Inbreeding in Pinus radiata III: the effect of inbreeding on age-age correlation and early selection efficiency

A breeding strategy involving inbreeding followed by crossbreeding of inbreds requires that the production of superior inbred lines must be possible, but crosses between lines should exhibit heterosis, inbreeding should not substantially delay reproduction, and early selection between lines to be effective. Age-age correlation and the effectiveness of early selection have been extensively reported for outcrossed populations of different species, but there are no reports for inbred populations. In this study, age-age correlations based on both family means and individual trees were investigated and compared in radiata pine populations with five different inbreeding levels (F = 0, 0.125, 0.25, 0.5 and 0.75). Trends in additive genetic variance, environmental variance, heritability and age-age additive genetic correlations were estimated from an outcrossed population (F = 0). For cross-sectional area at breast height, additive genetic variance increased from 3.7% at age 3 to 29.4% at age 5, remained at about 30% up to age 10, then declined to 15.6% at age 13.