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{{Short description|Fungus-like eukaryotic microorganism}}
{{Automatic taxobox
| name = Oomycetes
| image = Phytophtora reproduction.png
| image_upright = 1.2
| image_caption = Asexual (A: sporangia, B: zoospores, C: chlamydospores) and sexual (D: oospores) reproductive structures of ''[[Phytophthora infestans]]'' ([[Peronosporales]])
| image_alt = Asexual (A: sporangia, B: zoospores, C: chlamydospores) and sexual (D: oospores) reproductive structures of Phytophthora infestans (Peronosporales)
| taxon = Oomycetes
| authority = [[Heinrich Georg Winter|Winter]], 1880<ref>Winter, G. ''[[Gottlob Ludwig Rabenhorst#works|Rabenhorst's Kryptogamen-Flora]]'', 2nd ed., vol. 1, part 1, [http://bibdigital.rjb.csic.es/ing/Libro.php?Libro=987&Pagina=39 p. 32] {{Webarchive|url=https://web.archive.org/web/20141213014755/http://bibdigital.rjb.csic.es/ing/Libro.php?Libro=987&Pagina=39 |date=2014-12-13 }}, 1880 [1879].</ref>
| synonyms = * Peronosporomycetes Dick, 2001<ref>Dick, M. W. (2001). ''Straminipilous fungus''. Dordrecht, the Netherlands: Kluwer Academic Publishers, p. 289.</ref>
| subdivision_ranks = Orders and families
| subdivision = *[[Diatomophthoraceae]]
*[[Miraculaceae]]
*[[Albuginales]]
**[[Albuginaceae]]
*[[Lagenidiales]]
**[[Lagenidiaceae]]
**[[Olpidiosidaceae]]
**[[Sirolpidiaceae]]
*[[Leptomitales]]
**[[Leptomitaceae]]
*[[Peronosporales]]
**[[Albuginaceae]]
**[[Peronosporaceae]]
**[[Pythiaceae]]
*[[Rhipidiales]]
**[[Rhipidaceae]]
*[[Saprolegniales]]
**[[Ectrogellaceae]]
**[[Haliphthoraceae]]
**[[Leptolegniellaceae]]
**[[Saprolegniaceae]]
}}

The '''Oomycetes''' ({{IPAc-en|ˌ|oʊ|.|ə|ˈ|m|aɪ|s|iː|t|s}}),<ref>{{cite Collins Dictionary|oomycete|access-date=5 September 2023}}</ref> or '''Oomycota''', form a distinct [[phylogeny|phylogenetic]] lineage of [[fungus]]-like [[eukaryotic]] [[microorganism]]s within the [[Stramenopiles]]. They are [[mycelia|filamentous]] and [[heterotrophic]], and can reproduce both [[Sexual reproduction|sexually]] and [[Asexual reproduction|asexually]]. Sexual reproduction of an [[oospore]] is the result of contact between [[hyphae]] of male [[antheridia]] and female [[oogonia]]; these spores can overwinter and are known as resting spores.<ref name="Agrios-2005">{{Cite book|title=Plant Pathology|last=Agrios|first=George|publisher=Academic Press |edition=5 |isbn=978-0-12-044565-3 }}</ref>{{rp|409}} Asexual reproduction involves the formation of [[chlamydospores]] and [[Sporangium|sporangia]], producing [[motile]] [[Zoospore|zoospores]].<ref name="Agrios-2005" /> Oomycetes occupy both [[saprophytic]] and [[pathogenic]] lifestyles, and include some of the most notorious pathogens of plants, causing devastating diseases such as [[late blight of potato]] and [[sudden oak death]]. One oomycete, the [[Mycoparasitism|mycoparasite]] ''[[Pythium oligandrum]]'', is used for [[biocontrol]], attacking plant pathogenic fungi.<ref>{{cite journal|doi=10.1128/AEM.02643-08|pmid=19447961|title=Influence of Pythium oligandrum Biocontrol on Fungal and Oomycete Population Dynamics in the Rhizosphere|journal=Applied and Environmental Microbiology|volume=75|issue=14|pages=4790–800|year=2009|last1=Vallance|first1=J.|last2=Le Floch|first2=G.|last3=Deniel|first3=F.|last4=Barbier|first4=G.|last5=Levesque|first5=C. A.|last6=Rey|first6=P.|pmc=2708430|bibcode=2009ApEnM..75.4790V}}</ref> The oomycetes are also often referred to as '''water molds''' (or '''water moulds'''), although the water-preferring nature which led to that name is not true of most species, which are terrestrial pathogens.

