Fungal diversity in the roots of four epiphytic orchids endemic to Southwest Mexico is related to the breadth of plant distribution

Fungi associated with plant roots are important for different plant processes, including germination and development. In Mexico, the knowledge about fungal species that interact with orchid roots and their possible roles in plant success and dispersion in different geographical locations is still very limited. For this reason, this work aimed to determine the community composition and diversity of fungi associated with orchid roots at seven sites in the Transversal Volcanic Belt region in Michoacán, México. The roots of four endemic orchid species were analyzed: Laelia autumnalis, L. speciosa, Euchile citrina and P. squalida. In total, 71 isolates were obtained and classified into 20 genera, including one mycorrhizal genus (Tulasnella) and 19 genera classified as basidiomycetes and ascomycetes, such as Coprinus, Trichoderma and Xylaria. The diversity among different orchid species and sampling sites was compared using the Chao 1, Shannon-Wiener and Whittaker indexes. In this work, species such as L. autumnalis, L. speciosa and P. squalida were found in different sites and seemed to be more generalists with regard to endophytes; they were typically associated with and found to be in symbiosis with species from the orchid mycorrhizal genus Tulasnella. Other orchids seem to be more specific, such as E. citrina, which showed the lowest diversity index and poor local distribution. This situation has been reported for species with a high degree of endemism.