Time Trends in Genetic Parameter Estimates and Selection Efficiency for Scots Pine in Relation to Field Testing Methods

2001

S. 129-144

8 Abb., 3 Tab., zahlr. Lit. Ang.

Unselbständiges Werk

200090056

Multiple assessments of cumulative tree height in 26 Pinus sylvestris L. progeny trials in Finland, ranging between 5 and 18 years of age, were analysed to determine time trends in variance components, heritability, coefficient of additive genetic variation, age-age and site-site genetic correlations, and to estimate the impact of test characteristics on these parameters. Two distinctive methods of field progeny testing were investigated, conventional "forestry trials" and intensively managed test orchard (farm-field) trials. The effects of contrasting stand densities (2,500 vs. 8,888 trees planted per ha) and site quality (forest vs. field sites) on the levels and trends of variance components and genetic parameter estimates were quantified by means of repeated-measures mixed models. Responses to parental and within-family selection were computed using parameters derived from these models. The trials, which were arranged in groups by spacing and site quality, showed markedly different levels of heritability. The highest estimates occurred on the fast-growing test orchard sites. On average, additive genetic variances and heritabilities from single-site analyses were inflated by 60% due to the family-by-site interaction. No systematic time trends were detected for heritability and type-b correlation. Furthermore, the relative magnitude of the family-by-site interaction was independent of the degree of heterogeneity among the trial sites. Age-age correlations were positive and moderately high, and showed a moderate fit to the log of the age ratio. Selection efficiencies were examined using tree height at age 20 as the target trait. The correlated responses per year to early parental (backward) selection peaked at the age of around 5 to 7 years and were always greater than the gains from direct selection for tree height at the age of 20 years. In within-family (forward) selection, the annual responses were initially low, increasing toward the target age. The optimum age of within-family selection occurred later (at the age of 8, ..., 16 years) than in parental selection. The highest selection efficiencies were consitently associated with the densely spaced test orchard scenarios. Correspondingly, widely spaced trials on site of poor quality produced the least responses to early selection.