Characterization and Identification of Orchid Mycorrhizal Fungi Enhancing Seed Germination in Cymbidium from Southern Vietnam

Background: Cymbidium is a genus of orchids that grow in soil, on substrates, or epiphytically, forming symbiotic associations with orchid mycorrhizal fungi (OMF). These fungi play a crucial role in facilitating water and nutrient uptake, which is essential for seed germination in natural environments. This study aimed to characterize and identify OMF strains associated with Cymbidium orchids cultivated in Southern Vietnam and to evaluate their effects on symbiotic seed germination on tree fern fibre medium. Methods: Roots and growing media from thirty Cymbidium accessions, collected in Southern Vietnam, were stained with Trypan Blue and examined under a light microscope. OMF isolates were cultured on potato dextrose agar (PDA) medium and tested for their ability to promote seed germination on tree fern fiber. The fungal isolates that significantly enhanced germination rates were identified based on morphological characteristics and sequencing of the internal transcribed spacer (ITS) region using ITS1/ITS4 primers, followed by BLAST analysis against the NCBI database. Result: Five distinct fungal morphotypes were observed in Cymbidium roots, with occurrence rates ranging from 3.3% to 40.0%. Two isolates, designated as OMF-S1 and OMF-S3, significantly promoted seed germination, achieving rates of 15.3% and 13.7%, respectively. Molecular identification results showed that OMF-S1 had high similarity to Fusarium sp., while OMF-S3 had high similarity to Trichoderma sp. These findings highlight the potential application of specific OMF strains in Cymbidium cultivation, propagation and conservation efforts.