Theoretical Expected Genetic Gains for Among‐and‐Within‐Family Selection Methods in Perennial Forage Crops

Abstract

Genetic gains in forage yield lag far behind the gains made in grain yield of cereal crops, partly because of 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 (i) to compute expected genetic gains for among‐and‐within‐family (AWF) selection methods, (ii) to compare these selection methods to standard family and progeny‐test selection methods, and (iii) to define the conditions under which AWF selection methods may be superior to progeny‐test selection. Among‐and‐within‐family selection is equal to or better than family selection under all circumstances provided the within‐family selection criterion (X or Y) is heritable and has a positive genetic correlation with the desired trait (Y). Among‐and‐within‐family selection is favored over progeny‐test selection by (i) high heritability on an individual‐plant basis (relative to heritability on a family‐mean basis), (ii) within‐family selection intensity ≥ among‐family selection intensity, and (iii) 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.