Genetic effects on wood quality traits of plantation-grown white spruce (Picea glauca) and their relationships with growth

Abstract

Clonal repeatabilities on individual tree ($H_i^2$) and clonal mean ($H_{{\overline C }}^2$) bases for growth (14-year height and volume), wood quality traits (latewood proportion, wood density, fiber length, and microfibril angle), and genotypic correlations among the traits were estimated, using 30 white spruce (Picea glauca [Moench] Voss) clones from six full-sib families (five per family). These families were selected from a clonally replicated test to represent different early growth categories: fast, moderate, and slow. Wood increment cores of the 30 clones were collected from two contrasting sites at age 19 years. For growth traits, in contrast to most wood quality traits, more genetic variation was accounted for by clone within family than by family within growth category. Both growth and wood quality traits appear to be under moderate genetic control, with $\widehat{H}_i^2 = 0.20 - 0.36$ and $\widehat{H}_{{\overline C }}^2 = 0.70 - 0.83$. The only exception was microfibril angle ($\widehat{H}_i^2 = 0.10\;{\text{and}}\;\widehat{H}_{{\overline C }}^2 = 0.34$). Generally, faster growth resulted in a significantly lower latewood proportion and lower overall wood density. Selection for faster growth does not appear to impact on either fiber length or microfibril angle. Among the wood quality traits, significant genotypic association was observed only between latewood proportion and wood density. Despite the generally negative association between growth and wood density among families, several fast-growing clones maintained above-average density. This implies that, by adopting multiclonal forestry, one can simultaneously improve growth and wood density.