Assessing wood grain and twist in a 2-year-old Eucalyptus bosistoana breeding population

Key message: Radial grain patterns in young E. bosistoana trees are not random but are under genetic control and are correlated to other properties. Detailed high-resolution grain assessments match results from economical larger resolution techniques. Abstract: Interlocked grain affects stem properties and timber value. Eucalyptus bosistoana is an emerging plantation species that is supported by a breeding programme, and which shows prominent interlocked grain. Grain assessments are difficult, either restricted in their spatial resolution or resource demanding. Comparative analysis of flexible and high-resolution X-ray microtomography grain measurements were shown to match the economical splitting test. Splitting demonstrated that, on average, grain in the 2-year-old E. bosistoana trees was straight close to the pith becoming slightly left-handed over the first 4 mm, but then developing a strong right-handed twist reaching an average of almost 5° by 12 mm. There was, however, a large degree of variability. Further, grain measures obtained from splitting tests correlated to the observed twisting of the stems. Lastly, twisting of timber was under genetic control. The combination of a heritability (h²) value of 0.34 and a coefficient of genetic variation value (r_g) of 44% means that our assessment techniques for young trees could be incorporated into a breeding programme.