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Abstract Twenty-seven fungus species with diverse sporocarp-host associations were tested for ectomycorrhiza formation with seven Pacific Northwest conifers: Pseudotsuga menziesii , Tsuga heterophylla , Larix occidentalis , Picea sitchensis , Pinus contorta , P. ponderosa , and P. monticola . The fungi varied widely in their ability to form mycorrhizae with the various conifers but can be placed into three groups: (1) fungi with wide ectomycorrhizal host potential, low specificity, sporocarps usually associated with diverse hosts in the field, (2) fungi with intermediate host potential yet specific or limited in sporocarp-host associations, and (3) fungi with narrow host potential, only able to form ectomycorrhizae with a specific host species or species within a genus and likewise limited in their sporocarp association. Numerous fungi which produce sporocarps exclusively in association with specific hosts were able to form well-developed ectomycorrhizae with one or more nonassociated hosts. Thus, specific sporocarp-host association does not necessarily limit mycorrhizal associations with other hosts. Often, however, fungi with known sporocarp-specific hosts showed best mycorrhiza development with that particular host suggesting further specialization in those associations. Among the conifers, the three Pinus spp. showed little infrageneric differences in their ability to form ectomycorrhizae with the various fungi. Pseudotsuga menziesii and Larix occidentalis were able to form ectomycorrhizae with fungi that fruit only with one or the other. The fungi with wide sporocarp-host associations showed no incompatibility with any of the hosts, and it is suggested that they may share a compatibility or recognition factor common to many ectomycorrhizal hosts. The specialized fungi with specific sporocarp-host associations often showed incompatibility with other nonassociated hosts. Disruption of the cortex by the invading fungus and lignification as indicated by intense safranin staining of cortical cells were the most common indicators of incompatibility. This host reaction suggests a type of phenolic defense mechanism as displayed in many plant-pathogen interactions. The need for future research on the mechanisms and factors determining ectomycorrhizal host-fungus compatibility and specificity is emphasized. Forest Sci. 28:423-458.
Molina et al. (Wed,) studied this question.