The epiphytic orchid Vanda falcata is predominantly associated with a single Tulasnellaceae fungus in adulthood, and Ceratobasidiaceae fungi strongly induce its seed germination in vitro

Abstract

Vanda falcata is an epiphytic orchid native to East Asia with high horticultural and ornamental value. However, its wild populations are at risk of extinction due to overcollection and habitat loss. Orchids are highly dependent on mycorrhizal fungi for their nutrient acquisition from seed germination to adulthood; therefore, understanding their mycorrhizal associations throughout the life cycle is essential for their conservation. We investigated the mycorrhizal fungi of adult V. falcata plants through the molecular identification of root samples from 40 individual plants from 13 sites, covering a distance of 1200 km across Japan. To identify the fungi that promote V. falcata seed germination, we performed seed germination tests in vitro with fungal isolates from V. falcata and other epiphytic orchids. In adult plants, we detected a total of 11 operational taxonomic units (OTUs) within two fungal families, Ceratobasidiaceae and Tulasnellaceae, and a single Tulasnellaceae OTU (TU11) was found in samples from 12 sites. However, Vanda falcata seed germination and early development were induced in vitro by Ceratobasidiaceae fungi rather than Tulasnellaceae fungi, including TU11. These results suggest that different mycorrhizal fungi may be predominantly associated with V. falcata in the adult and seed germination stages. This mycorrhizal switching suggests that effective mycorrhizal fungi for conservation may differ between the adult and juvenile stages, even within a single orchid species. Our findings clarify the mycorrhizal associations of endangered epiphytic orchid species and could improve conservation efforts for these rare plants.