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pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...
ic fungus ''Cryphonectria parasitica'' (formerly ''Endothia parasitica'') is a member of the
Ascomycota Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...
(sac fungi). This
necrotrophic A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from t ...
fungus is native to East Asia and South East Asia and was introduced into Europe and North America in the early 1900s. The fungus spread rapidly and caused significant tree loss in both regions.


Overview

''Cryphonectria parasitica'' is a parasitic
fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...
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; or, by another count, 3.5 billion trees through 2013. 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. The American chestnut (''Castanea dentata'') and American chinquapin (''Ca. pumila'') are highly susceptible to chestnut blight. The European chestnut (''Ca. sativa'') is also susceptible, but due to widespread CHV1 hypoviruluence, blight-induced tree death is less common. The fungus can infect other tree species such as oaks, red maples, staghorn sumacs, and shagbark hickories. Once infected, these trees also exhibit orange bark with cankers but they do not die. The pathogen can persist in these trees, producing
spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...
s that may infect other trees. 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 . 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
shoot In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the spri ...
s growing from existing root bases. However, these regrown shoots seldom reach the sexually reproductive stage before being killed by the fungus. The fungus originally infects the Chinese chestnut (''Ca. mollissima'') and the Japanese chestnut (''Ca. crenata''). These two species have co-evolved with the pathogen, making them resistant to its ill effects.


History


North American infection

The chestnut
blight Blight refers to a specific symptom affecting plants in response to infection by a pathogenic organism. Description Blight is a rapid and complete chlorosis, browning, then death of plant tissues such as leaves, branches, twigs, or floral org ...
was accidentally introduced to North America around 1904 when ''Cryphonectria parasitica'' was introduced into the United States from
East Asia East Asia is the eastern region of Asia, which is defined in both geographical and ethno-cultural terms. The modern states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. China, North Korea, South Korea and ...
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 William Alphonso Murrill (October 13, 1869 – December 25, 1957) was an American mycologist, known for his contributions to the knowledge of the Agaricales and Polyporaceae. In 1904, he became the assistant Curator at the New York Botanical Ga ...
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. Infection of American chestnut trees with ''C. parasitica'' simultaneously appeared in numerous places elsewhere on the East Coast, most likely from Japanese chestnuts, which had become popular imports. Japanese and Chinese chestnut trees have resistance to infection by ''C. parasitica'': the infection usually does not kill these Asian chestnut species. Within 40 years the nearly four-billion-strong American chestnut population in North America was devastated; only a few clumps of trees remained in Michigan, Wisconsin, and the Pacific Northwest. Because of the disease, American chestnut wood almost disappeared from the market for decades, although it can still be obtained as
reclaimed lumber Reclaimed lumber is processed wood retrieved from its original application for purposes of subsequent use. Most reclaimed lumber comes from timbers and decking rescued from old barns, factories and warehouses, although some companies use wood fr ...
. It is estimated that in some places, such as the
Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...
, one in every four
hardwood Hardwood is wood from dicot trees. These are usually found in broad-leaved temperate and tropical forests. In temperate and boreal latitudes they are mostly deciduous, but in tropics and subtropics mostly evergreen. Hardwood (which comes from ...
s was an American chestnut. Mature trees often grew straight and branch-free for 50 feet and could grow up to 100 feet tall with a trunk diameter of 14 feet at a few feet above ground level. The reddish-brown wood was lightweight, soft, easy to split, very resistant to decay, and did not warp or shrink. For three centuries many
barn A barn is an agricultural building usually on farms and used for various purposes. In North America, a barn refers to structures that house livestock, including cattle and horses, as well as equipment and fodder, and often grain.Allen G. ...
s and homes near the
Appalachian Mountains The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...
were made from American chestnut. Its straight-grained wood was ideal for building furniture and caskets. The fruit that fell to the ground was an important cash crop and food source. The bark and wood were rich in tannic acid, which provided tannins for use in the tanning of leather. Many native animals fed on chestnuts, and chestnuts were used for livestock feed, which kept the cost of raising livestock low. Efforts started in the 1930s and are still ongoing, in
Massachusetts Massachusetts (Massachusett language, Massachusett: ''Muhsachuweesut assachusett writing systems, məhswatʃəwiːsət'' English: , ), officially the Commonwealth of Massachusetts, is the most populous U.S. state, state in the New England ...
and many other places in the United States, to repopulate the country with chestnut trees.American Chestnut Foundation
Surviving American chestnut trees are being bred for resistance to the blight, notably by
The American Chestnut Foundation The American Chestnut Foundation (TACF) is a nonprofit United States, American organization dedicated to breeding a chestnut blight, blight-resistant American chestnut, American chestnut (''Castanea dentata'') tree and the reintroduction of thi ...
, which aims to reintroduce a blight-resistant American chestnut to its original forest range within the early decades of the 21st century.
Japanese chestnut ''Castanea crenata'', the Japanese chestnut, also known as the Korean chestnut is a species of chestnut native to Japan and Korea. ''Castanea crenata'' exhibits resistance to ''Phytophthora cinnamomi'', the fungal pathogen that causes ink disease ...
and Chinese chestnut, as well as Seguin's chestnut and Henry's chestnut, have been used in these breeding programs in the US to create disease-resistant
hybrid Hybrid may refer to: Science * Hybrid (biology), an offspring resulting from cross-breeding ** Hybrid grape, grape varieties produced by cross-breeding two ''Vitis'' species ** Hybridity, the property of a hybrid plant which is a union of two dif ...
s with the American chestnut.''New RHS Dictionary of Gardening''. By A. Huxley ed. 1992. Macmillan . Chinese chestnut trees have been found to have the highest resistance to chestnut blight; however, individuals within the Chinese chestnut species may vary in blight resistance. Some individuals are still quite susceptible while others are essentially immune. Hypovirulence is not widespread in the US and attempts to commercially introduce CHV1 have not been widely successful. Though CHV1 persists in the applied tree, it does not spread naturally as it does in Europe, preventing it from being an effective form of biocontrol.


