Genetically based resistance of black spruce (Picea mariana) to the yellowheaded spruce sawfly (Pikonema alaskensis)

We evaluated the effect of plant genotype on resistance of black spruce (Picea mariana (Mill.) BSP) to the yellowheaded spruce sawfly (Pikonema alaskensis (Roh.)) in three half-sib family test sites and in a clonal seed orchard in New Brunswick, Canada. Heritability estimates were positively correlated to the percentage of trees defoliated by the sawfly in the half-sib family tests. At the site where the most damage occurred, the estimated individual heritability of resistance was 0.84, while that based on family means was 0.57. In the clonal seed orchard, the variability among clones explained 39.3% of the variation in defoliation, and individual clone heritability and clone mean heritability estimates were 0.40 and 0.82, respectively. Positive phenotypic and genetic correlations between tree height and damage suggest that selection for resistance may result in slightly slower tree height growth in some cases. These results suggest that there is good potential to select trees resistant to the sawfly that display other commercially desirable traits.