Early Selection in Tree Breeding: Principles for Applying Index Selection and Inferring Input Parameters

1989

S. 499-504

1 Abb., 1 Tab., 18 Lit. Ang.

Unselbständiges Werk

200038985

Early selection is essential after the first generation of a tree-breeding programme. Two main issues that it raises are (i) the optimal age for selection for the next generation and (ii) how the best to use early assessment data for the selection. Attention is given mainly to the latter issue. Early selection is considered as a special type of indirect selection that can embrace multiple traits. Where a sequence of early measurements has been made for single traits it is possible to treat the expressions of a trait at different dates as separate traits in a selection index. Constructing a least-squares selection index with this feature involves a number of questions. Outstanding among these is whether, and in what way, early measurements should be used as covariates for adjusting later ones. Such indices depend, however, on good estimates of phenotypic and genetic variance-covariance matrices. Potential aids for deriving and refining such matrices are reviewed, including the "Lambeth relationship" for age-age correlations and partical correlation analysis. However, analysis of the sensitivity of expected gains with respect to variations in assumed genetic parameters is strongly advocated before decisions are made on age of selection.