Distribution of the orchid mycorrhizal fungus, Rhizoctonia solani, in relation to its host, Pterostylis acuminata, in the field

The plant pathology model was tested as an explanation of the distribution of orchid mycorrhizal fungi in the field. The mycorrhizal fungus, Rhizoctonia solani Kuhn AG 6, was isolated from adult plants and protocorms of Pterostylis acuminata R.Br. at a study site and from adult plants at five other locations in the Sydney region. In litter and trap seedlings, R. solani AG 6 was found within 50 cm of adult plants of the orchid P. acuminata and was more abundant close to the host plant. In the laboratory, protocorms of P. acuminata became infected with R. solani AG 6, but not with fungi isolated from the other orchids, P. concinna R.Br., P. ophioglossa R.Br. and Caladenia catenata (Smith) Druce, found at the site. It was concluded that the co-distribution model better explains the distribution of fungus and host in this case.