Two novel orchids mycorrhizal Tulasnella species and their ability to facilitate symbiotic seed germination

Many Tulasnella species have been identified as true mycorrhizal fungi, playing key roles in nutrient exchange between hosts and their environments, which is crucial for seed germination and seedling development. This study describes four Tulasnella strains isolated from Dendrobium and Paphiopedilum species collected in Thailand. Based on single-locus ITS and four-gene (ITS + mtLSU + ATP + GS) phylogenetic analyses, we introduced two novel species – Tulasnella thailandica sp. nov. and T. epidendroidearum sp. nov. Additionally, two known taxa - T. deliquescens and T. ellipsoidea were identified. Notably, T. ellipsoidea was first identified from Dendrobium chrysotoxum and reported in Thailand. Both ex vitro and in vitro symbiotic seed germination experiments confirmed that all four strains are true orchid mycobionts and are fully compatible with D. chrysotoxum , as they formed pelotons within orchid protocorms, promoted seed germination, and supported protocorm development to advanced stages. Furthermore, T. epidendroidearum sp. nov. Dch-PK-1 significantly increased the protocorm developmental rate of D. chrysotoxum in ex vitro symbiotic seed germination compared to the uninoculated control. This study marks the first attempt to demonstrate that T. ellipsoidea are true mycorrhizal fungi associated with Dendrobium species. The findings on seed germination and seedling growth suggest that these four strains have potential applications for the ex vitro conservation of Dendrobium species.