Chestnut blight
The pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

ic fungus Cryphonectria parasitica (formerly Endothia parasitica) is a member of the ascomycota (sac fungus) category, and is the main cause of chestnut blight, a devastating disease of the American chestnut
American Chestnut
The American Chestnut is a large, deciduous tree of the beech family native to eastern North America. Before the species was devastated by the chestnut blight, a fungal disease, it was one of the most important forest trees throughout its range...

 tree that caused a mass extinction in the early 1900s of this once plentiful tree from its historic range in the eastern United States.


The chestnut blight
Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. It is simply a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral organs. Accordingly, many diseases that primarily exhibit this...

 was accidentally introduced to North America around 1900, either through imported chestnut
Chestnut , some species called chinkapin or chinquapin, is a genus of eight or nine species of deciduous trees and shrubs in the beech family Fagaceae, native to temperate regions of the Northern Hemisphere. The name also refers to the edible nuts they produce.-Species:The chestnut belongs to the...

 lumber or through imported chestnut trees. In 1905, American mycologist William Murrill
William Murrill
William Alphonso Murrill was an American mycologist, known for his contributions to the knowledge of the Agaricales and Polyporaceae.- Education :...

 studied the disease, 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, mature American chestnut
American Chestnut
The American Chestnut is a large, deciduous tree of the beech family native to eastern North America. Before the species was devastated by the chestnut blight, a fungal disease, it was one of the most important forest trees throughout its range...

 trees were virtually wiped out by the disease.

Infection of Asian chestnut trees with the chestnut blight fungus was discovered on Long Island
Long Island
Long Island is an island located in the southeast part of the U.S. state of New York, just east of Manhattan. Stretching northeast into the Atlantic Ocean, Long Island contains four counties, two of which are boroughs of New York City , and two of which are mainly suburban...

 in 1904. The blight appears to have been introduced from either China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

 or Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

. Japanese and some Chinese chestnut trees show some resistance to infection by C. parasitica: they may be infected, but the fungus does not usually kill them. Within 40 years the near-4 billion-strong American chestnut population in Northern America was devastated – only a few clumps of trees remained in California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 and the Pacific northwest. Because of the disease, American Chestnut wood almost disappeared from the market for decades, although American chestnut wood can still be obtained as reclaimed lumber
Reclaimed lumber
Reclaimed lumber is wood taken for re-use. Most reclaimed lumber comes from timbers and decking rescued from old barns, factories and warehouses although some companies use wood from less traditional structures such as boxcars, coal mines and wine barrels...

. The root collar and root system of the chestnut tree are fairly resistant to the fungal infection, so a large number of small American chestnut trees still exist as shoots from existing root bases. However, the shoots are seldom able to grow enough to reproduce before the blight attacks them. So they only survive as living stump
Living stump
A living stump is created when a live tree is cut and its stump remains in the ground. The stump and root system may remain alive for several years if its roots graft to nearby living trees. A living stump capable of producing sprouts or cuttings is known as a stool, and is used in the coppicing...

s, or "stools", with only a few growing enough shoot
Shoots are new plant growth, they can include stems, flowering stems with flower buds, and leaves. The new growth from seed germination that grows upward is a shoot where leaves will develop...

s to produce seeds shortly before dying. This is just enough to preserve the genetic material used to engineer an American chestnut tree with the minimal necessary genetic input from any of the disease-immune Asiatic species. Efforts started in the 1930s and are still ongoing to repopulate the country with these trees, in Massachusetts
The Commonwealth of Massachusetts is a state in the New England region of the northeastern United States of America. It is bordered by Rhode Island and Connecticut to the south, New York to the west, and Vermont and New Hampshire to the north; at its east lies the Atlantic Ocean. As of the 2010...

 and many other places in the United States.

In some places such as the Appalachian Mountains
Appalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...

, it is estimated that one in every four hardwood
Hardwood is wood from angiosperm trees . It may also be used for those trees themselves: these are usually broad-leaved; in temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen.Hardwood contrasts with softwood...

s was an American chestnut. Mature trees often grew straight and branch-free for 50 feet (sometimes up to one hundred feet), and could grow up to 200 feet tall with a trunk diameter of 14 feet at a few feet above ground level. For three centuries most barn
A barn is an agricultural building used for storage and as a covered workplace. It may sometimes be used to house livestock or to store farming vehicles and equipment...

s and homes east of the Mississippi
Mississippi River
The Mississippi River is the largest river system in North America. Flowing entirely in the United States, this river rises in western Minnesota and meanders slowly southwards for to the Mississippi River Delta at the Gulf of Mexico. With its many tributaries, the Mississippi's watershed drains...

 were made from American chestnut. The chestnut blight caused by C. parasitica has destroyed about 4 billion American chestnut trees, and dramatically reduced the tree population throughout the East Coast
East Coast of the United States
The East Coast of the United States, also known as the Eastern Seaboard, refers to the easternmost coastal states in the United States, which touch the Atlantic Ocean and stretch up to Canada. The term includes the U.S...