European infection

Chestnut blight was first identified around Genoa in 1938. This quickly spread and was identified in France in 1946, Switzerland in 1951, and Greece in 1963. It has most recently been found in the UK. Due to genetic differences between the fungal populations, it is likely that a second introduction of chestnut blight occurred in Georgia and Azerbaijan in 1938. The fungal infections initially caused widespread tree death in Europe. However, in the early 1950s trees were identified in Italy that survived fungal infection. On these trees, the fungus caused more superficial cankers, that appeared to be healing. The reduced infection was due to the presence of CHV1, an RNA virus that infects ''C. parasitica''. CHV1 spread naturally throughout Europe but is also spread artificially as a biocontrol measure (particularly in France). CHV1 is currently not present in the UK, Northern France, or Eastern Georgia but an introduction for biocontrol is being considered.


Symptoms

The fungus enters through wounds on susceptible trees and grows in and beneath the bark, eventually killing the
cambium A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cells for plant growth. It is found in the area between xylem and phloem. A cambium can also be defined as a cellular plant tissue from w ...
all the way around the twig, branch, or trunk. The first symptom of ''C. parasitica'' infection is a small orange-brown area on the tree bark. A sunken canker then forms as the
mycelial Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrates. A typical single spore germinates ...
fan spreads under the bark. As the hyphae spread, they produce several toxic compounds, the most notable of which is
oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early inve ...
. This acid lowers the pH of the infected tissue from around the normal 5.5 to approximately 2.8, which is toxic to plant cells. The canker eventually girdles the tree, killing everything above it. Distinctive yellow
tendril In botany, a tendril is a specialized stem, leaf or petiole with a threadlike shape used by climbing plants for support and attachment, as well as cellular invasion by parasitic plants such as '' Cuscuta''. There are many plants that have tend ...
s (cirrus) of conidia can be seen extruding in wet weather.