Oomycetes were originally grouped with [[fungi]] due to similarities in morphology and lifestyle. However, molecular and phylogenetic studies revealed significant differences between fungi and oomycetes which means the latter are now grouped with the [[stramenopiles]] (which include some types of [[algae]]). The Oomycota have a very sparse fossil record; a possible oomycete has been described from [[Cretaceous]] [[amber]].<ref name="urlIntroduction to the Oomycota">{{cite web |url=http://www.ucmp.berkeley.edu/chromista/oomycota.html |title=Introduction to the Oomycota |access-date=2014-07-07 |archive-date=2003-10-09 |archive-url=https://web.archive.org/web/20031009134355/http://www.ucmp.berkeley.edu/chromista/oomycota.html |url-status=live }}</ref>

== Etymology ==
Oomycota comes from ''[[wikt:oo-|oo-]]'' ({{Langx|grc|[[wikt:ᾠόν|ωόν]]|ōon|egg}}) and ''[[wikt:-mycete|-mycete]]'' ({{Langx|grc|[[wikt:μύκητας|μύκητας]]|mýkitas|fungus}}), referring to the large round [[oogonia]], structures containing the female gametes, that are characteristic of the oomycetes.

The name "water mold" refers to their earlier classification as fungi and their preference for conditions of high humidity and running surface water, which is characteristic for the basal taxa of the oomycetes.

== Morphology ==
The oomycetes rarely have septa (see [[hypha]]), and if they do, they are scarce,<ref name="Kortekamp2005">{{cite journal
| last1 = Kortekamp | first1 = A.
| title = Growth, occurrence and development of septa in Plasmopara viticola and other members of the Peronosporaceae using light- and epifluorescence-microscopy
| journal = Mycological Research
| volume = 109
| issue = Pt 5
| pages = 640–648
| year = 2005
| pmid = 16018320
| doi=10.1017/S0953756205002418
}}</ref> appearing at the bases of sporangia, and sometimes in older parts of the filaments.<ref name="books.google.ca">{{cite book
| url = https://books.google.com/books?id=RU_H_DtbtpEC&pg=PA66
| title = The fungi
| isbn = 978-1-84265-153-7
| last1 = Sumbali
| first1 = Geeta
| last2 = Johri
| first2 = B. M
| date = January 2005}}</ref> Some are unicellular, while others are filamentous and branching.<ref name="books.google.ca" />
[[File:2023 Oomycete.svg|thumb|center|upright=2|{{center|'''Representation of an oomycete'''}}{{ordered list|Anterior [[flagellum]]|
[[Mastigoneme|Mastigonemes]], "hairs" attached to flagellum|
[[Cisterna|Flattened cisternae]]|
Peripheral [[Vesicle (biology and chemistry)|vesicle]]|
[[Phospholipid]] vesicle|
[[Contractile vacuole]], regulates the quantity of water inside a cell|
Groove|
[[Golgi apparatus]]; modifies [[protein]]s and sends them out of the cell|
Flagellar rootlet|
K-body (microbody)|
[[Basal body]]|
[[Nucleolus]]|
[[Cell nucleus|Nucleus]]|
[[Endoplasmic reticulum]], the transport network for molecules going to specific parts of the cell|
[[Mitochondria|Mitochondrion]], creates [[Adenosine triphosphate|ATP]] (energy) for the cell|
Lipid vesicle|
[[Cellulose]] vesicle|
Posterior flagellum
}}]]

== Classification ==
[[File:07 01 filogenia, simplificada, Oomycota (M. Piepenbring).png|thumb|right|Simplified phylogeny.{{citation needed|date=February 2024}}]]
[[File:07 07 asexual structures, Saprolegniales, Albuginales, Peronosporales, Oomycota (M. Piepenbring).png|thumb|right|Asexual structures (sporangia) in [[Saprolegniales]], [[Albuginales]] and [[Peronosporales]]{{citation needed|date=February 2024}}]]
[[File:Oomy1002L.jpg|thumb|right|Sexual structures (only [[oogonia]], antheridia not shown) of ''[[Saprolegnia]]''.{{citation needed|date=February 2024}}]]

