Genetic variation of wood chemical traits and association with underlying genes in Eucalyptus urophylla
We developed a quantitative and association genetic study with Eucalyptus urophylla using a progeny trial. Based on a sample of 831 trees distributed in 84 half-sib families whose wood was phenotyped by near-infrared spectroscopy, the results showed that traits related to lignin, cellulose, and wood extractives presented significant additive genetic variability with moderate to high narrow sense heritability ( h 2 =0.28 to 0.93). Genetic correlations varied with high standard error and showed low to moderate values. Using three cellulose synthase genes (EuCesA1, EuCesA2, and EuCesA3) and three candidate genes involved in the lignin pathway (EuC4H1, EuC4H2, and EuCAD2), an association study was performed for each of the gene action models (co-dominant, recessive, and dominant) using two methods. Firstly, single-marker association tests were done and 539 tests (49 single nucleotide polymorphisms (SNPs)×11 traits) were analyzed. After Bonferroni correction with a significance level of P = 0.00102, only four SNPs presented significant association with syringyl and syringyl-to-guaiacyl ratio with an adjusted coefficient of determination varying between 2.6 and 4.4 %. Secondly, a model selection method, the backward approach, was implemented. Similar SNPs were detected by both the backward selection and the individual marker approaches. However, the latter detected new associations with other traits, genes, and SNPs and improved the quality of the model as shown by the BIC criteria and the higher adjusted determination coefficient (1.5 to 8.3 %). Our results reveal that cellulose genes can be associated with lignin traits (syringyl-to-guaiacyl ratio) and stress the possible pleiotropic effect of some genes.