(Burrill 1882) Winslow et al. 1920 Type strain = NCPPB 683
Fire blight, also written fireblight, is a contagious disease affecting apples, pears, and some other members of the family Rosaceae. It is a serious concern to apple and pear producers. Under optimal conditions, it can destroy an entire orchard in a single growing season.
Fire blight is not believed to be present in Australia though it might possibly exist there.[2] It has been a major reason for a long-standing embargo on the importation of New Zealand apples to Australia.[3] In Europe it is listed as a quarantine disease, and has been spreading along Hawthorn (Crataegus) hedges planted alongside railways, motorways and main roads.
It is believed that the pathogen was first introduced into Northern Europe in the 1950's through fruit containers, contaminated with bacterial ooze, imported from the USA.[4] During the 1950s-1960's, E. amylovora spread through much of Northern Europe. Initially large areas of Germany and France seemed untouched by fireblight, but the disease, and E. amylovora, were discovered in the later 1990s in Germany. In the 1980s the bacterium was found in isolated regions in the Eastern Mediterranean and from the years 1995-1996 cases of fireblight began to be reported in countries such as Hungary, Romania, Northern Italy and Northern Spain.[citation needed]
Dissemination
Gala apple branch with “scorched” leaves after a severe fire blight infection.
Erwinia amylovora overwinters in cankers formed during the previous season. In the spring warmer temperatures support development and bacteria-filled ooze begins to exude from the cankers.[5] The factors that determine whether or not cankers become active are not well known, but it is thought that cankers found on larger or older tree limbs are more likely to become active.[6]Honeybees and other insects are attracted to this ooze and can spread bacteria to susceptible tissue, such as flower stigmata.[7]Birds, rain and wind can also transmit the bacterium to susceptible tissue, the colonisation of which will be heavily decided by temperature (21-27 C is most favourable) and moisture either from rain or heavy dew. Bacterial procession into the nectaries– cause "blossom blight". Flowers one to three days old are more susceptible than those five to eight days old. See Curry 1987 for the source and further review of this subject.[8]
Other than through the flowers, the bacterium can enter the plant through the stomata. Also highly susceptible to infection are lesions such as punctures caused by plant-sucking insects and tears caused by a variety of means, including infected cultivating tools. A few minutes of heavy hail can spread the disease throughout an entire orchard and growers normally do not wait until symptoms appear but begin control measures[citation needed] within a few hours.[citation needed]
Once the bacterium gains access to the xylem or cortical parenchyma of the plant, it causes blackened, necrotic lesions, 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 infections. The disease spreads most quickly during hot, wet weather and is dormant in the winter when temperatures drop.[citation needed]
The pathogen spreads through the tree from the point of infection via the plant's vascular system, eventually reaching the roots and/or graft junction of the plant. Once the plant's roots are affected, the death of the plant often results. Over-pruning and too much fertilization (especially with nitrogen) can lead to water sprout and other midsummer growth that leave the tree more susceptible.[citation needed]
Unfortunately, there is no known cure for fire blight; the best that can be done is to prevent its spread by measures such as avoidance of overhead water systems, as falling water can spread the disease and the careful pruning of tainted stems or branches. Great attention must be paid to any gardening tools that have been exposed to the causitive microorganisms. These tools should be disinfected in an alcohol solution containing three parts denatured alcohol to one part water. Diluted household bleach (one part bleach to nine parts water) can likewise be utilized. Of course, implements should afterwards be dried and oiled to forestall corrosion.[9]
The fly Delia platura has been observed visiting fire blight wounds to feed and can successfully transmit fire blight to already damaged apple shoots.[10] Fire blight exopolysaccharide also served as the adhesive to attach propagated cells to D. platura.[10]D. platura shed fire blight at a constant rate[10] - and did not suffer from doing so - for at least five days.[10]
Pathogenesis
Pathogenicity depends on many different factors such as the production of the siderophore desferrioxamine, metalloproteases, plasmids, and histone-like proteins. However, some essential factors of pathogenicity are variations in the synthesis of extracellular polysaccharides (EPS) and the mechanism of type III secretion system and its associated proteins.[11] EPS helps bacterial pathogens avoid plant defenses, “clog” the host’s vascular system, protect bacteria against desiccation and attach to both surfaces and one another. One EPS is amylovoran, a polymer of pentasaccharide repeating units. If a strain of E. amylovora cannot produce amylovoran it will not be pathogenic and will be unable to spread in plants. Levan is another EPS, and a lack of it will slow development of symptoms. Type III secretion systems are used for exporting and delivering effector proteins into the cytosol of host plants. This system mainly consists of Hrc proteins. Motility is another major virulence factor.[12] Since E. amylovora is not an obligate biotroph, it is able to survive outside the host. This fact allows the organism to be spread by such a variety if methods.[citation needed]
