Forward selection in a maritime pine polycross progeny trial using pedigree reconstruction

Abstract

Molecular markers were used for paternity recovery in a maritime pine ( Pinus pinaster Ait.) polycross trial, facilitating forward selection. Different breeding strategies for seed orchard establishment were evaluated by comparing genetic gains and diversity. This work opens up new perspectives in maritime pine breeding. Polycross mating designs are widely used in forest tree breeding to evaluate parental breeding values for backward selection. Alternatively, polycross progeny trials may be used to select the best trees on the basis of individual breeding values and molecular pedigree analysis. This study aimed to test such a forward selection strategy for the maritime pine breeding program. In a maritime pine polycross trial, progeny with higher breeding values for growth and stem straightness was first preselected with or without relatedness constraints. After paternity recovery, the preselected trees were ranked on the basis of their breeding values, estimated from the recovered full pedigree. Finally, the best candidates were selected with three different strategies (forward, backward, mixed) and three levels of coancestry constraints to establish a virtual clonal seed orchard. Complete pedigrees were successfully recovered for most of the preselected trees. There was no major difference in expected genetic gains between the two preselection strategies which differed for relatedness constraints. Genetic gains were slightly higher for forward selection than for classical backward selection. This seminal study opens up new perspectives for using forward selection within the French maritime pine breeding program.