title: The rare terrestrial orchid Nervilia nipponica consistently associates with a single group of novel mycobionts.
abstract: Nervilia nipponica is a tuberous terrestrial orchid that has a highly restricted distribution within common secondary evergreen forest communities in central and western Japan. Such a limited occurrence could be attributable to a requirement for a specific mycorrhizal fungus. As part of a broader examination of this hypothesis, we sought to elucidate the mycorrhizal associations of N. nipponica. Seventy-five samples of mycorrhizae from forty individuals were collected at ten populations throughout the orchid's range in Japan. The identity of mycorrhizal fungi was investigated by sequencing two genetic markers (nrDNA ITS and nrDNA 28S LSU) and their relationships were assessed via phylogenetic analyses. The most frequently encountered mycorrhizal fungi consisted of four closely related Agaricomycetes that infected an average of 78.7 % of individuals per population. All four formed a discrete, monophyletic clade with low sequence homology to other fungi registered in GenBank, indicating that they belong to a novel, unnamed family. Two additional fungal groups, belonging to Ceratobasidiaceae and "Group B" Sebacinales, were found in 22.0 and 21.5 % of individuals per population, respectively. The orchid probably uses these two groups opportunistically, because they were found at lower densities and always in combination with the unidentified Agaricomycete. These findings suggest that a group of novel Agaricomycete fungi constitutes the dominant mycobiont of N. nipponica.
authors.affiliation: Tsukuba Botanical Garden, National Museum of Nature and Science, Amakubo 4-1-1, Tsukuba, Japan. nomura.naofumi@gmail.com
authors.forename: Naofumi
authors.initials: N
authors.lastname: Nomura
authors.forename: Yuki
authors.initials: Y
authors.lastname: Ogura-Tsujita
authors.forename: Stephan W
authors.initials: SW
authors.lastname: Gale
authors.forename: Ayako
authors.initials: A
authors.lastname: Maeda
authors.forename: Hidetaka
authors.initials: H
authors.lastname: Umata
authors.forename: Kentaro
authors.initials: K
authors.lastname: Hosaka
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Yukawa
mesh_terms: D001483:Base Sequence; D001487:Basidiomycota / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics; D058507:Host Specificity; D007564:Japan; D008969:Molecular Sequence Data; D038821:Mycorrhizae / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D029595:Orchidaceae / Q000382:microbiology*; D010802:Phylogeny; D012339:RNA, Ribosomal, 28S / Q000235:genetics; D017422:Sequence Analysis, DNA; D013559:Symbiosis
chemical_list: D004271:DNA, Fungal; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer; D012339:RNA, Ribosomal, 28S
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