Life cycle and reproduction

The primary plant tissues targeted by ''C. parasitica'' are the inner bark, an area containing the conductive tissue, and the cambium, a layer of actively dividing cells that give rise to secondary vascular tissues. In these tissues, the pathogen forms diffuse cankers in which the mycelium overwinters. In the following spring, two types of fruiting bodies will form: pycnidia, usually first, and perithecia. Following rainfall, the pycnidia ooze orange tendrils of conidia, the asexual spores, while perithecia forcibly eject ascospores, the sexual spores. Upon becoming airborne, ascospores are carried by eddies of wind to new hosts or infect other parts of the same tree. When insects, birds, or other wildlife come into contact with the cankers, they can mechanically disperse the conidia to a new host. Additionally, the asexual spores can be dispersed by rain splash. Once on the new host, or new area of the tree, the spores can germinate and infect the inner bark through insect wounds and fissures in the outer bark. If cankers continue to form and expand, the fungus can girdle the stem, severing the flow of nutrients and water to the vital vegetative tissues. The absence of nutrient dispersal will result in tree death; however, the root system will survive. As a result, American chestnuts exist mainly as shrubs sprouting from the old, surviving roots. These sprouts usually succumb to infection by ''C. parasitica'' before reaching sexual maturity.


Management: hypovirulence, sanitation, and chemical control

In Europe, during the late 1960s, it was found that a strain of ''C. parasitica'' was less virulent, only able to produce shallow cankers that the tree's callus tissue could eventually limit and isolate. The trait of hypovirulence could be transferred from an avirulent strain to a lethal strain through
anastomosis An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf#Veins, leaf veins, or streams. Such a connection m ...
—the fusion of hyphae. It was later discovered that this attenuated virulence was due to infection by a
dsRNA Ribonucleic acid (RNA) is a polymeric molecule essential in various biological roles in coding, decoding, regulation and expression of genes. RNA and deoxyribonucleic acid ( DNA) are nucleic acids. Along with lipids, proteins, and carbohydra ...
mycovirus Mycoviruses (Ancient Greek: μύκης ' ("fungus") + Latin '), also known as mycophages, are viruses that infect fungi. The majority of mycoviruses have double-stranded RNA (dsRNA) genomes and isometric particles, but approximately 30% have po ...
, ''Cryphonectria hypovirus 1'' (CHV1) of genus ''
Hypovirus ''Hypovirus'' is a genus of viruses, in the family ''Hypoviridae''. Fungi serve as natural hosts. There are four species in this genus. Infection reduces the virulence of its parasitic host, making it a hyperparasite useful for blight control. ...
''. Considering the nature of hypovirulent strains, there has been a strong interest to use them to manage lethal ''C. parasitica'' strains. In Europe, natural dissemination of hypovirulence in pathogen populations resulted in the restoration of economically valuable chestnuts. Unfortunately, this was not the case in the United States. Compared to Europe, the US has a greater diversity of ''C. parasitica'' strains. Thus, the spread of the mycovirus in American ''C. parasitica'' populations is inhibited by vegetative incompatibility, an
allorecognition Allorecognition is the ability of an individual organism to distinguish its own tissues from those of another. It manifests itself in the recognition of antigens expressed on the surface of cells of non-self origin. Allorecognition has been descri ...
system that inhibits the fusion of hyphae between individuals that are genetically distinct at specific loci. In 2016, however, "super mycovirus donor strains" of ''C. parasitica'' were engineered to overcome this incompatibility system. This could potentially be employed as a method of biological control. As mentioned above some soil microorganisms suppress ''C. parasitica''. This can be used to treat the cankers, by using a soil compress, a quantity of soil held against the trunk itself with
plastic wrap Plastic wrap, cling film, Saran wrap, cling wrap, Glad wrap or food wrap is a thin plastic film typically used for sealing food items in containers to keep them fresh over a longer period of time. Plastic wrap, typically sold on rolls in boxe ...
and some adhesive tape around that. 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. Additionally, some fungicides may be effective at controlling this fungal disease. A study on the chemical control of chestnut blight in ''Castanea sativa'', may have found that the external application of both
copper oxychloride Dicopper chloride trihydroxide is the chemical compound with the formula Cu2(OH)3Cl. It is often referred to as tribasic copper chloride (TBCC), copper trihydroxyl chloride or copper hydroxychloride. It is a greenish crystalline solid encount ...
and carbendazim could reduce the rate of disease by almost 50%


