Fireblight
Encyclopedia
Fire blight, also written fireblight, is a contagious disease
affecting apple
s, pear
s, and some other members of the family Rosaceae
. It is a serious concern to producers of apples and pears. Under optimal conditions, it can destroy an entire orchard
in a single growing season.
The causal pathogen
is Erwinia amylovora, a Gram-negative
bacterium in the family Enterobacteriaceae
. Pear
s are the most susceptible, but apple
s, loquat
, crabapple
s, quince
s, hawthorn
, cotoneaster
, pyracantha
, raspberry
and some other rosaceous plants are also vulnerable. The disease is believed to be indigenous to North America
, from where it spread to most of the rest of the world.
Fire blight is not believed to be present in Australia
though it might possibly exist there. It has been a major reason for a long-standing embargo on the importation of New Zealand apples to Australia . Japan was likewise believed to be without the disease, but it was discovered in pears grown in northern Japan. Japanese authorities are however still denying its existence and the Japanese scientist who discovered it is believed to have committed suicide after his name was leaked to affected farmers.
. The term "fireblight" describes the appearance of the disease, which can make affected areas appear blackened, shrunken and cracked, as though scorched by fire
.
Primary infections are established in open blossom
s and tender new shoot
s and leaves
in the spring when blossoms are open.
s, bird
s, rain
and wind
can transmit the bacterium to susceptible tissue. Injured tissue is also highly susceptible to infection
, including punctures and tears caused by plant-sucking or biting insects. Hail
storms can infect an entire orchard in a few minutes, and growers do not wait until symptoms appear, normally beginning control measures within a few hours.
Once deposited, the bacterium enters the plant through open stomata and causes blackened, necrotic lesion
s, which may also produce a viscous exudate
. This bacteria-laden exudate can be distributed to other parts of the same plant or to susceptible areas of different plants by rain, birds or insects, causing secondary infection
s. The disease spreads most quickly during hot, wet weather
and is dormant in the winter when temperatures drop. Infected plant tissue contains viable bacteria, however, and will resume production of exudate upon the return of warm weather in the following spring. This exudate is then the source for new rounds of primary infections.
The pathogen spreads through the tree from the point of infection via the plant's vascular
system, eventually reaching the root
s and/or graft
junction of the plant. Once the plant's roots are affected, the death of the plant often results. Over pruning and over fertilization (especially with nitrogen
) can lead to watersprouts and other midsummer growth that leave the tree more susceptible.
s streptomycin
or terramycin
can prevent new infections. The use of such sprays has led to streptomycin-resistant bacteria in some areas, such as California
and Washington. Certain biological controls consisting of beneficial bacteria can also prevent fireblight from infecting new trees. The only effective treatment for plants already infected is to prune off the affected branches and remove them from the area. Plants or trees should be inspected routinely for the appearance of new infections. The rest of the plant can be saved if the blighted wood
is removed before the infection spreads to the roots.
Contagious disease
A contagious disease is a subset category of infectious diseases , which are easily transmitted by physical contact with the person suffering the disease, or by their secretions or objects touched by them....
affecting apple
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
s, pear
Pear
The pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....
s, and some other members of the family Rosaceae
Rosaceae
Rosaceae are a medium-sized family of flowering plants, including about 2830 species in 95 genera. The name is derived from the type genus Rosa. Among the largest genera are Alchemilla , Sorbus , Crataegus , Cotoneaster , and Rubus...
. It is a serious concern to producers of apples and pears. Under optimal conditions, it can destroy an entire orchard
Orchard
An orchard is an intentional planting of trees or shrubs that is maintained for food production. Orchards comprise fruit or nut-producing trees which are grown for commercial production. Orchards are also sometimes a feature of large gardens, where they serve an aesthetic as well as a productive...
in a single growing season.
The causal pathogen
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...
is Erwinia amylovora, a Gram-negative
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
bacterium in the family Enterobacteriaceae
Enterobacteriaceae
The Enterobacteriaceae is a large family of bacteria that includes many of the more familiar pathogens, such as Salmonella, Escherichia coli, Yersinia pestis, Klebsiella and Shigella. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the...
. Pear
Pear
The pear is any of several tree species of genus Pyrus and also the name of the pomaceous fruit of these trees. Several species of pear are valued by humans for their edible fruit, but the fruit of other species is small, hard, and astringent....
s are the most susceptible, but apple
Apple
The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...
s, loquat
Loquat
The loquat , Eriobotrya japonica, is a fruit tree in the family Rosaceae, indigenous to southeastern China. It was formerly thought to be closely related to the genus Mespilus, and is still sometimes known as the Japanese medlar...
, crabapple
Crabapple
Crabapple is a term used for several species of Malus in the family Rosaceae, which are characterized by small sour fruit resembling familiar table apples . They are usually small trees or shrubs....
s, quince
Quince
The quince , or Cydonia oblonga, is the sole member of the genus Cydonia and native to warm-temperate southwest Asia in the Caucasus region...
s, hawthorn
Crataegus
Crataegus , commonly called hawthorn or thornapple, is a large genus of shrubs and trees in the rose family, Rosaceae, native to temperate regions of the Northern Hemisphere in Europe, Asia and North America. The name hawthorn was originally applied to the species native to northern Europe,...
