Most theories on the evolution of parasite virulence assume a positive relationship between transmission success of the parasite and its virulence, but there are few experimental tests of this relationship. Understanding the degree to which the host, versus the parasite, controls transmission mode would contribute substantially to models of parasite evolution by testing this common assumption. This research exploits a variable plant-fungus interaction to explore the phenotypic and genetic relationships between virulence and transmission mode (horizontal or vertical). Experiments are planned to determine if horizontal transmission is positively related to parasite virulence, the relationship between horizontal transmission and vertical transmission, if parasite growth rate predicts transmission success or parasite virulence, and if the parasite or the host - or their interaction - controls the mode of parasite transmission. The proposed studies will provide empirical data on the relationship between parasite transmission mode and virulence, which is broadly applicable to human health and agriculture. The project will support the training and development of a non-traditional graduate student.
