9623416 Jarosz Pathogen virulence refers to the negative effects of infection on host fitness. This research investigates the relationship between pathogen virulence and host plant demography. Theoretical models assume that reductions in pathogen virulence lead to increases in host population size and density. Research funded by this award represents one of the first tests of these models for plant systems. The project will determine whether changes in virulence actually cause commensurate changes in plant population growth for a system of economic and aesthetic importance, the American chestnut, Castanea dentata, and the chestnut blight pathogen, Cryphonectria parasitica. Reductions in pathogen virulence in this system result from infection of the pathogen by double-stranded RNA hypoviruses. When the pathogen is attacked by hypoviruses, its host tree produces wound callus tissue and can survive the infection. At a population scale, such survival events result in a recovering population. Seedling recruitment and population growth rates will be compared for recovering, non-recovering, and disease-free chestnut populations. This work will contribute to the development of cost effective management strategies for the American chestnut. If, for example, chestnut population growth rates are most sensitive to loss of saplings and saplings are most affected by infection, efforts to protect the American chestnut should be directed at young individuals. More generally, this study will provide insight into the effect of pathogens on individuals of different life history stages and on population level demographic processes.
