title: The host bias of three epiphytic Aeridinae orchid species is reflected, but not explained, by mycorrhizal fungal associations.
abstract: OBJECTIVE
  The three co-occurring epiphytic orchid species, Sarcochilus hillii, Plectorrhiza tridentata, and Sarcochilus parviflorus vary in host specificity; all are found predominantly on the tree Backhousia myrtifolia but some also associate with a broad range of species. Despite this specialization, no fitness advantage has been detected for adult orchid plants growing on the preferred host. Therefore, we predicted that the host specialization of these orchid species is a consequence of a bias toward particular orchid mycorrhizal fungi, which are in turn biased toward particular woody plant species.
  
  
  METHODS
  To test this hypothesis, we sampled representatives of each orchid species on B. myrtifolia and other host species across sites. Rhizoctonia-like fungi were isolated from orchid roots and identified using molecular markers.
  
  
  RESULTS
  Three groups of fungi were identified, and the orchid species varied in their specificity for these. All fungal groups were found on the host B. myrtifolia; yet at all sites, only one orchid species, S. hillii, associated with all three groups.
  
  
  CONCLUSIONS
  Our results demonstrate that these orchid species did vary in their mycorrhizal specificity; however, the distribution of their mycorrhizal associates did not directly explain their host associations. Rather, we propose that the mycorrhizal relationship of these orchid species is complex and have suggested future avenues of research.
authors.affiliation: Research School of Biology, Building 116, Daley Road, The Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Kelli M
authors.initials: KM
authors.lastname: Gowland
authors.forename: Marlien M
authors.initials: MM
authors.lastname: van der Merwe
authors.forename: Celeste C
authors.initials: CC
authors.lastname: Linde
authors.forename: Mark A
authors.initials: MA
authors.lastname: Clements
authors.forename: Adrienne B
authors.initials: AB
authors.lastname: Nicotra
mesh_terms: D016172:DNA Fingerprinting; D021901:DNA, Intergenic / Q000737:chemistry; D004272:DNA, Mitochondrial / Q000737:chemistry*; D038821:Mycorrhizae / Q000737:chemistry / Q000502:physiology*; D029595:Orchidaceae / Q000382:microbiology*; D017422:Sequence Analysis, DNA; D013045:Species Specificity; D014197:Trees / Q000382:microbiology*
chemical_list: D021901:DNA, Intergenic; D004272:DNA, Mitochondrial