Editing Fusarium ear blight

{{Short description|Fungal disease of cereals}}
[[Image:Wheat scab.jpg|180px|thumb|right|Symptom on wheat caused by ''F. graminearum'' (right: inoculated, left: non-inoculated)]]
'''Fusarium ear blight''' ('''FEB''') (also called '''Fusarium head blight''', '''FHB''', or '''scab'''), is a [[fungus|fungal]] disease of [[cereal]]s, including wheat, barley, oats, rye and triticale.<ref name=":0">{{Cite journal|last1=Parry|first1=D. W.|last2=Jenkinson|first2=P.|last3=McLeod|first3=L.|year=1995|title=Fusarium ear blight (scab) in small grain cereals—a review|journal=Plant Pathology|language=en|volume=44|issue=2|pages=207–238|doi=10.1111/j.1365-3059.1995.tb02773.x|issn=1365-3059}}</ref> FEB is caused by a range of ''[[Fusarium]]'' fungi, which infects the heads of the crop, reducing grain yield. The disease is often associated with contamination by [[mycotoxin]]s produced by the fungi already when the crop is growing in the field. The disease can cause severe economic losses as mycotoxin-contaminated grain cannot be sold for food or feed.

==Causal organism==
Fusarium ear blight is caused by several species of ''[[Fusarium]]'' fungi, belonging to the [[Ascomycota]]. The most common species causing FEB are:<ref name=":0" />
* ''[[Gibberella avenacea|Fusarium avenaceum]]'' ([[Teleomorph, anamorph and holomorph|teleomorph]]: ''Gibberella avenacea'')
* ''[[Fusarium culmorum]]''
* ''[[Gibberella zeae|Fusarium graminearum]]'' (teleomorph: ''Gibberella zeae'')
* ''[[Fusarium poae]]''
* ''[[Microdochium nivale]]'' (teleomorph: ''Monographella nivalis'', formerly ''Fusarium nivale'')
* ''[[Fusarium tricinctum]]''<ref>{{cite journal |last1=Wang |first1=Yun |last2=Wang |first2=Ruoyu |last3=Sha |first3=Yuexia |title=Distribution, pathogenicity and disease control of ''Fusarium tricinctum'' |journal=  Frontiers in Microbiology|date=26 July 2022 |volume=13 |page=939927 |doi=10.3389/fmicb.2022.939927|pmid=35958126 |pmc=9360978 |doi-access=free }}</ref>
''Fusarium graminearum'' was considered the most important causal organism.<ref name=":2">{{Cite journal|title=Fusarium head blight (FHB) or scab|url=http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/Fusarium.aspx|journal=APSnet Feature Articles|doi=10.1094/phi-i-2003-0612-01|year=2003|access-date=2011-12-21|archive-date=2012-02-03|archive-url=https://web.archive.org/web/20120203195337/http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/Fusarium.aspx|url-status=dead}}</ref> 
[[File:F.graminearum.JPG|thumb|Macroconidia of ''F''. ''graminearum'']]

''Fusarium'' species causing FEB can produce several types of [[spore]]s. The asexual stage of the fungus produces spores called [[Conidium|macroconidia]]. Some ''Fusarium'' fungi have a more complex life cycle including a [[Teleomorph, anamorph and holomorph|sexual stage]], for example ''F. graminearum''. In the sexual stage the fungus produces spores called ascospores. The sexual stage form fruiting bodies called perithecia, in which ascospores are formed in a sac known as an ascus (plural asci).<ref name=":2" /> Some species, including ''F. culmorum,'' produce resistant chlamydospores which can survive for a long time in the soil.

