RHIZANTHELLA GARDNERI (ORCHIDACEAE), ITS RHIZOCTONIA ENDOPHYTE AND CLOSE ASSOCIATION WITH MELALEUCA UNCINATA (MYRTACEAE) IN WESTERN AUSTRALIA

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Summary

Rhizanthella gardneri R. S. Rogers, a rare subterranean achlorophyllous orchid which grows in Western Australia near plants of the Myrtaceous shrub Meialeuca uncinata R. Br. ex Alton f., is associated with an undescribed species of Rhizoctonia which forms hyphal coils within cortical cells of the orchid rhizome. The Rhizoctonia also forms ectomycorrhizas with sheath and Hartig net on Meialeuca uncinata and other ectomycorrhizal plants including Eucalyptus.

Seeds of R. gardneri may germinate without the Rhizoctonia but their growth soon ceases unless the protocorm is invaded by the fungus through the protocorm hairs. Two plants of R. gardneri raised from seed in association with Rhizoctonia ectomycorrhizas on M. uncinata have flowered after 15 months.

The Rhizanthella endophyte stimulated germination of seed of R. gardneri but not seed of two chlorophyllous terrestrial orchids, Prasophyllum regium R. Rogers and Microtis unifolia (Forster f.) Reichb. f. However, germination of these two orchids was stimulated by five of six other Rhizoctonias, including Tkanatephorus cucumeris (Frank) Donk and two species of Tulasnella, also isolated from soil and litter from two Rhizanthella sites.

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