For many Americans, the Fraser fir -- a North Carolina native -- is the perfect Christmas tree. With its conical shape, pleasant scent, rich green foliage, strong branches and good needle retention, this popular species has made North Carolina the second largest Christmas tree producer in the nation.
A fungus from Asia, however, is capable of decimating North Carolina Fraser fir plantations -- and threatening the long-term health of the state's $100 million annual Christmas tree industry. A team of researchers at North Carolina State University is investigating ways to keep that from happening.
The threat is from Phytophthora (pronounced "fy-tof-thor-a") root rot, a disease caused by the fungus Phytophthora cinnamoni. The disease, which is fatal to Fraser fir, attacks and kills the roots, leading to the death of the tree.
Research indicates that trees in about 7 percent of North Carolina Fraser fir plantations have been infected by the disease. "There's also been a large amount of land that's been taken out of Christmas tree production because of Phytophthora root rot," says Dr. John Frampton, NC State associate professor of forestry. "It's a concern possibly to the long-term sustainability of the Christmas tree industry in North Carolina."
North Carolina produces more than 6 million Christmas trees each year, about 15 percent of the nation's natural Christmas trees -- second only to Oregon. Nearly all of those North Carolina trees -- 96 percent -- are Fraser firs, mostly grown in 14 mountain counties.
Phytophthora root rot -- which scientists believe was introduced to the United States from Southeast Asia in the 1700s -- can be devastating to Fraser fir growers because it's impossible to eliminate the fungus from the soil once it's established."It's really a big problem for growers because if they get hit by it, it could put them out of business or take a large area of their plantation out of production," Frampton says.
Spread by the movement of plants, roots, soil and water, the root rot fungus can remain dormant for months or years before attacking Fraser fir or one of the many other susceptible plant species.
Frampton, a Christmas tree geneticist, and two other NC State researchers -- Dr. Eric Hinesley, professor of horticultural science, and Dr. Michael Benson, professor of plant pathology -- are investigating ways to develop resistence to root rot in Fraser fir.
Frampton and Hinesley are testing the feasibility of grafting Fraser fir shoots onto the roots of fir species less susceptible to root rot; those trees were planted on sites that have and have not been infected with Phythophthora. The two most promising species so far, they say, are momi fir, a species from Japan, and Turkish fir, which is a popular Christmas tree in Europe.
The researchers are using the same approach to investigate growing Fraser fir in the eastern part of North Carolina, where Fraser firs can't grow on their own. Frampton says momi fir, Turkish fir and Nordmann fir, another Asian species, appear to offer the most promising root stock. "Nordmann fir is actually the No. 1 Christmas tree in Europe, and so far it seems to be doing pretty well here," he says, though he adds the grafted trees appear to grow slower than Fraser firs that haven't been grafted.
Meanwhile, Frampton and Benson are working to develop Fraser firs that are genetically resistant to Phytophthora root rot. In that research, Fraser fir seedlings grown in a greenhouse are inoculated with the root rot fungus, which kills 98 to 99 percent of the trees. Those that survive could be planted in "orchards" to produce seeds for future Fraser fir plantings.
It will be many years before those trees become available to growers, however, because it can take up to 12 years to grow a 6-to-7-foot-tall Fraser fir, the average retail height. Meanwhile, the NC State researchers are working to clone the trees that appear to be resistant to root rot.
The researchers are also working to understand the genetics of the root rot pathogen itself. They suspect that, in the North Carolina mountains, the Phytophthora fungus reproduces asexually rather than sexually -- which might mean that the fungus has low genetic diversity. Such a finding, Frampton explains, would be helpful in deploying Fraser firs that are genetically resistant to root rot.
Root rot is not the only threat to Fraser firs, the researchers note. Christmas tree growers may have to spray their plantations every few years to prevent outbreaks of the balsam woody adelgid -- an introduced pest that has ravaged natural Fraser fir stands high in the Appalachians.
The above story is based on materials provided by North Carolina State University. Note: Materials may be edited for content and length.
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