Ectendomycorrhizal associations – characteristics and functions

Mycorrhizal symbioses are widespread mutualistic associations of many plant hosts found in many habitats. One type of putative mycorrhizal association, ectendomycorrhiza, is confined to Pinus and Larix spp. and is common in conifer nurseries and in disturbed habitats. This association is characterized by the unique combination of a fungal mantle, Hartig net, and intracellular hyphae, the latter forming soon after Hartig net development. Many reports of the occurrence of ectendomycorrhizas from field-collected specimens are likely erroneous and instead may represent senescent ectomycorrhizas. The fungus species involved in the formation of ectendomycorrhizas were initially called E-strain fungi and their identification was based on characteristics of hyphae and chlamydospores. With the discovery of teleomorphs for some of these fungi, they were found to be ascomycetes. More recently, molecular methods have been used to clarify their systematics and phylogeny and it is apparent that most of the isolates belong to two species, Wilcoxina mikolae and Wilcoxina rehmii. Two species of dematiaceous fungi and a member of the Pezizales, Sphaerosporella brunnea, also have been reported to form ectendomycorrhizas. These fungi can form ectendomycorrhizas with their hosts over a broad pH range and may utilize many substrates as a carbon source. Ectendomycorrhizas may be important in the revegetation of disturbed sites and in the establishment of conifer seedlings in post-fire situations.