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Partners Fight Invasive Blister Rust Disease to Save Whitebark Pines

The Forest Service is working to combat blister rust, an invasive fungal infection originally from Asia that affects whitebark pines and other five-needle pine trees. Partners for the ongoing efforts include the National Forest Foundation, American Forests, Arbor Day Foundation, and Plant-A-Tree.

Eradicating blister rust would not be possible, so the Forest Service and its partners have developed a program to breed whitebark pines that are resistant to the disease. First they identify wild trees that show no signs of blister rust infection; only a very small percentage have this natural resistance. Cones are collected from these trees and sent to the Coeur d’Alene Nursery, where their seeds are grown. Those seedlings are then exposed to high levels of blister rust spores in order to test their level of resistance to the fungal disease.

Photo of a branch with blister rust.The results are sent to the Moscow Forestry Sciences Lab in Moscow, Idaho, where the Regional Geneticist determines which whitebark pine seedlings to select for the breeding program. The best seedlings from the resistant wild parent trees are then planted in an orchard, grown, and later bred with each other to produce seedlings that possess both strong resistance to blister rust and genetic diversity. Finally these seedlings are planted on Forest Service lands to bolster wild populations with their blister rust-resistant genes. Region 4 forests that have planted seedlings from this program include the Boise, Sawtooth, Bridger-Teton, and Caribou-Targhee National Forests.

Many wildlife species eat the seeds of whitebark pines, but they are especially important to grizzly bears with cubs. The mothers need the fat stored in the nutritious seeds in order to survive winter hibernation.

The seeds are also vital to a mountain bird called the Clark’s nutcracker. In fact, the nutcracker has a symbiotic relationship with the whitebark pine, which means that both organisms benefit from each other. Each bird stashes thousands of seeds every year, which they later retrieve to eat. They remember the locations of most of the seeds; those they forget grow into new trees. The nutcrackers help to disperse the seeds, but moreover they are essential to helping the seeds germinate. An enzyme in the bird’s saliva breaks down the seed’s hard outer coating; without it, the plants inside would be unable to break through their seed cases.

These two very different species depended on each other for survival for thousands of years before blister rust interrupted their harmonious relationship to threaten them both. Thanks to the efforts of the Forest Service and its partners, they are overcoming this invasive disease to continue their cycle of life.

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