AGE-AGE CORRELATIONS AND EARLY SELECTION FOR WOOD DENSITY IN YOUNG COASTAL DOUGLAS-FIR

Age-age correlations and age-associated changes in the genetic control of wood density and its components (earlywood density, latewood density, and latewood proportion) were investigated in 15-yr-old trees of 60 open-pollinated families of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco). The possibility of using wood density components as secondary traits to increase the efficiency of early selection for overall wood density was also explored. Heritability estimates for overall density and its components increased with age, mainly because of a decrease in the error variance as the number of rings in the core sample increased. Overall density and its components at age 15 had strong genetic correlations with their respective traits at all younger ages analyzed. Moreover, with few exceptions, age-age genetic correlations were greater than phenotypic correlations. Early selection to improve overall density at age 15 was quite efficient (relative efficiency above 79%), even when selection was based on core density at the youngest age (age 7). Using wood density components as secondary traits produced a slight increase in the efficiency of early selection only at the youngest ages, presumably because age-age correlations for overall core density were already strong, limiting the possibility of additional improvement.