| Phytomyxea | |
|---|---|
 | |
| Resting spores of different species | |
Scientific classification | |
| Domain: | Eukaryota |
| Clade: | Diaphoretickes |
| Clade: | SAR |
| Clade: | Rhizaria |
| Phylum: | Endomyxa |
| Class: | Phytomyxea Cavalier-Smith, 1993 |
| Orders | |
| Synonyms | |
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ThePhytomyxea are aclass ofparasites that are cosmopolitan, obligate biotrophic protist parasites of plants, diatoms, oomycetes and brown algae.[1] They are divided into the ordersPlasmodiophorida (ICZN, orPlasmodiophoromycota,ICBN) andPhagomyxida.[2]Plasmodiophorids are best known as pathogens or vectors for viruses of arable crops (e.g.club root inBrassicaceae,powdery scab in potatoes, andrhizomania in beets, especiallysugar beets and some spinaches).[3]
They typically develop within plant cells, causing the infected tissue to grow into a gall or scab. Important diseases caused by phytomyxeans includeclub root in cabbage and its relatives, andpowdery scab in potatoes.[4] These are caused by species ofPlasmodiophora andSpongospora, respectively.[5]
The vegetative form is amultinucleate cell, called aplasmodium. This ultimately divides to form new spores, which are released when the host's cells burst. Both resting spores and motilezoospores, which generally have two smoothflagella, are produced at different stages. Within the plasmodium, dividing nuclei have a distinctive cross-like appearance.
Plasmodiophorids were traditionally consideredslime moulds, because of the plasmodial stage and are often wrongly classified asfungi, and given names such as thePlasmodiophoromycota. However, genetic and ultrastructural studies indicate they belong to a diverse group of protists called theCercozoa, are closely related to them.