Previously the group was arranged into six orders.<ref name="books.google.ca"/>
* The [[Saprolegniales]] are the most widespread. Many break down decaying matter; others are parasites.
* The [[Leptomitales]] have wall thickenings that give their continuous cell body the appearance of septation. They bear chitin and often reproduce asexually.
* The [[Rhipidiales]] use rhizoids to attach their thallus to the bed of stagnant or polluted water bodies.
* The [[Albuginales]] are considered by some authors to be a family (Albuginaceae) within the Peronosporales, although it has been shown that they are phylogenetically distinct from this order.
* The [[Peronosporales]] too are mainly saprophytic or parasitic on plants, and have an aseptate, branching form. Many of the most damaging agricultural parasites belong to this order.
* The [[Lagenidiales]] are the most primitive; some are filamentous, others unicellular; they are generally parasitic.

However more recently this has been expanded considerably.<ref>{{citation | date=2015| author = Ruggiero| title = Higher Level Classification of All Living Organisms | volume=10 |issue=4 | article-number = e0119248|journal=PLOS ONE | doi=10.1371/journal.pone.0119248 | pmid = 25923521| pmc = 4418965|display-authors=etal| bibcode = 2015PLoSO..1019248R| doi-access = free}}</ref><ref>{{citation| date=2016| author=Silar, Philippe| title=Protistes Eucaryotes: Origine, Evolution et Biologie des Microbes Eucaryotes| url=https://hal.archives-ouvertes.fr/hal-01263138| pages=1–462| journal=HAL Archives-ouvertes| access-date=2016-07-16| archive-date=2016-05-13| archive-url=https://web.archive.org/web/20160513001929/https://hal.archives-ouvertes.fr/hal-01263138| url-status=live}}</ref>
* [[Anisolpidiales]] Dick 2001
** [[Anisolpidiaceae]] Karling 1943
* [[Lagenismatales]] Dick 2001
** [[Lagenismataceae]] Dick 1995
* [[Salilagenidiales]] Dick 2001
** [[Salilagenidiaceae]] Dick 1995
* [[Rozellopsidales]] Dick 2001
** [[Rozellopsidaceae]] Dick 1995
** [[Pseudosphaeritaceae]] Dick 1995
* [[Ectrogellales]]
** [[Ectrogellaceae]]
* [[Haptoglossales]]
** [[Haptoglossaceae]]
* [[Eurychasmales]]
** [[Eurychasmataceae]] Petersen 1905
* [[Haliphthorales]]
** [[Haliphthoraceae]] Vishniac 1958
* [[Olpidiopsidales]]
** [[Sirolpidiaceae]] Cejp 1959
** [[Pontismataceae]] Petersen 1909 (contains ''Petersenia'' {{Au|Sparrow, 1934}}, ''Pontisma'' {{Au|H.E.Petersen, 1905}}
** [[Olpidiopsidaceae]] Cejp 1959
* [[Atkinsiellales]]
** [[Atkinisellaceae]]
** [[Crypticolaceae]] Dick 1995
* [[Saprolegniales]]
** [[Achlyaceae]]
** [[Verrucalvaceae]] Dick 1984
** [[Saprolegniaceae]] Warm. 1884 [Leptolegniaceae]
* [[Leptomitales]]
** [[Leptomitaceae]] Kuetz. 1843 [Apodachlyellaceae Dick 1986]
** [[Leptolegniellaceae]] Dick 1971 [Ducellieriaceae Dick 1995]
* [[Rhipidiales]]
** [[Rhipidiaceae]] Cejp 1959
* [[Albuginales]]
** [[Albuginaceae]] Schroet. 1893
* [[Peronosporales]] [Pythiales; Sclerosporales; Lagenidiales]
** [[Salisapiliaceae]]
** [[Pythiaceae]] Schroet. 1893 [Pythiogetonaceae; Lagenaceae Dick 1994; Lagenidiaceae; Peronophythoraceae; Myzocytiopsidaceae Dick 1995]
** [[Peronosporaceae]] Warm. 1884 [Sclerosporaceae Dick 1984]

