Elucidation of rust life-cycle using molecular approaches

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Rusts are among the most important pathogens of plants and occur worldwide on almost all plant groups. Pine trees are very susceptible to rust diseases which cause stem and branch cankers and tree mortality. White pine blister rust, caused by the fungal pathogen Cronartium ribicola, was introduced to North America over 100 years ago. The disease is so devastating that it has rendered soft pines unattractive for reforestation because mortality can reach 100% in plantations. Recently, the pathogen has moved to new geographic areas and to new hosts, including high elevation pines which appear to be extremely sensitive to the disease. The disappearance of these keystone species is dramatic and is impacting entire alpine ecosystems. Yet, much is unknown of the pine rust epidemiology and capacity for adaptation. Questions are still unanswered regarding source of inoculum, means of spread, the role of various spore types, and host specificity. I propose to address the following questions to better understand the epidemiology and adaptation of white pine blister rust. 1) I propose to investigate the molecular epidemiology of white pine blister rust on different hosts across a diverse landscape. In particular, I will test whether or not altitudinal and latitudinal gradients and host specialization are observed in the fungal population. 2) I want to determine the epidemiological contribution of interspecific C. ribicola x C. comandra (= C. x flexilis) rust hybrids. Although we demonstrated that these two rusts can hybridize, we still don't know what, if any, is the contribution of the hybrids to the rust epidemics. 3) I propose to scan the Cronartium ribicola genome for the signature of specific adaptation by using a population genomics approach. To test this, I plan to perform a broad genome scan on rust populations from different hosts to search for genes that are under selection with regards to host. This research will generate new data that will contribute to our understanding of the epidemiology and adaptation of this important tree pathogen. Answers to these questions will allow better monitoring and management of this important disease.