Fire blight

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Fire blight
Apple tree with fire blight

Apple tree with fire blight

Systematics
Department : Proteobacteria
Class : Gammaproteobacteria
Order : Enterobacterales
Family : Enterobacteriaceae
Genre : Erwinia
Type : Fire blight
Scientific name
Erwinia amylovora
( Burrill 1882) Winslow et al. 1920

Fire blight is a dangerous plant disease caused by the Erwinia amylovora bacterium . It mainly affects pome fruit plants and can spread quickly like an epidemic. There is no danger to human health.

pathology

Pathogen

The causative agent of the fire blight is the enterobacterium Erwinia amylovora . The rod-shaped bacterium is flagellated evenly over its cell surface , is gram-negative and viable even in the absence of air . The optimal growth temperature is between 21 and 28 ° C; the minimum and maximum temperatures for this bacterium to develop are between 3 and 12 ° C and between 32 and 42 ° C.

Routes of infection

Due to the high potential for infection, there are a variety of potential vectors for spread.

The bacteria penetrate the plant tissue during the active growth of the plant via natural entry ports such as stomata , lenticels and nectaries or via wounds on leaves , shoots or twigs . There are therefore three types of infection:

  • Flower infection ( English Blossom blight ) - most common variant
  • Drive infection ( shoot blight )
  • Infection from infected areas that become active again ( canker blight )

infection

Gram-negative bacteria such as fire blight form a needle-like structure (the pilus ) with which they penetrate the cells of apple plants and inject effector proteins that block parts of the plant's immune system . If the plant does not recognize the effector protein, it cannot initiate a defense mechanism and becomes infected.

The dangerous time of infection is spring and summer, especially the flowering time when the weather is warm and humid: the flowers are then the main points of infection, the spread of insects is high and the germ has good conditions to multiply so strongly that it naturally grows can overcome existing defenses and penetrate the plant.

Clinical picture

Infested apple
Tree that has been marked for felling by the authorities (Tyrol)

The symptoms of fire blight are expressed by the fact that leaves and flowers of infected plants suddenly wilt from the petiole and turn brown or black. The shoot tips curve downwards like a hook due to the loss of water. The plant looks like it has been burned (hence the name "fire blight").

Young plants die within two to three weeks. In older plants, the disease spreads within one or more years and leads to their death. A laboratory examination is necessary for a clear diagnosis .

In addition, a bacterial mucus escapes at the infection sites , and in winter the bark can sink in ( canker sites).

The severity of the infestation of the plant depends on various factors and their interaction. These are: climatic and location conditions, plant type - in the case of cultivated plants also the variety - and their vitality, bacterial density on the plant and its surroundings, cultivation measures.

Epidemiology

The host plant circle

The host plant circle of the fire blight pathogen includes around 174  species from 40  genera in the rose family (Rosaceae). The subfamily of the pome fruit family (Pyrinae) is particularly susceptible ; it is considered to be the main host plant group, because the pathogen can only hibernate in these species .

The most susceptible hosts are:

The service tree (Sorbus torminalis) may also be affected by fire blight. To date, however, no infestation has been detected.

Of the apple varieties that have proven to be robust, for example, Schöner from Boskoop or McIntosh . In the meantime, however, resistant varieties are also being bred, such as Enterprise or Remo , as well as the Harrow Sweet variety for pears .

distribution

Spread of the fire blight 2007
Source: AGES

The fire blight was first observed in America about 200 years ago .

In 1957 the disease reached Europe, where it spread from southern England across the entire European continent. It was first detected in Austria in 1993 in Vorarlberg and in 2001 in South Tyrol . Until 2006, it spread mostly as a result of the transport of infected plants to the whole of Austria and also to Germany , Switzerland and northern Italy .

In 2007 the fire blight was already widespread in almost all European countries, in the Middle East and Egypt , North America to Central America , and New Zealand . In 2007 the infection spread across Europe, particularly in apple growing. In Switzerland, the cantons of eastern and central Switzerland and the Lake Constance region are particularly hard hit. In the Lake Constance region - in the Swiss canton of Thurgau , in the south of the German district of Lindau and in Vorarlberg in Austria - at least two thirds of all orchards are affected. Even Salzburg , Upper Austria and Styria were severely affected, and in all other Austrian provinces cases have occurred.