==Phylogenetic relationships==
[[File:Pythium (257 23).jpg|thumb|right|''[[Pythium]]'' sp. ([[Peronosporales]]), which causes [[pythiosis]] in animals, under microscope.]]
[[File:Late blight on potato leaf 2.jpg|thumb|right|Symptom of [[late blight]] (''P. infestans'', Peronosporales) on the underside of a potato leaf.]]
[[File:Albugo candida.jpg|thumb|right|''[[Albugo candida]]'' (Albuginales) on shepherd's purse (''[[Capsella bursa-pastoris]]'', Brassicales).]]

===Internal===
{{Unreferenced section|date=February 2024}}
{{clade| style=font-size:90%;line-height:80%
|label1=
|1={{Clade
|1={{Clade
|1=[[Haptoglossales]]
|2=[[Eurychasmales]]
}}
|2={{Clade
|1=[[Haliphthorales]]
|2={{Clade
|1=[[Olpidiopsidales]]
|label2=Oogametia
|2={{Clade
|label1=Saprolegniomycetes
|1={{Clade
|1=[[Atkinsiellales]]
|2={{Clade
|1=[[Saprolegniales]]
|2=[[Leptomitales]]
}}
}}
|label2=Peronosporomycetes s.s.
|2={{Clade
|1=[[Rhipidiales]]
|2={{Clade
|1=[[Albuginales]]
|2=[[Peronosporales]]
}}
}}
}}
}}
}}
}}
}}

===External===

This group was originally classified among the [[fungi]] (the name "oomycota" means "egg fungus") and later treated as [[protists]], based on general morphology and lifestyle.<ref name="urlIntroduction to the Oomycota" /> A [[cladistic]] analysis based on modern discoveries about the biology of these organisms supports a relatively close relationship with some [[photosynthetic organism]]s, such as [[brown algae]] and [[diatom]]s.<ref>{{Citation |last=Yoon |first=H. S. |title=Stramenopiles |date=2009-01-01 |work=Encyclopedia of Microbiology (Third Edition) |pages=721–731 |editor-last=Schaechter |editor-first=Moselio |url=https://linkinghub.elsevier.com/retrieve/pii/B9780123739445002534 |access-date=2025-01-05 |place=Oxford |publisher=Academic Press |doi=10.1016/b978-012373944-5.00253-4 |isbn=978-0-12-373944-5 |last2=Andersen |first2=R. A. |last3=Boo |first3=S. M. |last4=Bhattacharya |first4=D.|url-access=subscription }}</ref> A common [[Taxonomy (biology)|taxonomic classification]] based on these data, places the [[class (biology)|class]] oomycetes class along with other classes such as the brown algae within the [[phylum]] [[Stramenopile]].

This relationship is supported by a number of observed differences between the characteristics of oomycetes and fungi. For instance, the [[cell wall]]s of oomycetes are composed of [[cellulose]] rather than [[chitin]]<ref name="pmid7659021">{{cite journal |vauthors=Van der Auwera G, De Baere R, Van de Peer Y, De Rijk P, Van den Broeck I, De Wachter R |title=The phylogeny of the Hyphochytriomycota as deduced from ribosomal RNA sequences of Hyphochytrium catenoides |journal=Mol. Biol. Evol. |volume=12 |issue=4 |pages=671–8 |date=July 1995 |pmid=7659021 |doi= 10.1093/oxfordjournals.molbev.a040245}}</ref> and generally do not have [[septum|septations]]. Also, in the vegetative state they have [[diploid]] nuclei, whereas fungi have [[haploid]] nuclei. Most oomycetes produce self-motile zoospores with two [[flagellum|flagella]]. One flagellum has a "whiplash" morphology, and the other a branched "tinsel" morphology. The "tinsel" flagellum is unique to the Kingdom Heterokonta. Spores of the few fungal groups which retain flagella (such as the [[Chytridiomycetes]]) have only one whiplash flagellum.<ref name="pmid7659021" /> Oomycota and fungi have different metabolic pathways for synthesizing [[lysine]] and have a number of enzymes that differ.<ref name="pmid7659021" /> The ultrastructure is also different, with oomycota having tubular mitochondrial [[cristae]] and fungi having flattened cristae.<ref name="pmid7659021" />

In spite of this, many [[species]] of oomycetes are still described or listed as types of fungi and may sometimes be referred to as [[pseudofungi]], or lower fungi.

