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Fungicides are biocidal
chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical bonds. A homonuclear molecule, m ...
s or biological organisms used to kill
parasitic fungi Parasitism is a Symbiosis, symbiotic biological interactions, relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is adaptation (biology), ad ...
or their
spore )'', growing on a thinning, thinned hybrid black poplar ''(populus, Populus x canadensis)''. The last stage of the moss#Life cycle, moss lifecycle is shown, where the sporophytes are visible before dispersion of their spores: the calyptra (1) is ...
s. A
fungistaticFungistatics are anti-fungal agents that inhibit the growth of fungus A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as w ...
inhibits their growth. Fungi can cause serious damage in
agriculture Agriculture is the science, art and practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary Image:Family watching television 1958.jpg, Exercise trends, Increases in sedentary behaviors su ...

agriculture
, resulting in critical losses of
yield Yield may refer to: Measures of output/function Computer science * Yield (multithreading) is an action that occurs in a computer program during multithreading * See generator (computer programming) Physics/chemistry * Yield (chemistry), the amou ...
, quality, and
profit Profit may refer to: Business and law * Profit (accounting) Profit, in accounting Accounting or Accountancy is the measurement, processing, and communication of financial and non financial information about economic entity, economic en ...
. Fungicides are used both in agriculture and to fight
fungal infections in animals Mycosis is an Infection, infectious disease caused by pathogenic fungus in humans and animals. Mycoses are common and a variety of environmental and physiological conditions can contribute to the development of fungal diseases. Inhalation of funga ...
. 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 and protect only 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 and redistributed through the xylem vessels. Few fungicides move to all parts of a plant. Some are locally systemic, and some move upwardly. Most fungicides that can be bought retail are sold in a liquid form. A very common active ingredient is
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
, 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, also known as margosa oil, is a vegetable oil pressed from the fruits and seeds of the neem (''Azadirachta indica''), a tree which is indigenous to the Indian subcontinent and has been introduced to many other areas in the tropics. It is ...

neem oil
,
rosemary ''Salvia rosmarinus'', commonly known as rosemary, is a shrub with fragrant, evergreen, needle-like leaves and white, pink, purple, or blue flowers, native plant, native to the Mediterranean Region, Mediterranean region. Until 2017, it was known ...

rosemary
oil,
jojoba oil Jojoba oil is the liquid produced in the seed of the ''Simmondsia chinensis'' (jojoba Jojoba (; : ''Simmondsia chinensis'')also goat nut, deer nut, pignut, wild hazel, quinine nut, coffeeberry, and gray box bushis native to the Southwestern ...
, the bacterium ''
Bacillus subtilis ''Bacillus subtilis'', known also as the hay bacillus or grass bacillus, is a Gram-positive 300px, Violet-stained gram-positive cocci and pink-stained gram-negative bacillus (shape), bacilli In bacteriology, gram-positive bacteria are bacteria ...

Bacillus subtilis
'', and the beneficial fungus ''
Ulocladium ''Ulocladium'' is a genus of fungi. Species of this genus contain both plant pathogens and food spoilage agents. Other species contain enzymes that are biological control agents. Some members of the genus can invade homes and are a sign of mois ...
oudemansii''. Fungicide residues have been found on food for human consumption, mostly from post-harvest treatments. Some fungicides are dangerous to human
health Health, according to the World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations United Nations Specialized Agencies are autonomous organizations working with the United Nations and each ...

health
, such as
vinclozolin Vinclozolin (trade names Ronilan, Curalan, Vorlan, Touche) is a common dicarboximide fungicide used to control diseases, such as blights, rots and molds in vineyards, and on fruits and vegetables such as raspberries, lettuce, kiwi, snap beans, a ...

vinclozolin
, which has now been removed from use.
Ziram Zinc dimethyldithiocarbamate is a coordination complex A coordination complex consists of a central atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass a ...

Ziram
is also a fungicide that is toxic to humans with long-term exposure, and fatal if ingested. A number of fungicides are also used in human health care.


Types


Organic chemicals

*
Mancozeb Mancozeb is a dithiocarbamate non-systemic agricultural fungicide with multi-site, protective action on contact. It is a combination of two other dithiocarbamates: maneb and zineb. The mixture controls many fungal diseases in a wide range of field ...

Mancozeb
*
Myclobutanil
Myclobutanil


Inorganic chemicals

*
Copper Copper is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

Copper
*
Sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

Sulfur
*
Phosphorous acid Phosphorous acid is the Compound (chemistry), compound described by the chemical formula, formula H3PO3. This acid is diprotic (readily ionizes two protons), not triprotic as might be suggested by this formula. Phosphorous acid is an intermediate ...

