Genetic variances and covariances in Pinus contorta : estimates of genetic gains from index selection

Journal Article

Transfer Guideline: Recommendation

Genetic variances and covariances were estimated for 6-year-old trees from 10 families within eight populations of Pinus contorta from the northern Rocky Mountains (USA). Analyses of 10 traits reflecting growth, quality, and adaptedness revealed sustantial genetic variances for nearly all traits. As a consequence, univariate selection for height should provide genetic gains of about 5% per unit selection intensity. However, strong genetic correlations linked height with branch length (0.75), crown width (0.75), and the amount of shoot elongation that continues into mid-summer (0.70). Height was also related to the number of whorls on the current shoot and, consequently, to the number of branches. Thus, multi-trait selections are necessary to prevent genetic gains in productivity from being accompanied by inadvertent degeneration of traits related to adaptation and quality. Multi-trait selections, however, reduce anticipated genetic gains in productivity. Restricted selection indices are developed to exemplify procedures for holding constant the correlated responses while maximizing gains in height.