Heterosis of Agronomic Traits in Alfalfa

Abstract

Increasing forage yields remains a top priority of most alfalfa (Medicago sativa L.) breeding programs. Studies of crosses between dormant to moderately dormant M. sativa subsp. sativa and M. sativa subsp. falcata suggest a heterotic pattern for yield exists between the two subspecies. However, other agronomic traits need to be considered in addition to yield, especially when trying to develop breeding material from nonadapted sources. The objective of this study was to quantify the agronomic performance of sativa × falcata crosses (SFC) in relation to 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 Nashua and Ames, IA. During the 1999 growing season, winter injury, spring regrowth, vigor, growth habit, maturity, height, midseason regrowth, and autumn regrowth were measured. The 14 parental genotypes differed for general combining ability (GCA) for all traits; specific combining ability (SCA) was noted for height, maturity, winter injury, and vigor. Sativa × sativa crosses were superior to FFC for all traits except winter injury and vigor. Sativa × falcata crosses per se had slightly increased agronomic performance over the expected mid-subspecies for many traits. Most of the hybrids are intermediate to SSC and FFC, suggesting potential agronomic weaknesses of falcata germplasm in a breeding program. Improving regrowth, height, and growth habit of falcata breeding material would likely be needed to create commercially successful sativa–falcata semihybrid cultivars.