Genetic resistance of Sitka spruce (Picea sitchensis) populations to the white pine weevil (Pissodes strobi): distribution of resistance

Summary Sitka spruce (Picea sitchensis) is highly susceptible to leader damage by the white pine weevil (Pissodes strobi). Population differences for resistance have been previously noted from older IUFRO provenance trials both from hybrid sources (the natural hybrids of Sitka and white spruce), but also in populations of pure Sitka from dryer ecological zones. It was postulated that this resistance might be common within this high hazard ‘dry’ zone because of potentially higher selection pressures from increased weevil density. Results from a population transect of this zone, established as an openpollinated progeny/provenance trial, show that resistance is not broadly based but is centred about one of the original IUFRO resistant sources. Although hazard-zone differences were significant, sources within zone, had the strongest effect in our model; particularly evident was a strongly defined population effect around the original IUFRO source. Heritability estimates for resistance were also affected by this strong source population effect.