Phosphorous acid


Mycoviruses

Some of the most common
fungal crop pathogen Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungus, fungi ...
s are known to suffer from
mycovirus Mycoviruses (Ancient Greek: μύκης ' ("fungus") + Latin '), also known as mycophages, are viruses that infect fungi. The majority of mycoviruses have dsRNA virus, double-stranded RNA (dsRNA) genomes and isometric particles, but approximately 3 ...
es, and it is likely that they are as common as for plant and animal viruses, although not as well studied. Given the obligately parasitic nature of mycoviruses, it is likely that all of these are detrimental to their hosts, and thus are potential
biocontrol Biological control or biocontrol is a method of controlling pests such as insect Insects (from Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of commu ...
s/biofungicides.


Natural fungicides

Proponents of natural pest management claim that certain plant-based chemical have fungicidal activity. Plants and other organisms have chemical defenses that give them an advantage against microorganisms such as fungi. Some of these compounds are used as fungicides, although their efficacy is doubted: * (present in
essential oils An essential oil is a concentrated hydrophobic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, s ...
of different plants) *
Citronella oil file:Óleo de citronela.jpg, Citronella oil Citronella oil is an essential oil obtained from the leaves and stems of different species of ''Cymbopogon'' (lemongrass). The oil is used extensively as a source of perfumery chemicals such as citronella ...
*
Gmelinol Gmelinol is a lignan. (+)-Gmelinol can be isolated from the heartwood of ''Gmelina arborea''. This compound, along with four other chemicals also found in the same species, (+)-7′-O-ethyl arboreol, (+)-paulownin, (+)-epieudesmin and (−)-β-sitos ...

Gmelinol
(isolated from ''
Gmelina arborea ''Gmelina arborea'', (in English beechwood, gmelina, goomar teak, Kashmir tree, Malay beechwood, white teak, yamane ), locally known as gamhar, is a fast-growing deciduous tree in the family Lamiaceae. Description ''Gmelina arborea'' is a fast ...

Gmelina arborea
'') *
Hinokitiol Hinokitiol (β-thujaplicin) is a natural monoterpenoid found in the wood of trees in the family Cupressaceae Cupressaceae is a conifer Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up ...

Hinokitiol
(isolated from ''
Cupressaceae Cupressaceae is a conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The ...

Cupressaceae
'' trees) *
Jojoba oil Jojoba oil is the liquid produced in the seed of the ''Simmondsia chinensis'' (jojoba Jojoba (; : ''Simmondsia chinensis'')also goat nut, deer nut, pignut, wild hazel, quinine nut, coffeeberry, and gray box bushis native to the Southwestern ...
*
Mesquitol Mesquitol is a flavan-3-ol Flavan-3-ols (sometimes referred to as flavanols) are derivatives of flavans that possess a 2-phenyl-3,4-dihydro-2''H''-chromen-3-ol skeleton. These compounds include catechin, epicatechin gallate, epigallocatechin, ...

Mesquitol
(isolated from ''
Prosopis ''Prosopis'' is a genus Genus /ˈdʒiː.nəs/ (plural genera /ˈdʒen.ər.ə/) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. ...
'' trees) * Nimbin (isolated from
neem ''Azadirachta indica'', commonly known as neem, nimtree or Indian lilac, is a tree in the mahogany Honduran mahogany Mahogany is a straight-Wood grain, grained, reddish-brown timber of three Tropics, tropical hardwood species of the genus ...

neem
)


Resistance

Pathogen In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanism ...
s respond to the use of fungicides by evolving
resistance Resistance may refer to: Arts, entertainment, and media Comics * Either of two similarly named but otherwise unrelated comic book series, both published by Wildstorm: ** ''Resistance'' (comics), based on the video game of the same title ** ''Th ...

