Abstract:

Quantitative genetics has long been viewed as a mere tool for solving the problems of tree breeding. However, this view has been challenged by current development of molecular technologies. The development of molecular genetics applied to plant breeding includes two major steps. The first step is the identification of important genetic loci (quantitative trait loci or QTLs)that affect the expression of a quantitative trait using DNA polymorphism markers and the second is the incorporation of the QTLs of interest into commercial populations through genetic manipulation or marker assisted selection strategies. During the past several years, a number of genetic linkage maps based on DNA markers have been constructed in different forest tree species and many QTLs controlling growth, morphology, physiology, and wood properties have been identified. It now turns out to develop efficient breeding strategies for utilizing these QTLs detected to increase genetic gains in operational forestry. In this review, we discuss the fundamental principles of quantitative genetics applied to tree breeding, followed by the strategies for using molecular markers to improve quantitative traits. When a small number of QTLs are targeted, a backcrossing strategy is an efficient way to transfer target genes into recipient species or populations. This strategy can also efficiently remove those undesirable genes that are linked or unlinked with the target genes. The index selection strategy combining both phenotypic and molecular information can be very efficient for improving quantitative traits in which many QTLs are involved. The influences of the index selection strategy on breeding efficiency are discussed.

Key words: Breeding, Forest tree, Marker assisted selection (MAS), Quantitative trait locus (QTL), Quantitative genetics