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CROP BREEDING, GENETICS & CYTOLOGY

Diallel Analysis of Carbon Isotope Discrimination and Its Association with Forage Yield among Nine Historically Recognized Alfalfa Germplasms

^a Dep. of Agronomy and Horticulture, New Mexico State Univ., Las Cruces, NM 88003
^b University Statistics Center, New Mexico State Univ., Las Cruces, NM 88003

^* Corresponding author (iaray{at}nmsu.edu)

Designing effective breeding strategies to integrate selection for carbon isotope discrimination (), as a means to improve alfalfa (Medicago sativa L.) water-use efficiency (WUE), will depend upon the association between and forage yield. The current study was conducted to determine responses in affiliated with significant yield responses that were previously observed among 36 diallel hybrids of nine alfalfa germplasms (commonly referred to as African, Chilean, Flemish, Indian, Ladak, M. falcata, M. varia, Peruvian, and Turkistan). The influence of additive and nonadditive gene action on , and the behavior of across harvests was also determined. Forage yield and of the germplasms and their half-diallel hybrids were evaluated near Las Cruces, NM, during May, June, and July in each of 2 yr in seeded plots that were flood irrigated every 14 d. Values for of hybrids did not significantly exceed those of the most extreme parents in any harvest. Variation for among crosses was attributed primarily to general combining ability (GCA) effects. The magnitude of parental per se and GCA effects, and their ability to predict hybrid varied substantially between the first harvest and later harvests. Variety effects for in Ladak, M. varia, and M. falcata became increasingly negative as the growing season progressed, while those for African, Chilean, Flemish, Indian, Peruvian, and Turkistan increased. Results suggest that fundamental differences in stomatal conductance exist between subspecies sativa and falcata.

Abbreviations: , carbon isotope discrimination • GCA, general combining ability • SCA, specific combining ability • WUE, water-use efficiency