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Fungal Biodiversity: origins, estimation and significance
BAINBRIDGE, BRIAN
Microbiology Group, Division of Life Sciences, King's College, Campden
Hill Road, London W8 7AH, UK
Invited Speaker
Symposium: Biodiversity of Mycorrhizal Fungi: Problems of Measurement
and Meaning
Organised by Thomas Odell and Adolphe Zeze
ICOM1 Abstract
Interest in biodiversity may be motivated by a desire to conserve rare
species, to investigate the effects of fungi on environmental or
agricultural productivity or to search for novel compounds of
therapeutic value. Biodiversity at the morphological level must be
reflected in diversity at the genetic and molecular levels. The origin
of diversity is complex and involves mutation/selection as well as
random and neutral changes. The processes resulting in change can be
classified into genetic, molecular and cytoplasmic effects. Genetic
processes involve mutation, mitotic and meiotic recombination,
nondisjunction, chromosomal rearrangement and translocation. Molecular
processes include gene conversion, transposition, molecular drive and
molecular switching. Cytoplasmic factors such as mitochondrial DNA,
mycoviruses, retrotransposons and plasmids have all been shown to
influence phenotypes. Estimation of fungal biodiversity is difficult
for a variety of reasons. Fungi can reproduce asexually and may even be
imperfect. This can mean that the concept of the organism or of the
species, in the plant or animal sense, is problematical. Consequently
it is difficult to estimate richness or abundance by simple counts.
Molecular methods show considerable promise and have influenced the
analysis of phylogenetic relationships, the detection of organisms in
the environment and the structure of fungal populations. However the
choice of molecular targets is crucial and can vary from fungus to
fungus. For example mitochondrial DNA may show high variability, where
recombination between heterologous molecules can occur, but very little
where there is uniparental inheritance. Major progress has been made by
the application of the polymerase chain reaction which offers the
possibilities of detecting and sequencing DNA from unculturable fungi as
well as the in situ analysis of hyphae in the rhizosphere.