No abstract

The symbiotic associations of Australian orchids have heen examined hy isolating Rhizoctonia endophytes from orchids growing in the field and hy symbiotic germination of orchid seed. Many Rhizoctonia isolates fruited and were identified to their perfect states. The isolation studies showed considerable specificity in association between many orchids and their endophytes. In particular Sehaciiia vermifera was generally associated with Caladenia and several related genera. Tiilasnctia calospora was closely associated with Diuris and Ortlioceras and it and other species of Ttilasitetla with Thelyinitra and Dcndrobium. Cercitobasidium cornigerum was associated with Prasophylttim and Pterostylis and, with other species of Ceratohcisidiiim, with orchids of the subtribe Sarcanthinae. Specificity, however, was not absolute for different Rhizoctonias may occur in an orchid either alone or with the more usual endophyte. A few orchids had a wide range of endophytes commonly present. Symbiotic germination studies generally substantiated the field isolations hut showed further levels of specificity in that isolates of a fungus often differed markedly in their ability to germinate seed of a host or of different hosts under the conditions used. With orchids specificity seemed to occur at different levels, from species to at least subtribe, though the data are imprecise. If there is specificity to suhtribe then there are some anomalies in classification. For instance all Caladeniinae sampled were associated with Sebacina vermifera except Lypcranthus which was associated with a wide range of other fungi. Microtis and Prasophvtttim, though not considered closely associated, areplaced together in the Prasophyllinae; their endophytes are quite different.

SUMMARYRhizoctoma isolates obtained from terrestrial orchids in South Australia and Great Britain have been induced to fruit in culture. The perfect states thus obtained belong to Thanatephortis cucitmeris (Frank) Donk, T. sterigmaticus (Bourdot) Talbot, T. orchidicola Warcup and Talbot, Ceratobasidiinn cornigerum (Bourdot) Rogers, C. obscurum Rogers, Ceratobasidium sp. indet., Tulasnella calospora (Boudier) Juel, T. asymmetrica sp. nov., Tulasnella sp. indet. and Sebacina lermifera Oberwinkler. Tulasnelta calospora was found to be the perfect state of three cultures considered to be Rhizoctonia repeiis Bernard. The status of the orchid-fungus association is discussed.

S U M M A R ^'Isolates of Scbaciua icriiujera Oberwinkler (Trcmelhiceac), idetitilied by their teleomorpbs, from orchid and nonorchid ho.sts ha\e been examined for their mycorrhizal associations. AU isolates stimulated germination of seed of species of Microtis (Orchidaceac). Three isolates from ectomycorrhizal hosts formed ectomycorrhizas on Melaleuca uncinata R. Br. ex .Anon f. and other ectomycoi rbizal plants. None of the orchid isolates nor an isolate which was endophytic in Phyllanthus formed ectomycorrhizas but in addition to species ai Microtis they stimulated germination of one or more species of Catadeiiia, Cyrtostylis or Glossodia but not other terrestrial orcbids.Protocorms of Microtis developed at depth in soil in the presence but not tbe absence of ectomycorrhizal S. vertnifera on M. uticinata. Young albino plants of Microlis rara R. Hr. grew for 4 montbs in tbe presence of ectomycorrhizal S. fcrmijera with M. uncinata but mycorrhizal albino plants on tbeir own all died, suggesting a possible tripartite mycorrhizal association.

SUMMARY In symbiosis tests on an agar medium with powdered cellulose as carbon source, isolates of several species of Tulasnella and of Ceratobasidium cornigerum were compared on seven species of Thelymitra and two each of Diuris and Pterostylis. The Pterostylis species were stimulated to germinate only by Ceratobasidium cornigerum, the Diuris species only by Tulasnella calospora but, in general, the Thelymitra species were stimulated by more than one species of Tulasnella, but not markedly by Ceratobasidium cornigerum. These results correlate well with specificities noted in isolations from the roots of mature orchids of these genera in nature. It was found that different isolates of Tulasnella calospora differed markedly in the efficiency with which they stimulated germination of the species of Diuris and Thelymitra. The most efficient isolates were not necessarily those isolated from these orchids.