Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

Document Type



Fungal toxins are pathogenicity/virulence factors for many plant diseases, including Cercospora leaf blight (CLB) of soybean (Glycine max (L.) Merr.). The pathogen, Cercospora cf. flagellaris, produces a perylenequinone toxin, cercosporin, which is activated by light to produce damaging reactive oxygen species. To identify novel solutions for CLB management, we studied factors that may impact the biology of cercoporin: fungal lipid droplets (LDs) and mineral and trace element composition (ionome) of the host. Furthermore, since artificial inoculation with the pathogen has been challenging, we also explored the usefulness of a previously developed cercosporin-based assay to study disease resistance. LDs can play a role in fungal self-resistance to perylenequinone toxins, though currently unknown for cercosporin. Confocal micrographs of light-cultured C. cf. flagellaris indicated that 3-day old hyphae contained two forms of cercosporin. Reduced cercosporin was uniformly distributed in the cytoplasm of thick hyphae, and contrary to previous studies, active cercosporin was observed specifically in LDs of thin hyphae. The production of hyphae of two different thicknesses are similar to other hemibiotrophic plant pathogens, a finding not previously documented for C. cf. flagellaris. Our testing of the cercosporin leaf disk assay, indicated that the assay was not a suitable proxy for variety resistance, but continued to be suitable as a measure of cercosporin damage. Since cercosporin production and toxicity can be affected by several nutrients, we used compositional data analysis to study the effect of the soybean ionome on CLB severity. CLB resistant varieties were observed to have an ionome with higher ratios of Al to other elements (Ca, Mg, N, Mn, Mg, B, S, P and Fe), slightly different from the ionomes of susceptible and intermediate varieties. The present investigation thus lays a foundation to explore LD inhibitors as a new target for fungicide chemistries, and the importance of the host ionome in variety resistance, providing a path to translating our findings into practical CLB management



Committee Chair

Thomas-Sharma, Sara