Genetic Control of Air-Dried Wood Density, Mechanical Properties and Its Implication for Veneer Timber Breeding of New Triploid Clones in Populus tomentosa Carr.

The wood samples of 9 triploid clones of Populus tomentosa Carr.taken from a 9-year-old clonal test site were analyzed in order to investigate the genetic variation of wood properties, including air-dried wood density and some mechanical properties. The results showed that significant or extremely significant difference in air-dried wood density and the mechanical properties existed among the clones, this means these wood properties were under moderate or strong genetic controls and could be improved by genetic manipulations. The radial and vertical variation patterns of air-dried wood density were also studied and the results were found to coordinate with other previous research results. The vertical variation patterns of most mechanical properties within the individual tree also conformed to the general wood theories except the modulus of elasticity and cross section hardness. Among the mechanical properties, modulus of elasticity (MOE)and tangent section hardness were under strong genetic control, with the clonal repeatabilities being 0.90 and 0.80, respectively. However, the clonal repeatabilities of other mechanical properties under study were a little lower than above two indexes. Genetic correlation analysis indicated that super clonal selection and breeding for veneer timber could be realized through indirect selection of wood density and form indexes.