Genetic mapping forage yield, plant height, and regrowth at multiple harvests in tetraploid alfalfa (Medicago sativa L.)

Hybrids between Medicago sativa subsp. falcata and M. sativa subsp. sativa can result in high levels of heterosis for alfalfa forage production. However, commercially viable alfalfa cultivars also must have acceptable performance for other agronomic traits, including regrowth following harvest and appropriate autumn dormancy. In this study, we characterized an F, population derived from the cross of the two subspecies for the genetics of forage production, forage height, and forage regrowth at three harvests in two Iowa locations for 1 yr. Quantitative trait loci (QTLs) controlling these traits were mapped on a genetic linkage map developed from this population. Broad-sense heritabilities and genetic correlations among the traits were high. Marker alleles associated with QTLs for these traits were contributed by each parental genome, suggesting that both subspecies of cultivated alfalfa may contribute to the improvement of these traits. Multiple regression models accounted for between 11 and 44% of the trait variation. The most marker-trait associations were detected during the first harvest. Marker effects were generally similar across harvests. Markers associated with autumn regrowth tended to be different from those associated with regrowth earlier in the season, suggestive of the identification of autumn dormancy effects. The winter hardiness gene MsaciB is a candidate locus for yield and regrowth, being associated with yield across three harvests and with autumn regrowth. A subset of alleles was associated with more than one of the traits. Major alleles for the three traits appear to reside primarily on linkage groups (LGs) 3, 4, 5, and 7.