Genetic parameter estimates for growth traits and stem straightness in a breeding seedling orchard of Eucalyptus grandis

Genetic parameters for growth and stem straightness were determined for a fourth generation breeding seedling orchard (BSO) of Eucalyptus grandis in Zimbabwe. Data were from 30 half-sib open pollinated families assessed at two, five and six years of age. Growth traits had low to moderate heritability estimates (0.04 to 0.20). Age-age genetic correlations were large and positive for all traits (r(A) = 0.80). Both heritability estimates and genetic correlations were unaffected by systematic thinning. However, selective thinning inflated heritability estimates at age of thinning and reduced them at subsequent ages after selective thinning. The latter was attributed to compensatory growth. Selective thinning reduced genetic correlations. Thus for unbiased estimates of genetic parameters from BSOs, analysis should be done on data collected prior to thinning or from systematically thinned tests.