TIME TRENDS IN THE GENETIC-CONTROL OF WOOD MICROSTRUCTURE TRAITS IN PINUS-RADIATA

Age-related changes in the genetic and environmental components of rin g width, density and fibre traits (diameter; wall thickness, coarsenes s and specific surface area) were studied Fibre diameter and coarsenes s both came under strong genetic control by age 4-5 years. The other t raits first exhibited stable genetic control lit around age 8-9 years (crown-closure). Selection efficiencies of all traits become optimal a fter crown-closure. 80055 progeny, which is renowned for producing bri ght newsprint requiring low refining energy has the widest growth ring s, largest fibre perimeter, highest fibre coarseness and the lowest de nsity. This family has a density range that was half that of family 12 197, which has the densest wood in the experiment. However, the fibre perimeter range of 80055 progeny is three times that of 12197 progeny, indicating more variability across the stem in this trait. The study shows that strengths of correlations between pairs of traits change wi th time ann genotype.