Heterosis between semidormant and nondormant derived alfalfa germplasm
Alfalfa (Medicago sativa L.) yield has not increased over the past 25 years in the Midwestern United States. One way to increase yield in alfalfa is through capturing heterosis. Heterotic groups are genetically distinct germplasms that, when hybridized, repeatedly produce progeny that express heterosis. In alfalfa, three main heterotic groups have been proposed in the United States: dormant M. falcata, semidormant M. sativa, and nondormant M. sativa. Nondormant alfalfa cannot be used in the upper Midwestern United States due to severe winterkill. Three cycles of recurrent selection were conducted in four nondormant cultivars and winter hardiness was substantially improved in all four. The objective of this study was to test the hypothesis that the nondormant derived alfalfa germplasm represents a heterotic group distinct from Midwestern United States cultivars. Four elite Midwestern alfalfa cultivars and the four nondormant derived populations were hand crossed in a half diallel mating design. A seeded trial was established at one Iowa location in 2003 and transplanted trials grown at two locations at 2004. In spite of the observation of better yield in some of the particular crosses, a general heterotic pattern was not observed between the two proposed groups.