Forestry and Forest Products Research Institute, lbaraki, 305-8687, Japan

Background and objectives
Pine wilt disease is one of the most serious tree diseases in Japan, and the pathogen has been designated as pine wood nematode, Bursaphelenchus xylophilus. Native Japanese pines, e.g. Pinups densiflora and P. thunbergii, are susceptible, but introduced pine species, e.g. P. strobus and P. taeda, are resistant to the nematode. In order to establish an ecologically safe method to manage the disease, there is an urgent need to clarify the defensive mechanisms of resistant trees to the nematode. Nematode immobilizing activity was detected in the nematode inoculated branch of P. strobus [1]. Chemical factors for anti-nematode and antifungal activities and their fates in the nematode-inoculated P. strobus were investigated.

Materials and methods
The pine wood nematode was inoculated to P. strobus, subsequently the anti-nematode and antifungal activities in the trees were examined. The active components in the methanol extract of the nematode-inoculated bark were purified chromatographically. MS, and 1H- and 13C-NMR were measured to identify the chemical structures of the isolated active compounds. The nature of anti-nematode activity of the compound was investigated. The time course accumulations of the active compounds in the bark were measured by GC.

Results and conclusions
3-O-methyldihydropinosylvin was isolated and identified as anti-nematode and also the antifungal compound in the bark of the nematode inoculated trees. 5-pinocembrin was identified as an additional antifungal compound in the same bark. Nematicidal activity was detected in the 250 ppm solution of 3-O-methyldihydropinosylvin, but 50 ppm solution had no effect on the nematode. At 1 week after inoculation, the amount of 3-O-methyldihydropinosylvin accumulated should be enough to inhibit reproduction and also to kill the nematode near the inoculation site. These results indicated that 3-O-methyldihydropinosylvin in the bark and pinosylvin monomethylether in the wood [2] are defensive chemicals for the pine wood nematode infection in P. strobus.

1. Yaniada T, Ito S, 1993. Annual Phytopathological Society of Japan 59, 666-672.

2. Suga T, Ohta S, Munesada K et al., 1993. Phytochemistry 33, 1395-1401.