Genetic variation of piperidine alkaloids in Pinus ponderosa: a common garden study.

BACKGROUND AND AIMS: Previous measurements of conifer alkaloids have revealed significant variation attributable to many sources, environmental and genetic. The present study takes a complementary and intensive, common garden approach to examine genetic variation in Pinus ponderosa var. ponderosa alkaloid production. Additionally, this study investigates the potential trade-off between seedling growth and alkaloid production, and associations between topographic/climatic variables and alkaloid production. METHODS: Piperidine alkaloids were quantified in foliage of 501 nursery seedlings grown from seed sources in west-central Washington, Oregon and California, roughly covering the western half of the native range of ponderosa pine. A nested mixed model was used to test differences among broad-scale regions and among families within regions. Alkaloid concentrations were regressed on seedling growth measurements to test metabolite allocation theory. Likewise, climate characteristics at the seed sources were also considered as explanatory variables. KEY RESULTS: Quantitative variation from seedling to seedling was high, and regional variation exceeded variation among families. Regions along the western margin of the species range exhibited the highest alkaloid concentrations, while those further east had relatively low alkaloid levels. Qualitative variation in alkaloid profiles was low. All measures of seedling growth related negatively to alkaloid concentrations on a natural log scale; however, coefficients of determination were low. At best, annual height increment explained 19.4 % of the variation in ln(total alkaloids). Among the climate variables, temperature range showed a negative, linear association that explained 41.8 % of the variation. CONCLUSIONS: Given the wide geographic scope of the seed sources and the uniformity of resources in the seedlings' environment, observed differences in alkaloid concentrations are evidence for genetic regulation of alkaloid secondary metabolism in ponderosa pine. The theoretical trade-off with seedling growth appeared to be real, however slight. The climate variables provided little evidence for adaptive alkaloid variation, especially within regions.

Piperidine alkaloids in sitka spruce with varying levels of resistance to white pine weevil (Coleoptera: Curculionidae).

Our objective was to evaluate piperidine alkaloids as potential resistance factors in Sitka spruce, Picea sitchensis (Bong.) Carr, at risk to attack by white pine weevils, Pissodes strobi (Peck). We sampled 72 seedlings in each of two replicated field trials in the Oregon Coast Range. The seedlings were grown from open-pollinated seeds of putatively "resistant" or "susceptible" off-site parental sources. Alkaloid concentrations in bark and foliage were measured in previously unattacked trees at the time of weevil host selection. Leader mortality was evaluated in the fall to gauge actual resistance in the sample trees. Five families had < or = 25% topkill and seven sustained >50% topkill. Alkaloid concentrations differed significantly among families, but the major alkaloids did not appear to be functionally linked with topkill or useful indicators of resistance. However, our study design did not address all potential resistance mechanisms. Therefore, before concluding that Sitka spruce alkaloids have no influence on white pine weevils, complementary laboratory and field experiments are needed.