Symptoms
Fire blight on a pear tree caused by Erwinia amylovora
Tissues affected by the symptoms of Erwinia amylovora include blossoms, fruits, shoots, and branches of apple (Pomoideae), pear, and many other rosaceous plants. All symptoms are above ground and are typically easy to recognize. Symptoms on blossoms include water soaking of the floral receptacle, ovary, and peduncles.[13] This results in a dull, gray-green appearance 1–2 weeks after petal fall, and eventually tissues will shrivel and turn black. The base of the blossom and young fruit show similar symptoms as infection spreads. Opaque white- or amber-colored droplets of bacterial ooze can be seen on the infected tissue in high humidity. Shoots show similar symptoms but these develop much more rapidly. A “Shepherd's Crook” can occur when the tip of the shoot wilts, and diseased shoot leaves typically have blackening along the mid-vein and before they die. When numerous, diseased shoots give the tree a blighted appearance. Infection of blossoms and shoots can spread to larger tree limbs. Branches will darken and become water soaked, eventually cracks will develop in bark. Wood under the bark will become streaked with black discoloration. Immature fruit forms water-soaked lesions and later turns black. Bacterial ooze can be found on these lesions. Severe infections result in fruit turning entirely black and shrivelling.[14]
Management
In an attempt to prevent new infections, plants have been sprayed with either streptomycin, copper sulfate or both in some parts of the world, such as the USA, but has been found to be effective only for slowing or temporarily stopping growth in already diseased plants.[15] The widespread use of streptomycin spray has led to antibiotic resistance in some areas, such as California and Washington. Certain biological controls consisting of beneficial bacteria or yeast can also prevent fire blight 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.[15] 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.[16] There is no known cure; prevention is the key.[17]
Methods to predict the likelihood of an outbreak so that control measures can be best targeted, were introduced from the 1980s following the work of Eve Billings at East Malling Research Station, UK. These were based on temperature and rainfall, and have been developed further by Billings and others.[18][19]
E. amylovora generally needs to be destroyed externally, before it enters plant tissues because once it enters the host, it spreads during the endophytic phase of pathogenesis. Once this happens external control methods become ineffective. The application of copper and antibiotics to the plant externally is the most effective method of prevention. Currently it has been noted that E. amylovora has developed a resistance to the antibiotic streptomycin, as do most bacteria able to transfer preferential genes horizontally from species to species.[20]
New research conducted by John C. Wise out of Michigan State University shows that E. amylovora can be controlled with relative efficacy through tree trunk injection of either streptomycin, potassium phosphites (PH), or acibenzolar-S-methyl (ASM). PH and ASM both work through gene inductions of PR-1, PR-2, and PR-8 in the leafy material.[21] Oxytetracycline Hydrochloride (OTC) was also tested and found to greatly reduce the activity of the bacteria within the tree. These new control methods are still being researched and have not been approved for fruit crop production by the EPA.[citation needed]
Phytosanitary measures have been employed as the best sanitary measures against E. amylovora dispersal. High risk countries are encouraged not to import plants susceptible to the pathogen into their territory because, once the bacteria become established in an area it is nearly impossible to eradicate the disease. Nurseries and orchards in such regions are placed on strict phytosanitary surveillance measures and well-monitored. Imported and infected crops are destroyed as soon as they are noticed since the bacteria spreads very rapidly and eradication methods are usually costly and inefficient.[citation needed]
Current fire blight strategies depend upon phytosanitary measures to lessen inoculum in the plantation and the utilization of splash medicines to forestall contamination, particularly blossom infections. Decreasing essential inoculum in the plantation by removing remainder holdover cankers during winter pruning is a set up as a basic method of control fire blight disease.[22]
In seriously influenced plantations, social practices that moderate the development pace of the tree will likewise slow the pace of canker improvement. This incorporates retaining irrigation water, nitrogen fertilizer, and agriculture. Also, practices that decrease tree injuring and bacterial development can diminish auxiliary disease. This incorporates controlling bugs, for example, plant bugs and psylla, constraining utilization of appendage spreaders in youthful plantations, and avoiding use of overhead sprinklers.[14]
Cultural control options include selecting resistant cultivars, however most commercially successful apple cultivars lack fire blight resistance. Breeders have developed fire blight resistant rootstocks, but resistance is not conferred to the grafted scion.[23]