== Disease cycle and epidemiology ==
''Fusarium'' fungi can overwinter as [[saprotrophs]] in the soil or on crop debris that can serve as [[wikt:inoculum|inoculum]] for the following crop. The fungus can also spread via infected seed. The presence of ''Fusarium'' fungi on crop debris or seed can cause ''Fusarium'' seedling blight and foot and [[Common root rot (wheat)|root rot]].<ref name=":0" /> Later, infection of the heads can occur with spores spreading by rain splash from infected crop residues. Another major infection route is airborne inoculum as spores can travel long distances with the wind.<ref>{{Cite journal|last1=Keller|first1=Melissa D.|last2=Bergstrom|first2=Gary C.|last3=Shields|first3=Elson J.|date=2014-06-01|title=The aerobiology of Fusarium graminearum|journal=Aerobiologia|language=en|volume=30|issue=2|pages=123–136|doi=10.1007/s10453-013-9321-3|bibcode=2014Aerob..30..123K |s2cid=84048532|issn=0393-5965}}</ref> The cereal crop is most susceptible at [[Anthesis|flowering]] and the probability of infection rises with high moisture and humidity at flowering.<ref name=":2" />

==Symptoms==
In wheat, ''Fusarium'' infects the head (hence the name "Fusarium head blight") and causes the kernels to shrivel up and become chalky white. Additionally, the fungus can produce [[mycotoxins]] that further reduce the quality of the kernel.

Infected florets (especially the outer glumes) become slightly darkened and oily in appearance. Macroconidia are produced in sporodochia, which gives the spike a bright pink or orange color. Infected kernels may be permeated with mycelia and the surface of the florets totally covered by white, matted mycelia.

== Mycotoxins ==
''Fusarium'' species associated with FEB produce a range of mycotoxins—fungal [[secondary metabolite]]s with toxic effects on animals. One mycotoxin can be produced by several ''Fusarium'' species, and one species can produce several mycotoxins. Important ''Fusarium'' mycotoxins include: 
* [[Vomitoxin|Deoxynivalenol]] (DON) produced by ''F''. ''graminearum'' and ''F''. ''culmorum''
* [[Zearalenone]] (ZEN) produced by ''F''. ''graminearum'' and ''F''. ''culmorum''
* HT-2 and T-2 produced by ''F''. ''langsethiae''
Fusarium toxins have negative effects on the immune, gastrointestinal and reproductive systems of animals.<ref>{{Cite journal|last1=D’Mello|first1=J.P.F.|last2=Placinta|first2=C.M.|last3=Macdonald|first3=A.M.C.|title=Fusarium mycotoxins: a review of global implications for animal health, welfare and productivity|journal=Animal Feed Science and Technology|volume=80|issue=3–4|pages=183–205|doi=10.1016/s0377-8401(99)00059-0|year=1999|citeseerx=10.1.1.453.2615}}</ref> DON is a protein synthesis inhibitor, also called vomitoxin, due to its negative effects on feed intake in [[Domestic pig|pigs]]. Pigs are the most sensitive to DON, while [[ruminant]] animals such as cattle have higher tolerance.<ref>{{Cite journal|last=Miller|first=J. David|date=2008-02-01|title=Mycotoxins in small grains and maize: Old problems, new challenges|journal=Food Additives & Contaminants: Part A|volume=25|issue=2|pages=219–230|doi=10.1080/02652030701744520|pmid=18286412|s2cid=32428433|issn=1944-0049|doi-access=free}}</ref>

Many countries monitor ''Fusarium'' mycotoxins in grain to limit negative health effects. In the U.S. there are advisory levels for DON in human food and livestock feed.<ref>{{Cite web|url=https://www.fda.gov/Food/GuidanceRegulation/GuidanceDocumentsRegulatoryInformation/ChemicalContaminantsMetalsNaturalToxinsPesticides/ucm120184.htm|title=Chemical Contaminants, Metals, Natural Toxins & Pesticides - Guidance for Industry and FDA: Advisory Levels for Deoxynivalenol (DON) in Finished Wheat Products for Human Consumption and Grains and Grain By-Products used for Animal Feed|last=Nutrition|first=Center for Food Safety and Applied|website=www.fda.gov|language=en|access-date=2017-03-13}}</ref> The [[European Union]] has legislative limits for several ''Fusarium'' mycotoxins in grain aimed for human consumption<ref>{{CELEX|32006R1881|text=Commission Regulation (EC) No 1881/2006 of 19 December 2006 setting maximum levels for certain contaminants in foodstuffs}}</ref> <sup>repealed by</sup> <ref>{{CELEX|32023R0915|text=Commission Regulation (EU) 2023/915 of 25 April 2023 on maximum levels for certain contaminants in food and repealing Regulation (EC) No 1881/2006}}</ref> and recommended limits for animal feed.<ref>{{CELEX|32006H0576|text=Commission Recommendation of 17 August 2006 on the presence of deoxynivalenol, zearalenone, ochratoxin A, T-2 and HT-2 and fumonisins in products intended for animal feeding}}</ref>

