9407919 Power Relatively little is known about the impact of viruses on natural plant populations. The objectives of this research project are to measure the movement of a plant virus between natural and agricultural communities and to determine the effect of this virus on wild grasses growing in old-field succession sites. This project focuses on the barley yellow dwarf virus, a widespread virus transmitted to both wild and cultivated grasses by aphids. This research will improve our understanding of the relationship between viruses and their wild and native hosts and on the potential for disease and genetic material to spread between agricultural plants and their wild relatives and vice versa. The results will have direct application in plant pathology, pest control, and agriculture. They may also have application to environmental-impact studies of the field cultivation of genetically altered crop plants.