Genetic parameters for spiral grain, stem form, pilodyn and growth in 13 years old clones of Sitka spruce (Picea sitchensis (Bong.) Carr.)

Summary Spiral grain measured at ring number 6 or 8 from the pith on 13-years old ramets coming from 191 Sitka spruce clones tested at 4 sites showed a broad sense heritability on single tree level from 0.36 to 0.54. Standard deviations were in the interval from 1.61 to 1.97 degrees and the mean was on all sites about 5 degrees to the left. Predicted genetic gains equal to about 2 degrees reduction of spiral grain in the juvenile wood seems realistic even with moderate selection intensities. Genetic correlations with height, diameter, stem form and pilodyn were small or absent, and almost no genotypeenvironment interaction was present. Individual broad sense heritabilities for heights and diameters were moderate to low ranging from 0.08 to 0.31 and with coefficients of variation about 0.30. Moderate genotype-environment interaction was present for the 2 traits with genetic correlations across sites ranging from 0.57 to 0.85. Pilodyn had a moderate heritability about 0.32 and a coefficient of variation about 8%. The genetic correlation with diameter was 0.53 and with height 0.22 so the density must be taken in consideration when selecting for growth in Sitka spruce. The broad sense heritability for stem form using a scale from 1 to 9 was 0.37 and the coefficient of variation 0.22. Positive, but moderate genetic correlations with diameter and height was present, 0.27 and 0.21 respectively. Pilodyn and stem form were only measured in one trial.

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