Virulence of ophiostomatoid fungi associated with the spruce bark beetleIps typographus f.japonicus in Yezo spruce

Yezo spruce trees (Picea jezoensis), approximately 40-year-old were inoculated with eight ophiostomatoid fungi associated withIps typographus f.japonicus to compare relative virulence of the fungi. Among them,Ophistoma penicillatum formed the longest necrotic lesion on inner bark around inoculation points, followed byO. aenigmaticum, Ceratocystis polonica, andO. bicolor, whileC. polonica formed a larger dry zone in sapwood than the other fungi. Yezo spruce trees were also mass inoculated withC. polonica, O. penicillatum, O. piceae singly or mixed to demonstrate the ability of the fungi to kill Yezo spruce trees. The trees inoculated withC. polonica, O. penicillatum or the mixed inoculum showed discoloration of needles in the early summer of the next year and died by autumn. However, the trees inoculated withO. piceae or the control inocula did not die, except for one tree. These results indicated thatC. polonica andO. penicillatum were more virulent thanO. piceae and suggested that they might be at least partially responsible for the mortality of the beetle-infested Yezo spruce trees. Part of this study was supported by the Sumitomo Foundation, Japan to Y. Yamaoka and I. Takahashi. Part of this study was presented at the 107th meeting of the Japanese Forestry Society, April 1–4, 1996, Tsukuba, Ibaraki, at the 42nd annual meeting of the Mycological Society of Japan, May 16–17, 1998, Kyoto, and at the 110th meeting of the Japanese Forestry Society, April 2–5, 1999, Matsuyama, Ehime. Contribution No. 143, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.