Five Mycena species that induce seed germination in the mycoheterotrophic orchid Gastrodia

The fungus genus Mycena is saprotrophic, but several lineages form orchid mycorrhizae or associate closely with plant roots. To elucidate which Mycena species form mycorrhizal associations with orchids, fungal isolates of five Mycena species (M. epipterygia, M. haematopus, M. polygramma, M. pura, and Mycena sp.) from four sections (Calodontes, Fragilipedes, Hygrocyboideae, and Lactipedes) were cultured with the seeds of mycoheterotrophic orchids, including Gastrodia confusa, G. elata, G. nipponica, and G. pubilabiata. All five Mycena species stimulated seed germination in all four Gastrodia species. Mycena haematopus and M. polygramma had a high affinity for Gastrodia and induced protocorm formation in all of them and tuberization in seedlings of two of them. Phylogenetic analyses indicated that Mycena species that associate with Gastrodia are dispersed throughout the genus and do not form a monophyletic group. Gastrodia species differ in fungal specificity, with G. confusa having a narrow specificity for specific Mycena species, whereas G. pubilabiata and G. nipponica have a broader specificity with multiple Mycena lineages and non-Mycena species, Cyanotrama gypsea and Collybiopsis dichroa. Our results imply that phylogenetically diverse Mycena taxa associate with Gastrodia species as orchid mycorrhizal fungi.