Prohexadione calcium (BASF brand name Apogee in the United States) is a plant growth inhibitor which is recommended for shoot blight. Since fire blight relies on gibberellin-dependent growth for much of its own life cycle, prohexadione's gibberellin synthesis inhibition effect also suppresses blight. Not effective in blossom blight.[24]
Importance
Besides the historical significance of being the first bacterium proven to be a plant pathogen, fire blight is extremely important economically.[14] Costs for control and loss are estimated to be approximately $100 million per year in the USA. Specifically, in Michigan in the year 2000, $42 million in losses were estimated because of the removal of about 400,000 apple trees.[25] Warm, humid, and wet weather in May gave rise to this epidemic. In Washington and northern Oregon approximately $68 million in losses were estimated. E. amylovora has spread throughout the USA and much of the world,causing heavy losses, although it so far has not caused severe damage in northern Europe and, as long as E. amylovora is not introduced to Central Asia where wild apple trees still grow, it will not modify any ecosystems. Biodiversity is not impacted either, as no plant species are threatened with extinction due to this pathogen. Growing pears in Emilia-Romagna in Italy is a traditional activity for some families, and fire blight threatens this tradition which has been passed down for several generations.[26] In southern Germany apple and pear trees have been a part of the landscape for a long time, and are difficult to protect. The decline of apple and pear trees from their landscape can be expensive to replace and could have a negative effect on tourism. In the long-run, fire blight is a very important factor of economy and society.[citation needed]
A relatively small number of apple cultivars are responsible for an enormous proportion of yearly apple production. Food sellers and shoppers prize these cultivars for their appearance, quality, flavour, and storability, while cultivators additionally esteem their orchard attributes and guaranteed market due to this popularity. To maintain the desirable qualities of a cultivar while at the same time changing its disease resistance through ordinary breeding techniques is for all intents and purposes impossible due to the apple's heterozygosity, self-incongruence, and long growth span. Hereditary designing offers an appealing option since it can be faster, resistance qualities can be acquired from numerous sources, the statement of local apple qualities can be altered, and the attractive characteristics of the changed cultivar or rootstock can be safeguarded.[22]
Association with Asian pear blight
Asian pear blight, a disease affecting Japanese and Korean pears, has been associated with fire blight, including in the popular press.[27] Genetic testing has shown Asian pear blight to be a variant of Erwinia pyrifoliae, unrelated to fire blight.[28][29]
Related Research Articles
Blight is a specific symptom affecting plants in response to infection by a pathogenic organism.
Erwinia is a genus of Enterobacterales bacteria containing mostly plant pathogenic species which was named for the famous plant pathologist, Erwin Frink Smith. It contains Gram-negative bacteria related to Escherichia coli, Shigella, Salmonella, and Yersinia. They are primarily rod-shaped bacteria.
Stewart's wilt is a bacterial disease of corn caused by the bacterium Pantoea stewartii. The disease is also known as bacterial wilt or bacterial leaf blight and has been shown to be quite problematic in sweet corn. The causal organism is a facultatively anaerobic, gram-negative, rod-shaped bacterium. The disease is endemic in the mid-Atlantic and Ohio River Valley regions and in the southern portion of the Corn Belt. Stewart's Wilt causes minor reductions in field corn yield, despite common occurrence, because most hybrids grown in the Midwest have adequate resistance. However, the disease can be problematic in seed production because many countries have restrictions on maize seed from areas where the Stewart's Wilt occurs.
Citrus canker is a disease affecting Citrus species caused by the bacterium Xanthomonas. Infection causes lesions on the leaves, stems, and fruit of citrus trees, including lime, oranges, and grapefruit. While not harmful to humans, canker significantly affects the vitality of citrus trees, causing leaves and fruit to drop prematurely; a fruit infected with canker is safe to eat, but too unsightly to be sold. Citrus canker is mainly a leaf-spotting and rind-blemishing disease, but when conditions are highly favorable, it can cause defoliation, shoot dieback, and fruit drop.
Dickeya dadantii is a gram-negative bacillus that belongs to the family Pectobacteriaceae. It was formerly known as Erwinia chrysanthemi but was reassigned as Dickeya dadantii in 2005. Members of this family are facultative anaerobes, able to ferment sugars to lactic acid, have nitrate reductase, but lack oxidases. Even though many clinical pathogens are part of the order Enterobacterales, most members of this family are plant pathogens. D. dadantii is a motile, nonsporing, straight rod-shaped cell with rounded ends, much like the other members of the genus, Dickeya. Cells range in size from 0.8 to 3.2 μm by 0.5 to 0.8 μm and are surrounded by numerous flagella (peritrichous).
