ABSTRACT
Fundamental to current efforts towards the genetic improvement of forest tree species is our understanding of the molecular basis for genetic control of phenotype. In an evolutionary sense it is specifi cally the ability of trees to undergo secondary growth and the versatility of the process of wood formation that enables them to adapt to ever-changing environments over long period of time. Short rotation times together with silvicultural support allow us to specifi cally target for ‘improvement’ in such traits that are of commercial (rather than biological) interest. Such complex traits, which do not follow the classical Mendelian monogenic inheritance, are not easily dissected and efforts to do so are hindered by the variability of wood properties within and between stems, long generation times, late age expression of commercially important traits, high heterozygosity, high genetic load, seasonal dormancy, long mature trait establishment period and the sheer physical size of mature trees (Bossinger et al. 2007). It is also diffi cult to identify markers that exhibit perfect cosegregation with complex traits because of epistasis, incomplete penetrance, phenocopy, locus heterogeneity, and polygenic inheritance (Lander and Schork 1994).
