Time Trends in Genetic Parameters for Height and Optimal Age for Parental Selection in Scots Pine

Abstract

Abstract Data used to estimate time trends in genetic parameters and the optimal age for parental selection were obtained from 13 Scots pine (Pinus sylvestris L.) progeny tests in southern Sweden. The final age at measurement was between 24 and 39 yr, corresponding to approximately half the rotation age in southern Sweden. Trees in each test have been measured for height 4–6 times, covering ages from 5 to 39 yr. Individual tree heritability for height averaged 0.16, and increased slightly over time, although there were differences among tests. The average additive coefficient of variation for height (CVA), which decreased with age, was 6.0% while the average nonadditive coefficient of variation (CVD) was 3.8% and did not show any significant trend over time. A model based on the natural logarithm of the ratio between the two ages at measurement was used to predict genetic age-age correlations. The efficiency of early selection was also examined, in an analysis considering total height at age 30 as the target trait. The optimal age for parental selection based on gain per unit time peaked at 11 yr, with a time lag for breeding of 10 yr. In the southern tests, the peak came some years earlier than in the northern tests. Selection efficiency based on present value with an interest rate of 5% showed the optimum at 11 yr.