Molecular Approaches to Investigate Biodiversity in Mycorrhizal Fungi

Abstract

Mycorrhizal fungi interact symbiotically with the roots of about 90% of land plants forming different types of mycorrhiza. The total number of soil fungi involved in this symbiosis is still unknown, but in order to evaluate their biodiversity it is first necessary to make an identification at species and isolate level. This goal has received substantial impetus thanks to the development of molecular techniques based on the polymerase chain reaction (PCR), which allow the characterization of nucleic acids amplified from minute amounts of fungal samples. PCR-based techniques have already been applied to those endo- and ectomycorrhizal fungi where morphological characters are in conflict, ambiguous or missing. This approach has allowed the development of molecular tools for their identification (Henrion et al. 1992; Gardes and Bruns 1993; Lanfranco et al. 1993, 1995a, b; Wyss and Bonfante 1993). PCR-based techniques include a wide range of protocols, among which the most commonly used are: amplification of variable regions in the ribosomal genes (ITS or IGS), restriction fragment length polymorphism (RFLP) of PCR-generated fragments, amplification of short repeated sequences (microsatellites) and random amplification of polymorphic DNA (RAPD) (Erlich et al. 1991). These techniques provide a different degree of resolution in the study of genetic polymorphisms. For example, amplified ITS regions usually reveal interspecific variations, although differences in fragment length may not be found among closely related species and may require further restriction analysis.