Mapping Genetic Factors Associated with Winter Hardiness, Fall Growth, and Freezing Injury in Autotetraploid Alfalfa

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Abstract
Winter hardiness is a complex trait and one of the most important adaptations for alfalfa (Medicago sativa L.) grown in northern climates. In the absence of winter hardiness data, alfalfa breeders predict the potential of genotypes with component traits related to winter hardiness. This research was undertaken to identify and compare some of the genomic regions that control winter injury (WI) and two component traits, fall growth (FG) and freezing injury (FI). Two plants, B17 and P13, representing the extremes for each trait were crossed, and a F1 plant was backcrossed to each parent to create two populations of 101 individuals each. Each population was scored for 82 single dose restriction fragment loci, and 17 or 19 two‐allele loci and evaluated for FG, FI, and WI in 2 yr of replicated field trials. Trait measures over the 2 yr were significantly correlated (r = 0.71, r = 0.42, and r = 0.76 for FG, FI, and WI, respectively). Significant correlations also existed between WI and FG (r = 0.50 and 0.56) and FI (r = 0.34 and 0.58) for each year. One to six single dose restriction fragment were significant factors in multiple regression models that explained 6.3 to 52.2% of the phenotypic variation for each trait in each year and the average of 2 yr. More of the phenotypic variation was explained in the backcross to B17 (the winter hardy, fall dormant parent) than in the backcross to P13 (the winter sensitive, non‐fall dormant parent) and for FG than for FI and WI. Partial dominance was detected for P13 alleles at most loci associated with FG and for B17 at loci associated with FI. Additive gene action predominated for loci associated with WI. Severe winter kill and the association of FG with plant vigor may have masked identification of quantitative trait loci (QTL) in the P13 backcross. In the B17 backcross, genomic regions that contain QTL affecting FG, FI, and WI were identified on linkage groups 5 and 8, but QTL affecting only FG and FI were identified on linkage groups 1 and 3. These data indicate that there is a genetic basis for the use of predictor traits in the absence of winter hardiness data. However, they also suggest that genetic components of fall dormancy and winter hardiness can be manipulated independently, and they reveal regions that may be useful for marker‐assisted selection with this material.
Funding Information
  • Univ. of Wisconsin-Madison