Genetic parameters for bole straightness and branch angle in jack pine estimated using linear and generalized linear mixed models

Abstract

Desirable bole form and branch angle are important targets for jack pine tree improvement. In this study, we calculated the genetic parameters of bole straightness (ordinal response in five categories) and branch angle (binary response) from a progeny test replicated on three sites in Ontario, Canada. Three analytical models were used: an ordinal, multithreshold generalized linear mixed model (GLMM), a binary GLMM, and the conventional linear mixed model (LMM). Results showed the following: (1) that differences in parameter estimates among the models were small, although the LMM consistently yielded lower values than the other two; (2) genetic control of bole straightness was moderately strong (individual heritability = 0.19) in 11-year-old trees; (3) at 8 years old, genetic control of branch angle was moderately strong at one site (individual heritability = 0.16), but family differentiation was not observed at the other two sites; (4) genetic correlations between branch angle and bole straightness were significant and positive, but they were significant and negative between bole straightness and volume, and were negligible between branch angle and volume. Our results suggest that reasonable gains could be obtained from incorporating tree form quality targets into current jack pine breeding programs.