Diverse Mycena Fungi and Their Potential for Gastrodia elata Germination

Mycena from different continents have been published over the years [1][2][3][4][5].According to the tenth edition of Ainsworth & Bisby's Dictionary of the Fungi, Mycena is one of the most diverse genera in Agaricales, comprising more than 500 described species worldwide [5].As of 2023, Index Fungorum lists 2412 records for this genus.Most species of Mycena are saprotrophic fungi that decompose litter and contribute to the forest ecosystem [6,7].However, some species have symbiotic or parasitic interactions with plants.For example, Mycena galopus forms beneficial associations with Vaccinium corymbosum [8]; M. citrinomarginata colonizes the roots of Festuca roemeri [9]; and Mycena citricolor infects coffee trees and causes American leaf spot disease [10].The Orchidaceae family is exceptionally diverse and widespread [11], comprising over 750 genera and approximately 27000 species, and is the most species-rich, accounting for approximately 10% of the world's flowering plants [12,13].Orchid seeds are very small (dust-like), lack endosperm and have limited nutrition for germination, so they depend on certain fungi to supply them with nutrients.These plants are known as "initially mycoheterotrophic" plants [14][15][16][17].All orchids are at least initially mycoheterotrophic [18,19] and depend entirely on orchid mycorrhizal fungi (OMFs) for seed germination and protocorm formation [20,21].Subsequently, most orchids develop green leaves and perform photosynthesis (partially mycoheterotrophic type), whereas more than 200 orchid species never photosynthesize and rely entirely on fungal nutrition for growth (fully mycoheterotrophic type) [11,22].Gastrodia elata Bl. belongs to the fully mycoheterotrophic type and has important medicinal and edible value.It is widely used in China, Korea and Japan [23].Each of its capsules produces tens of thousands of seeds [24], but they lack nutrition and require symbiosis with Mycena fungi to germinate and form protocorms. Subsequent nutritional growth depends on symbiosis with another fungus, Armillaria mellea, to complete the whole life cycle [25].Although related cultivation technology and practices have achieved success, natural G. elata populations are still facing threats and are rated vulnerable on the IUCN Red List (IUCN 2022).Currently, it is generally believed that G. elata seeds can only germinate in symbiosis with Mycena [26].In the 1980s, Xu and Guo [27] were the first to successfully induce the fruiting body of a fungal strain for G. elata seed It remains to be determined whether there is a geographical distribution pattern and phylogenetic signals for the Mycena strains with seed germination of the orchid plant Gastrodia elata.This study analyzed the community composition and phylogenetics of 72 Mycena strains associated with G. elata varieties (G.elata.f. glauca and G. elata.f. viridis) using multiple gene fragments (ITS+nLSU+SSU).We found that (1) these diverse Mycena phylogenetically belong to the Basidiospore amyloid group.(2) There is a phylogenetic signal of Mycena for germination of G. elata.Those strains phylogenetically close to M. abramsii, M. polygramma, and an unclassified Mycena had significantly higher germination rates than those to M. citrinomarginata.(3) The Mycena distribution depends on geographic site and G. elata variety.Both unclassified Mycena group 1 and the M. abramsii group were dominant for the two varieties of G. elata; in contrast, the M. citrinomarginata group was dominant in G. elata f. glauca but absent in G. elata f. viridis.Our results indicate that the community composition of numerous Mycena resources in the Zhaotong area varies by geographical location and G. elata variety.Importantly, our results also indicate that Mycena's phylogenetic status is correlated with its germination rate.