Evidence for a fungal liaison between Corallorhiza trifida (Orchidaceae) and Pinus contorta (Pinaceae)

Abstract

Corallorhiza trifida Châtelain, or pale coral root orchid, is a heterotrophic, leafless, rootless, terrestrial orchid with a circumboreal distribution. Because of its relative inability to photosynthesize, the orchid obtains energy through the digestion of fungal hyphae that grow within the cells of its contorted, yellowish, coralloid rhizomes. Recently, we isolated and cultured strains of a slow-growing basidiomycete with bright yellow, clamped hyphae that are typical of the fungal cells present in C. trifida endomycorrhizas from different treed habitats at widely distributed locations in the northern hemisphere. By inoculating the roots of Pinus contorta Douglas ex Loudon seedlings with this fungus we were able to demonstrate its ability to form distinctive ectomycorrhizas with an ectotrophic, woody plant. The formation of endomycorrhizas with C. trifida and ectomycorrhizas with P. contorta indicates that in nature a triple symbiosis, with a circumboreal distribution, exists among certain trees, the coral root orchid, and this yellow basidiomycete that links the two and functions as a mycorrhizal symbiont in both. Key words: Corallorhiza trifida, orchid mycorrhiza, triple symbiosis, ectomycorrhiza, Pinus contorta.