Fire blight

Fire blight
Scientific classification
Domain: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Enterobacterales
Family: Erwiniaceae
Genus: Erwinia
Species:
E. amylovora
Binomial name
Erwinia amylovora
(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.

The causal pathogen is Erwinia amylovora,[1] a Gram-negative bacterium in the order Enterobacterales. Pears are the most susceptible, but apples, loquat, crabapples, quinces, 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.[2] It has been a major reason for a long-standing embargo on the importation of New Zealand apples to Australia.[3] 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.[4] In Europe it is listed as a quarantine disease, and has been spreading along Hawthorn (Crataegus) hedges planted alongside railways, motorways and main roads.

History

In the early 1800s, E. amylovora was the first bacterium that could be used in experiments to demonstrate that it did indeed cause disease in plants. It is accepted that this destructive crop bacterium had initially originated in North America. Today, E. amylovora can currently be found in all the provinces of Canada, as well as in some parts of the United States of America; states include Alabama, California, Colorado, Connecticut, Georgia, Illinois, Maine, Maryland, Massachusetts, Michigan, New York, North Carolina, Ohio, Oregon, Pennsylvania, Texas, Utah, Virginia, Washington, West Virginia and Wisconsin. In the Americas it also occurs in other countries including, but not limited to, Mexico and Bermuda. On the African continent, E. amylovora has been confirmed in Egypt.

It is believed that the pathogen was first introduced into Northern Europe through bacterial ooze from fruit containers in the 1950s, imported from the USA.[5] During the 1950s-1960's, E. amylovora had spread through much of Northern Europe, yet leaving large areas of Germany and France seemingly untouched by the disease of which the bacteria cause a devastating disease known as "fireblight". This was short lived, as the disease and E. amylovora were discovered in the later 1990s in Germany. Nonetheless by the 1980s the E. amylovora bacteria had been found in the Eastern Mediterranean, although its appearance in this region is thought to be an isolated appearance and not as a result of local transmission. Finally from the years 1995-1996 cases of fireblight had begun to be reported in countries such as Hungary, Romania, Northern Italy and Northern Spain.

Dissemination

Gala apple branch with “scorched” leaves after a severe fire blight infection.

Erwinia amylovora overwinter in cankers formed during the previous season, serving as the primary inoculum. Bacteria exude from ooze in the spring when temperatures support optimal development.[6] The factors that determine whether or not cankers become active are not well known, but it is thought that cankers found on larger tree limbs are more likely to become active. It is also thought that age may be a factor.[7] Honeybees and other insects are attracted to bacterial ooze and can spread bacteria to susceptible tissue, such as flower stigmata.[8] Birds, rain and wind can also transmit the bacterium to susceptible tissue. Upon reaching the stigma further colonisation will be heavily decided by temperature. 21–27 °C (70–81 °F) is most favourable. Rain or heavy dew will allow procession further into the nectaries – this is the microscopic cause of the macroscopic blossom blight symptom. Flowers one to three days old are more susceptible than are those five to eight days old. See Curry 1987 for the source and further review of this subject.[9]

Injured tissue is also highly susceptible to infection, including punctures and tears caused by plant-sucking or biting insects. Hailstorms 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 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. 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 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 over fertilization (especially with nitrogen) can lead to water sprout and other midsummer growth that leave the tree more susceptible.

Erwinia amylovora typically makes its entry into its host xylem or cortical parenchyma. It can also enter through stomata, lenticels and hydathodes. It is dispersed by rain and or insects naturally, but this mode of dispersal is very ineffective and can only be effective for local transmission of the pathogen. Aerosols are also suspected in playing a role in its transmission due to the detection of E. amylovora in Mediterranean regions. In composition the pathogen is composed of short rods with rounded ends made motile by many peritrichous flagellae. E. amylovara is a gram negative bacterium (as stated above).

