Forest trees are ideally suited to association mapping due to their high levels of diversity and low genomic linkage disequilibrium. Using an association mapping approach, single-nucleotide polymorphism (SNP) markers influencing quantitative variation in wood quality were identified in a natural population of Pinus radiata. Of 149 sites examined, 10 demonstrated significant associations (P , 0.05, q , 0.1) with one or more traits after accounting for population structure and experimentwise error. Without accounting for marker interactions, phenotypic variation attributed to individual SNPs ranged from 2 to 6.5%. Undesirable negative correlations between wood quality and growth were not observed, indicating potential to break negative correlations by selecting for individual SNPs in breeding programs. Markers that yielded significant associations were reexamined in an Australian land race. SNPs from three genes (PAL1, PCBER, and SUSY) yielded significant associations. Importantly, associations with two of these genes validated associations with density previously observed in the discovery population. In both cases, decreased wood density was associated with the minor allele, suggesting that these SNPs may be under weak negative purifying selection for density in the natural populations. These results demonstrate the utility of LD mapping to detect associations, even when the power to detect SNPs with small effect is anticipated to be low. N UMEROUS traits of agronomic importance are demonstrated to be under genetic control (Keurentjes et al. 2008), and there is considerable interest in characterizing the causative polymorphisms underlying their quantitative variation. In forest trees, quantitative variation in traits such as mechanical and pulping properties of wood, growth, cold hardiness, and drought acclimation are likely to result from allelic variation within multiple genes (Neale and Savolainen 2004;Oraguzie and Wilcox 2007). Because of the commercial importance of radiata pine (Pinus radiata D. Don), we are exploring the molecular basis of variation in its wood properties using an association genetics approach.Radiata pine wood properties are variable in domesticated populations and exhibit a quantitative mode of inheritance with high heritability, indicating a strong underlying genetic component. High heritabilities have been observed for solid wood traits including density, cellulose microfibril angle (MFA), and modulus of elasticy (MOE) (Baltunis et al. 2007) and for carbohydrate composition, pulp yield, fiber length, and perimeter (Evans et al. 1997;Kibblewhite 1999); and genetic control has been established for several important production traits (Kumar 2004;Dungey et al. 2006;Gapare et al. 2006;Wu et al. 2007).It is anticipated that variation in wood quality will be dependent on variation in numerous genes involved in xylogenesis. Studies of gene expression in developing xylem have revealed genes involved in spatially and temporally regulated processes such as cambial division, cell different...