Diversity and dynamics of culturable fungi associated with the roots of the endemic and endangered orchid Rhynchostele cervantesii

Endophytic and mycorrhizal fungi are vital for the life cycle of orchid species, as they lack nutrient reserves and rely entirely on these symbionts for early growth and seedling establishment in their natural environment. Identifying the symbiotic fungi of orchids enhances understanding of this relationship, especially mycorrhizal fungi characterized by the formation of pelotons, structures formed by the coiling of hyphae within the cortical cells of roots. This study aimed to analyze the diversity and dynamics of culturable endophytic and putatively mycorrhizal fungi associated with the endemic and endangered orchid species Rhynchostele cervantesii. Seventeen fungal strains were isolated from the roots and protocorms of R. cervantesii collected from a single natural population located at the Tenderio Property within the Voluntary Conservation Area of the Indigenous Community of Santiago Tingambato, Michoacán, Mexico. Blastn search and complementary phylogenetic analysis of the ribosomal DNA internal transcribed spacer (ITS1-5.8 S-ITS2) of these fungal isolates allowed the identification of ten different OTUs, all belonging to the phylum Ascomycota, within the genera Apiospora, Aspergillus, Diaporthe, Didymella, Leptosphaeria, Nemania, Penicillium, and Xylaria. The community of culturable endophytic fungi associated with R. cervantesii roots shows seasonal and developmental variation. The specific roles of these taxonomic groups in establishing and providing resistance to abiotic stress in R. cervantesii remain to be clarified. Notably, Diaporthe sp. stands out as a strain capable of supporting in vitro plant cultivation due to its ability to produce indole-3-acetic acid (IAA), while Apiospora appears to play a significant role throughout the life cycle of this endangered species.