BIOLOGY OF THE ECTOMYCORRHIZAL GENUS, RHIZOPOGON .2. PATTERNS OF HOST-FUNGUS SPECIFICITY FOLLOWING SPORE INOCULATION OF DIVERSE HOSTS GROWN IN MONOCULTURE AND DUAL CULTURE

Seedlings of Abies grandis, Alnus rubra, Pinus ponderosa, Picea sitchensis, Pseudotsuga menziesii and Tsuga hetevophylla were grown in monoculture and dual culture in the greenhouse and inoculated with spore slurries of 20 isolates representing 15 species of ectomycorrhizal hypogeous fungi (11 Rhizopogon species, Alpova diplophloeus, Truncocolumella citrina, Melanogaster euryspermus and Zelleromyces gilkeyae). The primary objectives were to assess and compare the pattern of host specificity between symbionts and to study the influence of neighbouring plants on ectomycorrhiza development. None of the fungal species had broad host range affinities. A variety of specificity responses were exhibited by the different fungal taxa, ranging from genus-restricted to intermediate host range. In monoculture, nine species of Rhizopogon (R. arctostaphyli, R. ellenae, R. flavofibrillosus, R. occidentalis, R. rubescens, R. smithii, R. subcaerulescens, R. truncatus and R. vulgaris) formed ectomycorrhizas on Pinus ponderosa whereas three Rhizopogon species (R. parksii, R. vinicolor and R. subcaerulescens) formed ectomycorrhizas on Pseudotsuga menziesii. Truncocolumella citrina associated with Pseudotsuga menziesii and Alpova diplophloeus with Alnus rubra. Melanogaster euryspermus and Z. gilkeyae did not form ectomycorrhizas with any hosts. None of the fungi tested developed ectomycorrhizas on Abies grandis, Tsuga heterophylla or Picea sitchensis in monoculture. In dual culture, the same nine Rhizopogon species that formed abundant ectomycorrhizas on Pinus ponderosa formed some ectomycorrhizas on secondary hosts such as Abies grandis, Tsuga heterophylla, Pseudotsuga menziesii and Picea sitchensis. Similarly, Truncocolumella citrina formed abundant ectomycorrhizas on Pseudotsuga menziesii and low levels on the secondary hosts Abies grandis, Tsuga heterophylla and Picea sitchensis. Rhizopogon parksii and R. vinicolor only formed ectomycorrhizas on Pseudotsuga menziesii, and Alpova diplophloeus only formed ectomycorrhizas on Alnus rubra. The specificity pattern obtained by using this dual-culture approach is contrasted with previous pure-culture synthesis data and is discussed in terms of potential interplant linkages and community dynamics.