Biocontrol of weedy Sporobolus grasses in Australia using fungal pathogens

Abstract

In Australia there are five weedy Sporobolus grass (WSG) species that heavily impact agricultural industries and native biodiversity. WSG have been the subject of several efforts to find host-specific pathogens with potential for classical and inundative biocontrol. Most of these studies are only discussed in unpublished reports or theses, so in this paper we synthesise the available peer-reviewed and ‘grey’ literature that discuss classical, augmentative and inundative biocontrol of WSG in Australia using fungal pathogens. We consider the hundreds of fungal pathogens previously isolated from Sporobolus hosts on an international and national scale. Of the pathogens investigated for WSG biocontrol previously, the only promising classical biocontrol agent was a smut fungus (Ustilago sporoboli-indici) from South Africa that is now present in Queensland and New South Wales, Australia. Its method of introduction to Australia is unknown. We hence discuss the history and potential for augmentative biocontrol of WSG using U. sporoboli-indici. Next, we summarise inundative biocontrol efforts. Several ascomycetes isolated from Australian WSG populations have been tested in this regard, including species of Nigrospora, Fusarium, Curvularia, Microdochium, Pestalotiopsis, and Neopestalotiopsis. However, a lack of host-specificity or efficacy subsequently precluded their further development, and potential improvements on those inundative biocontrol studies are discussed. Finally, we discuss a collection of endemic fungal taxa isolated from diseased Sporobolus in Australia, which are currently undergoing virulence, pathogenicity, and host-specificity screening as potential inundative biocontrol agents for WSG. Our intention is that the lessons learned from previous studies and summarised herein, will support ongoing development of WSG biocontrol agents in Australia, and more broadly, weed biocontrol using plant pathogens anywhere in the world.