Fire blight microorganisms are spread through different effectively means also, for example, downpour or water sprinkling, bugs, and winged animals, other tainted plants, and unclean cultivating instruments. The most extreme danger of presentation to this bacterium is pre-summer or late-spring as it rises up out of dormancy. Shockingly, there is no solution for fire blight; in this way, the best fire blight cures are standard pruning and expulsion of any tainted stems or branches. It might likewise assist with staying away from the overhead water system, as water sprinkling is one of the most well-known approaches to spread the disease. There should be cautious attention towards the digging tools, particularly those that have been exposed to the microscopic organisms. The 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. Continuously make a point to altogether dry the tools to forestall corrosion. It can also help with assisting to oil them down also.[10]

The fly Delia platura has been observed visiting fire blight wounds to feed but was unconfirmed as an effective vector. Eventually it was demonstrated that D. platura does successfully transmit fire blight to already damaged apple shoots.[11] Fire blight exopolysaccharide also served as the adhesive to attach propagated cells to D. platura.[11] D. platura shed fire blight at a constant rate[11] - and did not suffer from doing so - for at least five days.[11]

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.[12] 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 can not produce amylovoran it is not pathogenic and can not 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.[13] Since E. amylovora is not an obligate biotroph, it is able to survive outside the host which allows it to spread in many ways such as rain.

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.[14] This results in a dull, gray-green appearance at 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 when the environment is high in humidity. Shoots show similar symptoms but develop much more rapidly. A “Shepherd's Crook” can be seen when the tip of the shoot wilts, and diseased shoot leaves typically have blackening along the mid-vein and then die. In number, diseased shoots give the tree a blighted appearance. Initial infection of blossoms and shoots can spread to larger tree limbs. Branches will darken and become water soaked. Advanced infection develops cracks in bark and a sunken surface. Wood under the bark will become streaked with black discoloration. Immature fruit forms water-soaked lesions and later turned black. Bacterial ooze can be found on these lesions. Severe infections result in fruit turning entirely black and shriveling.[15]

Management

Spraying plants with either streptomycin, copper sulfate or both have been used in some parts of the world, such as the USA, in an attempt to prevent new infections, but being only effective into slowing or temporarily stopping growth in already diseased plants.[16] 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.[16] 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.[17] There is no known cure; prevention is the key.[18]

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.[19][20]

E. amylovora generally needs to be destroyed externally, before it enters the cell. This is because once it enters the host, it spreads during the endophytic phase of pathogenesis. Once this happens external control methods become ineffective. The ideal control method is to apply copper and antibiotics to the plant externally. This is the only effective method and it is indeed preventative. Currently it has been noted that E. amylovora has developed a resistance to the antibiotic streptomycin, as do most bacteria due to their flexible ability to transfer preferential genes promoting resistance to antibiotics horizontally from species to species.[21]

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.[22] 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.

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.

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.[23]

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.[15]

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.[24]

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.[25]

Importance

Besides the historical importance of being the first bacterium proven to be a plant pathogen, it is extremely economically important.[15] Control and loss costs are estimated approximately $100 million a year in the USA. Specifically, in Michigan in the year 2000, $42 million in losses is estimated because of the removal of about 400,000 apple trees.[26] Warm, humid, and wet weather in May resulted in this epidemic. While approximately $68 million is estimated in losses in Washington and northern Oregon. E. amylovora is spread all through the USA and worldwide causing severe damage although it is unlikely to cause severe damage in northern Europe. 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 that has been passed down for several generations.[27] 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.

A predetermined number of apple cultivars are answerable for an enormous extent of yearly creation. Shoppers and general stores prize these cultivars for their appearance, quality, flavor, and storability, while cultivators additionally esteem their plantation attributes and prepared market coming about because of purchaser request. To hold the desirable qualities of a fruiting cultivar while presenting malady opposition qualities through ordinary reproducing techniques is for all intents and purposes unimaginable due to apple's heterozygosity, long age time, and self-incongruence. Hereditary designing offers an appealing option since it can possibly give quicker outcomes, 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.[28]

