Monoterpene Composition and Fusiform Rust Resistance in Slash Pine

Cortical monoterpene composition was determined for 43 relatively resistant and 42 relatively susceptible slash pine clones selected on the basis of their fusiform rust resistance breeding values. Fifty-seven percent of the clones having high proportions of b-phellandrene were relatively resistant, while only 15% of the low b-phellandrene clones were relatively resistant. Reasons for the relationship are not clear, but presence of the high b-phellandrene gene may be linked with other traits more directly involved with resistance. Certain combinations of monoterpenes, including particular minor constituents, may be more indicative of resistance than b-phellandrene alone, but further work is needed. For the present, tree improvement workers should consider determining monoterpene composition of candidate trees prior to progeny testing, and culling trees with low b-phellandrene content.