== Biology ==
=== Reproduction ===
[[File:07 08 life cycle, Phytophthora infestans on potato, Peronosporales, Oomycota (M. Piepenbring).png|thumb|right|Life cycle of ''[[Phytophthora infestans]]'' (Peronosporales) on [[potato]]. M: [[meiosis]], P: [[plasmogamy]], K: [[karyogamy]], n: [[haploid]], 2n: [[diploid]].]]
Most of the oomycetes produce two distinct types of spores. The main dispersive spores are asexual, self-motile [[spore]]s called [[zoospore]]s, which are capable of chemotaxis (movement toward or away from a chemical signal, such as those released by potential food sources) in surface water (including precipitation on plant surfaces). A few oomycetes produce aerial asexual spores that are distributed by wind. They also produce sexual spores, called [[oospore]]s, that are translucent, double-walled, spherical structures used to survive adverse environmental conditions.

=== Ecology and pathogenicity ===
[[File:Water mold.JPG|thumb|right|Unidentified water mold on dead larval mayfly.]]
[[File:Water mold Mizukabi colony.jpg|thumb|right|A [[Microbiological culture|culture]] of ''[[Achlya]]'' sp. (Saprolegniales) isolated from a stream.]]
[[File:Seatrout UDN saprolegnia.jpg|thumb|right|[[Sea trout]] suffering from [[Ulcerative dermal necrosis|UDN]] with secondary ''[[Saprolegnia]]'' infections.]]

Many oomycetes species are economically important, aggressive algae and [[plant pathology|plant pathogens]].<ref>Agrios, George N. (2005). ''Plant Pathology''. 5th ed. Academic Press. [https://books.google.com/books?id=CnzbgZgby60C link].</ref><ref>{{cite journal | vauthors = Schwelm A, Badstöber J, Bulman S, Desoignies N, Etemadi M, Falloon RE, Gachon CM, Legreve A, Lukeš J, Merz U, Nenarokova A, Strittmatter M, Sullivan BK, Neuhauser S | title = Not in your usual Top 10: protists that infect plants and algae | journal = Molecular Plant Pathology | volume = 19 | issue = 4 | pages = 1029–1044 | date = April 2018 | pmid = 29024322 | pmc = 5772912 | doi = 10.1111/mpp.12580 }}</ref> Some species can [[Fish diseases and parasites|cause disease in fish]], and at least one is a pathogen of mammals. The majority of the plant pathogenic species can be classified into four groups, although more exist.