Countermeasures

Quarantine and mandatory reporting

Any spread of the germ is controlled internationally and nationally primarily through quarantine measures and trade restrictions .

The Community law of the European Union does not provide for a uniform procedure for fighting fires. Council Directive 2000/29 / EC on measures to protect against the introduction and spread of harmful organisms in plants and plant products provides for the establishment of protected areas that are not yet contaminated and the possibility of designating buffer zones of around 50 square kilometers around important ones Production facilities in which regular official inspections and the keeping of a ZP plant passport (zona protecta) for host plants are mandatory. However, this measure has not proven to be very effective in practice because fire blight usually occurs epidemically in an entire region. Since Erwinia amylovora is a quarantine pathogen , there are different national requirements as to whether the respective plant protection service should be informed about it.

In Germany, the occurrence and suspicion of fire blight have been reportable since 1985. The competent authority (depending on the federal state, the state office or the state agency for agriculture) can order a quarantine zone of 5 kilometers around infested or suspected land; In this "demarcated area", for example, it can order the destruction of infested and highly susceptible host plants or the ban on beekeeping and even order that land be cleared and kept free of host plants that have not yet been infested.

Even in case of suspicion - - In Austria and South Tyrol any occurrence is fire blight reporting requirements , generally both owners and other authorized to dispose of land with host plants in commercial distributors of plants and plant products, as well as anyone who infested plants or plant parts holds . The contacts are fire blight officers from the municipalities.

There is also an obligation to report suspicions in Switzerland, as an EPPO member in accordance with the regulations on protection and buffer zones and the plant passport. In addition, there are also bans on the import, production and marketing of certain host plants. To this end, inspections are carried out every year in the municipalities of eastern Switzerland to check the tree population for symptoms.

This disease has never occurred in Australia. To prevent the disease from being introduced into the country, the country had imposed an import ban on apples since 1921. New Zealand, however, filed a lawsuit against Australia with the World Trade Organization's Arbitration Court on August 20, 2007 . In 2010 the WTO ruled in favor of New Zealand in two instances in this lawsuit.

Cutting and clearing

The fire blight is caused by a highly infectious bacterium. Infested lower trunks in particular are endangered by their small crown. If the infected parts and the safety margin (cut into the healthy wood) are carried out correctly, this often corresponds to almost complete clearing . High trunks are initially more robust due to their large mass; the removal of an equally large infested area still leaves a tree with only slightly restricted function. Possibly rarer, old varieties can also be found in standard trunks, which under certain circumstances can also show variety-dependent resistances. In the majority of cases, some standard apple trees are free of pathogens in the following year (provided they are not attacked by renewed flower infections). Little is known about wild plants.

Pesticides

Streptomycin

The antibiotic streptomycin is used for prevention in some countries . This reduces the fire blight by around 80%. Its use is controversial because streptomycin has been detected in honey and because resistance from the pathogen and cross effects in other germs are feared.

In Germany, the Julius Kühn Institute (before 2008 Biological Federal Institute ), fruit growing , beekeeping and environmental associations have had a consensual strategy for combating fire blight in fruit growing without antibiotics since 2003 , which was extended for the period 2008–2012. In the context of alternative research to streptomycin, various yeast preparations, most recently in particular Candida sake, have been developed as almost equivalent substitutes. Nevertheless, there is still a considerable need for research. Streptomycin has been used in Germany since 2003; it is no longer permitted as a plant protection product.

So far, it has been banned in Switzerland. In 2007, in the context of a severe fire blight, there were violent disputes between standard fruit growers and representatives of cantonal authorities who wanted to enforce the clearing of standard trees. After fire blight attack caused damage of more than 30 million francs in 2007, the Swiss Federal Office for Agriculture wants to allow a locally limited and temporary use of streptomycin for spring 2008. Targeted use on low-stem fruit crops requiring a permit may only be carried out. The use of streptomycin outside of commercial fruit growing is generally prohibited, as is its use on standard fruit crops. Clearing was still carried out here in 2011. Streptomycin is prohibited in organic fruit growing.

