The chestnut blight was accidentally introduced to North America around 1904 when Cryphonectria parasitica was introduced into the United States from East Asia from the introduction of the cultivation of Japanese chestnut trees into the United States for commercial purposes.
Full Answer
The chestnut blight fungus was accidentally introduced into the U.S. on Japanese chestnut trees imported at the end of the 1800s. It was spread all over the range of our native chestnut trees by "mail order" as people bought chestnut trees from nurseries, and was spread locally by every creature that walked over the cankers.
Chestnut blight is a canker disease. Perhaps it is called blight because infected branches and stems die quickly, as in a shoot blight. But it doesn’t just infect shoots; it infects branches and stems of any size. The cankers are of the diffuse type.
"Biological control of chestnut blight: an example of virus-mediated attenuation of fungal pathogenesis". Microbiological Reviews. 56 (4): 561–576. doi: 10.1128/MMBR.56.4.561-576.1992.
The root collar and root system of the chestnut tree have some resistance to blight infection due to soil organisms adversely reacting to the fungus; consequently, a large number of small American chestnut trees still exist as shoots growing from existing root bases.
Plant Disease 66:87-90. The chestnut blight fungus was accidentally introduced into the U.S. on Japanese chestnut trees imported at the end of the 1800s.
1904Accidentally imported from Asia, the disease was first observed in 1904 in the New York Zoological Gardens. By 1925 it had decimated the American chestnut (Castanea dentata) population in an area extending over 1,600 km (1,000 miles) north, south, and west of its entry point.
Mature American chestnuts have been virtually extinct for decades. The tree's demise started with something called ink disease in the early 1800s, which steadily killed chestnut in the southern portion of its range.
All of this began to change at the turn of the 20th century with the introduction of a deadly blight from Asia. In about 50 years, the pathogen, Cryphonectria parasitica, reduced the American chestnut from its invaluable role to a tree that now grows mostly as an early-successional-stage shrub.
The American chestnut tree (Castanea dentata) once occupied forests as far south as central Alabama, west through Tennessee, and as far north as Maine and southern Ontario. In some forests, they made up more than half the mass of living trees.
Beginning in the early 1900s, an introduced fungus known as the chestnut blight devastated chestnut populations.
Chestnut decline, attributed to blight, is caused by an Asian bark fungus (Cryphonectria parasitica), which was unknowingly imported from Asia on infected Chinese Chestnut trees. While the Chinese variety adapted and developed a sturdy resistance to the blight, the American chestnut was no match for it.
The total number of chestnut trees in eastern North America was estimated at over three billion, and 25% of the trees in the Appalachian Mountains were American chestnut.
Not extinctAmerican chestnut / Extinction status
It reached southern Ontario in the 1920s, and by the 1950s, the American chestnut population was considered “effectively extinct”. But the American chestnut is not actually extinct. In fact, there are millions of sprouts that can be found throughout its native range.
Castanea dentataAmerican chestnut / Scientific name
The American chestnut tree reigned over 200 million acres of eastern woodlands from Maine to Florida, and from the Piedmont plateau in the Carolinas west to the Ohio Valley, until succumbing to a lethal fungus infestation, known as the chestnut blight, during the first half of the 20th century.
Chestnut blight is a canker disease. Perhaps it is called blight because infected branches and stems die quickly, as in a shoot blight. But it doesn’t just infect shoots; it infects branches and stems of any size.
The pathogen is Cryphonectria parasitica. It is an ascomycete, and produces perithecia in small stromata. They can appear at any time of year when conditions are suitable. The perithecial necks are very long and come together where they protrude through the bark. The ascospores are forcibly ejected and wind-dispersed.
Perithecia of Cryphonectria parasitica in a stroma. The perithecia contain many asci (left) with 8 ascospores each. The ascospores are forcibly ejected and carried in air currents. Usually prior to perithecia, pycnidia are produced in the same small stroma or in other stromata.
Chestnut blight canker in Pennsylvania, USA. Note that canker callus grew for a time, but then the fungus overgrew the callus and continued its invasion.
Conidia may be carried by rain splash or catch a ride on an insect or bird. In 1913 a USDA plant explorer found the fungus in its native land of China [4]. There, it was hardly a pathogen, colonizing dying twigs and small patches of bark. The spread rate of chestnut blight was very fast.
The wood was nearly ideal. As George Hepting [4] has written, “Not only was baby’s crib likely made of chestnut, but chances were, so was the old man’s coffin.”. One of its good qualities was high durability.
The reason there is little resistance in American chestnut is that the pathogen was introduced . In 1904, the disease was observed in the New York Zoo killing chestnuts, but there is reason to suspect it was here as early as 1893 [4].
Cryphonectria parasitica is a parasitic fungus of chestnut trees. This disease came to be known as chestnut blight. Naturally found in South East Asia, accidental introductions led to invasive populations of C. parasitica in North America and Europe. The fungal disease has had a devastating economic and social impact on communities in the eastern United States. In the first half of the 20th century it killed an estimated four billion trees. Less severe impacts have occurred in Europe due to widespread CHV1 -induced hypovirulence. CHV1 is one of at least two viral pathogens that weaken the fungus through hypovirulence and helps trees survive.
In addition to biocontrol, chestnut blight can also be managed by sanitation practices and chemical control ; however, such management strategies are only feasible on a small scale, such as in an orchard. Sanitation practices like the pruning of symptomatic limbs and removal of infected trees can serve to eliminate sources of inoculum and limit the spread of the pathogen.
The chestnut blight was accidentally introduced to North America around 1904 when Cryphonectria parasitica was introduced into the United States from East Asia from the introduction of the cultivation of Japanese chestnut trees into the United States for commercial purposes. It was first found in the chestnut trees on the grounds of the New York Zoological Garden (the "Bronx Zoo") by Herman W. Merkel, a forester at the zoo. In 1905, American mycologist William Murrill isolated and described the fungus responsible (which he named Diaporthe parasitica ), and demonstrated by inoculation into healthy plants that the fungus caused the disease. By 1940, most mature American chestnut trees had been wiped out by the disease.
At the start there are very few such engineered chestnut trees. For seed multiplication, grafting would work. Normal tree growth requires 6, 7, or even 8 years before a chestnut will flower. However normal orchard management will accelerate that up to 2-3 years for pollen production (although still without fruiting). Powell's lab has been able to use growth chambers with higher light inputs to get it down to less than a year to pollen production.
The chestnut fruit was a major food source for animals in the low elevation Appalachian forests. This loss resulted in a drastic decrease of the squirrel population, the extinction of seven native moth species, and the slowed recovery of deer, Cooper's hawk, cougar, and bobcat populations.
Scientists are working to try to save the trees. There is a program to bring American chestnut back to the Eastern forest funded by the American Chestnut Foundation, Wisconsin Department of Natural Resources, USDA Forest Service, West Virginia University, Michigan State University, and Cornell University.
There are approximately 2,500 chestnut trees growing on 60 acres (24 ha) near West Salem, Wisconsin, which is the world's largest remaining stand of American chestnut. These trees are the descendants of those planted by Martin Hicks, an early settler in the area.