Botanic Gardens Trust, Sydney, Australia

Fusarium oxysporum

Dr Edward Liew - Manager, Plant Pathology & Matthew Laurence - PHD student

The Fusarium oxysporum species complex causes catastrophic crop losses in over 150 plant species and is considered one of the world’s most economically significant soil borne plant pathogens. This species is, however, primarily non-pathogenic and forms endophytic, saprophytic and latent pathogenic relationships with its plant hosts. It is also widely distributed and has been isolated from the permafrost of the Arctic to the sands of the Sahara and even in coastal marine sediments! Despite its near ubiquity, research has mainly focused on strains from agricultural ecosystems. This overemphasis on agricultural strains is unlikely to represent the underlying natural diversity, hence limiting our understanding of the distribution, ecology and evolution of this species complex. 

Cotton wilt, caused by Fusarium oxysporum f.sp. vasinfectum, was reported in Australia for the first time in 1993 and investigations into the source of this incursion by scientist at CSIRO revealed an indigenous origin from fungal populations associated with native cotton relatives. This revealed a substantial knowledge gap in our understanding of the whole F. oxysporum species complex in Australia. In order to assess its evolutionary potential, we have sampled a large population associated with native vegetation geographically isolated from cultivation throughout the continent. Lineage composition of the native soil population was investigated on the basis of DNA sequences of four loci. We found a high level of genetic diversity, indicating that Australia is a centre of diversity. This high level of diversity is unexpected as the centre of origin of most members of this species complex has been thought to be Asia and that many strains were introduced to other parts of the world, including Australia, since the advent of agriculture. Based on our findings, this centre of origin could very well encompass the whole of the Australasian region. Our investigation continues to elucidate the evolutionary potential of this species complex in Australia through analysis of gene flow, genetic diversity and the potential for recombination. 


 

Matthew Laurence
PhD student, Matthew Laurence, collecting soil samples from national parks for fungal isolation.

 Fusarium locations

Fusarium oxysporum was isolated from soil samples collected from sites with no cultivation history throughout Australia.

Fusarium plates 
Cultures of Fusarium oxysporum showing large variation in colony morphology.