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Quantitative genetics and QTL mapping of growth and wood quality traits in coastal Douglas-fir Ukrainetz, Nicholas K.


Coastal Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var menziesii) is one of the most commercially important tree species on the west coast of British Columbia and the United States due largely to its superior wood quality. Several growth and wood quality traits, including height, diameter, volume, earlywood, latewood and average density, latewood proportion, fibre length and coarseness, and complete cell wall chemistry, were measured for 600, 26 year old Douglas-fir trees from 15 full-sib families located on four sites in southwestern British Columbia. Bud samples were collected and DNA isolated for molecular marker analysis. Family data were used to calculate broad-sense heritabilities, and genetic, phenotypic and family mean correlations for all traits. Amplified fragment length polymorphism (AFLP) data from eight families was used to generate a linkage map employing a joint likelihood function, which contained 19 linkage groups with 120 markers spanning 938.6cM of the Douglas-fir genome. A QTL map for commercially important traits was created using a combination of interval mapping by sib-pair analysis and single locus analysis by analysis of variance. Fibre properties have the lowest heritability (0.10 - 0.18), while glucose content has the highest heritability (0.98). Growth traits are under moderate genetic control (0.23 - 0.30) as is microfibril angle (0.20). For growth ring traits, earlywood density and average density have moderately high heritabilities (0.54 and 0.47, respectively) followed by latewood proportion (0.30) and latewood density (0.21). Average density is influenced primarily by the proportion of latewood (0.85) and earlywood density (0.74). Growth traits, which are important components of tree improvement programs, are generally positively correlated with fibre traits, microfibril angle and lignin content, but negatively correlated with density and cell wall carbohydrate content. Twenty-two QTLs were detected for compound traits that explained between 3.6% and 17.7% of the phenotypic variation. An additional 78 individual ring density QTLs were identified which form 11 QTL clusters and 11 independent QTLs. The resulting map should serve as a valuable scaffold for future metabolite QTL mapping and comparative genomic projects.

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