Mycorrhizal Morphology and Symbiotic Fungi on the Root of Pyrola renifolia

Introduction: Pyrola renifolia (Ericaceae) is a sciophyte that thrives in shaded forests. Although it is considered to be a mixotrophic plant, little is known about its root system and fungal associates.

Aims: This work aimed clarifying the root morphological feature and the symbiotic fungi.

Methodology: Subterranean parts of the pyroloid were collected from a Sakhalin fir (Abies sachalinensis) stand at Hokkaido, Japan, and analyzed the root system and mycorrhizal morphology and fungal symbionts with common methods.

Results: The sciophyte has a well-developed subterranean system with highly extended rhizomes and mycorrhizal short roots, which are categorized into three morphotypes. Typical arbutoid mycorrhizae with thick mantle structures were formed on the root tip. The main fungal ectomycorrhizal basidiomycete associates were identified as Filobasidiella spp., Russula spp., and Tomentella spp. A mantleless morphotype with Hartig net and the intracellular hyphal coil was mainly associated with root endophyte ascomycetes, viz. Cladophiaphora spp., Didymella spp., Helotiales spp., Leptodontidium orchidicola, and Phialocephala fortinii. Further, we observed ericoid-type mycorrhizae and dark septate endophyte colonization in the middle of the root.

Conclusion: Pyrolaceae have mycorrhizae that are similar to the ERM widely observed in Ericaceae, and also those similar to monotropoid mycorrhizae. Among Ericaceae, pyroloids supplement any carbon source insufficiency from photosynthesis with the mycorrhizal fungal resources to adapt to the shaded growth environment, while monotropoids do not photosynthesize and completely rely on mycotrophy. P. renifolia is a mixotrophic plant that relies on both autotrophic photosynthesis and heterotrophic nutrition via mycorrhizal fungi.