Mycorrhizal state of epiphytic orchids was controversially discussed and state and mycobionts of the pleurothallidin orchids, occurring abundantly and with a high number of species on stems of trees in the Andean cloud forest, were unknown. Root samples of 77 adult individuals on total of the epiphytic orchids Stelis hallii, Stelis superbiens, Pleurothallis lilijae, and Stelis concinna were collected in a tropical mountain rain forest of southern Ecuador. Ultrastructural evidence of symbiotic interaction was combined with molecular sequencing of fungi directly from the mycorrhizas and isolation of mycobionts. Ultrastructural analyses displayed vital orchid mycorrhizas formed by fungi with an imperforate parenthesome and cell wall slime bodies typical for the genus Tulasnella. Three different Tulasnella isolates were obtained in pure culture. Phylogenetic analysis of the mycorrhiza forming Tulasnella and the Tulasnella isolates based on coding regions of the ribosomal large subunit (nucLSU) and the 5.8S subunit, including parts of the internal transcribed spacers, yielded seven distinct Tulasnella clades. Tulasnella mycobionts in Stelis concinna were restricted to two Tulasnella sequence types while the other orchids were associated with up to six Tulasnella sequence types. All Tulasnella sequences were new to science and distinct from known sequences of mycobionts of terrestrial orchids. These results indicate that tulasnelloid fungi, adapted to the conditions on tree stems, might be important for orchid growth and maintenance in the Andean cloud forest.
Technical details published in Mycological Research 110: 1257-1270, 2006, Diverse tulasnelloid fungi form mycorrhizas with epiphytic orchids in an Andean cloud forest.
Juan Pablo Suáreza, Michael Weiss, Andrea Abele, Sigisfredo Garnica, Franz Oberwinkler and Ingrid Kottke