Is rarity of pinedrops (Pterospora andromedea) in eastern North America linked to rarity of its unique fungal symbiont?

Like other myco-heterotrophic plants, Pterospora andromedea (pinedrops) is dependent upon its specific fungal symbionts for survival. The rarity of pinedrops fungal symbiont was investigated in the eastern United States where pinedrops are rare. Wild populations of eastern pinedrops were sampled, and the plant haplotypes and fungal symbionts were characterized with molecular techniques; these data were compared to those from the West with phylogenetic analyses. The frequency of the fungal symbiont in eastern white pine forests was assessed using a laboratory soil bioassay and in situ pinedrops seed baiting. Only one plant haplotype and fungal symbiont was detected. The plant haplotype was not unique to the East. The fungal symbiont appears to be a new species within the genus Rhizopogon, closely related to the western symbionts. This fungal species was not frequent in soils with or without pinedrops, but was less frequent in the latter and in comparison to the fungal symbionts in western forests. Seed baiting resulted in few germinants, suggesting that mycelial networks produced by the eastern fungal symbiont were rare. Results suggest that eastern pinedrops rarity is influenced by the distribution and rarity of its fungal symbiont.