Abstract
White pine blister rust is a disease caused by an introduced fungal pathogen (Cronartium ribicola). The disease system is a complex cross-Kingdom interaction between three groups of organisms (white pines, Ribes, and a fungal pathogen). The pathogen alternates between white pine hosts (subgenus Strobus) where it persists as a perennial and often lethal infection, and currant and goosebeny hosts (members of the genus Ribes) where it infects the deciduous leaves and results in relatively minor impacts. In many areas of North America white pines are severely threatened by the disease, which is often recognized as the most devastating disease of conifers (Klinkowski 1970). Since the early 1900s when the pathogen first arrived in North America, forest managers have been challenged by the difficulties of blister rust control and predictions of damage and spread. Recent control efforts have focused on developing rust-resistant white pines (Maloy 1997). Advances in molecular techniques have led to a rapid increase in our understanding of pathogen virulence and plant disease resistance. Thus thorough research on white pine blister rust will encompass a combination of investigations of small parts of the system, including molecular descriptions of individual members and controlled-environment studies of simplified interactions, and ecological investigations of infection patterns in real-world forest conditions (where all the parts are interacting simultaneously). This study is a field investigation of white pine blister rust in the Greater Yellowstone Area (GYA).