Genetic response to within-family selection using molecular markers in some radiata pine breeding schemes

Marker-assisted selection (MAS) provides an opportunity to increase the eff iciency of within-family selection in forest tree breeding. Within-family M AS involves selection decisions first made on conventional breeding values and quantitative trait loci (QTL) information used for within-family select ion. In this study genetic response obtained by using MAS was compared with conventional methods for three options: "full-sib family forestry," "clona l forestry," and "forward selection for deployment." This comparison was un dertaken using stochastic simulation for a locus that explained 10 or 20% o f the genetic variance. In the full-sib family forestry scenario, markers w ere used to select genotypes (among juvenile individuals in a family) for v egetative propagation. Markers were used to preselect genotypes for clonal testing in clonal forestry option. In case of forward selection for deploym ent option, offspring that have favourable marker haplotype and a superior phenotype were selected from each family. The comparison between the MAS an d the conventional strategy was evaluated in genetic terms based on compari son of the average genetic merit of the genotypes used for deployment in pr oduction plantations. The relative genetic gain (%) using MAS were found to be 4-8% and 2-3% higher compared with conventional strategy for full-sib f amily forestry and clonal forestry options, respectively. In case of forwar d selection for deployment option, MAS was generally found to be providing higher genetic gain only when the heritability is low.