THE RHIZOCTONIA ENDOPHYTES OF RHIZANTHELLA (ORCHIDACEAE)

The endophytes of the endemic Australian underground orchids, Rhizanthella gardneri from Western Australia and R. slateri from New South Wales and southern Queensland, are rhizoctonias that form endomycorrhizas with the orchids and ectomycorrhizas with many other plants. Isolates from the two orchids differ in cultural characters but whether they are different species cannot be decided on anamorphs alone. The isolates from R. gardneri formed a teleomorph that is described as Thanatephorus gardneri sp. nov. In Western Australia Rhizanthella gardneri has only been found closely associated with the shrub Melaleuca uncinata as ectomycorrhizal companion plant. Seeds of the orchid, however, germinated and formed protocorms in association with Thanatephorus gardneri on 4 species of Eucalyptus. Whether R. gardneri can grow to maturity in association with eucalypts remains unresolved.