DECISIVE MATERIALS TO CAUSE DEVELOPMENT OF PINE WILT DISEASE

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Monoterpene is the consituent of oleoresin known as essential oil, which possesses antimicrobial activity. The wood, in which the contents of monoterpene and other oleoresin components are high, is called light wood. Monoterpene is thought to be an important component of the defense mechanism in the stem of pine trees. Excessive monoterpene synthesis is hypothesized to cause tracheid cavitaion. Therefore, we examined the role of monoterpene during the development of pine wilt disease. From the result, monoterpene content had no relations with development of xylem sysfunction, population density of pine wood nematode in the wood, and needle discoloration. The results suggest that monoterpene does not have close connection with induced cavitation in the wood, and that the disease develops regardless of monoterpene content.We investigated surface tension of sap which has close connection with cavitation in the living wood. After inoculations of pine wood nematodes, disease symptoms of pines develop fast when surface tension began to decrease in the wood. This phenomenon indicates that pine wilt disease accompanied with surface tension decrease of the sap of pines.