Influence of water deficit on the induced and constitutive responses of pines to infection by mountain pine beetle fungal associates

Background The ongoing outbreak of mountain pine beetle (MPB; Dendroctonus ponderasae Hopkins) and its associated pathogenic fungi (e.g. Grosmannia clavigera [RobinsonJeffrey and Davidson] Zipfel, de Beer and Wingfield) in western North America has resulted in the loss of more than 13 million hectares of pines since 1999 in British Columbia alone [1]. MPB has principally attacked lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia) in British Columbia. However, since 2006 MPB has spread into northern Alberta, where lodgepole pine hybridizes with jack pine (Pinus banksiana Lamb.) [2]. Few studies have compared lodgepole and jack pine defense responses, but given that lodgepole pine and MPB share a co-evolutionary history [1] whereas jack pine is a new host for MPB [2], it is reasonable to expect that differences might exist. Some regions affected by the current outbreak have experienced drought conditions during the last decade. Water deficit can limit carbon assimilation, potentially increasing tree susceptibility to MPB and their symbiotic fungi [3]. We are testing the hypotheses that lodgepole and jack pine defenses against MPB and G. clavigera differ, and that water deficit affects these responses.