Fungicide
Overview
 
Fungicides are chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s or biological organisms used to kill or inhibit fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 or fungal spores
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...

. Fungi can cause serious damage in agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...

, resulting in critical losses of yield
Crop yield
In agriculture, crop yield is not only a measure of the yield of cereal per unit area of land under cultivation, yield is also the seed generation of the plant itself...

, quality and profit
Profit (economics)
In economics, the term profit has two related but distinct meanings. Normal profit represents the total opportunity costs of a venture to an entrepreneur or investor, whilst economic profit In economics, the term profit has two related but distinct meanings. Normal profit represents the total...

. Fungicides are used both in agriculture and to fight fungal infections in animals. Chemicals used to control oomycetes, which are not fungi, are also referred to as fungicides as oomycetes use the same mechanisms as fungi to infect plants.

Fungicides can either be contact, translaminar or systemic.
Encyclopedia
Fungicides are chemical compound
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...

s or biological organisms used to kill or inhibit fungi
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 or fungal spores
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...

. Fungi can cause serious damage in agriculture
Agriculture
Agriculture is the cultivation of animals, plants, fungi and other life forms for food, fiber, and other products used to sustain life. Agriculture was the key implement in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that nurtured the...

, resulting in critical losses of yield
Crop yield
In agriculture, crop yield is not only a measure of the yield of cereal per unit area of land under cultivation, yield is also the seed generation of the plant itself...

, quality and profit
Profit (economics)
In economics, the term profit has two related but distinct meanings. Normal profit represents the total opportunity costs of a venture to an entrepreneur or investor, whilst economic profit In economics, the term profit has two related but distinct meanings. Normal profit represents the total...

. Fungicides are used both in agriculture and to fight fungal infections in animals. Chemicals used to control oomycetes, which are not fungi, are also referred to as fungicides as oomycetes use the same mechanisms as fungi to infect plants.

Fungicides can either be contact, translaminar or systemic. Contact fungicides are not taken up into the plant tissue, & only protect the plant where the spray is deposited; translaminar fungicides redistribute the fungicide from the upper, sprayed leaf surface to the lower, unsprayed surface;
systemic fungicides are taken up & redistributed through the xylem vessels to the upper parts of the plant. New leaf growth is protected for a short period.
.

Most fungicides that can be bought retail are sold in a liquid form. A very common active ingredient is sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

, present at 0.08% in weaker concentrates, and as high as 0.5% for more potent fungicides. Fungicides in powdered form are usually around 90% sulfur and are very toxic. Other active ingredients in fungicides include neem oil
Neem oil
Neem oil is a vegetable oil pressed from the fruits and seeds of the neem , an evergreen tree which is endemic to the Indian subcontinent and has been introduced to many other areas in the tropics...

, rosemary
Rosemary
Rosemary, , is a woody, perennial herb with fragrant, evergreen, needle-like leaves and white, pink, purple or blue flowers, native to the Mediterranean region. It is a member of the mint family Lamiaceae, which includes many other herbs, and is one of two species in the genus Rosmarinus...

 oil, jojoba oil
Jojoba oil
Jojoba oil is the liquid wax produced in the seed of the jojoba plant, a shrub native to southern Arizona, southern California, and northwestern Mexico. The oil makes up approximately 50% of the jojoba seed by weight....

, and the bacterium Bacillus subtilis
Bacillus subtilis
Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...

.

Fungicide residues have been found on food for human consumption, mostly from post-harvest treatments. Some fungicides are dangerous to human health
Health
Health is the level of functional or metabolic efficiency of a living being. In humans, it is the general condition of a person's mind, body and spirit, usually meaning to be free from illness, injury or pain...

, such as vinclozolin
Vinclozolin
- Introduction :Vinclozolin is a common dicarboximide fungicide used to control various diseases in vineyards, and on fruits and vegetables such as raspberries, lettuce, kiwi, beans and onions. It is also used on turf on golf courses...

, which has now been removed from use.

Natural fungicides

Plants and other organisms have chemical defenses that give them an advantage against microorganisms such as fungi. Some of these compounds can be used as fungicides:
  • Tea tree oil
    Tea tree oil
    Tea tree oil, or melaleuca oil, is a pale yellow colour to nearly clear essential oil with a fresh camphoraceous odor. It is taken from the leaves of the Melaleuca alternifolia, which is native to the northeast coast of New South Wales, Australia...

