RESUMO
Multinucleate rhizoctonias isolated from the roots of non-orchid plants were used in symbiotic germination tests with seed of 18 orchid species from 10 genera. The rhizoctonias only stimulated germination of Microtis. Investigation of the natural mycosymbionts of adult Microtis failed to yield fungi similar to the original multinucleate rhizoctonias: 27 Microtis plants collected at seven sites in the Sydney region yielded 26 binucleate rhizoctonias tentatively identified as Tulasnella calospora (Boudier) Juel and one very slow growing multinucleate rhizoctonia tentatively identified as Sebacina vermifera Oberwinkler. Fungi closely resembling the original multinucleate rhizoctonias were isolated by baiting the soil with subterranean clover (Trifolium subterraneum L.) plants at three of the seven Microtis sites.