Inoculation test with three isolates of dieback fungus Guignardia cryptomeriae with different virulence was conducted into Cryptomeria japonica trees to investigate whether inoculum dosage influenced the size of canker lesion and wood discoloration. Toothpicks containing fungal hyphae were inoculated into the trunk of four trees of 13 years old. These trees were harvested and put to investigation one year after the inoculation. The size of wound made by sterilized toothpicks (control) affected the axial expansion of cambial necrosis, but not the expansion of wood discoloration. In the case of inoculation with fungal isolates with varying virulence, the inoculum dosage did not give any influence to the size of cambial necrosis and wood discoloration.
The trans-root electric potential (TRP) of pine root was measured by a pair of Ag/AgCl unpolarizable electrode via 10 mM KCl liquid junction. The difference in TRP between the control and those inoculated with pine wood nematode began to shift toward minus direction 8 or 9 days after inoculation. Those results and visual observation suggest that the xylem side-cell membrane of the root symplast is damaged by the pine wood nematode prior to the discoloration of pine needle.
Larvae and newly emerged adult beetles of genus Dorcus (Coleoptera, Lucanidae) were surveyed in white rot wood of willow trees (Salix spp.) including dead fallen trees, dead standing trees and dead parts of living trees on dry riverbeds in the northern part of Mie Prefecture. Dorcus rectus was most abundant, whereas D. titanus and D. hopei were also found. The numbers of beetles boring into dead parts of living trees was not different from those boring into dead fallen trees. The larvae in dead parts at high position tended to be comparatively larger. D. hopei, a rare species, was found only three dead parts of living trees. In this study, the importance of dead parts of living trees as food resource and as habitat for genus Dorcus was suggested.