This measure is also being discussed in Austria, but met with resistance due to the high market share of organic products , and the associations and trademarks announced that they would suspend recognition as an organic producer if the producer uses the antibiotic. Whether it is actually used will be decided by the damage in the 2008 season (spread due to the weather conditions at the time of flowering). Streptomycin is used in Austria.

LMA (potash alum)

LMA is the trade name for potassium aluminum sulfate ( aluminum potassium sulfate dodecahydrate ), which has a bactericidal effect and thus prevents infection. The application is more complex than that of streptomycin, since the water-soluble powder has to be pre-dissolved outside the syringe .

LMA was approved in Germany for the years 2013 to 2019 as approval for emergency situations in accordance with Article 53 of Regulation (EC) No. 1107/2009 (Plant Protection Product Ordinance) for the period from April 1 to July 29.

Genetic engineering

Since some wild apple varieties are resistant to fire blight, attempts have been made to cross the corresponding resistance genes into popular apple varieties. However, this process is very time-consuming because it takes at least 5 generations, i.e. H. 20 to 50 years of age, has to breed in order to select away undesirable properties such as small fruits without losing the resistance gene. With the help of green genetic engineering , however, it is possible to transfer resistance genes from wild apples to popular edible apples in just a few years. In contrast to transgenic trees, in which foreign genes would be transferred, these cisgenic apple trees could have a higher level of consumer acceptance or also be subject to less strict regulation by the authorities. Joint research by ETH Zurich , the Agroscope Research Station and the Julius Kühn Institute has shown that the fire blight resistance gene can be successfully transferred from the Siberian crab apple to the Gala apple variety . In 2016, the Agroscope research institute in Switzerland was granted a license by the Federal Office for the Environment ( FOEN ) to test the properties of this cisgenic apple in field trials until 2021. The successful cultivation of the cisgenic apple trees is documented in a first interim report from November 2018.

literature

  • BBA Federal Agency for Agriculture and Forestry (Ed.): A threat to orchard cultivation: The fire blight / An investigation as part of the federal organic farming program. Berlin / Braunschweig 2003.
  • Wolfgang Zeller (edit.): Scientific conference on fire blight. Ladenburg, June 13-14, 1991 . (= Information from the Federal Biological Research Center for Agriculture and Forestry, Berlin-Dahlem. Issue 282). Parey, Berlin / Hamburg 1992, ISBN 3-489-28200-0 .
  • J. Mayr: The flight of fire blight host plants by bees. Diploma thesis. University of Natural Resources and Life Sciences, Vienna 2004.
  • M. Pfattner: Fire blight in South Tyrol. An investigation into the danger and endangerment of autochthonous fire blight host plants in the forest. Diploma thesis. University of Natural Resources and Life Sciences, Vienna 2005.
  • CEA Winslow, J. Broadhurst, RE Buchanan, C. Krumwiede Jr., LA Rogers, GH Smith: The families and the genera of the bacteria. Final report of the Committee of the Society of American Bacteriologists on characterization and classification of bacterial types. In: Journal of Bacteriology. 5, 1920, pp. 191-229.

