Over the past decade the use of molecular techniques has provided new ways to study old questions about how ectomycorrhizal fungi interact with each other and their environment. In their simplest form, these methods enable researchers to identify vegetative stages of fungi that would be difficult, slow, or impossible to identify by morphological or culture-based methods. This has resulted in quantitative views of complex fungal communities, which in turn have revealed new and unexpected patterns in community structure. In addition, molecular methods have been used to identify individual genotypes of fungi. This information has provided insights into the way that particular species of ectomycorrhizal fungi spread in nature. In this article we will mention the basic techniques and briefly discuss some of the findings that have resulted. Advances in this field have recently been comprehensively reviewed for scientific audiences, and we refer readers that have a more technical interest or a need to access the current literature to these reviews (Dahlberg, 2001; Horton & Bruns, 2001).

Sarcodes sanguinea and Pterospora andromedea (Ericaceae, Monotropoideae) are nonphotosynthetic myco-heterotrophic plants. Recent studies have shown that the roots of the adult plants are always associated with closely related but exclusive sets of Rhizopogon species (Basidiomycota, Boletales) from section Amylopogon. We have isolated Rhizopogon species that were associated with the adult plants and used them to germinate seeds under gnotobiotic conditions. All Rhizopogon species isolated from either plant species were capable of stimulating seed germination in both Sarcodes and Pterospora. Under the primary conditions used, germination varied from 9 to 73% in the case of Sarcodes and 0 to 13% in that of Pterospora. The single Rhizopogon strain that failed to elicit germination in Pterospora under these conditions did stimulate germination under slightly different conditions. By contrast, seeds failed to germinate on all media which lacked these Rhizopogon species, or in the presence of six other genera of basidiomycetes. Seed germination could be stimulated either through cellophane or at the edge of fungal colonies without direct fungus–seed contact. These results suggest that a diffusible or volatile compound that is unique to Rhizopogon stimulates germination of these plant seeds. Seed lots of Sarcodes from two successive years had similar germination levels. Sarcodes seeds that had overwintered under natural conditions were also stimulated to germinate. These results demonstrate the potential for long-term dormancy. We suggest that a combination of dormancy and the use of specific germination cues might increase the opportunities of these plants for recruitment. In addition, the specific germination response explains at least a part of the specialized associations observed in the adult plants. Nevertheless, the seeds respond to a slightly broader range of Rhizopogon species than has been observed to be associated with the adult plants; thus other factors must also be involved with specificity under natural conditions.