Bayesian analysis of growth, stem straightness and branching quality in full-sib families of Eucalyptus globulus

ABSTRACT Eucalyptus globulus is one of the most commonly planted hardwood species for industrial use in various temperate regions around the world. The present study aimed to evaluate 62 full-sib families of E. globulus in one of the southernmost progeny trials of the species in the south of Chile. Estimates of genetic parameters for stem straightness, branching quality and growth traits were based on a Bayesian modelling approach using Gibbs sampling. A Bayes Factor (BF) analysis supported the hypothesis of significant additive genetic variation for all traits under study. Conversely, the BF supported a model with significant dominance effects for the diameter at breast height and stem volume, which explained up to 25% of the phenotypic variation. The greatest narrow-sense heritability estimates were found for the tree height and stem straightness, which were 0.15 (0.08 to 0.26) and 0.18 (0.10 to 0.28), respectively (mean of posterior distributions and 90% credible sets). In turn, the branching quality had a low heritability (narrow-sense) that varied from 0.05 to 0.10 (90% Bayesian credible region). The mean posterior estimate of genetic correlation between both quality traits was 0.22 (0.01 to 0.63, 90% credible set from a bi-trait threshold model), which indicates that stem straightness is positively related to branching quality. Our findings reveal that the study population responds to common patterns of breeding populations of E. globulus. This information is valuable for the development of improved seeds in the southern zone of Chile.

摘要：蓝桉（Eucalyptus globulus）是全球诸多温带区域工业化栽培最为广泛的硬阔树种之一。本研究依托智利南部该物种最南端的子代试验林（progeny trials），对62个蓝桉全同胞家系（full-sib families）开展评估。针对树干通直度、分枝品质与生长性状的遗传参数估算，采用基于吉布斯采样（Gibbs sampling）的贝叶斯建模方法完成。贝叶斯因子（Bayes Factor, BF）分析证实，所有待测性状均存在显著加性遗传变异。与之相对，贝叶斯因子分析支持胸径（diameter at breast height）与材积（stem volume）存在显著显性效应的模型，该效应可解释最高达25%的表型变异。树高与树干通直度的狭义遗传力（narrow-sense heritability）估算值最高，分别为0.15（90%可信区间：0.08~0.26）与0.18（90%可信区间：0.10~0.28），上述数值为后验分布（posterior distributions）均值及90%可信区间。分枝品质的狭义遗传力较低，取值范围为0.05~0.10（90%贝叶斯可信域）。双性状阈值模型（bi-trait threshold model）得到的两类品质性状间遗传相关的后验均值估算值为0.22（90%可信区间：0.01~0.63），表明树干通直度与分枝品质呈正相关。本研究结果显示，试验群体契合蓝桉育种群体的通用模式。该研究成果对智利南部区域的优良种子选育工作具备重要参考价值。