Bacterial-fungal interactions can influence fungal phenotypes and shape the outcomes of plant-fungal interactions. Species of the fungus Fusarium, including F. graminearum, cause Fusarium head blight (FHB) of cereal crops and contaminate grain with harmful trichothecene mycotoxins. One approach to sustainably manage FHB includes harnessing the power of parasitic or antagonistic bacteria against F. graminearum in agroecosystems. In this talk, I will highlight two different approaches to managing FHB through use of isolated bacterial strains. First, through the study of existing F. graminearum genomes, a parasitic Paenibacillus species was identified and isolated. Scanning electron microscopy (SEM) imaging data indicate the association is at least partially ectopic, or ecto-hyphal, to the fungus. Experiments in planta (wheat) comparing wild type associations of the parasitic Paenibacillus – F. graminearum to the same F. graminearum strain cured of the bacteria, showed up to a 6-fold decrease in toxin (DON) when the parasitic bacteria were present. Additional tests to re-establish the association by simple mixing of the fungus and bacteria failed to reduce FHB spread and toxin accumulation in planta. In a second experiment, seven different species of bacteria were tested for their ability to reduce FHB in vitro and in planta. Results from a detached wheat head assay were promising, showing up to a 10-fold decrease in F. graminearum spread across several different environmental conditions tested. However, seed soak inoculations of the same bacteria in two different wheat varieties, varying in disease resistance, showed minimal changes in disease spread relative to the non-inoculated controls. Interestingly, the endophytic bacteria did have an impact on plant photosynthetic response, but not on metrics of disease. The results of these two studies highlight the complexities of harnessing bacterial-fungal associations to reduce FHB spread in living host plants and indicate more research is needed to understand the holistic response of small grain hosts to biocontrol applications.

Acknowledgements – The authors thank Nathan Kemp and Jacob Brown for their assistance in the SEM imaging and bacterial inoculation experiments.