Diplodia tip blight, also known as Sphaeropsis blight, is a widespread disease affecting conifers caused by an opportunistic fungal pathogen, Diplodia sapinea. It is found in “both hemispheres between the latitudes 30° and 50° north and south". The diseases symptoms include: damping off and collar rot of seedlings, stem canker, root disease, and, most commonly, shoot blight. These symptoms have caused significant economic loss to nurseries and pine plantations. In a nursery in the north-central United States, losses of 35% have been reported. Shoot blight and eventual die back can cause a reduction of marketable volume in timber by 63%. Infection of terminal shoots can result in dead-top which significantly limits the usable length of the tree trunk. The presence of the pathogen in concert with severe weather conditions can lead to extreme loss. Following a severe hailstorm in South Africa, nearly 5,000 acres of pine plantation were infected with Diplodia tip blight. It was necessary to prematurely harvest large swaths of the plantations resulting in a loss of 45%. Areas that were not harvested prematurely still suffered an average timber loss of 11%.
Xylella fastidiosa is an aerobic, Gram-negative bacterium of the genus Xylella. It is a plant pathogen, that grows in the water transport tissues of plants and is transmitted exclusively by xylem sap-feeding insects such as sharpshooters and spittlebugs. Many plant diseases are due to infections of X. fastidiosa, including bacterial leaf scorch, oleander leaf scorch, coffee leaf scorch (CLS), alfalfa dwarf, phony peach disease, and the economically important Pierce's disease of grapes (PD), olive quick decline syndrome (OQDS), and citrus variegated chlorosis (CVC). While the largest outbreaks of X. fastidiosa–related diseases have occurred in the Americas and Europe, this pathogen has also been found in Taiwan, Israel, and a few other countries worldwide.
Pantoea agglomerans is a Gram-negative bacterium that belongs to the family Erwiniaceae.
Clavibacter michiganensis is an aerobic non-sporulating Gram-positive plant pathogenic actinomycete of the genus Clavibacter. Clavibacter michiganensis has several subspecies. Clavibacter michiganensis subsp. michiganensis causes substantial economic losses worldwide by damaging tomatoes and potatoes.
Curtobacterium flaccumfaciens is a Gram-positive bacterium that causes disease on a variety of plants. Gram-positive bacteria characteristics include small irregular rods, lateral flagella, the ability to persist in aerobic environments, and cells containing catalase. In the interest of studying pathogenicity in plants, this species is broken down further into pathovars, which help to better describe the pathogen.
Xanthomonas arboricola is a species of bacteria. This phytopathogenic bacterium can cause disease in trees like Prunus, hazelnut and walnut.
A wilt disease is any number of diseases that affect the vascular system of plants. Attacks by fungi, bacteria, and nematodes can cause rapid killing of plants, large tree branches or even entire trees.
Fusarium circinatum is a fungal plant pathogen that causes the serious disease pitch canker on pine trees and Douglas firs. The most common hosts of the pathogen include slash pine, loblolly pine, Monterey pine, Mexican weeping pine, and Douglas fir. Like other Fusarium species in the phylum Ascomycota, it is the asexual reproductive state of the fungus and has a teleomorph, Gibberella circinata.
Beet vascular necrosis and rot is a soft rot disease caused by the bacterium Pectobacterium carotovorum subsp. betavasculorum, which has also been known as Pectobacterium betavasculorum and Erwinia carotovora subsp. betavasculorum. It was classified in the genus Erwinia until genetic evidence suggested that it belongs to its own group; however, the name Erwinia is still in use. As such, the disease is sometimes called Erwinia rot today. It is a very destructive disease that has been reported across the United States as well as in Egypt. Symptoms include wilting and black streaks on the leaves and petioles. It is usually not fatal to the plant, but in severe cases the beets will become hollowed and unmarketable. The bacteria is a generalist species which rots beets and other plants by secreting digestive enzymes that break down the cell wall and parenchyma tissues. The bacteria thrive in warm and wet conditions, but cannot survive long in fallow soil. However, it is able to persist for long periods of time in the rhizosphere of weeds and non-host crops. While it is difficult to eradicate, there are cultural practices that can be used to control the spread of the disease, such as avoiding injury to the plants and reducing or eliminating application of nitrogen fertilizer.
Gummy stem blight is a cucurbit-rot disease caused by the fungal plant pathogen Didymella bryoniae. Gummy stem blight can affect a host at any stage of growth in its development and affects all parts of the host including leaves, stems and fruits. Symptoms generally consist of circular dark tan lesions that blight the leaf, water soaked leaves, stem cankers, and gummy brown ooze that exudes from cankers, giving it the name gummy stem blight. Gummy stem blight reduces yields of edible cucurbits by devastating the vines and leaves and rotting the fruits. There are various methods to control gummy stem blight, including use of treated seed, crop rotation, using preventative fungicides, eradication of diseased material, and deep plowing previous debris.