==Control measures==

=== Resistant cultivars ===
[[Plant disease resistance|Resistant cultivars]] could be the most efficient method to control Fusarium ear blight.<ref>{{Cite journal|last1=Steiner|first1=Barbara|last2=Buerstmayr|first2=Maria|last3=Michel|first3=Sebastian|last4=Schweiger|first4=Wolfgang|last5=Lemmens|first5=Marc|last6=Buerstmayr|first6=Hermann|date=2017-02-21|title=Breeding strategies and advances in line selection for Fusarium head blight resistance in wheat|journal=Tropical Plant Pathology|volume=42|issue=3|language=en|pages=165–174|doi=10.1007/s40858-017-0127-7|issn=1983-2052|doi-access=free}}</ref> Resistance [[Plant breeding|breeding]] involves screening of plant lines subjected to artificial inoculation with ''Fusarium''. Plant lines having reduced fungal growth and low levels of seed mycotoxin contamination are selected for additional breeding trials. In parallel, [[genetic marker]]s associated with resistance are screened for, so called [[marker-assisted selection]]. Fusarium ear blight resistance is a complex [[Phenotypic trait|trait]], involving several genes, and is dependent of interaction with the environment.<ref name=":3" /><ref>{{Cite journal|last1=Buerstmayr|first1=H.|last2=Ban|first2=T.|last3=Anderson|first3=J. A.|date=2009-02-01|title=QTL mapping and marker-assisted selection for Fusarium head blight resistance in wheat: a review|journal=Plant Breeding|language=en|volume=128|issue=1|pages=1–26|doi=10.1111/j.1439-0523.2008.01550.x|issn=1439-0523|doi-access=free}}</ref>

Fusarium ear blight resistance has been identified in wheat [[cultivar]]s from Asia. However, the challenge is to combine resistant material with other desirable traits such as high yield and adaptation to different growing areas.<ref name=":3">Bai GH, Shaner GE (2004) Management and resistance in wheat Bai GH, Shaner GE (2004) Management and resistance in wheat 42:135–161</ref>

=== Agricultural practices ===
Several [[agricultural practices]] affect the risk of FEB. One of the major infection routes are infected crop residues from the previous crop where both the quality and quantity are important. Crop residues from susceptible crops such as cereals increase the risk of FEB in the following crop. [[Maize]] has been associated with especially high risk.<ref>{{Cite journal|last1=Dill-Macky|first1=R.|last2=Jones|first2=R. K.|date=2000-01-01|title=The Effect of Previous Crop Residues and Tillage on Fusarium Head Blight of Wheat|journal=Plant Disease|volume=84|issue=1|pages=71–76|doi=10.1094/PDIS.2000.84.1.71|pmid=30841225|issn=0191-2917|doi-access=free}}</ref> Reduced [[Tillage|soil tillage]] can also increase the risk of FEB.<ref name=":2" /> The amount of crop residues can be reduced by [[plough]]ing, where residues are incorporated in the soil where they [[Decomposition|decompose]] faster.<ref>{{Cite journal|last1=Leplat|first1=Johann|last2=Friberg|first2=Hanna|last3=Abid|first3=Muhammad|last4=Steinberg|first4=Christian|date=2013-01-01|title=Survival of Fusarium graminearum, the causal agent of Fusarium head blight. A review|journal=Agronomy for Sustainable Development|language=en|volume=33|issue=1|pages=97–111|doi=10.1007/s13593-012-0098-5|s2cid=21709401|issn=1774-0746|url=https://hal.archives-ouvertes.fr/hal-01201382/file/13593_2012_Article_98.pdf}}</ref> High [[Fertilizer|nitrogen application]] has also been associated with increased risk of ''Fusarium'' infection.<ref>{{Cite journal|last1=Bernhoft|first1=A.|last2=Torp|first2=M.|last3=Clasen|first3=P.-E.|last4=Løes|first4=A.-K.|last5=Kristoffersen|first5=A. B.|date=2012-07-01|title=Influence of agronomic and climatic factors on Fusarium infestation and mycotoxin contamination of cereals in Norway|journal=Food Additives & Contaminants: Part A|volume=29|issue=7|pages=1129–1140|doi=10.1080/19440049.2012.672476|issn=1944-0049|pmc=3379782|pmid=22494553}}</ref> Preventive agricultural practices may be less effective if a lot of airborne inoculum is present in the area.<ref name=":2" />

