Native Fusarium species from indigenous fynbos soils of the Western Cape
Date
2008-12
Authors
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Publisher
Stellenbosch : Stellenbosch University
Abstract
The genus Fusarium contains members that are phytopathogens of a number of
agricultural commodities causing severe diseases such as wilts and rots. Fusarium
species also secrete mycotoxins that have devastating effects on humans and animals.
The ability of Fusarium species to change their genetic makeup in response to their
immediate environment allows these fungi to exist in diverse habitats. Due to the
ubiquitous nature of Fusarium, it forms part of the fungal communities in both
agricultural and native soils. Fynbos is the major vegetation type of the Cape Floristic
Region (CFR), which is a region that is renowned for its high plant species diversity and
endemism. In this study, the occurrence and distribution of Fusarium species in
indigenous fynbos soils and associated plant debris is investigated. In addition, the
phylogenetic relationships between Fusarium species occurring in this particular habitat
are evaluated.
Fusarium isolates were recovered from soils and associated plant debris, and
identified based on morphological characteristics. The morphological identification of
isolates was confirmed using Polymerase Chain Reaction (PCR) based restriction
fragment length polymorphism (RFLP) analyses of the translation elongation factor 1
alpha (TEF-1α) and internal transcribed spacer (ITS) regions. Furthermore, phylogenetic
relationships between Fusarium species were based on the TEF-1α, ITS and β-tubulin
gene regions.
One-hundred-and-twenty-two (122) Fusarium strains were isolated from the
fynbos soils in the Cape Peninsula area (Western Cape). Based on both morphological
and molecular identification, the most prevalent Fusarium species in the fynbos soils were F. oxysporum Schlecht. emend. Snyd. and Hans., F. solani (Martius) Appel and
Wollenw. emend. Snyd. and Hans., F. equiseti (Corda) Sacc. and an undescribed
Fusarium species. Fusarium oxysporum was the dominant species in fynbos soils and
strains of this species displayed significant genetic variability. Some strains of both
F. oxysporum and F. solani showed close phylogenetic affinities to formae speciales
(strains pathogenic to specific plant hosts) in the phylogenetic analyses. However, no
diseased plants were observed in and within the vicinity of our sampling sites.
In the third chapter, the undescribed Fusarium strains are described as Fusarium
peninsulae prov. nom. Morphologically these strains are characterized by falcate
macroconidia produced from brown sporodochia. The macroconidia are pedicellate,
falcate to curved with hooked apical cells. Also, this fungus produces apedicellate
mesoconidia on polyphialides in the aerial mycelium and forms microconidia sparsely.
Chlamydospores are formed abundantly on aerial mycelium and submerged hyphae. All
these morphological characteristics closely relate this fungus to F. camptoceras species
complex in Fusarium section Arthrosporiella. However, phylogenetic analysis based on
the ITS sequences differentiate these strains from F. camptoceras and other related
species in section Arthrosporiella.
Considering the fact that both as phytopathogens and saprophytic fungi, Fusarium
species secrete a variety of cell wall degrading enzymes such as cellulases and xylanases.
These enzymes allow the fungi to degrade the plant cell wall components to obtain
nutrients. In Fusarium, notably endoxylanases play a role in phytopathogenesis of these
fungi. Endoxylanase enzymes from F. oxysporum f. sp. lycopersici, F. verticillioides and
F. graminearum have been characterized. In this final chapter, the use of the endoxylanase encoding gene, as a molecular marker in phylogenetic analysis was
evaluated using F. graminearum (Fg) clade species as model. Degenerated primers were
designed and the endoxylanase region amplified by PCR, cloned and sequenced. PAUPgenerated
neighbour-joining analysis of the endoxylanase (XYL) region enabled all
species to be distinguished and was as informative as the analysis generated with UTPammonia
ligase (URA), phosphate permase (PHO), reductase (RED) and trichothecene 3-
О-acetyltransferase (TRI101). Furthermore, the results of the phylogenetic analysis of
XYL showed better species resolution in comparison to the analysis of the structural
genes (TEF-1α and histone H3). Overall, the results demonstrated that phylogenetic
analysis of XYL combined with other functional genes (URA, PHO, RED and TRI101)
clearly distinguished between the Fg clade species far better than the analysis of
structural genes (TEF-1α and histone H3).
Description
Thesis (MSc (Microbiology))--Stellenbosch University, 2008.
Keywords
Fusarium, Fynbos ecology, Soil microbiology, Dissertations -- Microbiology, Theses -- Microbiology