Genetic linkage map and QTL analysis of a cross between Fusarium subglutinans and Fusarium circinatum

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.