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

Seedlings of Abies grandis, Alnus rubra, Pinus ponderosa, Picea sitche nsis, Pseudotsuga menziesii and Tsuga hetevophylla were grown in monoc ulture and dual culture in the greenhouse and inoculated with spore sl urries of 20 isolates representing 15 species of ectomycorrhizal hypog eous fungi (11 Rhizopogon species, Alpova diplophloeus, Truncocolumell a citrina, Melanogaster euryspermus and Zelleromyces gilkeyae). The pr imary objectives were to assess and compare the pattern of host specif icity between symbionts and to study the influence of neighbouring pla nts on ectomycorrhiza development. None of the fungal species had broa d host range affinities. A variety of specificity responses were exhib ited by the different fungal taxa, ranging from genus-restricted to in termediate host range. In monoculture, nine species of Rhizopogon (R. arctostaphyli, R. ellenae, R. flavofibrillosus, R. occidentalis, R. ru bescens, R. smithii, R. subcaerulescens, R. truncatus and R. vulgaris) formed ectomycorrhizas on Pinus ponderosa whereas three Rhizopogon sp ecies (R. parksii, R. vinicolor and R. subcaerulescens) formed ectomyc orrhizas on Pseudotsuga menziesii. Truncocolumella citrina associated with Pseudotsuga menziesii and Alpova diplophloeus with Alnus rubra. M elanogaster euryspermus and Z. gilkeyae did not form ectomycorrhizas w ith any hosts. None of the fungi tested developed ectomycorrhizas on A bies grandis, Tsuga heterophylla or Picea sitchensis in monoculture. I n dual culture, the same nine Rhizopogon species that formed abundant ectomycorrhizas on Pinus ponderosa formed some ectomycorrhizas on seco ndary hosts such as Abies grandis, Tsuga heterophylla, Pseudotsuga men ziesii and Picea sitchensis. Similarly, Truncocolumella citrina formed abundant ectomycorrhizas on Pseudotsuga menziesii and low levels on t he secondary hosts Abies grandis, Tsuga heterophylla and Picea sitchen sis. Rhizopogon parksii and R. vinicolor only formed ectomycorrhizas o n Pseudotsuga menziesii, and Alpova diplophloeus only formed ectomycor rhizas on Alnus rubra. The specificity pattern obtained by using this dual-culture approach is contrasted with previous pure-culture synthes is data and is discussed in terms of potential interplant linkages and community dynamics.