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

Abstract

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.

Global distribution patterns of mycoheterotrophy

“…Previous studies, focusing on a finer taxonomic scale, suggested that the abundance of mycoheterotrophic plant species is related to the abundance of their specific fungal partners (Hazard, Lilleskov, & Horton, ; Yamato et al, ). This indicates that the mere presence of a suitable fungal partner is not sufficient to promote a mycoheterotrophic relationship of a plant with its mycorrhizal partners, even though the abundance of autotrophic plants supports the required mycorrhizal type.…”

Microsatellite primers for the fungi Rhizopogon kretzerae and R. salebrosus (Rhizopogonaceae) from 454 shotgun pyrosequencing

“…Grubisha & Trappe are obligately ectomycorrhizal with several pine species and are the symbiotic mycobiont host to the mycoheterotrophic plant, Pterospora andromedea Nutt. (Ericaceae; Bidartondo and Bruns, 2002; Dowie et al, 2011, 2012; Hazard et al, 2012; Grubisha et al, 2014), a North American endemic divided into eastern and western populations (Bakshi, 1959). Pterospora andromedea primarily associates with two closely related Rhizopogon species: western P. andromedea are symbiotic primarily with R. salebrosus while eastern populations are found with R. kretzerae (Grubisha et al, 2014).…”

“…Pterospora andromedea primarily associates with two closely related Rhizopogon species: western P. andromedea are symbiotic primarily with R. salebrosus while eastern populations are found with R. kretzerae (Grubisha et al, 2014). Rhizopogon kretzerae is currently only known from collections of P. andromedea roots and only found in association with Pinus strobus L. (Hazard et al, 2012; Grubisha et al, 2014). Eastern P. andromedea populations have undergone recent decreases in population size and possible local extinction from a variety of anthropogenic factors (Schori, 2002).…”

Gibberellic Acid Induces Asymbiotic Germination of the Obligate MycoheterotrophPterospora andromedea(Ericaceae)

“…(Dowie et al 2011). In eastern North America, Hazard et al (2011) found that a related, but undescribed, Rhizopogon species serves as the host for P. andromedea. This eastern species is less common than Rhizopogon in western forests and may be limiting the range and frequency of P. andromedea in the East (Hazard et al 2011).…”

“…Then, using a broader sampling of fungi, they demonstrated that only members of the Amylogogon subgenus of Rhizopogon induced germination. Each mature plant demonstrates even greater host specificity and only associates with a single species within the same subgenus of fungi identified by the germination experiments (Bidartondo and Bruns 2002;Hazard et al 2011).…”