  • Cinnamaldehyde
    Cinnamaldehyde
    Cinnamaldehyde is the organic compound that gives cinnamon its flavor and odor. This pale yellow viscous liquid occurs naturally in the bark of cinnamon trees and other species of the genus Cinnamomum...

  • Cinnamon
    Cinnamon
    Cinnamon is a spice obtained from the inner bark of several trees from the genus Cinnamomum that is used in both sweet and savoury foods...

     essential oil
    Essential oil
    An essential oil is a concentrated hydrophobic liquid containing volatile aroma compounds from plants. Essential oils are also known as volatile oils, ethereal oils or aetherolea, or simply as the "oil of" the plant from which they were extracted, such as oil of clove...

  • Jojoba oil
    Jojoba oil
    Jojoba oil is the liquid wax produced in the seed of the jojoba plant, a shrub native to southern Arizona, southern California, and northwestern Mexico. The oil makes up approximately 50% of the jojoba seed by weight....

  • Neem oil
    Neem oil
    Neem oil is a vegetable oil pressed from the fruits and seeds of the neem , an evergreen tree which is endemic to the Indian subcontinent and has been introduced to many other areas in the tropics...

  • Rosemary oil
    Rosemary
    Rosemary, , is a woody, perennial herb with fragrant, evergreen, needle-like leaves and white, pink, purple or blue flowers, native to the Mediterranean region. It is a member of the mint family Lamiaceae, which includes many other herbs, and is one of two species in the genus Rosmarinus...

  • Monocerin
    Monocerin
    Monocerin is a polyketide metabolite that originates from various fungal species. It has been shown to display antifungal, plant pathogenic, and insecticidal characteristics. Monocerin has been isolated from Dreschlera monoceras,D. ravenelii, Exserohilum turcicum, and Fusarium...

  • Milk
    Milk
    Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

  • Ampelomyces quisqualis
    Ampelomyces quisqualis
    Ampelomyces quisqualis is an anamorphic fungus that is a hyperparasite of powdery mildews. This parasitism reduces growth and may eventually kill the mildew, so investigations on biological control of powdery mildews have taken place for over 50 years, resulting in the development of products...

     AQ10, CNCM I-807

Whole live or dead organisms that are efficient at killing or inhibiting fungi can sometimes be used as fungicides:
  • The bacterium Bacillus subtilis
    Bacillus subtilis
    Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium commonly found in soil. A member of the genus Bacillus, B. subtilis is rod-shaped, and has the ability to form a tough, protective endospore, allowing the organism to tolerate...

  • Kelp
    Kelp
    Kelps are large seaweeds belonging to the brown algae in the order Laminariales. There are about 30 different genera....

     (powdered dried kelp is fed to cattle to protect them from fungi in grass)

Resistance

Pathogens respond to the use of fungicides by evolving resistance
Pesticide resistance
Pesticide resistance is the adaptation of pest population targeted by a pesticide resulting in decreased susceptibility to that chemical. In other words, pests develop a resistance to a chemical through natural selection: the most resistant organisms are the ones to survive and pass on their...

. In the field several mechanisms of resistance have been identified. The evolution of fungicide resistance can be gradual or sudden. In qualitative or discrete resistance a mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...

 (normally to a single gene) produces a race
Race (biology)
In biology, races are distinct genetically divergent populations within the same species with relatively small morphological and genetic differences. The populations can be described as ecological races if they arise from adaptation to different local habitats or geographic races when they are...

 of a fungus with a high degree of resistance. Such resistant varieties also tend to show stability, persisting after the fungicide has been removed from the market. For example sugar beet
Sugar beet
Sugar beet, a cultivated plant of Beta vulgaris, is a plant whose tuber contains a high concentration of sucrose. It is grown commercially for sugar production. Sugar beets and other B...

 leaf blotch remains resistant to azole
Azole
An azole is a class of five-membered nitrogen heterocyclic ring compounds containing at least one other non-carbon atom of either nitrogen, sulfur, or oxygen. The parent compounds are aromatic and have two double bonds; there are successively reduced analogs with fewer...

s years after they were no longer used for control of the disease. This is because such mutations often have a high selection pressure when the fungicide is used, but there is low selection pressure to remove them in the absence of the fungicide.