. The American Chinquapin (Chinkapin) chestnut trees are also very susceptible to chestnut blight. The European chestnut and the West Asian species are susceptible but less so than the American species. The resistant species (particularly Japanese chestnut
Japanese Chestnut
Japanese Chestnut is a species of chestnut originally native to Japan and South Korea. It is a small to medium-sized deciduous tree growing to 10-15 m tall. The leaves are similar to those of the Sweet Chestnut, though usually a little smaller, 8-19 cm long and 3-5 cm broad...

 and Chinese chestnut
Castanea mollissima
Castanea mollissima is a member of the family Fagaceae, and a species of chestnut native to China.- Description :...

 but also Seguin's chestnut and Henry's chestnut) have been used in breeding programs in the US to create hybrids with the American chestnut that are disease-resistant.

The fungus is spread by wind-borne ascospores and, over a shorter distance, conidia distributed by rain-splash action. Infection is local in range, so some isolated American chestnuts survive where there is no other tree within 10 km. Also, there are at least two viral
Mycoviruses are viruses that infect fungi. They have been identified in all major fungal families. Most identified so far have had double stranded RNA genomes, often with more than one dsRNA present per virus particle, and have been spherical in shape. To be a true mycovirus, they must demonstrate...

 pathogens that weaken the fungus (hypovirulence) and help trees to survive.

Surviving chestnut trees are being bred for resistance to the blight, notably by The American Chestnut Foundation
The American Chestnut Foundation
The American Chestnut Foundation is a nonprofit American organization dedicated to breeding a blight-resistant American chestnut tree and the reintroduction of this tree to the forests of the Eastern United States....

, which aims to reintroduce a blight-resistant American chestnut to its original forest range within the early decades of the 21st century.

A small stand of surviving American chestnuts was found in F. D. Roosevelt State Park
F. D. Roosevelt State Park
F.D. Roosevelt State Park is an 9,049 acre Georgia state park located near Pine Mountain and Warm Springs. The park is named for former U.S. President Franklin Delano Roosevelt, who sought a treatment for his paralytic illness in nearby Warm Springs at Little White House Historic Site...

 near Warm Springs, Georgia
Warm Springs, Georgia
Warm Springs is a city in Meriwether County, Georgia, United States. The population was 478 at the 2010 census.-History:Warm Springs first came to prominence in the 19th century as a spa town, due to its mineral springs which flow constantly at nearly 32 °C...

 on April 22, 2006 by Nathan Klaus of the Georgia Department of Natural Resources.


The fungus makes its entry at wounds and grows in and beneath the bark which eventually kills the cambium
Cork cambium
Cork cambium is a tissue found in many vascular plants as part of the periderm. The cork cambium is a lateral meristem and is responsible for secondary growth that replaces the epidermis in roots and stems...

 all the way round the twig, branch or trunk. The first symptom is a small orange-brown area on the bark of a twig or branch. A sunken canker may form and the bark may split. Yellowish-orange stromata containing conidiomata break through the bark of the canker and perithecia
An ascocarp, or ascoma , is the fruiting body of an ascomycete fungus. It consists of very tightly interwoven hyphae and may contain millions of asci, each of which typically contains eight ascospores...

 may be formed on the same stroma. Distinctive yellow tendrils (cirrhi) of conidia can be seen extruding from the stroma in wet weather. The canker expands around the circumference of the twig or branch resulting in wilting and death of the plant material above the canker which is deprived of nourishment.

Hybrid chestnut trees

In the years since the chestnut blight, many scientists and botanists have worked to create a resistant hybrid chestnut tree that retains the main characteristics of the American chestnut tree. In the early 1950s, a large living American chestnut
American Chestnut
The American Chestnut is a large, deciduous tree of the beech family native to eastern North America. Before the species was devastated by the chestnut blight, a fungal disease, it was one of the most important forest trees throughout its range...

 was discovered in a grove of dead and dying trees in Ohio that showed no evidence of blight infection. Budwood was sent to Dr. Robert T. Dunstan, a plant breeder in Greensboro, North Carolina
Greensboro, North Carolina
Greensboro is a city in the U.S. state of North Carolina. It is the third-largest city by population in North Carolina and the largest city in Guilford County and the surrounding Piedmont Triad metropolitan region. According to the 2010 U.S...

. Dunstan grafted the scions onto chestnut rootstock and the trees grew well. He cross-pollinated one with a mixture of 3 Chinese chestnut selections: "Kuling", "Meiling
Meiling may refer to:*Meiling , also spelled as Mei Ling or Mei-ling, Chinese given name*Connie Meiling , Danish child actress of the 1930s*Marc Meiling , German judoka...

", and "Nanking". The resulting fruit-producing hybrid was named the Dunstan Chestnut.

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