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Title: The genetics of growth and wood density in Sitka spruce estimated using mixed analysis techniques
Author: John, L. S.
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1997
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This study estimated the variance and covariance components for growth (height and diameter) and wood density within a randomly selected population of Sitka spruce (Picea sitchensis, (Bong.) Carr.) trees known to derive from a single origin. Open-pollinated progeny from the original ortets had previously been planted in a replicated trial and assessed periodically for height, diameter and wood density (indirectly using the Pilodyn) from 1 to 19-years old; 23-year diameter was collected during the study period. Increment cores were also collected from a representative sub-sample of trees identified using a genotypic selection ellipse. Ring-by-ring wood density analysis was carried out using X-ray densitometry. Variance and covariance components for all height, diameter and wood density assessments were estimated using Restricted Maximum Likelihood (REML). Family heritability for growth traits varied little over a 23-year period (1-year height = 0.61; 23-year diameter = 0.57). Individual tree heritability was more variable, reaching a peak at 7-year height (0.38) and then falling with age to 17-year diameter (0.12). Optimum family and individual tree selection ages for growth were found to be 5-year and 9-year height (breeding goal of 23-year diameter), and 3-year and 7-year height (breeding goal of 40-year diameter) from planting respectively; the latter were estimated with the use of a Lambeth regression equation. Wood density was found to be more heritable than growth at equivalent ages, although estimates decreased with increasing age (individual tree heritability of the outer 4 rings at 9 and 22-years old of 0.85 and 0.34 respectively). Precision and accuracy of estimated variance components and heritabilities were unacceptable unless the traits used to calibrate the selection ellipse were included as covariates. Genetic correlations between all juvenile ring-groupings and the selection goal (outer 4-rings at 22-years from planting) were near unity. The optimum family and individual tree selection age for wood density was found to be the outer 4-rings at 9-years from planting.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available