Genetic parameters for wood and growth properties in Araucaria cunninghamii.
All available information on genetic variation in wood properties of Queensland hoop pine is drawn together and examined. Results come from two half-sib progeny trials and one full-sib progeny trial, all about 15 years old. Previously reported parameter estimates, from a wood study on one of the half-sib progeny trials containing 25 families, were supported with new results from 22 families of which 17 were unrelated to the families in the earlier trial. Pooled narrow-sense heritability estimates obtained from the combined data of the two half-sib progeny trials were 0.60 for basic density, 0.19 for percentage compression wood, 0.36 for mean spiral grain, 0.17 for diameter and 0.58 for straightness. Approximate standard errors of the 4 estimates ranged from 0.10 to 0.16. Heritability of grain spirality at 6 equally spaced points from pith to bark averaged about 0.20 but peaked at 0.35 (approximate standard error = 0.12) for the third sampling point from the pith, where average spirality was greatest. Selection procedures that emphasize growth and straightness and ignore wood quality traits are likely to increase basic density, decrease spiral grain and lead to a small increase in compression wood. Improvements in spiral grain and compression wood can be ensured by further selecting plus tree candidates for these wood traits. However, genetically controlled increases in density can probably only be restricted by decreasing the rate of improvement in straightness. Estimation of non-additive or dominance variance, by comparing the components of variance of the full-sib and half-sib results, was not successful. Negative estimates of dominance variance for compression wood and mean spiral grain, as well as high standard errors associated with all estimates, called into question the value of this technique. Offspring-parent regressions suggested that screening plus trees for basic density and spiral grain could be effective in providing a genetic ranking for these parameters, even though the plus trees may be of different ages and growing in different environments.