THE MYCORRHIZAL RELATIONSHIPS OF AUSTRALIAN ORCHIDS

Abstract

The symbiotic associations of Australian orchids have been examined by isolating Rhizoctonia endophytes from orchids growing in the field and by 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 Sebacina vermifera was generally associated with Caladenia and several related genera. Tulasnella calospora was closely associated with Diuris and Orthoceras and it and other species of Tulasnella with Thelymitra and Dendrobium. Ceratobasidium cornigerum was associated with Prasophyllum and Pterostylis and, with other species of Ceratobasidium, 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 but 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 subtribe then there are some anomalies in classification. For instance all Caladeniinae sampled were associated with Sebacina vermifera except Lyperanthus which was associated with a wide range of other fungi. Microtis and Prasophyllum, though not considered closely associated, are placed together in the Prasophyllinae; their endophytes are quite different. Copyright © 1981, Wiley Blackwell. All rights reserved