Genetic variance of early height growth and expected gains from selection in a Minnesota population of black spruce

Abstract

A genetic improvement project for black spruce (Piceamariana (Mill.) B.S.P.) was initiated in Minnesota in 1974, with an objective of improving the inherent growth rate of the local population. This study reports some field results from the initial phase of the project. Study objectives were to (i) estimate genetic and environmental variance components of early (age 10 years) tree height, (ii) estimate expected genetic gains from various selection methods in three seedling seed orchards and a clonal seed orchard, and (iii) evaluate the effect that these selection methods have on inbreeding levels in the rogued seedling orchards. Additive genetic variance accounted for 15 to 22% of the phenotypic variance in three wind-pollinated family tests and 10% of the phenotypic variance across the tests. Expected gains from combined-index (family and individual) selection in the family test - seed orchards (selection of 22 to 27%) ranged from 4.6 to 6.1%. Family + within-family selection and individual selection were 18 and 32% less efficient, respectively. Index selection resulted in the highest estimated levels of inbreeding in the rogued orchards. However, the largest difference between the various selection methods resulted in a difference in the average inbreeding coefficient of less than 0.15%. Based on this small difference, index selection could be used in roguing similarly designed seedling seed orchards with minimal risk of elevated inbreeding levels.