Fungal Damage Caused by Racodium therryanum to Regeneration of Japanese Larch by Natural Seeding

Occurrence of Japanese larch (Larix kaempferi CARR.) seed decay caused by Racodium therryanum THUEM., the causal fungus of dark snow blight, in forest soils of different layers was investigated both in laboratory and in field.Seed germination ability decreased severely in soils of surface organic layers (L, F -H) and less severely in soils of less organic layer (A), but not at all in the mineral soils of B layer.The high percentage of R. therryanum isolation from the seeds was found only in soil of surface organic layers, suggesting that the great majority of the R. therryaum population in forest soil inhabit the surface organic layers.The regeneration of Japanese larch by natural seeding is known to be restricted to the locations where the soils are deficient in organic matter.The occurrence of R. therryanum-caused Japanese larch seed decay, related to the organicity of the soils as shown in the present study, can in part explain such restricted regeneration pattern of Japanese larch.