Fungal endophytes of Orchidaceae: specificity and opportunism

      Orchids are parasitic on basidiomycetes.  Leafless groups may derive essentially all of their energy from fungi, while others require interaction with a fungus for germination and then to a greater or lesser degree as mature plants.  Since the same fungi participate with orchids from different groups and different regions of the world, it is clear that there are no broad coevolutionary patterns between the orchids and fungi.  A more relevant question is what happens on a smaller scale, within species.  What are the patterns of association within an orchid species and among closely related species?  How specific is the interaction at this level?  Does more than one fungus participate?  We are approaching these questions using molecular techniques to identify the fungus that interacts with native North American species of Corallorhiza.  This genus is leafless and exhibits the shift from Rhizoctonia-type basidiomycetes to ectomycorrhizal basidiomycetes, where the association between orchid and fungus may be more specific.

Photograph of Dactylorhiza majalis protocorm by Dr. Hanne Rasmussen