Conservation efforts in North America

There are approximately 2,500 chestnut trees growing on near
West Salem, Wisconsin West Salem is a village in La Crosse County, Wisconsin, United States, along the La Crosse River. It is part of the La Crosse-Onalaska, WI-MN Metropolitan Statistical Area. The population was 4,799 as of the 2010 Census. History West Salem was p ...
, 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. In the late 1800s, Hicks planted fewer than a dozen chestnuts. Planted outside the natural range of American chestnut, these trees escaped the initial wave of infection by chestnut blight, but in 1987 scientists found blight also in this stand. 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 The Wisconsin Department of Natural Resources (WDNR) is a government agency of the U.S. state of Wisconsin charged with conserving and managing Wisconsin's natural resources. The Wisconsin Natural Resources Board has the authority to set policy ...
,
USDA Forest Service The United States Forest Service (USFS) is an agency of the U.S. Department of Agriculture that administers the nation's 154 national forests and 20 national grasslands. The Forest Service manages of land. Major divisions of the agency inc ...
,
West Virginia University West Virginia University (WVU) is a public land-grant research university with its main campus in Morgantown, West Virginia. Its other campuses are those of the West Virginia University Institute of Technology in Beckley, Potomac State College ...
,
Michigan State University Michigan State University (Michigan State, MSU) is a public university, public Land-grant university, land-grant research university in East Lansing, Michigan. It was founded in 1855 as the Agricultural College of the State of Michigan, the fi ...
, and
Cornell University Cornell University is a private statutory land-grant research university based in Ithaca, New York. It is a member of the Ivy League. Founded in 1865 by Ezra Cornell and Andrew Dickson White, Cornell was founded with the intention to teach an ...
. Removing blighted trees to control the disease was first attempted when the blight was discovered, but this proved to be an ineffective solution. Scientists then set out to introduce a hyperparasitic
hypovirus ''Hypovirus'' is a genus of viruses, in the family ''Hypoviridae''. Fungi serve as natural hosts. There are four species in this genus. Infection reduces the virulence of its parasitic host, making it a hyperparasite useful for blight control. ...
into the chestnut blight fungus. The trees infected with virus-treated fungus responded immediately and began to heal over their cankers. However, the virus was so efficient at attenuating fungal growth that it prevented the spreading of the virus from an infected fungus growing on one tree to that growing on another tree. Only the virus-treated trees recovered. Scientific opinion regarding the future of the stand varies.


Hybrid chestnut trees

Current efforts are underway by the Forest Health Initiative to use modern breeding techniques and genetic engineering to create resistant tree strains, with contributions from
SUNY College of Environmental Science and Forestry The State University of New York College of Environmental Science and Forestry (ESF) is a public research university in Syracuse, New York focused on the environment and natural resources. It is part of the State University of New York (SUNY) sys ...
,
Penn State #Redirect Pennsylvania State University The Pennsylvania State University (Penn State or PSU) is a Public university, public Commonwealth System of Higher Education, state-related Land-grant university, land-grant research university with campu ...
, the
University of Georgia , mottoeng = "To teach, to serve, and to inquire into the nature of things.""To serve" was later added to the motto without changing the seal; the Latin motto directly translates as "To teach and to inquire into the nature of things." , establ ...
, and the
US Forest Service The United States Forest Service (USFS) is an agency of the U.S. Department of Agriculture that administers the nation's 154 national forests and 20 national grasslands. The Forest Service manages of land. Major divisions of the agency inc ...
. One of the most successful methods of breeding is to create a back cross of a resistant species (such as one from China or Japan) and American chestnut. Researchers identified two or three genes that allow for blight resistance, and are focusing on giving the American chestnut hybrids only those genes from the Chinese or Japanese chestnut. The two species are first bred to create a 50/50 hybrid. After three backcrosses with American chestnut, the remaining genome is approximately 1/16 that of the resistant tree and 15/16 American. The strategy is to select blight-resistance genes during the backcrossing while preserving the more wild-type traits of American chestnut as the dominant
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...
. Thus, the newly bred hybrid chestnut trees should reach the same heights as the original American chestnut. Many of these 15/16 American chestnut hybrids have been planted along the East Coast, including in the Jefferson National Forest and on the
Flight 93 National Memorial The Flight 93 National Memorial is a memorial built to commemorate the crash of United Airlines Flight 93, which was one of four aircraft hijacked during the September 11 attacks in 2001. The memorial is located in Stonycreek Township in Somer ...
. Some of these sites have had researchers check on the saplings that have been planted to see their survival rate. For the hybrids to do well, they need areas with decent drainage and abundant sunlight. Meeting these needs can be hard to do, so not all restoration areas have been successful with hybrid survival.


