Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/30/1998
Publication Date: N/A
Interpretive Summary: Production of alfalfa under low-water conditions may be the only way to produce alfalfa in the desert Southwestern USA. Before germplasm can be developed that performs well under these conditions, information must be obtained on how yield can be increased under low-water conditions. This research was performed to investigate various means of identifying variation in traits in alfalfa that can be used to select for yield increases without selecting for yield per se. The primary goal was to identify a means to improve water use efficiency in alfalfa. Carbon isotope discrimination, one technique used to determine the efficiency of water use, was positively correlated with forage yield and forage maturity. The results of this paper indicate that differences in stomatal conductance or photosynthetic capacity exists among the nine populations and that germplasms the with lower carbon isotope discrimination tended to have slower growth and development rates under irrigated conditions.
Technical Abstract: Alfalfa production under irrigated and rain-fed conditions may benefit from improvements in water use efficiency, the amount of forage and root biomass produced per unit of water transpired. This study characterized variation for dry matter yield, forage maturity, leaf to stem ratio, carbon isotope discrimination, canopy temperature, ash content, and specific leaf mass in alfalfa. Nine alfalfa germplasms representing eight of the nine historical genetic diversity groups, and a very fall dormant population, were established in seeded, irrigated plots for two-years near Las Cruces, New Mexico. Significant variation was detected for all traits and was greatest for carbon isotope discrimination and maturity, intermediate for yield, canopy temperature, ash content, and leaf to stem ratio, and least for specific leaf mass. The African, Peruvian, and Indian germplasm exhibited higher carbon isotope discrimination than the Turkistan, M. varia, very fall dormant, or Ladak germplasm. Carbon isotope discrimination was positively correlated with forage yield and forage maturity. The results indicate that differences in stomatal conductance tests or photosynthetic capacity exists among the nine populations, and that germplasms with low carbon isotope discrimination tend to have slower growth and development rates under irrigated conditions.