Study systems include
Free-living (wild) gourds and cultivated squash and their pathosystem including cucumber beetles, aphids, bacterial wilt disease, and various mosaic viruses.
Horsenettle weeds and closely related crop species (tomato/potato/eggplant) and their pathosystems.
Shapiro, L., C.M. De Moraes, A.G. Stephenson and M.C. Mescher. (2012). Pathogen effects on vegetative and floral odors mediate vector attraction and host exposure in a complex pathosystem. Ecology Letters 15:1430-1438 doi: 10.1111/ele.12001Simmons, H.E., J. Dunham, J. Stack, B. Dickins, I. Pagan, E.C. Holmes and A.G. Stephenson. (2012). Deep sequencing reveals persistence of intra- and inter-host genetic diversity in natural and greenhouse populations of Zucchini yellow mosaic virus. Journal of General Virology 93:1831-1840.
Simmons, H. E., Holmes, E. C., Gildow, F. E., Bothe-Goralczyk, M. A., & Stephenson, A. G. (2011). Experimental verification of seed transmission in zucchini yellow mosaic virus. Plant Disease.
Sasu, M.A., Wall, K. L., & Stephenson, A. G. (2010). Antimicrobial nectar inhibits a floral transmitted pathogen of a wild Cucurbita pepo (Cucurbitaceae). American Journal of Botany, 97, 1025-1030.
Sasu, M. A., Seidl-Adams, I., Wall, K., Winsor, J. A., & Stephenson, A. G. (2010). Floral transmission of Erwinia tracheiphila by cucumber beetles in a wild Cucurbita pepo. Environmental Entomology, 39, 140-148.
Sasu, M.A., Ferrari, M. J., Du, D., Winsor, J. A., & Stephenson, A. G. (2009). Indirect costs of a non-target pathogen mitigate the direct benefits of a virus resistant transgene in wild Cucubita. Proceedings of the National Academy of Science (USA). 106,19067-19071.
My research focuses on the role of inbreeding and genetic variation on the establishment and transmission of plant diseases. My research has three interrelated themes
1) Interrelationships among inbreeding, herbivory, and transmission of bacterial and viral diseases vectored by herbivores
How does inbreeding affect:
- The pattern, timing and magnitude of herbivory?
- Rates of exposure to pathogens transmitted by herbivores?
- When — and the extent to which — plant defense systems respond to herbivores and pathogens?
2) Production of volatile organic compounds that signal herbivores (pathogen vectors)
- How do plant volatiles vary with inbreeding in natural populations? How do herbivores respond to these differences?
- How does the composition of plant volatiles change upon damage by an herbivore or infection by a pathogen?
- Do herbivores/vectors respond differently to the volatile compounds produced by healthy and diseased plants?
3) Impact of the escape of viral resistance transgenes from agricultural crops to wild populations
- How do viral resistance transgenes affect the fitness of plants during introgression into natural populations?
- Is there a cost associated with viral resistance transgenes when the viral disease is not present in the population?
- How do viral resistance transgenes affect non-target pathogens?