Transgenic blight-resistant chestnut trees

A 1983 study on
hypovirulence ''Hypovirus'' is a genus of viruses, in the family ''Hypoviridae''. Fungi serve as natural hosts. There are four species in this genus. Infection reduces the virulence of its parasitic host, making it a hyperparasite useful for blight control. ...
had shown that chestnut blight infected with hypovirus produced less oxalic acid when attacking the
cambium A cambium (plural cambia or cambiums), in plants, is a tissue layer that provides partially undifferentiated cells for plant growth. It is found in the area between xylem and phloem. A cambium can also be defined as a cellular plant tissue from w ...
. Meanwhile, a plant pathologist, Dr. William Powell, had been trying to figure out how to transfer all of the Asian chestnut's resistance genetics to its American relatives. In the 1990s, he had the idea to give up on the more complicated and larger job, and instead look around for a single gene elsewhere. (In related work, in 2001 Liang, Mayard, Allen, and Powell successfully inserted an
oxalate oxidase In enzymology, an oxalate oxidase () is an oxalate degrading enzyme that catalyzes the chemical reaction: :oxalate + O2 + 2 H+ \rightleftharpoons 2 CO2 + H2O2 The 3 substrates of this enzyme are oxalate, O2, and H+, whereas its two products a ...
(OxO) gene from
wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...
into ''
Populus ''Populus'' is a genus of 25–30 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar (), aspen, and cottonwood. The we ...
× euramericana'' ("Ogy") for ''
Septoria musiva ''Septoria musiva'', correct taxonomic name: ''Sphaerulina musiva'' (teleomorph: ''Mycosphaerella populorum''), is an ascomycete fungus responsible of a leaf spot and canker disease on poplar trees. It is native on the eastern cottonwood popla ...
'' resistance. This enzyme breaks down the
oxalic acid Oxalic acid is an organic acid with the systematic name ethanedioic acid and formula . It is the simplest dicarboxylic acid. It is a white crystalline solid that forms a colorless solution in water. Its name comes from the fact that early inve ...
secreted by the fungus into carbon dioxide and hydrogen peroxide.) In 2007 Welch, Stipanovic, Maynard, and Powell showed that transgenic ''C. dentata'' expressing a wheat OxO did indeed have lower
lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidity ...
degradation by OA, and suggested this was the path to take. A few years later this line of research culminated in the final product: Powell and another plant pathologist, Dr. Charles Maynard, working at the
State University of New York College of Environmental Science and Forestry The State University of New York College of Environmental Science and Forestry (ESF) is a public research university in Syracuse, New York focused on the environment and natural resources. It is part of the State University of New York (SUNY) s ...
have developed American chestnuts which have full
blight resistance Plant disease resistance protects plants from pathogens in two ways: by pre-formed structures and chemicals, and by infection-induced responses of the immune system. Relative to a susceptible plant, disease resistance is the reduction of pathoge ...
. Full resistance was attained by introducing a wheat OxO gene into the American chestnut genome. (Because an unrelated gene was transferred, this did not make the chestnut trees produce
gluten Gluten is a structural protein naturally found in certain cereal grains. Although "gluten" often only refers to wheat proteins, in medical literature it refers to the combination of prolamin and glutelin proteins naturally occurring in all grain ...
, and the nuts remain
gluten free A gluten-free diet (GFD) is a nutritional plan that strictly excludes gluten, which is a mixture of proteins found in wheat (and all of its species and hybrids, such as spelt, kamut, and triticale), as well as barley, rye, and oats. The inclu ...
.) The
transgenic A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the ...
trees have blight resistance either equal to or surpassing that of ''
Castanea mollissima ''Castanea mollissima'' (), also known as the Chinese chestnut, is a member of the family Fagaceae, and a species of chestnut native to China, Taiwan, and Korea. Description It is a deciduous tree growing to 20 m tall with a broad crown. T ...
'', Chinese chestnuts. In 2013, SUNY ESF had over 100 individual events being tested, with more than 400 slated to be in the field or in the lab for various assay tests in the next several years and more than 1,000 trees growing in several field sites in 2014. Government approval will be required before returning any of these blight resistant trees to the wild. The
New York Botanical Garden The New York Botanical Garden (NYBG) is a botanical garden at Bronx Park in the Bronx, New York City. Established in 1891, it is located on a site that contains a landscape with over one million living plants; the Enid A. Haupt Conservatory, ...
has planted several of the transgenic trees for public display. At the start, there are very few such engineered chestnut trees. For seed multiplication,
grafting Grafting or graftage is a horticultural technique whereby tissues of plants are joined so as to continue their growth together. The upper part of the combined plant is called the scion () while the lower part is called the rootstock. The succ ...
would work. Normal tree growth requires 6, 7, or even 8 years before a chestnut will flower. However normal
orchard An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit- or nut-producing trees which are generally grown for commercial production. Orchards are also sometimes a feature of larg ...
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 chamber Growth may refer to: Biology * Auxology, the study of all aspects of human physical growth * Bacterial growth * Cell growth * Growth hormone, a peptide hormone that stimulates growth * Human development (biology) * Plant growth * Secondary gro ...
s with higher light inputs to get it down to less than a year to pollen production.


