Genetic parameters from a clonally replicated test of black spruce (Picea mariana)

A clonally replicated field test of full-sib black spruce (Picea mariana (Mill.) B.S.P.) progeny was established at four locations in Nova Scotia. Estimated variance components for 5-year height growth and survival were interpreted according to an additive-dominance-epistasis genetic model and used to derive estimates of gain from various selection and deployment strategies. Five years after striking, 64% of the total genetic variance for height growth was due to additive variance. Virtually all of the remaining nonadditive variance was composed of epistatic variances: dominance variance was negligible. Narrow-sense heritability for 5-year height growth was low at 0.059. Substantial nonadditive variance contributed to a somewhat higher estimate of broad-sense heritability at 0.093. Family-mean heritabilities were much higher: 0.823 and 0.697 for half-sib and full-sib family means, respectively. Comparable heritabilities for survival were estimated with high standard errors and were considered unreliable. Results from this study indicate that clonal selection may provide large increases in genetic gain by capturing (I) genetic variance due to epistasis and (II) a greater portion of the additive variance. Genetic gains for 5-year height growth in the order of 22.6% might be achieved using the best 1% of tested clones for operational planting. Clonal propagation may also he a preferred method to capture substantial genetic gain (about 11%) from selection at the family level, resulting in simplified management of breeding populations while reducing costs associated with conventional soil-based orchards.