Little Heterosis between Alfalfa Populations Derived from the Midwestern and Southwestern United States

Increasing the yield of alfalfa ( Medicago sativa L.) is a desirable breeding goal. The objective of this experiment was to test the hypothesis that hybrids between nondormant‐derived alfalfa germplasm selected for winter hardiness and semidormant germplasm will express heterosis for yield. Four semidormant cultivars and four nondormant‐derived populations were handcrossed in a half‐diallel mating design to form population hybrids. Both seeded and transplanted trials were grown in Iowa between 2003 and 2005. Total biomass yield was measured at four harvests each year. The nondormant‐derived germplasm produced lower yields than the semidormant cultivars. The hybrids between groups were intermediate to the parents with little evidence of heterosis in any environment or for any harvest during the year. Although particular crosses produced high yields in certain environments, no general heterotic pattern was observed between the two proposed groups. A Gardner and Eberhart Analysis III indicated the presence of variation for both general combining ability and specific combining ability effects of approximately equal magnitude among these eight populations. The nondormant germplasm sources used here do not form a new heterotic group for midwestern U.S. alfalfa breeding programs.