Tulasnella calospora is the best-known orchid mycorrhizal fungus in the genus and one of the most common Rhizoctonia-like fungi in the roots of terrestrial and epiphytic orchids. It is widely used to germinate orchid seed in symbiotic culture, and effective strains are kept in culture collections. It also lives as a saprotroph on decayed wood. The name probably covers several species: studies describe it as a diverse assemblage whose limits are unclear.
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Habitat
In the roots of terrestrial and epiphytic orchids, with reported hosts including Serapias, Spiranthes, Cattleya, Dendrobium, Caladenia, Diuris, Microtis and Thelymitra. Free-living, it is saprobic on dead, decayed wood of broadleaved trees and conifers, and has been recorded on the hymenium of other crust fungi such as Botryobasidium and Sistotrema (BioImages, UK).
Distribution
Reported as near-cosmopolitan: Europe, Asia, Australia, North America (e.g. Florida) and South America (e.g. Brazil). Because the name covers a species complex, records from different regions may represent different species.
Characteristics
Sexual state: not observed in recent culture studies (Freitas et al. 2020); in Warcup and Talbot's work the spore-bearing tissue was slow to form and diffuse, and sometimes only spores showed above the casing soil (Linde et al. 2017). Culture (Brazilian orchid isolates, Freitas et al. 2020): on PDA at 25 °C colonies reach 45-67 mm in 8 days, white to cream, with an undulate, submerged edge, some with aerial mycelium; hyphae 3-4 µm wide, hyaline, regularly septate, branching at right angles, binucleate; monilioid cells barrel-shaped to elongated barrel-shaped, in branched chains of more than five cells, formed on corn meal agar after 4-6 weeks. Genus features: basidia with grossly swollen sterigmata.
Difficulty
Intermediate
Contamination risk
Medium
Substrates
oatmeal agar (OMA) · potato dextrose agar (PDA) · malt extract agar (MEA)