, cotoneaster
Cotoneaster
Cotoneaster is a genus of woody plants in the rose family, Rosaceae, native to the Palaearctic region , with a strong concentration of diversity in the genus in the mountains of southwestern China and the Himalayas...
, pyracantha
Pyracantha
Pyracantha is a genus of thorny evergreen large shrubs in the family Rosaceae, with common names Firethorn or Pyracantha. They are native to an area extending from Southeast Europe east to Southeast Asia, resemble and are related to Cotoneaster, but have serrated leaf margins and numerous thorns...
, raspberry
Raspberry
The raspberry or hindberry is the edible fruit of a multitude of plant species in the genus Rubus, most of which are in the subgenus Idaeobatus; the name also applies to these plants themselves...
and some other rosaceous plants are also vulnerable. The disease is believed to be indigenous to North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, from where it spread to most of the rest of the world.
Fire blight is not believed to be present in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
though it might possibly exist there. It has been a major reason for a long-standing embargo on the importation of New Zealand apples to Australia . Japan was likewise believed to be without the disease, but it was discovered in pears grown in northern Japan. Japanese authorities are however still denying its existence and the Japanese scientist who discovered it is believed to have committed suicide after his name was leaked to affected farmers.
Symptoms
Fireblight is a systemic diseaseDisease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...
. The term "fireblight" describes the appearance of the disease, which can make affected areas appear blackened, shrunken and cracked, as though scorched by fire
Fire
Fire is the rapid oxidation of a material in the chemical process of combustion, releasing heat, light, and various reaction products. Slower oxidative processes like rusting or digestion are not included by this definition....
.
Primary infections are established in open blossom
Blossom
In botany, blossom is a term given to the flowers of stone fruit trees and of some other plants with a similar appearance that flower profusely for a period of time in spring...
s and tender new shoot
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 and leaves
Leaves
-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...
in the spring when blossoms are open.
Dissemination
Honeybees and other insectInsect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
s, rain
Rain
Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...
and wind
Wind
Wind is the flow of gases on a large scale. On Earth, wind consists of the bulk movement of air. In outer space, solar wind is the movement of gases or charged particles from the sun through space, while planetary wind is the outgassing of light chemical elements from a planet's atmosphere into space...
can transmit the bacterium to susceptible tissue. Injured tissue is also highly susceptible to infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
, including punctures and tears caused by plant-sucking or biting insects. Hail
Hail
Hail is a form of solid precipitation. It consists of balls or irregular lumps of ice, each of which is referred to as a hail stone. Hail stones on Earth consist mostly of water ice and measure between and in diameter, with the larger stones coming from severe thunderstorms...
storms can infect an entire orchard in a few minutes, and growers do not wait until symptoms appear, normally beginning control measures within a few hours.
Once deposited, the bacterium enters the plant through open stomata and causes blackened, necrotic lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s, which may also produce a viscous exudate
Exudate
An exudate is any fluid that filters from the circulatory system into lesions or areas of inflammation. It can apply to plants as well as animals. Its composition varies but generally includes water and the dissolved solutes of the main circulatory fluid such as sap or blood...
. This bacteria-laden exudate can be distributed to other parts of the same plant or to susceptible areas of different plants by rain, birds or insects, causing secondary infection
Infection
An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...
s. The disease spreads most quickly during hot, wet weather
Weather
Weather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
and is dormant in the winter when temperatures drop. Infected plant tissue contains viable bacteria, however, and will resume production of exudate upon the return of warm weather in the following spring. This exudate is then the source for new rounds of primary infections.
The pathogen spreads through the tree from the point of infection via the plant's vascular
Vascular tissue
Vascular tissue is a complex conducting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. There are also two meristems associated with vascular tissue:...
system, eventually reaching the root
Root
In vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
s and/or graft
Grafting
Grafting is a horticultural technique whereby tissues from one plant are inserted into those of another so that the two sets of vascular tissues may join together. This vascular joining is called inosculation...
junction of the plant. Once the plant's roots are affected, the death of the plant often results. Over pruning and over fertilization (especially with nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
) can lead to watersprouts and other midsummer growth that leave the tree more susceptible.
Treatment
Sprays of the antibioticAntibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
s streptomycin
Streptomycin
Streptomycin is an antibiotic drug, the first of a class of drugs called aminoglycosides to be discovered, and was the first antibiotic remedy for tuberculosis. It is derived from the actinobacterium Streptomyces griseus. Streptomycin is a bactericidal antibiotic. Streptomycin cannot be given...
or terramycin
Oxytetracycline
Oxytetracycline was the second of the broad-spectrum tetracycline group of antibiotics to be discovered.Oxytetracycline works by interfering with the ability of bacteria to produce proteins that are essential to them. Without these proteins the bacteria cannot grow, multiply and increase in numbers...
can prevent new infections. The use of such sprays has led to streptomycin-resistant bacteria in some areas, such as California
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 Washington. Certain biological controls consisting of beneficial bacteria can also prevent fireblight from infecting new trees. The only effective treatment for plants already infected is to prune off the affected branches and remove them from the area. Plants or trees should be inspected routinely for the appearance of new infections. The rest of the plant can be saved if the blighted wood
Wood
Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...
is removed before the infection spreads to the roots.