Pedicularis and Castilleja are natural hosts of Cronartium ribicola in North America: a first report

Summary White pine blister rust disease, caused by the introduced pathogen Cronartium ribicola , has severely disrupted five‐needled pine ecosystems in North America. A 100‐year effort to manage this disease was predicated in part on the premise that the pathogen utilizes only species of Ribes ( Grossulariaceae ) as alternate hosts on this continent. The current study presents the first conclusive demonstration that some species in the family Orobanchaceae ( Pedicularis racemosa and Castilleja miniata ) are functioning as alternate hosts in a natural ecosystem of North America. This finding has implications for improving our understanding of epidemiology, pathogen adaptation and host–pathogen interactions within white pine blister rust.