Forestry + genetics = a blister rust solution?

  • Whitebark pine cones are caged to protect them from Clark's nutcrackers.

    USDA Forest Service
  • Whitebark pine resistance trials at Dorena Genetic Resource Center in Cottage Grove, Oregon.

    USDA Forest Service

In 1926, the U.S. Forest Service first found blister rust, a deadly fungus, on high-elevation whitebark pines in Montana. Since then, the Asian invader has spread through several species of five-needled pines in the West; it was first discovered in Arizona in 2009. The U.S. Fish and Wildlife service is now considering whether whitebark pines, a key food source for grizzlies, birds and small mammals, should be listed as endangered.

There is hope, though. Some five-needled pines have a gene that makes them completely resistant to all but a supercharged version of the disease. Others possess a set of genes that, while not making them totally resistant, allows them to fight -- and often stave off -- even the deadliest blister rust infection.

So foresters are seeking out trees that appear resistant, collecting their seeds, and then growing resistant saplings to replant wherever they can -- usually in disturbed areas that have lost their trees to fire or the disease. It's a "very laborious and expensive process" that can take decades, says Vicky Erickson, a Forest Service geneticist in Oregon who oversees breeding projects. And there's no guarantee that the saplings possess the most versatile form of genetic resistance.

That's where UC Davis geneticist David Neale comes in. He's sequencing the genome of three evergreens: the rust-susceptible sugar pine, Douglas fir and loblolly pine, an Eastern forest staple. After completing sequencing, Neale will use samples from thousands of trees to undertake a complex matching process that maps tree DNA to specific traits, such as disease resistance, drought tolerance and cold hardiness. He hopes to begin the process next year.

Once geneticists understand which sets of genes convey resistance, they can help foresters choose just the right trees to breed and replant. This will boost efforts to fight not only blister rust but other tree diseases. It will also help tree breeders ensure they're keeping enough genetic variation among the trees they plant in places like Mount Rainier and North Cascades national parks, and in Western national forests.

Mapping genetic adaptation also has implications for everything from post-fire restoration to climate change mitigation.  Until now, managers hoping to restore fire-damaged slopes have been "groping in the dark for traits," says Forest Service researcher Connie Millar. They might harvest seed from Douglas firs on a hot, dry slope with the hope that they're genetically adapted to that environment. But there might be other reasons why the trees thrive on that slope -- the presence of certain minerals in the soil, for example. With trait-mapping, "we can know where on the landscape these trees are adapted to," says Millar.

The information could also help the Forest Service designate areas to prioritize for conservation or seed banking, says Oregon's Erickson. But genetic research isn't cheap, and though costs have been going down, breeding and replanting is still labor- and time-intensive, she notes.

Public-lands managers will never have the time or money to manage every forest stand based on genetic information. For cases like the whitebark pine, though, where small, high-altitude stands are rapidly succumbing to disease, the new knowledge could help foresters do their work faster and smarter. That's good for the trees -- and the animals that rely on them.

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