=== Chemical control ===
[[Fungicide]]s can provide partial control of FEB but the effects may be variable.<ref name=":2" /> The type and timing of fungicide application is important as non-optimal applications may even increase ''Fusarium'' infection.<ref>{{Cite journal|last1=Henriksen|first1=B.|last2=Elen|first2=O.|date=2005-04-01|title=Natural Fusarium Grain Infection Level in Wheat, Barley and Oat after Early Application of Fungicides and Herbicides|journal=Journal of Phytopathology|language=en|volume=153|issue=4|pages=214–220|doi=10.1111/j.1439-0434.2005.00955.x|issn=1439-0434|doi-access=free}}</ref>

=== Biological control and integrated management ===
Research has also been put into development on [[Biological pest control|biological control strategies]] based on bacteria and fungi for example, ''[[Bacillus]]'' and ''[[Cryptococcus]]'' species''.''<ref>{{Cite journal|last1=Gilbert|first1=Jeannie|last2=Haber|first2=Steve|date=2013-04-01|title=Overview of some recent research developments in fusarium head blight of wheat|journal=Canadian Journal of Plant Pathology|volume=35|issue=2|pages=149–174|doi=10.1080/07060661.2013.772921|bibcode=2013CaJPP..35..149G |s2cid=83784062|issn=0706-0661}}</ref>

For FEB no control measure is completely effective and [[Integrated pest management|integrated management]] involving several control strategies such as preventive measures, disease monitoring and chemical control is necessary.<ref>{{Cite web|url=http://scabsmart.org/|title=ScabSmart {{!}} Management|website=scabsmart.org|language=en|access-date=2017-03-14}}</ref><ref>{{Cite book|url=https://www.food.gov.uk/sites/default/files/multimedia/pdfs/fusariumcop.pdf|title=The UK Code of Good Agricultural Practice to Reduce Fusarium Mycotoxins in Cereals|last=Food Standards Agency|year=2007|access-date=2017-03-14|archive-date=2017-03-15|archive-url=https://web.archive.org/web/20170315085650/https://www.food.gov.uk/sites/default/files/multimedia/pdfs/fusariumcop.pdf|url-status=dead}}</ref> Disease forecasting models have been developed to assess the risk of FEB depending on weather conditions.<ref>{{Cite web|url=http://www.wheatscab.psu.edu/riskTool_2010.html|title=Risk Map Tool|website=www.wheatscab.psu.edu|access-date=2017-03-14}}</ref>

== Economic importance ==
From an economic standpoint, it is one of the major [[cereal]] diseases, being responsible for significant grain yield reduction world-wide.