Economic and ecological impact of disease

In less than fifty years after its emergence, ''C. parasitica'' virtually eliminated American chestnut as a canopy species in of forest. The chestnut fruit was a major food source for animals in the low elevation Appalachian forests. This loss resulted in a drastic decrease in the squirrel population, the extinction of seven native moth species, and the slowed recovery of deer, Cooper's hawk, cougar, and bobcat populations. The effects of this disease also rippled further through the ecosystem, being linked to a decrease in the abundance of cavity-nesting birds and to a decrease in river water quality which negatively affected aquatic invertebrate populations. In 1912, standing chestnut timber in just three states was estimated to be $82.5 million ($1.9 billion in current dollars) in value. Therefore, in addition to ecological impacts, ''C. parasitica'' potentially caused a devastating loss in economic welfare for communities dependent on the chestnut tree. Mountaineers, residents of Appalachian Mountain communities, had to drastically alter their lifestyles to cope with the effects of this disease. Economic effects have also been considerable in Europe, particularly before CHV1 spreads naturally to a region. In Greece for example, the disease forced the migration of people who could no longer afford to live off chestnut trees. It has also led to a 40% decline in Greek chestnut production.


See also

*
American Chestnut Cooperators Foundation The American Chestnut Cooperators Foundation (ACCF) is a 501(c)(3) non-profit scientific and educational foundation organized in 1984. They are dedicated to restoring the American chestnut (''Castanea dentata'') to its former place in the United ...
*
Forest pathology Forest pathology is the research of both biotic and abiotic maladies affecting the health of a forest ecosystem, primarily fungal pathogens and their insect vectors. It is a subfield of forestry and plant pathology. Forest pathology is part ...
*
Lists of invasive species These are lists of invasive species by country or region. A species is regarded as invasive if it has been introduced by human action to a location, area, or region where it did not previously occur naturally (i.e., is not a native species), becom ...
*
Forest disturbance of invasive insects and diseases in the United States Species which are not native to a forest ecosystem can act as an agent of disturbance, changing forest dynamics as they invade and spread. Invasive insects and pathogens (diseases) are introduced to the United States through international trade, a ...
*
The Weeping Beech The Weeping Beech was a historic tree located at Weeping Beech Park in Flushing, Queens, New York City. It was the mother of all European weeping beeches in the United States. The Weeping Beech was imported by horticulturalist Samuel Parsons ...


References


Further reading

*


External links


American Chestnut Cooperators' Foundation - Blight FungusDon't Move Firewood - Gallery of Pests: Chestnut BlightSUNY ESF Chestnut Restoration ProjectForest Health InitiativeThe American Chestnut Foundation

Species Profile - Chestnut Blight (''Cryphonectria parasitica'')
National Invasive Species Information Center,
United States National Agricultural Library The United States National Agricultural Library (NAL) is one of the world's largest agricultural research libraries, and serves as a national library of the United States and as the library of the United States Department of Agriculture. Located ...
. {{DEFAULTSORT:Chestnut Blight Fungal tree pathogens and diseases Diaporthales Natural history of the United States Forestry in the United States Fungi described in 1906 Fungi of Asia Fungi of Europe Taxa named by William Alphonso Murrill