In instances where resistance occurs more gradually a shift in sensitivity in the pathogen to the fungicide can be seen. Such resistance is polygenic – an accumulation of many mutation in different genes each having a small additive effect. This type of resistance is known as quantitative or continuous resistance. In this kind of resistance the pathogen population will revert back to a sensitive state if the fungicide is no longer applied.

Little is known about how variations in fungicide treatment affect the selection pressure to evolve resistance to that fungicide. Evidence shows that the doses that provide the most control of the disease also provide the largest selection pressure to acquire resistance, and that lower doses decreased the selection pressure.

In some cases when a pathogen evolves resistance to one fungicide it automatically obtains resistance to others – a phenomenon known as cross resistance. These additional fungicides are normally of the same chemical family or have the same mode of action, or can be detoxified by the same mechanism. Sometimes negative cross resistance occurs, where resistance to one chemical class of fungicides leads to an increase in sensitivity to a different chemical class of fungicides. This has been seen with carbendazim
Carbendazim
Carbendazim is a widely used broad-spectrum benzimidazole fungicide. A 4.7% solution of carbendazim hydrochloride is sold as Eertavas, an effective treatment for Dutch elm disease....

 and diethofencarb.

There are also recorded incidences of pathogens evolving multiple drug resistance – resistance to two chemically different fungicides by separate mutation events. For example Botrytis cinerea
Botrytis cinerea
Botrytis cinerea is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as botrytis bunch rot; in horticulture, it is usually called grey mould or gray mold.The fungus gives rise to two different kinds of...

is resistant to both azoles and dicarboximide fungicides
Dicarboximide fungicides
Dicarboximide fungicides are a family of agricultural fungicides that include vinclozolin, iprodione and procymidone. Dicarboximides are believed to inhibit triglyceride biosynthesis in sclerotia-forming fungi, including Botrytis cinerea. These fungicides turn into 3,5-dichloroaniline in soil...

.

There are several routes by which pathogens can evolve fungicide resistance. The most common mechanism appears to be alteration of the target site, particular as a defence against single site of action fungicides. For example Black Sigatoka
Black sigatoka
Black Sigatoka is a leaf spot disease of banana plants caused by ascomycete fungusMycosphaerella fijiensis . Plants with leaves damaged by the disease may have up to 50% lower yield of fruit...

, an economically important pathogen of banana, is resistant to the QoI
QoI
Qo inhibitors , or Quinone outside inhibitors are a group of fungicides used in agriculture. They represent the most important development made in fungicides by the chemicals industry...

 fungicides, due to a single nucleotide
Nucleotide
Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...

 change resulting one amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

 (glycine) being replaced by another (alanine) in the target protein of the QoI fungicides, cytochrome
Cytochrome
Cytochromes are, in general, membrane-bound hemoproteins that contain heme groups and carry out electron transport.They are found either as monomeric proteins or as subunits of bigger enzymatic complexes that catalyze redox reactions....

 b. This presumably disrupts the binding of the fungicide to the protein, rendering the fungicide ineffective.

Upregulation of target genes can also render the fungicide ineffective. This is seen in DMI resistant strains of Venturia inaequalis
Venturia inaequalis
Venturia inaequalis is an ascomycete fungus that causes the Apple scab disease.-Systematics:Venturia inaequalis anamorphs have been described under the names Fusicladium dendriticum and Spilocaea pomi. Whether V. inaequalis is a single species or contains several cryptic species has been a matter...

.

Resistance to fungicides can also be developed by efficient efflux
Efflux (microbiology)
Active efflux is a mechanism responsible for extrusion of toxic substances and antibiotics outside the cell; this is considered to be a vital part of xenobiotic metabolism...

 of the fungicide out of the cell. Septoria tritici
Septoria tritici
Septoria tritici is the causal agent of S. tritici leaf blotch, a foliar disease of wheat, and occasionally infects other grasses including barley...

has developed multiple drug resistance using this mechanism. The pathogen had 5 ABC type transporters with overlapping substrate
Substrate (biochemistry)
In biochemistry, a substrate is a molecule upon which an enzyme acts. Enzymes catalyze chemical reactions involving the substrate. In the case of a single substrate, the substrate binds with the enzyme active site, and an enzyme-substrate complex is formed. The substrate is transformed into one or...

 specificities that together work to effectively pump toxic chemicals out of the cell.

