The role of oleoresin flow in the induced response of loblolly pine to a southern pine beetle associated fungus

The influence of total resin flow in loblolly pine, Pinus taeda L., on initial inoculation of the blue stain fungus Ophiostoma minus (Hedgc.) Syd. & P. Syd., a fungal associate of southern pine beetle (Dendroctonus frontalis Zimmermann (Coleoptera:Scolytidae)), was investigated. Resin flow of trees was mechanically manipulated so that it followed the same pattern of decrease and near cessation as seen in trees successfully attacked by southern pine beetle. There were also intermediate treatments where resin flow was allowed to recover. The fungus was inoculated into holes drilled to the xylem surface and allowed to grow for a specified time period. The lesion that formed as a result of the induced reaction was then measured and compared with lesions formed in trees for which resin flow was not manipulated. The experiment was conducted three times in 1993 and 1994 and twice in 1995. It was hypothesized that with decreased resin flow, O. minus would be less inhibited and that growth would be greater before being stopped by the induced reaction. It was found that longer lesions occurred in trees where wounding was prolonged and resin flow was decreased below that of control trees. Mixed results were obtained for trees in intermediate wounding treatments.