1989 Volume 55 Issue 2 Pages 170-178
Following invasion by the pine wood nematode, Bursaphelenchus xylophilus, cavitation develops in the sapwood of Pinus thunbergii. This causes abnormal water conduction in the trunk, and is supposed to result in death of infected trees. Cavitation, assumed to be vapor blockage, can be induced by gas produced inside the tree without induction of air from outside. To detect the substances causing cavitation, constituents of vapor in the cavitation areas were analyzed by gas chromatography using xylem harvested 2 weeks after the inoculation with pine wood nematode. Amount of mono- and sesquiterpenes increased significantly in the nematodeinoculated sample: α-pinene was 2 to 4 times that of healthy tree, β-pinene and several other monoterpenes 2 to 3 times, and longiforene, a sesquiterpene, ca. 3 times. Terpene synthesis seemed to be activated before development of cavitation. Monoterpenes excessively produced and exuded in tracheids will vaporize easily under negative pressure in summer months, and will disrupt water columns of the tracheids throughout wide areas within short time. Even when water stress is reduced during night or in autumn, refilling of tracheids with water will be prevented by hydrophobic terpenoids. It is proposed that the vapor blockage of tracheids caused by evaporating terpenoids is responsible for extensive cavitation in pine sapwood within a short period after the invasion of pine wood nematode, and pine trees are eventually killed by water deficit following the cavitation.
