Terpenoid profiling and biosynthesis in Sitka spruce (Picea sitchensis) genotypes that are susceptible or resistant to attack by the white pine weevil (Pissodes strobi)

White pine weevil, Pissodes strobi, is an insect that occurs throughout Canada that attacks a number of conifers including Sitka spruce, Picea sitchensis, a commercially and ecologically important tree for coastal B.C.. Because of attack by weevils, Sitka spruce is no longer replanted as a commercial species. The re-introduction of this species would be a valuable asset for sustainable coastal forestry. My research addresses the terpene composition and the molecular-genetic underpinning of Sitka spruce resin defenses against attack by white pine weevil. In this thesis, I report that terpene profiles can be used to classify resistant tree genotypes. I analysed 111 different genotypes in order to determine the relationship of mono- and diterpenoid oleoresin compounds with the resistance rating. Dehydroabietic acid, a diterpene, was identified as a strong indicator of resistance. Two monoterpenes, (+)-3-carene and terpinolene were also associated with resistance in genotypes originating from the Haney region, an area which may have been subject to higher weevil pressure. In addition, I characterized weevil behavior and physiology (feeding patterns, host choice, ovary development, egg laying behavior, and larval development) in response to an extremely resistant Sitka spruce genotype (H898) in comparison to a highly susceptible genotype (Q903). My results suggest that the highly resistant genotype H898 has defense mechanisms that deter both male and female weevils during host selection and mating, that cause delayed ovary development in females, and prevent successful reproduction of weevils on H898 trees. Finally, I have identified the first (+)-3-carene and (+)-sabinene synthase genes in Sitka spruce. These terpene synthase (TPS) genes have very similar sequences, yet the encoded enzymes have different product profiles; this shows a new level of genetic diversity in the spruce TPS gene family. In addition, different (+)-3-carene synthase genes are expressed in the resistant H898 tree genotype producing large amounts of (+)-3-carene, versus the susceptible Q903 tree genotype that produces trace amounts of (+)-3-carene. This information will support the identification and breeding of resistant Sitka spruce in order to re-introduce it as a viable, native commercial species.Science, Faculty ofBotany, Department ofGraduat