Relationship between cortical resin acids and resistance of Sitka spruce to the white pine weevil

Abstract

Cortical resin acids were analyzed both quantitatively and qualitatively among 10 provenances and 11 genotypes of Sitka spruce, Picea sitchensis Bong (Carr.), putatively resistant to the white pine weevil, Pissodes strobi (Peck), and compared with susceptible trees. Trees in 5 of the 11 resistant genotypes had significantly greater amounts of cortical resin acid than susceptible trees. Of seven individual acids analyzed, pimaric, isopimaric, levopimaric, dehydroabietic, abietic, and neoabietic acid, but not palustric acid, were found in significantly greater amounts in trees from resistant than susceptible provenances. Eighteen percent of the variation in resin acid content could be accounted for by variation in the capacity of cortical resin ducts, indicating that the other 82% of variation is a result of differences in resin acid concentration in the resin. Trees with very high resin acid levels may have a greater capacity for resinosis than susceptible trees, may deter feeding, or may produce resin that is toxic to eggs and larvae. Canonical discriminant analysis revealed that several resistant clones, particularly two from the Kitwanga provenance, could be distinguished from others on the basis of their resin acid profiles. Because it separated trees on the basis of genotype, but not according to degree of resistance, canonical discriminant analysis may be more useful in "chemotyping" trees than in screening for resistance. Keywords: Picea, cortex, resin acids, Pissodes strobi, resistance.