MOLECULAR ANALYSIS OF ECTOMYCORRHIZAL FUNGAL COMMUNITIES

Despite advances in mycorrhizal identification, the goal of elucidating the structure and development of mycorrhizal communities remains elusive. Fruit body production can be sporadic, morphological typing of mycorrhizae is subject to variation with environmental conditions or host, and cultural studies are labor intensive and miss fungi that cannot be isolated. Molecular techniques for identification of fungal symbionts can supplement these techniques and offer an approach that is rapid, is independent of environmental variation, and can be applied directly to large numbers of samples. Molecular approaches to mycorrhizal community analysis attempt to distinguish taxonomic groups so they can be monitored and their interactions studied. Initial characterization of community structure involves enzymatic amplification of DNA directly from mycorrhizal roots using fungus-specific primers, followed by restriction endonuclease digestion to produce taxon-specific restriction fragment patterns. Comparison of these patterns with those obtained from fungal fruit bodies or reference cultures facilitates identification of fungal symbionts. Phylogenetic relationships of fungi that cannot be matched to reference isolates can be inferred by sequencing enzymatically amplified DNA. Future directions that will result from molecular approaches include development of sampling strategies, resolution of species complexes, field observations of host specificity, elucidation of the dynamics of replacement processes (succession), and determination of the role of dispersal in community development. As additional techniques are developed for population analysis, resolution of questions related to genetic structure, variation, and gene flow will become feasible.