References

  1. ↑ Type strain NCPPB 683 Archived 2012-07-11 at WebCite (dead link 3 December 2019)
  2. ↑ "Australia, New Zealand trade insults over fire blight. (tree disease)". Agra Europe. May 23, 1997.
  3. ↑ "Local apple producers say no to Kiwis' fruit". Australian Broadcasting Corporation. 2010-04-13. Retrieved November 11, 2014.
  4. ↑ Helm, Leslie; Eisenstodt, Gale (July 22, 1996). "Caught in Cross-Fire of Pacific Apple War". Los Angeles Times. Retrieved August 9, 2010.
  5. ↑ 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.
  6. ↑ van der Zwet, Tom; Keil, Harry L (1979). Fire Blight: a bacterial disease of rosaceous plants. U.S. Department of Agriculture. OCLC 256060652.
  7. ↑ 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.
  8. ↑ Thomson, S. V. (1986). "The role of the stigma in fire blight infections". Phytopathology. 76 (5): 476–482. doi:10.1094/Phyto-76-476.
  9. ↑ Malnoy, Mickael; Martens, Stefan; Norelli, John L.; Barny, Marie-Anne; Sundin, George W.; Smits, Theo H.M.; Duffy, Brion (2012-09-08). "Fire Blight: Applied Genomic Insights of the Pathogen and Host". Annual Review of Phytopathology. Annual Reviews. 50 (1): 475–494. doi:10.1146/annurev-phyto-081211-172931. ISSN 0066-4286.
  10. ↑ "StackPath".
  11. 1 2 3 4 Boucher, Matthew; Collins, Rowan; Harling, Kayli; Brind'Amour, Gabrielle; Cox, Kerik; Loeb, Greg (January 2021). "Interactions Between Delia platura and Erwinia amylovora Associated with Insect Mediated Transmission of Shoot Blight". PhytoFrontiers. 1 (1): 62–74. doi:10.1094/phytofr-08-20-0013-r.
  12. ↑ Piqué, Núria; Miñana-Galbis, David; Merino, Susana; Tomás, Juan (5 June 2015). "Virulence Factors of Erwinia amylovora: A Review". International Journal of Molecular Sciences. 16 (12): 12836–12854. doi:10.3390/ijms160612836. hdl:2445/67259. PMC 4490474. PMID 26057748.
  13. ↑ Vrancken, K.; Holtappels, M.; Schoofs, H.; Deckers, T.; Valcke, R. (1 May 2013). "Pathogenicity and infection strategies of the fire blight pathogen Erwinia amylovora in Rosaceae: State of the art". Microbiology. 159 (5): 823–832. doi:10.1099/mic.0.064881-0. PMID 23493063. S2CID 10127630.
  14. ↑ Schroth, M.N. (2010). "Fire Blight of Apple and Pear" (PDF). plantdiseases.org. Archived (PDF) from the original on January 18, 2020. Retrieved January 17, 2020.
  15. 1 2 3 Johnson, K. B. (2000). "Fire blight of apple and pear". The Plant Health Instructor. doi:10.1094/PHI-I-2000-0726-01.
  16. 1 2 Iljon, Tzvia; Stirling, Jenna; Smith, Robert J. (2012). "A mathematical model describing an outbreak of fire blight" (PDF). In Mushayabasa, Steady; Bhunu, Claver P. (eds.). Understanding the Dynamics of Emerging and Re-Emerging Infectious Diseases Using Mathematical Models. pp. 91–104. ISBN 978-81-7895-549-0.
  17. ↑ "Fireblight: Symptoms, Causes and Treatment". University of Georgia. Retrieved November 13, 2014.
  18. ↑ "Fire Blight". Colorado State University. Retrieved November 13, 2014.
  19. ↑ Schouten, Henk J. (1991). Studies on fire blight (Thesis).
  20. ↑ 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. PMID 18944167.
  21. ↑ "Superbug, super-fast evolution". evolution.berkeley.edu. April 2008. Retrieved 2016-12-12.
  22. ↑ Aćimović, Srđan G.; Zeng, Quan; McGhee, Gayle C.; Sundin, George W.; Wise, John C. (10 February 2015). "Control of fire blight (Erwinia amylovora) on apple trees with trunk-injected plant resistance inducers and antibiotics and assessment of induction of pathogenesis-related protein genes". Frontiers in Plant Science. 6: 16. doi:10.3389/fpls.2015.00016. PMC 4323746. PMID 25717330.
  23. ↑ 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. PMID 30812883.
  24. ↑ Ohlendorf, Barbara (1999). Integrated Pest Management for Apples & Pears (2nd ed.). University of California, Agriculture and Natural Resources. ISBN 978-1-879906-42-6.
  25. ↑ 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)
  26. ↑ Aćimović, Srđan G.; Zeng, Quan; McGhee, Gayle C.; Sundin, George W.; Wise, John C. (2015). "Control of fire blight (Erwinia amylovora) on apple trees with trunk-injected plant resistance inducers and antibiotics and assessment of induction of pathogenesis-related protein genes". Frontiers in Plant Science. 6: 16. doi:10.3389/fpls.2015.00016. PMC 4323746. PMID 25717330.
  27. ↑ "Erwinia Amylovora (fireblight)." The Centre for Agriculture and Bioscience International. N.p., n.d. Web. 15 Nov. 2016.
  28. ↑ 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. PMID 30812883.
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