- Measurements on growth traits up to 41 years of age
from 68 progeny sites in eight first-generation breeding
zones of coastal Douglas-fir (Pseudotsuga menziesii
[MIRB.] FRANCO var. menziesii) in the US Pacific Northwest
were used to investigate age trends of genetic parameters
and to determine optimum age of selection. Heritabilities
and age-age genetic correlations were estimated
using univariate or bivariate mixed model analyses.
Heritability estimates tended to increase with age for
both total growth and growth increment traits. The estimates
showed different age trends among breeding
zones, but the differences were generally small. Age-age
genetic correlations for total growth traits fitted Lambeth’s
model surprisingly well, despite the data being
collected from multiple breeding zones.
Using rotation-age (i.e., 50yr) volume as the selection
criterion, the greatest correlated gains per year were
achieved by making family selection at juvenile ages
(i.e., 9 for height, 13 for diameter, and 11 for volume).
Similar results were obtained for within-family selection
except that the optimum ages of selection were 2~4
years later than that from family selection, i.e., 11 for
height, 15 for diameter and volume. Early selection on
total height was always more efficient and had earlier
optimum ages than on other growth traits. The optimum
ages of early family selection on total growth were
4~11 years earlier than on the corresponding growth
increment traits. It was also evident that the optimum
ages of selection occurred later for slow-growth trials
than for fast-growing trials.
- This is the publisher’s final pdf. The published article is copyrighted by J. D. Sauerländer's Verlag and can be found at: http://www.sauerlaender-verlag.com/index.php?id=18.
- Keywords: Age-age genetic correlation, Heritability, Selection efficiency, Growth, Early selection, Douglas-fir, Growth increment, Optimum age
- Ye, T., & Jayawickrama, K. (2012). Early selection for improving volume growth in coastal douglas-fir breeding programs. Silvae Genetica, 61(4-5), 186-198.
|Funding Statement (additional comments about funding)
- The Northwest Tree Improvement Cooperative (NWTIC) funded this research work, as well as the measurement of all Vernonia program after age-15 and a couple of the other programs at age-20.