Forage Yield Heterosis in Alfalfa

Abstract

Increasing forage yields remains a top priority of most alfalfa (Medicago sativa L.) breeding programs, but yield trends suggest yield has stagnated over the past two decades. Little effort has been invested into capturing heterosis in alfalfa, but semihybrid breeding systems are a possible solutions to overcome forage yield stagnation. Development of alfalfa semihybrids will require identification of heterotic groups. Studies of crosses between dormant M. sativa ssp. sativa and M. sativa ssp. falcata suggest a heterotic pattern exists between the two subspecies. The objective of this study was to measure heterosis in elite sativa × falcata crosses (SFC) in relation to elite sativa × sativa crosses (SSC) and falcata × falcata crosses (FFC). Nine elite sativa clones and five falcata clones were crossed in a diallel mating design. Progeny were space planted in 1998 at Ames and Nashua, IA, and harvested for forage yield twice in 1998 and three times in 1999. A definite sativa–falcata heterotic pattern was observed. Sativa–falcata heterosis was observed at the subspecies, halfsib, and individual cross level calculated using subspecies comparisons, halfsib heterosis analysis, and combining ability analysis. On average, intersubspecific crosses yielded 18% more than the average of intrasubspecific crosses. The sativa–falcata heterotic pattern is a potentially useful resource in alfalfa breeding programs.