Roots of salal (Gaultheria shallon Pursh) collected from forest clearcuts were examined by light and scanning electron microscopy, and the ericoid mycorrhizal fungi were isolated and identified. Heavy colonization of typical ericoid mycorrhizae was present in and restricted to the first of the two layers of root cortical cells. Neither ectomycorrhizae nor arbutoid mycorrhizae were observed. In the field, over 85% of the roots and 90% of the cortical cells within colonized roots were colonized. One hundred and seventy-five of the 278 fungal isolates from salal roots formed ericoid mycorrhizae with salal in the laboratory, and these isolates were grouped into four species based on spore formation and cultural characteristics: Oidiodendron griseum Robak, Acremonium strictwn W. Gams, and two unidentified, nonsporulating fungal species. The association in the laboratory between A. strictum and salal was atypical in that the fungus improved the growth of salal seedlings but was slow to colonize roots and occasionally grew and even sporulated on the shoots. No differences in percent colonization or diversity of ericoid mycorrhizal fungi were found in salal growing on clearcuts from two different forest types. Keywords: Gaultheria shallon, Oidiodendron griseum, Acremonium strictum, ericoid mycorrhizal fungi.
Interactions of ericoid mycorrhizal fungi and root pathogens in Rhododendron: In vitro tests with plantlets in sterile liquid culture