The nonnative pathogen Cronartium ribicola, that causes white pine blister rust (WPBR), is spreading through limber pine and Rocky Mountain bristlecone pine forests of the Southern Rocky Mountains. An integrated regional program – the proactive strategy – is characterizing the infestation and gaining genetic and ecological knowledge of these formerly under-studied ecosystems.
The Southern Rockies Rust Resistance Trial (SRRRT) was initiated in 2013 to verify the stability of genetic resistance to white pine blister rust identified during artificial screening tests for limber and Rocky Mountain bristlecone pines conducted in collaboration with Dorena Genetic Resource Center in Cottage Grove, OR. Growing conditions and inoculum sources can affect the expression of disease resistance, so further verification that the resistance is stable under natural growing conditions increases restoration deployment guidance and the potential for restoration success.
Such research provides the science foundation for early interventions to mitigate the development of ecological impacts to the high mountain headwater ecosystems. Identifying and developing planting material with genetic resistance to WPBR is essential to sustain these forests into the future.
The former site of a U.S. Forest Service nursery on the Pole Mountain Unit of Laramie Ranger District, Medicine Bow National Forest was revitalized for this project. Seed from previously-tested resistant and susceptible individual-tree collections (i.e., families) was sown, and seedlings were grown at the Colorado State Forest Service Nursery. Administrative approval and site preparation were completed in 2012 and 2013.
Thirteen limber pine families and eleven Rocky Mountain bristlecone pine families are included in the study and represent seed sources from throughout the Southern Rocky Mountains (see map at right). Over 700 seedlings were outplanted in the fall 2013 and another 700 seedlings in spring 2014.
White pine blister rust is common in the forests in and around the SRRRT site, providing a natural source of inoculum to the seedlings. The seedlings will be periodically assessed for signs and symptoms of white pine blister rust over the next 10 years. Disease symptoms were first noted in 2016.
Installation of this project was funded largely by the Rocky Mountain Region - Regional Office, with in-kind contribution from the Medicine Bow National Forest, Rocky Mountain Research Station (RMRS), Forest Health Protection (FHP), Colorado State University (CSU), Wyoming Conservation Corps, and community volunteers. Maintenance and monitoring is funded by RMRS and Medicine Bow National Forest with in-kind contribution from FHP, CSU, and community volunteers.