resistance
. 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 In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechan ...
(normally to a single gene) produces a
race Race, RACE or "The Race" may refer to: * Race (biology), an informal taxonomic classification within a species, generally within a sub-species * Race (human categorization), classification of humans into groups based on physical traits, and/or s ...
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 A sugar beet is a plant whose root contains a high concentration of sucrose Sucrose is a type of sugar Sugar is the generic name for Sweetness, sweet-tasting, soluble carbohydrates, many of which are used in food. Table sugar, granulated ...
leaf blotch remains resistant to
azole Azoles are a class of five-membered heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s ...
s years after they were no longer used for control of the disease. This is because such mutations have a high
selection pressure Any cause that reduces or increases reproductive success in a portion of a population potentially exerts evolutionary pressure, selective pressure or selection pressure, driving natural selection Natural selection is the differential survi ...
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 A polygene is a member of a group of non-epistatic gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, ...
– an accumulation of many mutations 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 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 decrease 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 and . There are also recorded incidences of the evolution of
multiple drug resistance Multiple drug resistance (MDR), multidrug resistance or multiresistance is antimicrobial resistance shown by a species of microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism In biology, an organism (from A ...
by pathogens – resistance to two chemically different fungicides by separate mutation events. For example, ''
Botrytis cinerea ''Botrytis cinerea'' is a necrotrophic A fungus (plural: fungi or funguses) is any member of the group of Eukaryote, eukaryotic organisms that includes microorganisms such as yeasts and Mold (fungus), molds, as well as the more familiar mus ...
'' is resistant to both azoles and dicarboximide fungicides. There are several routes by which pathogens can evolve fungicide resistance. The most common mechanism appears to be alteration of the target site, in particular as a defence against single site of action fungicides. For example, , an economically important pathogen of banana, is resistant to the
QoI Qo inhibitors (QoI), or quinone outside inhibitors, are a group of fungicides used in agriculture. Some of these fungicides are among the most popular in the world. QoI are chemical compounds which act at the quinol ''outer'' binding site of the ...
fungicides, due to a single
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
change resulting in the replacement of one
amino acid Amino acids are organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, a ...

amino acid
(glycine) by another (alanine) in the target protein of the QoI fungicides,
cytochrome Cytochromes are redox-active protein Proteins are large biomolecule , showing alpha helices, represented by ribbons. This poten was the first to have its suckture solved by X-ray crystallography by Max Perutz and Sir John Cowdery Kendr ...
b. It is presumed that this 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'' is an ascomycota, 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. in ...
''. Resistance to fungicides can also be developed by efficient efflux of the fungicide out of the cell. '' Septoria tritici'' has developed multiple drug resistance using this mechanism. The pathogen had five ABC-type transporters with overlapping
substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached **Substrate (locomotion), the surface over which an organism loco ...
specificities that together work to pump toxic chemicals out of the cell. In addition to the mechanisms outlined above, fungi may also develop
metabolic pathway In biochemistry, a metabolic pathway is a linked series of chemical reactions occurring within a cell (biology), cell. The reactants, products, and intermediates of an enzymatic reaction are known as metabolites, which are modified by a sequence ...
s that circumvent the target protein, or acquire
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates in ...

enzyme
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 is the International Organization for Standardization, ISO trivial name, common name for an organic compound that is used as a fungicide. It is a broad spectrum Systemic pesticide, systemic active ingredient widely used in agriculture ...

azoxystrobin
. FRAC assigns groups of fungicides into classes where cross-resistance is likely, usually because the active ingredients share a common mode of action. FRAC is organized by
CropLife International CropLife International is an international trade association of agrochemical companies founded in 2001. It was previously known as ''Global Crop Protection Federation'' and started out as ''International Group of National Associations of Manufacture ...
. Products should not always 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's developing resistance is greatly decreased by the fact that any resistant isolates to one fungicide will 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 , a phenylamide fungicide. When used as the sole product in
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic. It is separated from Great Britain to its east by the North Channel (Great Britain and Ireland), North Channel, the Irish Sea ...

Ireland
to control potato blight (''
Phytophthora infestans ''Phytophthora infestans'' is an oomycete Oomycota or oomycetes () form a distinct phylogenetic In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry ...
''), resistance developed within one growing season. However, in countries like the where it was marketed only as a mixture, resistance problems developed more slowly. Fungicides should be applied only 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 means quantity (in units of energy/mass) in the fields of nutrition, medicine, and toxicology. Dosage is the rate of application of a dose, although in common and imprecise usage, the words are sometimes used synonymously. Music * Dose (Gov't ...
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 better to use an integrative pest management approach to disease control rather than relying on fungicides alone. This involves the use of resistant varieties and hygienic practices, 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

*
Antifungal drug An antifungal medication, also known as an antimycotic medication, is a pharmaceutical A medication (also referred to as medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug File:Aspirine macro shot.jpg, Uncoated aspi ...
*
Index of pesticide articles This is an index of articles relating to pesticide Pesticides are substances that are meant to control pests. The term pesticide includes all of the following: herbicide, insecticides (which may include insect growth regulators, termiticide ...
* List of fungicides * PHI-base (Pathogen-Host-Interaction database) *
Phytopathology Plant pathology (also phytopathology) is the scientific study of disease A disease is a particular abnormal condition that negatively affects the structure or function of all or part of an organism, and that is not due to any imme ...
* Plant disease forecasting


References


External links


Fungicide Resistance Action CommitteeFungicide Resistance Action Group
United Kingdom

- National Pesticide Information Center, Oregon State University, United States {{Authority control Mycology Biocides