Geske, Alissa2021-10-132021-10-132020-08https://hdl.handle.net/11299/224895University of Minnesota M.S. thesis. 2020. Major: Plant Pathology. Advisor: Dean Malvick. 1 computer file (PDF); 119 pages.Many diseases reduce soybean (Glycine max) yield every year, with root diseases often having the greatest impacts on yield in the Midwestern U.S. One important root pathogen of soybean is Fusarium virguliforme (Fv), the causal agent of sudden death syndrome (SDS). Even though soybean plants displaying SDS symptoms are commonly attacked by multiple fungal pathogens and insects, it is unknown how interactions between Fv and other attackers may alter SDS disease development and soybean growth. In our first study, we examined potential interactions between Fv and other common soybean root pathogens including F. acuminatum, F. oxysporum, F. solani, and Clonostachys rosea. Interactions were assessed in vitro and in soybean plants to evaluate their effect on SDS disease development and soybean growth. Results from the in vitro studies suggest that the growth of Fv was not affected by any of these fungi, but the growth of F. acuminatum and F. oxysporum isolates was reduced in the presence of Fv. Further results suggest that coinfection of soybean with Fv and C. rosea and Fv and F. solani can reduce SDS foliar disease severity and that coinfection of soybean with Fv and F. oxysporum and Fv and F. acuminatum can increase SDS foliar severity compared to the Fv-only treatment under growth chamber conditions. Coinfections of soybean with Fv and all eight fungal test isolates individually did not increase or decrease levels of root rot or plant biomass compared to infection by Fv alone. In our second study, we examined potential interactions between Fv and the soybean aphid, Aphis glycines, in greenhouse, growth chamber, and field experiments to evaluate their effect on SDS disease development, aphid growth, and soybean growth. Overall, the results suggest that Fv and soybean aphids have minimal to no interaction with one another while co-occurring on soybean when SDS develops to low levels, as was the case in these studies. There was no clear effect of soybean aphid herbivory on SDS foliar or root disease development in these studies nor did we detect a clear effect of combined soybean aphid herbivory and Fv infection on soybean growth. To our knowledge this is the first investigation into potential interactions between Fv and other common root pathogens and Fv and the soybean aphid.enAphidFusariumInteractionsPlant PathologyRoot RotSoybeanThesis or Dissertation