Improving the resistance of eastern white pine to white pine blister rust disease

Eastern white pine (EWP), Pinus strobus L., is an iconic forest tree in the north woods of eastern North America. White pine blister rust, caused by Cronartium ribicola, an invasive pathogen, entered North America in the early 20th century and infected all five-needled pines across the continent. Few genotypes of eastern white pine have demonstrated consistent, elevated resistance to the pathogen, so our objective was to identify additional genotypes with resistance. Since 1970, the USDA Forest Service has identified and grafted over 800 phenotypic plus tree selections from Michigan, Wisconsin and Minnesota. A protocol to artificially inoculate one-year old seedlings was used to screen 228 genotypes along with rust-resistant and susceptible standards across a four-year period, from 2010 to 2013. We identified 25 genotypes, based on survival assessed two years after inoculation, which exceeded the resistant standard. These genotypes will be grafted into new seed orchards to aid reforestation efforts aimed at restoring this keystone species to suitable habitats where regeneration is currently hindered by blister rust on privately-held land, state forests and national forests in the Lake States region.