ABSTRACT

Over 6000 species of ECM fungi belonging mainly to Basidiomycetes, some Ascomycetes and Zygomycetes have been recognized based on their morphological and/or molecular assessments (Molina et al. 1992). Many ECM fungi form epigeous fruiting bodies, but not all. A few of them produce hypogeous sequestrate (truffle-like) or resupinate (crusting) fruiting bodies; some others such as Cenococcum geophilum fruit infrequently, but propagate via sterile mycelia (Lobuglio et al. 1996; Shinohara et al. 1999). Phylogenetic analyses of DNA sequence data suggest that mushroomforming agarics and others such as Boletales or Russulales are derived from woodrotting fungi. The ability to form ECM is an important evolutionary trait among agarics. Several taxa of basidiomycetous ECM fungi such as Cortinariaceae, Boletaceae, Amanitaceae and Russulaceae probably occurred in the early Cretaceous period. Their evolutionary diversity was guided predominantly by host and habitat specificity. It is believed that ECM fungi evolved from saprophytic fungi, which is indicated by their ability to produce cell wall-digesting enzymes. The ECM fungi are polyphyletic have several saprophytic relatives. According to Brundrett (2002), ascomycetous ECM fungi are polyphyletic with separate origins. They possess considerable functional diversity. For example, a few ascomycetous ECM fungi utilize inorganic N, but most use organic N sources. The host range of ECM could be narrow or broad. Their preference to particular hosts is indicative of co-evolution with host tree species.