Web links

Commons : Feuerbrand  - Collection of images, videos and audio files

Individual evidence

  1. ↑ a b c d e f g h i j k l m n o p q r s t u v w x y z Recognize the danger - fight the danger. AGES, archived from the original on June 10, 2008 ; Retrieved April 26, 2008 .
  2. ↑ a b c d Plant diseases - fire blight - home garden. ACW, archived from the original on April 13, 2009 ; Retrieved April 26, 2008 .
  3. ↑ a b c d e f g h i j k l m n Fire blight susceptibility of pome fruit varieties. (No longer available online.) In: Plant diseases - Fire blight - Standard trees and nature conservation. ACW, 2007, archived from the original on December 14, 2013 ; accessed on December 31, 2014 .
  4. ↑ a b c Recommendations for promoting wild fruit and hawthorn despite the risk of fire blight. (PDF) (No longer available online.) In: Merkblatt Vollzug Umwelt. BUWAL, 2004, archived from the original on April 2, 2015 ; Retrieved April 26, 2008 .
  5. ↑ Bacterial fire blight of the Rosaceae . wsl.ch. Accessed June 1, 2020.
  6. ↑ a b oug.de: Apple varieties resistant to fire blight (PDF)
  7. ↑ Orchards info . In: ARGE Streuobst (ed.): Circular . No. 2 , 2007, p. 1–17 ( PDF [accessed April 26, 2008]).
  8. ↑ Explanation of the AGES regarding the establishment of fire blight buffer zones in areas not recognized as protected areas. (PDF) AGES, November 2007, accessed on August 22, 2016 .
  9. ↑ Ernst Pfeilstetter: Fire blight in the EU - new provisions for deliveries of host plants to protected areas. (PDF) (No longer available online.) Federal Biological Research Center for Agriculture and Forestry, Plant Health Department, Braunschweig, 2004, archived from the original on July 8, 2007 ; Retrieved April 26, 2008 .
  10. ↑ Ordinance on Combating Fire Blight Disease ( Fire Blight Ordinance ) of December 20, 1985, last amended on October 10, 2012
  11. ↑ according to § 6 paragraph 1 no. 3 of FeuerbrandV
  12. ↑ Fire blight ordinances and fire blight decrees of the federal states: Search term for queries that are available for the individual federal states at http://ris2.bka.gv.at/Land/ , ris.bka
  13. ↑ State Law No. 1/2003, Resolution of the State Government No. 746/2005: Suspected Infection - What to Do? In: General information> Fire blight> Suspected infestation. Autonomous Province of Bolzano, accessed April 26, 2008 .
  14. ↑ Plant passport : What you need to know about it. JardinSuisse, Swiss Gardeners Association, accessed on April 26, 2008 .
  15. ↑ Plants that are prohibited for import. In: Plants, cut flowers and species protection CITES. Federal Customs Administration FCA, accessed on December 31, 2014 .
  16. ↑ n-tv.de, New Zealand sues Australia - apple dispute escalates , August 20, 2007
  17. ↑ WTO: New Zealand is allowed to export apples to Australia. Agricultural Information Service, August 13, 2010, accessed October 13, 2018 .
  18. ↑ Australia is defeated in the apple dispute with New Zealand. Agricultural Information Service, November 30, 2010, accessed October 13, 2018 .
  19. ↑ retrieved from the BVL overview list , as of July 2019.
  20. ↑ Tages-Anzeiger : Mit Chemie gegen Feuerbland ( Memento from May 9, 2009 in the Internet Archive ) from January 29, 2008.
  21. ↑ Fire blight: Trade wants unsprayed fruit. ORF Tirol, April 15, 2008, accessed on April 25, 2008 .
  22. ↑ Abstract: Discussion about the use of streptomycin against fire blight. StreamOnTheFly, medienarchiv.fh-stpoelten.ac.at, archived from the original on May 9, 2009 ; accessed on December 31, 2014 .
  23. ↑ David Szalatnay: LMA / potassium aluminum sulfate - an overview of the current state of knowledge. Strickhof Fachstelle Obst, April 8, 2014, accessed on December 31, 2014 .
  24. ↑ Approvals for emergency situations. (No longer available online.) BVL , November 26, 2014, archived from the original on January 7, 2015 ; accessed on December 31, 2014 . , BVL list of approvals for emergency situations (accessed in August 2019), approval 2019
  25. ^ Thomas D. Kost et al .: Development of the First Cisgenic Apple with Increased Resistance to Fire Blight. In: PLoS ONE 10 (12), December 1, 2015: e0143980. doi: 10.1371 / journal.pone.0143980
  26. ↑ Cisgenic apple trees with improved fire blight resistance. In: admin.ch. Agroscope , accessed on November 27, 2018 .
  27. ↑ Field test with a fire blight resistant cisgenic "Gala" line. Agroscope , accessed on November 27, 2018 .