Photographer: Robert L. Anderson Affiliation: USDA Forest Service Source:www.bugwood.org Copyright:CC BY 3.0
Chestnut blight (Cryphonectria parasitica) is described as a cankrous disease that forms canker-like sores on chestnut tree branches. The canker forms a girdle around the branch cutting off nutrient supply from the rest of the tree resulting in death of the branch. Chestnut blight reproduces rapidly and is able to spread through an individual tree and a large group of trees rapidly.
Symptoms: Chestnut blight is considered a canker disease causing infected branches to die quickly after infection. Symptoms of infected trees will be apparent from dead branches and stems that quickly spread and end with death of the entire tree. The cankers appear as swollen or sunken rings around the branches of the host tree. Below the canker, the host tree often grows bark in attempt to heal or conceal the wound resulting in a swollen appearance.
Host(s): American chestnut (Castanea dentata), European chestnut (Castenea sativa), Chinese chestnut (Castenea mollissima)
The most frequently utilized host of chestnut blight is the American chestnut. As a relatively new host of chestnut blight, the American chestnut hasn't been able to evolve adequate defense mechanisms to the disease and is highly susceptible to infection. Large forested areas have been devastated by infection from chestnut blight resulting in the loss of trees in large quantities. Chestnut blight is able to infect other chestnut tree species as well, but the American chestnut is the most susceptible to infection.
Chestnut blight is transferred in a variety of methods such as air, wind, and animals. Host become infected by open vulnerable wounds that are moist, creating an ideal environment for chestnut blight. Once established the fungus forms yellow-orange fruiting found on the older areas of the cankers on the host tree.
Chestnut blight was introduced to the United States in the 1900's from Asia on infected nursery stock. Once introduced to a new potential host, the American Chestnut, chestnut blight was able to spread rapidly because the tree had no defense mechanism to cope with the disease.
Native Origin: China
U.S. Present: AL, CT, DE, GA, IN, KY, MA, ME, MD, MS, NC, NH, NJ, NY, OH, PA, RI, SC, TN, VA, VT, WV
Currently, a method of biocontrol is being developed by using hypovirulence, a viral disease of the blight fungus. The present issue with this method of control is the differing growth rates. Chestnut blight is able to reproduce at a rapid rate, while hypovirulence reproduces much more slowly. However, chestnut trees are able to better withstand infection with hypovirulence. There are also some cases of chestnut trees with natural defenses that slow the spread of chestnut blight preventing the tree from dieing, however the trees are not naturally immune.
Anagnostakis, Sandra L. 1987. Chestnut Blight: The Classical Problem of an Introduced Pathogen. Mycologia 79(1): 23-37.
Choi, D. H., and D. L. Nuss. 1992. Hypovirulence of Chestnut Blight Fungus Conferred by an Infectious Viral cDNA. Science 257(5071): 800-803.
Heiniger, Ursula, and Daniel Rigling. 1994. Biological Control of Chestnut Blight in Europe. Annual Review of Phytopathology 32: 581-589.