Abstract
Abnormal metabolites isolated from nematode-infected pine, benzoic acid, catechol, 8-hydroxycarvotanacetone (8-HCA), and dihydroconiferyl alcohol (DCA) were tested for biological activity to 1-month-old pine seedlings and pine wood nematodes. Seedlings of Pinus thumbergii, suscepible to pine wilt disease were more sensitive to benzoic acid, catechol, and DCA than the other species tested. D-Isomer of 8-HCA was more toxic than L-isomer. Weak synergistic effects were observed on the toxicity to pine seedlings between DCA and benzoic acid, and between D-8-HCA and benzoic acid. The synergistic effect seemed to appear more prominent against 3-year-old seedlings. L-Isomer of 8-HCA and DCA inhibited the multiplication of pine wood nematodes at 30 and 10ppm, respectively, whereas D-isomer of 8-HCA, benzoic acid, and catechol did not even at 100ppm. All 4 compounds stimulated the multiplication at lower concentrations. The biologically active concentrations of some of these compounds accumulated in the trunks of 15- to 25-year-old pine trees after inoculation with pathogenic nematodes, hence these abnormal metabolites seemed to be involved in the pathogenesis of pine wilt disease in complex manner.
