Fusarium ear blight (FEB) (also called Fusarium head blight, FHB, or scab), is a fungal disease of

cereal A cereal is any grass cultivated for the edible components of its grain (botanically, a type of fruit called a caryopsis), composed of the endosperm, germ, and bran. Cereal grain crops are grown in greater quantities and provide more food ...

s, including wheat, barley, oats, rye and triticale. FEB is caused by a range of ''

Fusarium ''Fusarium'' is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the soil mi ...

'' fungi, which infects the heads of the crop, reducing grain yield. The disease is often associated with contamination by

mycotoxin A mycotoxin (from the Greek μύκης , "fungus" and τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term '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 ''

'' fungi, belonging to the

Ascomycota Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defi ...

. The most common species causing FEB are: * '' Fusarium avenaceum'' ( teleomorph: ''Gibberella avenacea'') * '' Fusarium culmorum'' * '' Fusarium graminearum'' (teleomorph: ''Gibberella zeae'') * ''

Fusarium poae ''Fusarium'' is a large genus of filamentous fungi, part of a group often referred to as hyphomycetes, widely distributed in soil and associated with plants. Most species are harmless saprobes, and are relatively abundant members of the soil mi ...

'' * '' Microdochium nivale'' (teleomorph: ''Monographella nivalis'', formerly ''Fusarium nivale'') ''Fusarium graminearum'' is considered the most important causal organism.

''Fusarium'' species causing FEB can produce several types of

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

s. The asexual stage of the fungus produces spores called

macroconidia A conidium ( ; ), sometimes termed an asexual chlamydospore or chlamydoconidium (), is an asexual, non-motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also called mitospores due to ...

. Some ''Fusarium'' fungi have a more complex life cycle including a 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). 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 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

root rot Root rot is a condition in which anoxic conditions in the soil or potting media around the roots of a plant cause them to rot. This occurs due to excessive standing water around the roots. It is found in both indoor and outdoor plants, although ...

. 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. The cereal crop is most susceptible at flowering and the probability of infection rises with high moisture and humidity at flowering.

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 A mycotoxin (from the Greek μύκης , "fungus" and τοξίνη , "toxin") is a toxic secondary metabolite produced by organisms of kingdom Fungi and is capable of causing disease and death in both humans and other animals. The term 'mycotoxin' ...

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 metabolites 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: * 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. DON is a protein synthesis inhibitor, also called vomitoxin, due to its negative effects on feed intake in

pigs The pig (''Sus domesticus''), often called swine, hog, or domestic pig when distinguishing from other members of the genus '' Sus'', is an omnivorous, domesticated, even-toed, hoofed mammal. It is variously considered a subspecies of ''Sus ...

. Pigs are the most sensitive to DON, while

ruminant Ruminants (suborder Ruminantia) are hoofed herbivorous grazing or browsing mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through microbial actions. The ...

animals such as cattle have higher tolerance. 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. The

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...

has legislative limits for several ''Fusarium'' mycotoxins in grain aimed for human consumption and recommended limits for animal feed.

Control measures

Resistant cultivars

Resistant cultivars could be the most efficient method to control Fusarium ear blight. Resistance

breeding Breeding is sexual reproduction that produces offspring, usually animals or plants. It can only occur between a male and a female animal or plant. Breeding may refer to: * Animal husbandry, through selected specimens such as dogs, horses, and r ...

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 A genetic marker is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. It can be described as a variation (which may arise due to mutation or alteration in the genomic loci) that can be ...

s associated with resistance are screened for, so called

marker-assisted selection Marker assisted selection or marker aided selection (MAS) is an indirect selection process where a trait of interest is selected based on a marker ( morphological, biochemical or DNA/RNA variation) linked to a trait of interest (e.g. productivi ...

. Fusarium ear blight resistance is a complex trait, involving several genes, and is dependent of interaction with the environment. Fusarium ear blight resistance has been identified in wheat

cultivar A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture ...

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.Bai GH, Shaner GE (2004) Management and resistance in wheat Bai GH, Shaner GE (2004) Management and resistance in wheat 42:135–161

Agricultural practices

Several

agricultural practices Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people to ...

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 Maize ( ; ''Zea mays'' subsp. ''mays'', from es, maíz after tnq, mahiz), also known as corn (North American English, North American and Australian English), is a cereal grain first domesticated by indigenous peoples of Mexico, indigenous ...

has been associated with especially high risk. Reduced soil tillage can also increase the risk of FEB. The amount of crop residues can be reduced by

plough A plough or plow ( US; both ) is a farm tool for loosening or turning the soil before sowing seed or planting. Ploughs were traditionally drawn by oxen and horses, but in modern farms are drawn by tractors. A plough may have a wooden, iron or ...

ing, where residues are incorporated in the soil where they

decompose Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and is ...

faster. High nitrogen application has also been associated with increased risk of ''Fusarium'' infection. Preventive agricultural practices may be less effective if a lot of airborne inoculum is present in the area.

Chemical control

Fungicide Fungicides are biocidal chemical compounds or biological organisms used to kill parasitic fungi or their spores. A fungistatic inhibits their growth. Fungi can cause serious damage in agriculture, resulting in critical losses of yield, quality ...

s can provide partial control of FEB but the effects may be variable. The type and timing of fungicide application is important as non-optimal applications may even increase ''Fusarium'' infection.

Biological control and integrated management

Research has also been put into development on biological control strategies based on bacteria and fungi for example, ''

Bacillus ''Bacillus'' (Latin "stick") is a genus of Gram-positive, rod-shaped bacteria, a member of the phylum '' Bacillota'', with 266 named species. The term is also used to describe the shape (rod) of other so-shaped bacteria; and the plural ''Bacill ...

'' and '' Cryptococcus'' species''.'' For FEB no control measure is completely effective and integrated management involving several control strategies such as preventive measures, disease monitoring and chemical control is necessary. Disease forecasting models have been developed to assess the risk of FEB depending on weather conditions.

Economic importance

From an economic standpoint, it is one of the major

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. From 1998 to 2000 the

Midwestern United States The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four census regions of the United States Census Bureau (also known as "Region 2"). It occupies the northern central part of the United States. I ...

suffered $2.7 billion in losses following a FEB epidemic. If we include primary and secondary economic losses, FHB cost the entire US$7.67 billion from 1993 to 2001. 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.

References

External links

American Phytopathology FHB site
Return of an old problem: Fusarium head blight of small grains
http://www.apsnet.org/publications/apsnetfeatures/Pages/headblight.aspx
Fusarium head blight in Canada

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 *Fusarium Ear Blight Cereal diseases Wheat diseases Fungal plant pathogens and diseases