Single-Step GWAS Multi-Trait Threshold-Linear Model for Growth Rate and Heteroblasty in Eucalyptus globulus

Genome-wide association studies (GWAS) have provided significant insights into identifying variants associated with complex traits, but they have contributed little to the study of categorical data. The aim of this study was to identify genomic regions associated with quantitative traits (growth) and categorical traits (heteroblasty) in a tree breeding population of Eucalyptus globulus. Tree growth was measured as total height (TH) and diameter at breast height (DBH). Heterobasty was assed as the precocity of change from juvenile to adult foliage (ADFO). All traits were evaluated at 14 and 21 months. A multi-trait threshold-linear model was developed following the single-step genomic selection methodology. Variance components were estimated using Gibbs sampling process. Genetic correlations (rg) and the narrow sense heritability (h2) for all traits were estimated. Windows of 0.2 Mb were used and their variances were calculated. Only the windows with estimated variance higher than 1% were considered. The rg ranging from 0.51 to 0.97. The h2 were high for ADFO (0.83-0.84), and lower for HT (0.37) and DBH (0.53). In growth traits, no QTL were found that explained more than 1% of the variance. However, two genomic regions were found related with ADFO, in the chromosome 3 and 11.