Sock Chin Gouk is a research scientist with the Victorian Department of Environment and Primary Industries in Melbourne.
Xanthomonas oryzae pv. oryzae is a bacterial pathovar that causes a serious blight of rice, other grasses, and sedges.
Collar rot is a symptomatically described disease that is usually caused by any one of various fungal and oomycete plant pathogens. It is present where the pathogen causes a lesion localized at or about the collet between the stem and the root. The lesions develop around the stem eventually forming a "collar". Observationally, collar rot grades into "basal stem rot", and with some pathogens is the first phase of "basal stem rot" often followed by "root rot". Collar rot is most often observed in seedings grown in infected soil. The pathogens that cause collar rot may be species or genera specific. But generalist pathogens such as Agroathelia rolfsii are known to attack over 200 different species. While bacteria caused collar rot is not common, trees infected with Fire blight may develop collar rot. Non-parasitic collar rot may be caused by winter damage.
Erwinia papayae is a bacteria species causing bacterial crown rot, or bacterial canker, a noteworthy and grave disease of papaya.
Eve Billing (1923–2019) was a UK plant pathologist specialising in diseases of fruit trees especially fire blight caused by Erwinia amylovora bacteria. She introduced a modelling system to predict the likelihood of outbreaks of fire blight and also methods for pathogen identification and treatment.
↑ Billing, E.; Berrie, A.M. (November 2002). "A Re-Examination of Fire Blight Epidemiology in England". Acta Horticulturae (590): 61–67. doi:10.17660/ActaHortic.2002.590.6.
↑ Beer, Steven V.; Norelli, John L. (1977). "Fire Blight Epidemiology: Factors Affecting Release of Erwinia Amylovora by Cankers". Phytopathology. 77 (9): 1119–1125. doi:10.1094/Phyto-67-1119.
↑ Billing, Eve (2007). "Challenges in Adaptation of Plant Disease Warning Systems to New Locations: Re-Appraisal of Billing's Integrated System for Predicting Fire Blight in a Warm Dry Environment". Phytopathology. 97 (9): 1036–1039. doi:10.1094/PHYTO-97-9-1036. PMID18944167.
1 2 Norelli, John L.; Jones, Alan L.; Aldwinckle, Herb S. (July 2003). "Fire Blight Management in the Twenty-first Century: Using New Technologies that Enhance Host Resistance in Apple". Plant Disease. 87 (7): 756–765. doi:10.1094/PDIS.2003.87.7.756. PMID30812883.
↑ Ohlendorf, Barbara (1999). Integrated Pest Management for Apples & Pears (2nded.). University of California, Agriculture and Natural Resources. ISBN978-1-879906-42-6.[pageneeded]
↑ Midwest Fruit Workers Group; Babadoost, Mohammad; (University of Illinois, plant pathology); Wahle, Elizabeth; (University of Illinois, horticulture); Hannan, Joseph; (Iowa State University, horticulture); Onofre, Rodrigo; (University of Kansas, plant pathology); Gauthier, Nicole W.; (University of Kentucky, plant pathology); Smigell, Chris; (University of Kentucky, plant pathology); Wright, Shawn; (University of Kentucky, horticulture); Klodd, Annie; (University of Minnesota, horticulture); Beckerman, Janna; (Purdue University, plant pathology); Bordelon, Bruce; (Purdue University, horticulture); Haas, Megan Heller; (Purdue University, plant pathology); Meyers, Stephen; (Purdue University, horticulture); Tucker, Tristand; (Purdue University, horticulture); Guedot, Christelle; (University of Wisconsin, entomology); Holland, Leslie; (University of Wisconsin, plant pathology). Beckerman, Janna; (Purdue University, Co-Editor-in-Chief); Rodriguez-Salamanca, Lina; (Iowa State University, Co-Editor-in-Chief); Athey, Kacie; (University of Illinois, entomology); Long, Elizabeth; (Purdue University, entomology); Bessin, Ric; (University of Kentucky, entomology); Strang, John; (University of Kentucky, horticulture); Guedot, Christelle; (University of Wisconsin, entomology); Lewis, Donald; (Iowa State University, entomology); Lewis-Ivey, Melanie; (Ohio State University, plant pathology); Welty, Celeste; (Ohio State University, entomology) (eds.). "Midwest Fruit Pest Management Guide 2021-2022"(PDF). Archived from the original(PDF) on 2021-03-04.{{cite web}}: |editor2= has generic name (help)
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