In addition to the mechanisms outlined above, fungi may also develop metabolic pathway
Metabolic pathway
In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function...

s that circumvent the target protein, or acquire enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s that enable metabolism of the fungicide to a harmless substance.

Fungicide resistance management

The fungicide resistance action committee (FRAC) has several recommended practices to try to avoid the development of fungicide resistance, especially in at-risk fungicides including Strobilurins such as azoxystrobin
Azoxystrobin
Azoxystrobin is a fungicide commonly used in agriculture. The substance is used as an active agent protecting plants and fruit/vegetables from fungal diseases.-Origin:...

.

Products should not be used in isolation but rather as mixture, or alternate sprays, with another fungicide with a different mechanism of action. The likelihood of the pathogen developing resistance is greatly decreased by the fact that any resistant isolates to one fungicide will hopefully be killed by the other – in other words two mutations would be required rather than just one. The effectiveness of this technique can be demonstrated by Metalaxyl
Metalaxyl
Metalaxyl is a phenylamide fungicide with systemic function. Its chemical name is methyl N--N--DL-alaninate. It can be used to control Pythium in a number of vegetable crops, and Phytophthora in peas....

, a phenylamide fungicide. When used as the sole product in Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

 to control potato blight (Phytophthora infestans
Phytophthora infestans
Phytophthora infestans is an oomycete that causes the serious potato disease known as late blight or potato blight. . Late blight was a major culprit in the 1840s European, the 1845 Irish and 1846 Highland potato famines...

) resistance developed within one growing season. However in countries like the UK where it was only ever marketed as a mixture resistance problems developed more slowly .

Fungicides should only be applied when absolutely necessary, especially if they are in an at-risk group. Lowering the amount of fungicide in the environment lowers the selection pressure for resistance to develop.

Manufacturers’ dose
Dose (biochemistry)
A dose is a quantity of something that may impact an organism biologically; the greater the quantity, the larger the dose. In nutrition, the term is usually applied to how much of a specific nutrient is in a person's diet or in a particular food, meal, or dietary supplement...

s should always be followed. These doses are normally designed to give the right balance between controlling the disease and limiting the risk of resistance development. Higher doses increase the selection pressure for single site mutations that confer resistance, as all strains but those that carry the mutation will be eliminated, and thus the resistant strain will propagate. Lower doses greatly increase the risk of polygenic resistance, as strains that are slightly less sensitive to the fungicide may survive.

It is also recommended that where possible fungicides are only used in a protective manner, rather than to try to cure already infected crops. Far fewer fungicides have curative/eradicative ability than protectant. Thus fungicide preparations advertised as having curative action may only have one active chemical; a single fungicide acting in isolation increases the risk of fungicide resistance.

It is better to use an integrative pest management
Integrated Pest Management
Integrated pest management is an ecological approach to agricultural pest control that integrates pesticides/herbicides into a management system incorporating a range of practices for economic control of a pest...

 approach to disease control, rather than relying on fungicides alone. This involves the use of resistant varieties and hygienic practises, such as the removal of potato discard piles and stubble on which the pathogen can overwinter, greatly reducing the titre of the pathogen and thus the risk of fungicide resistance development.

See also

  • Index of pesticide articles
    Index of pesticide articles
    This is an index of articles relating to pesticides.-A:Abamectin- Acephate- Acetochlor- Acibenzolar- Acibenzolar-S-methyl- Acrylonitrile- Action level- Agent Blue- Agent Green- Agent Orange- Agent Pink- Agent Purple- Agent White- Agrochemical...


  • Antifungal drug
    Antifungal drug
    An antifungal medication is a medication used to treat fungal infections such as athlete's foot, ringworm, candidiasis , serious systemic infections such as cryptococcal meningitis, and others...

  • List of fungicides
  • Phytopathology
    Phytopathology
    Plant pathology is the scientific study of plant diseases caused by pathogens and environmental conditions . Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants...

  • Plant disease forecasting
    Plant disease forecasting
    Plant disease forecasting is a management system used to predict the occurrence or change in severity of plant diseases. At the field scale, these systems are used by growers to make economic decisions about disease treatments for control...

  • PHI-base
    PHI-base
    The Pathogen - Host Interaction database contains expertly curated molecular and biological information on genes proven to affect the outcome of pathogen-host interactions...

    (Pathogen-Host-Interaction database)

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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