Abstract
In order to clarify the ecology of fungi causing butt rot, damage to rot-infected stumps was investigated in three 36- to 41-year-old Japanese larch (Larix kaempferi) stands. Two kind of causal fungi, Phaeolus schweinitzii and Sparassis crispa were frequently isolated from rot-infected stumps in the stands examined. Periodic stump observations found that the fruiting bodies of P. schweinitzii and S. crispa formed from late June to early September, showing that the basidiospores of the causal fungi are dispersed over a relatively long period of time. In the excavated root systems of rot-infected stumps, one or two of the up to ten primary roots commonly sprouting from the stumps had wounds identified as obvious sites for the ingress of butt rot fungi. Wounds identified as invasion sites were classified into 5 types by morphological characters. The most frequent types of wound were open wounds or large scars, and rotted or cut roots. Most wounds were formed at the base of the stumps and in primary roots less than 30 cm below ground level. Observations of the annual rings at the wounds suggested that the fungal invasion had occurred in 7- to 31-year-old larch trees. Inspection of the stumps indicated that wound formation resulting in invasion sites was closely associated with environmental conditions. Significant causal factors were stones in the soil and strong winds.