In the U.S. and Canada, Fusarium ear blight emerged in the 1990s as a widespread and powerful threat to cereal production.<ref name=":1">{{Cite journal|last1=McMullen|first1=Marcia|last2=Bergstrom|first2=Gary|last3=De Wolf|first3=Erick|last4=Dill-Macky|first4=Ruth|last5=Hershman|first5=Don|last6=Shaner|first6=Greg|last7=Van Sanford|first7=Dave|date=2012-07-11|title=A Unified Effort to Fight an Enemy of Wheat and Barley: Fusarium Head Blight|journal=Plant Disease|volume=96|issue=12|pages=1712–1728|doi=10.1094/PDIS-03-12-0291-FE|pmid=30727259|issn=0191-2917|doi-access=free}}</ref> From 1998 to 2000 the [[Midwestern United States]] suffered $2.7 billion in losses following a FEB epidemic.<ref>{{Cite web|url=https://www.ars.usda.gov/news-events/news/research-news/2010/diverse-wheat-tapped-for-antifungal-genes/|title=Diverse Wheat Tapped for Antifungal Genes : USDA ARS|website=www.ars.usda.gov|access-date=2017-03-05}}</ref> If we include primary and secondary economic losses, FHB cost the entire US$7.67 billion from 1993 to 2001.<ref name="Rawat-et-al-2016">{{cite journal | last1=Rawat | first1=Nidhi | last2=Pumphrey | first2=Michael O | last3=Liu | first3=Sixin | last4=Zhang | first4=Xiaofei | last5=Tiwari | first5=Vijay K | last6=Ando | first6=Kaori | last7=Trick | first7=Harold N | last8=Bockus | first8=William W | last9=Akhunov | first9=Eduard | last10=Anderson | first10=James A | last11=Gill | first11=Bikram S | title=Wheat Fhb1 encodes a chimeric lectin with agglutinin domains and a pore-forming toxin-like domain conferring resistance to Fusarium head blight | journal=[[Nature Genetics]] | publisher=[[Nature Research]] | volume=48 | issue=12 | date=2016-10-24 | issn=1061-4036 | doi=10.1038/ng.3706 | pages=1576–1580 | pmid=27776114 | s2cid=4177196}}</ref> Since 1990, extensive research has been put into the development of control measures of Fusarium ear blight. An example is the US Wheat and Barley Scab Initiative (USWBSI), a collaborative effort of scientists, growers, food processors and consumer groups aiming to develop effective control measures, including the reduction of mycotoxins.<ref name=":1" />

== See also ==
* [[Plant disease epidemiology]]
* [[Plant pathology]]

== References ==
{{Reflist}}

==External links==
* [http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/Fusarium.aspx American Phytopathology FHB site ] {{Webarchive|url=https://web.archive.org/web/20120203195337/http://www.apsnet.org/edcenter/intropp/lessons/fungi/ascomycetes/Pages/Fusarium.aspx |date=2012-02-03 }}

Return of an old problem: Fusarium head blight of small grains
* [http://www.apsnet.org/publications/apsnetfeatures/Pages/headblight.aspx http://www.apsnet.org/publications/apsnetfeatures/Pages/headblight.aspx] {{Webarchive|url=https://web.archive.org/web/20170315174356/http://www.apsnet.org/publications/apsnetfeatures/Pages/headblight.aspx |date=2017-03-15 }}

Fusarium head blight in Canada
* [http://www.grainscanada.gc.ca/guides-guides/identification/fusarium/iwbfm-mibof-eng.htm http://www.grainscanada.gc.ca/guides-guides/identification/fusarium/iwbfm-mibof-eng.htm]

United States Wheat and Barley Scab Initiative
* http://scabusa.org/

Fusarium Head Blight Risk Assessment Tool
* http://www.wheatscab.psu.edu/riskTool_2010.html

Scab Smart
* http://www.ag.ndsu.edu/scabsmart/

{{DEFAULTSORT:Fusarium Ear Blight}}
[[Category:Fusarium|*Fusarium Ear Blight]]
[[Category:Cereal diseases]]
[[Category:Wheat diseases]]
[[Category:Fungal plant pathogens and diseases]]