Abstract:
The Gibberella fujikuroi species complex accommodates Fusarium spp. in the section
Liseola that are unified by a common Gibberella sexual state. These are ubiquitous and
economically important pathogens of plants, resulting in crop losses and the production of
health-threatening mycotoxins. In this thesis, an interspecific cross between Fusarium
circinatum and Fusarium subglutinans, both members of the G. fujikuroi species complex,
were examined. A genetic linkage map was produced using Amplified Fragment Length
Polymorphisms (AFLPs) and twelve linkage groups were identified. Distortion of the
expected segregation patterns of these markers was observed in half of the AFLP markers
genotyped. Distorted markers were found distributed throughout the genetic linkage map,
leading to the hypothesis that distortion was caused by the high level of genomic divergence
between the parental isolates. This was evident in that distorted alleles displayed genomewide
skewing towards the F. subglutinans parental genotype, as well as the differential
transmission of F. subglutinans alleles to F1 individuals. Investigations of Quantitative Trait
Loci (QTL) involved in mycelial growth of the F1 progeny at 25 and 30˚C, suggested that a
principle genomic region was involved. Localization of this QTL to the genomic sequence of
F. circinatum revealed a putative fungal transcription factor. The presence of this
transcription factor was detected only in F. circinatum, and not in F. verticillioides or F.
fujikuroi, the only additional species in the G. fujikuroi species complex for which genomic
data are available. The AFLP map allowed investigation of synteny among chromosomes
from F. circinatum, F. verticillioides and F. fujikuroi. A significant level of macrosynteny
was observed between representatives of the African, American and Asian clades of the G.
fujikuroi species complex, respectively. Evidence was also found for a putative reciprocal
translocation present only in F. circinatum and F. subglutinans. This region was found to be
translocated relative to the genomic sequence of both F. verticillioides and F. fujikuroi.
Jointly, these results provided considerable insight, at the genomic level, for species within
the G. fujikuroi species complex. Importantly, the utility of a genetic map together with
genomic sequence data was demonstrated, and the genetic basis of a growth QTL determined.
