ABSTRACT
Forest trees are fascinating organisms of considerable significance ecologically, aesthetically, and economically. The role of genetics is seldom apparent when observing natural populations of forest trees. Trees growing in nature are found in heterogeneous environments, often in uneven-aged stands, and in admixture with other species. Populus, along with other forest trees, is in the earliest stages of domestication. The choice of breeding and selection schemes presently made will have long-term impacts on the success of domestication and conservation of wild germplasm. One important outcome of quantitative trait loci (QTL) mapping in Populus is that for the first time there is objective evidence that “major” genes may be responsible for some of variation observed in quantitative traits, such as stem volume growth, in a forest tree. The discovery of “major” QTLs, often with nonadditive effects, might seem to present a challenge to the orthodox “infinitesimal” model of quantitative trait variation assumed by most quantitative genetics theory and by many tree breeders.
