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Numerous pathogenic Fusarium species have well-characterized sexual cycles, whereas others, including the crown rot fungus F. pseudograminearum, do not. We conducted studies to elucidate the potential frequency and nature of sexual reproduction in field populations of F. pseudograminearum and developed tester strains for controlled crossings under laboratory conditions. Studies on the role of sexual recombination in the life cycle of F. pseudograminearum revealed apparently low levels of female fertility under controlled laboratory conditions, despite the observation of naturally occurring perithecia of the teleomorph Gibberella coronicola at two field sites. Female fertility levels were experimentally increased to produce female fertile tester strains using four generations of single and multi-stage crossings between sibling progeny derived from fertile laboratory crosses between field isolates collected in northeastern Australia. The production of reliable female fertile tester strains has potential applications for the construction of biological species boundaries, elucidation of the physical characters of reproductive structures, and the generation of genetic diversity via sexual recombination in F. pseudograminearum. As such, the current study is a significant advancement in the understanding of G. coronicola, allowing for future characterisation of various biological, epidemiological, and genetic parameters.

Crown rot, caused by the fungus Fusarium pseudograminearum (teleomorph Gibberella coronicola) is a major disease of wheat in the Australian grain belt. However, there is little information available on the population structure of this pathogen. We measured genetic diversity as assessed with amplified fragment length polymorphism (AFLP) analysis within and between populations of F. pseudograminearum from northeastern, south central, and southwestern regions of the Australian grain belt. Amongst the 217 isolates, 176 haplotypes were identified and grouped into two main clusters. One cluster contained isolates from populations in northeastern Australia, and the other cluster contained isolates from populations in south central and southwestern Australia. The southern populations were distinguished from the northeastern populations by higher levels of population differentiation (Gst) between them and genetic identity amongst the regional populations. We hypothesize that the F. pseudograminearum populations from northeastern and southern Australia are independent, which could result from different founding events or from geographic isolation and the accumulation of genetic differences due to genetic drift and/or selection.