high WUE to minimize potential yield reductions that may result from selection based o nly on a. Moderate correlations between Delta and canopy temperature or ash content indicated that neither trait provided highly reliable estimates of Delta in water-stressed alfalfa.