The Phytomyxea are a class of

parasite Parasitism is a Symbiosis, close 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, adapted structurally to this way of lif ...

s that are cosmopolitan, obligate biotrophic protist parasites of plants, diatoms, oomycetes and brown algae. They are divided into the orders Plasmodiophorida (

ICZN The International Code of Zoological Nomenclature (ICZN) is a widely accepted convention in zoology that rules the formal scientific naming of organisms treated as animals. It is also informally known as the ICZN Code, for its publisher, the Int ...

, or Plasmodiophoromycota,

ICBN The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all those "trad ...

) and Phagomyxida. Plasmodiophorids are best known as pathogens or vectors for viruses of arable crops (e.g. club root in

Brassicaceae Brassicaceae () or (the older) Cruciferae () is a medium-sized and economically important family of flowering plants commonly known as the mustards, the crucifers, or the cabbage family. Most are herbaceous plants, while some are shrubs. The l ...

powdery scab Powdery scab is a disease of potato tubers. It is caused by the cercozoan ''Spongospora subterranea'' f. sp. ''subterranea'' and is widespread in potato growing countries. Symptoms of powdery scab include small lesions in the early stages of the d ...

in potatoes, and rhizomania in beets, especially

sugar beets Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double s ...

and some spinaches).

Life cycle

They typically develop within plant cells, causing the infected tissue to grow into a gall or scab. Important diseases caused by phytomyxeans include club root in cabbage and its relatives, and

in potatoes. These are caused by species of ''Plasmodiophora'' and ''Spongospora'', respectively.Agrios, George N. (2005). ''Plant Pathology''. 5th ed. Academic Press
link
The vegetative form is a multinucleate cell, called a

plasmodium ''Plasmodium'' is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of ''Plasmodium'' species involve development in a blood-feeding insect host which then injects parasites into a vert ...

. This ultimately divides to form new spores, which are released when the host's cells burst. Both resting spores and motile

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or m ...

s, which generally have two smooth

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have f ...

, are produced at different stages. Within the plasmodium, dividing nuclei have a distinctive cross-like appearance.

Classification

Plasmodiophorids were traditionally considered

slime mould Slime mold or slime mould is an informal name given to several kinds of unrelated eukaryotic organisms with a life cycle that includes a free-living single-celled stage and the formation of spores. Spores are often produced in macroscopic mul ...

s, because of the plasmodial stage and are often wrongly classified as

fungi 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 mushrooms. These organisms are classified ...

, and given names such as the Plasmodiophoromycota. However, genetic and ultrastructural studies indicate they belong to a diverse group of protists called the

Cercozoa Cercozoa is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead defined by molecular phylogenies of rRNA and actin or polyubiquitin. They were the first major ...

, are closely related to them. * Class Phytomyxea Engler & Prantl 1897 em. Cavalier-Smith 1993 ** Genus ?'' Pongomyxa'' ** Order Phagomyxida Cavalier-Smith 1993 *** Family Phagomyxidae Cavalier-Smith 1993 **** Genus '' Phagomyxa'' Karling 1944 ** Order Plasmodiophorida Cook 1928 em. Cavalier-Smith 1993 *** Family Endemosarcidae Olive & Erdos 1971 **** Genus '' Endemosarca'' Olive & Erdos 1971 *** Family Plasmodiophoridae Berl 1888 (plasmodial slime moulds) **** Genus '' Cystospora'' Elliott 1916 nomen dubium 'Acrocystis'' Ellis & Halsted ex Halsted 1890 non Zanardini 1872">Acrocystis.html" ;"title="'Acrocystis">'Acrocystis'' Ellis & Halsted ex Halsted 1890 non Zanardini 1872**** Genus ''Maullinia'' Maier et al. 2000 **** Genus ''Phytomyxa'' Schröter 1886 **** Genus ''Ligniera'' Maire & Tison 1911 [''Anisomyxa'' Němec 1913; ''

Rhizomyxa ''Ligniera'' is a protist genus of the family Plasmodiophoraceae. The genus name of ''Ligniera'' is in honour of Élie Antoine Octave Lignier (1855–1916), who was a French botanist, known for his work in the field of paleobotany Paleobota ...

'' Borzí 1884; '' Sorolpidium'' Němec 1911] **** Genus '' Membranosporus'' Ostenfeld & Petersen 1930 **** Genus '' Octomyxa'' Couch, Leitner & Whiffen 1939 **** Genus '' Plasmodiophora'' Woronin 1877 'Frankiella'' Maire & Tison 1909 non Speschnew 1900; ''Frankia">Frankiella.html" ;"title="'Frankiella">'Frankiella'' Maire & Tison 1909 non Speschnew 1900; ''Frankia'' Brunchorst 1886 non; ''Ostenfeldiella'' Ferdinandsen & Winge 1914] **** Genus ''Polymyxa'' Ledingham 1933 **** Genus ''Sorodiscus'' Lagerheim & Winge 1913 non Allman 1847 **** Genus '' Sorosphaera'' Schröter 1886 **** Genus '' Sorosphaerula'' Neuh. & Kirchm. 2011 **** Genus '' Spongospora'' Brunchorst 1887 'Clathrosorus'' Ferdinandsen & Winge 1920">Clathrosorus.html" ;"title="'Clathrosorus">'Clathrosorus'' Ferdinandsen & Winge 1920**** Genus ''Sporomyxa'' Léger 1908 **** Genus ''Tetramyxa'' Goebel 1884 [''Molliardia'' Maire & Tison 1911] **** Genus ''Woronina'' Cornu 1872

References

{{Taxonbar, from=Q134349 Endomyxa Parasitic rhizaria Parasites of plants Cercozoa classes