Marker-aided selection and propagation systems in trees: advantages of cloning for studying quantitative inheritance

Abstract

Genetic maps with a high density of markers have been used to locate discrete Mendelian components of quantitatively inherited traits in a few crop plants. In principle, a similar approach can be used to map economically important quantitative trait loci in trees; however, tree pedigrees and propagation systems are quite different from those used in crops. Recent theoretical work suggests that clonal propagation of advanced generation offspring from pedigrees segregating for molecular marker genotype, and with substantial segregating variation in the phenotype(s) of interest, is an effective strategy for linkage analysis of polygenic traits. The successful application of marker-aided selection to tree improvement depends upon precise estimation of phenotypic variation attributable to marker genotype even when heritability is low, and clonal testing is the best experimental design to achieve this goal. For many practical reasons (including replication of plantations in time and space, destructive sampling, or sharing known genotypes with other researchers), clonal propagation maximizes the benefits from genome mapping efforts.