Variation in secondary metabolite synthesis in lodgepole pine (pinus contorta) as a defence against Dothistroma septosporum

Dothistroma septosporum Dorog. Morelet is an emergent fungal pathogen of pine responsible for increasingly severe and widespread damage in British Columbia. Native lodgepole pine (Pinus contorta var. latifolia) is considered highly susceptible, but has been extensively planted due to its commercial value. Current management options involve either avoidance or species diversification. Quantitative resistance to Dothistroma has been observed in several pine species, and further identification of resistant lodgepole pine varieties is important for future management of the disease. My objectives were to determine the historical climatic influences on constitutive foliar terpene levels, identify foliar secondary metabolites associated with resistance and historical disease pressure, and to ascertain the in vitro effects of these compounds. I quantified foliar secondary metabolites from both seed orchard and resistance trial lodgepole pines, many of which were identified as terpenes. I quantified the Dothistroma outbreak history of lodgepole pine provenances using dendrochronological methods, and the climate history of these provenances using an interpolated historical climate model. I found that constitutive foliar levels of specific terpenes significantly correlated (P<0.05) with climate at provenance origin, Dothistroma resistance, and provenance outbreak history. I assessed the in vitro effects of the sesquiterpene alcohol (E,E)-farnesol on various D. septosporum isolates. Temperature normals at provenance origin were significantly negatively correlated with foliar terpene levels in orchard trees. Family crown retention variables were significantly positively correlated with levels of a number of sesquiterpenes and sesquiterpene alcohols. Provenance Dothistroma outbreak history was significantly positively correlated with levels of a wide range of monoterpenes, two sesquiterpenes, and two sesquiterpene alcohols. In vitro effects of the sesquiterpene alcohol (E,E)-farnesol were complex, with the compound conferring growth inhibition at high concentrations and stimulation at low concentrations. My results indicate that foliar terpenes play an important role in quantitative resistance of lodgepole pine to Dothistroma septosporum, and this work provides a basis for future investigation into the defensive role of these compounds. A more comprehensive knowledge of the Dothistroma-Pinus relationship is required for future identification of resistant lodgepole pine varieties, and to further our understanding of the forces driving emergence of this damaging fungal pathogen in British Columbia.