Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/4/2008
Publication Date: 5/20/2008
Citation: Casler, M.D., Brummer, E.C. 2008. Expected Genetic Gains for Four Among-and-Within-Family Selection Methods in Perennial Forage Crops. Crop Science. 48:890-902. Interpretive Summary: Among-and-within-family selection is a method of breeding forage crops that has received little use and attention by forage breeders. It involves planting families of plants in a replicated and randomized design, collecting data on every plant, and selecting only the best plants from within the best families. Our paper has defined the conditions under which this selection method is expected to be superior to more conventional selection methods. These include: more intensive selection within families, equal heritability among vs. within families, and shorter generation times. Our review of the literature indicates that these conditions should be realized in many breeding populations and many breeding programs, suggesting that forage breeders can greatly improve the efficiency of their breeding programs by using this selection method. Adoption of these selection methods will increase genetic gains, resulting in better forage varieties for forage producers.
Technical Abstract: Genetic gains in forage yield lag far behind the gains made in grain yield of cereal crops, partly due to the use of inefficient selection methods that make little use of additive genetic variance within half-sib or full-sib families. The objectives of this study were (1) to compute expected genetic gains for among-and-within-family (AWF) selection methods, (2) to compare these selection methods to standard family and progeny-test selection methods, and (3) to define the conditions under which among-and-within-family selection methods might be superior to progeny-test selection. AWF selection is equal to or better than family selection under all circumstances except when the genetic correlation between the within-family selection criterion (X) has positive heritability and a negative genetic correlation with the among-family selection criterion (Y). AWF selection is favored over progeny-test selection by: (1) high heritability on an individual-plant basis (relative to heritability on a family-mean basis), (2) within-family selection intensity among-family selection intensity, and (3) possibly a shorter cycle time (for some species and some breeding programs). These conditions are more frequently achieved for half-sib mating systems due to the greater partitioning of additive genetic variance within families, but AWF selection can also be heavily favored in a full-sib mating system, under conditions that are a bit more restrictive.