VARIATION FOR YIELD, WATER-USE EFFICIENCY, AND CANOPY MORPHOLOGY AMONG 9 ALFALFA GERMPLASMS

Alfalfa (Medicago sativa L,) production under irrigated and rainfed co nditions may benefit from improvements in water-use efficiency (WUE), the amount of forage and root biomass produced per unit of water trans pired. If benefits from improved WUE are to be realized, correlations between important agronomic traits and key physiological traits associ ated with WUE must be determined. This study characterized variation f or dry matter yield, forage maturity, leaf-to-stem ratio (LSR), carbon isotope discrimination (Delta), canopy temperature, ash content, and specific leaf mass (SLM) in alfalfa. Associations between traits were also determined. Nine alfalfa germplasms representing eight of the nin e historical genetic diversity groups, and a very fall-dormant (VFD) p opulation, were established in seeded, irrigated plots for 2 yr near L as Cruces, NM. Significant variation (P less than or equal to 0.10) wa s detected for all traits and was greatest for Delta and maturity, int ermediate for yield, canopy temperature, ash content, and LSR, and lea st for SLM. The African, Peruvian, and Indian germplasms exhibited a h igher Delta than either the Turkistan, VFD, M. varia Martyn., or Ladak germplasms, Carbon isotope discrimination was positively correlated w ith forage yield (r = 0.64; P less than or equal to 0.10; n = 9) and f orage maturity (r = 0.66; P less than or equal to 0.05; n = 9), No ass ociation was detected between Delta and either canopy temperature, ash content, SLM, or LSR. The results indicate that differences in stomat al conductance or photosynthetic capacity exist among the nine populat ions, and that germplasms with low Delta tended to have slower growth and development rates under irrigated conditions. Neither canopy tempe rature, ash content, nor SLM provided suitable alternate measurements of Delta among the nine alfalfa germplasms.