* The ''[[Phytophthora]]'' group is a [[paraphyletic]] [[genus]] that causes diseases such as [[Phytophthora cinnamomi|dieback]], [[late blight]] in [[potato]]es (the cause of the [[Great Famine (Ireland)|Great Famine]] of the 1840s that ravaged [[Ireland]] and other parts of Europe),<ref name="urlGenome of Irish potato famine pathogen decoded">{{cite journal | doi = 10.1038/nature08358 | pmid = 19741609 | year = 2009 | last1 = Haas | first1 = BJ | last2 = Kamoun | first2 = S | last3 = Zody | first3 = MC | last4 = Jiang | first4 = RH | last5 = Handsaker | first5 = RE | last6 = Cano | first6 = LM | last7 = Grabherr | first7 = M | last8 = Kodira | first8 = CD | last9 = Raffaele | first9 = S | last10 = Torto-Alalibo | first10 = Trudy | last11 = Bozkurt | first11 = Tolga O. | last12 = Ah-Fong | first12 = Audrey M. V. | last13 = Alvarado | first13 = Lucia | last14 = Anderson | first14 = Vicky L. | last15 = Armstrong | first15 = Miles R. | last16 = Avrova | first16 = Anna | last17 = Baxter | first17 = Laura | last18 = Beynon | first18 = Jim | last19 = Boevink | first19 = Petra C. | last20 = Bollmann | first20 = Stephanie R. | last21 = Bos | first21 = Jorunn I. B. | last22 = Bulone | first22 = Vincent | last23 = Cai | first23 = Guohong | last24 = Cakir | first24 = Cahid | last25 = Carrington | first25 = James C. | last26 = Chawner | first26 = Megan | last27 = Conti | first27 = Lucio | last28 = Costanzo | first28 = Stefano | last29 = Ewan | first29 = Richard | last30 = Fahlgren | first30 = Noah | title = Genome sequence and analysis of the Irish potato famine pathogen Phytophthora infestans | volume = 461 | issue = 7262 | pages = 393–8 | journal = Nature | display-authors = 8 | bibcode = 2009Natur.461..393H | doi-access = free | url = http://wrap.warwick.ac.uk/62453/1/WRAP_Jones_nature08358.pdf | access-date = 2024-02-20 | archive-date = 2024-02-20 | archive-url = https://web.archive.org/web/20240220232114/http://wrap.warwick.ac.uk/62453/1/WRAP_Jones_nature08358.pdf | url-status = live }}</ref> [[sudden oak death]], [[rhododendron root rot]], and [[Phytophthora cambivora|ink disease]] in the [[Castanea sativa|European chestnut]]<ref>{{cite journal|doi=10.1007/s10658-004-1882-0|pages=169–180|title=Occurrence and distribution of Phytophthora species in European chestnut stands, and their association with Ink Disease and crown decline|journal=European Journal of Plant Pathology|volume=111|issue=2|year=2005|last1=Vettraino|first1=A. M.|last2=Morel|first2=O.|last3=Perlerou|first3=C.|last4=Robin|first4=C.|last5=Diamandis|first5=S.|last6=Vannini|first6=A.|s2cid=2041934}}</ref>
* The [[paraphyletic]] ''[[Pythium]]'' group is more prevalent than ''Phytophthora'' and individual species have larger host ranges, although usually causing less damage. ''Pythium'' [[damping off]] is a very common problem in greenhouses, where the organism kills newly emerged seedlings. Mycoparasitic members of this group (e.g. ''[[Pythium oligandrum|P. oligandrum]]'') parasitize other oomycetes and fungi, and have been employed as biocontrol agents. One ''Pythium'' species, ''Pythium insidiosum'', also causes [[Pythiosis]] in mammals.
* The third group are the [[downy mildew]]s, which are easily identifiable by the appearance of white, brownish or olive "mildew" on the leaf undersides (although this group can be confused with the unrelated fungal [[powdery mildew]]s).
* The fourth group are the [[white blister rusts]], [[Albuginales]], which cause white blister disease on a variety of flowering plants. White blister rusts sporulate beneath the [[Epidermis (botany)|epidermis]] of their hosts, causing spore-filled blisters on stems, leaves and the [[inflorescence]]. The Albuginales are currently divided into three genera, ''[[Albugo]]'' parasitic predominantly to [[Brassicales]], ''[[Pustula (protist)|Pustula]]'', parasitic predominantly to [[Asterales]], and ''[[Wilsoniana]]'', predominantly parasitic to [[Caryophyllales]]. Like the [[downy mildews]], the [[white blister rusts]] are obligate [[biotrophic|biotrophs]], which means that they are unable to survive without the presence of a living host.

== References ==
{{Reflist|30em}}

== External links ==
*[http://comenius.susqu.edu/biol/202/CHROMALVEOLATA/HETEROKONTAE/Oomycota/default.htm Description of The Phylum Oomycota] {{Webarchive|url=https://web.archive.org/web/20150402143558/http://comenius.susqu.edu/biol/202/chromalveolata/heterokontae/oomycota/default.htm |date=2015-04-02 }} – Systematic Biology
*[http://www.ucmp.berkeley.edu/chromista/oomycota.html Introduction to the Oomycota] – University of California Museum of Paleontology (UCMP)
*[http://www.nature.com/nature/journal/v461/n7262/full/nature08358.html Genome sequence and analysis of the Irish potato famine pathogen Phytophthora infestans]
{{Life on Earth}}
{{Eukaryota|D.}}
{{Chromalveolata}}
{{Taxonbar|from1=Q21445833|from2=Q223597}}

[[Category:Water moulds| ]]

Oomycete - Revision history

imported>Iztwoz: /* External */ minor ce