Phytomyxea
Encyclopedia
The Phytomyxea are a group of protist
s that are parasites of plants. A more common name for them is the plasmodiophorids, but this does not always include Phagomyxa. 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 powdery scab
in potatoes. These are caused by species of Plasmodiophora and Spongospora, respectively.
The vegetative form is a multinucleate cell
, called a plasmodium
. This ultimately divides to form new spores, which are released when the host's cells burst. Both resting spores and motile zoospores, which generally have two smooth flagella
, are produced at different stages. Within the plasmodium, dividing nuclei have a distinctive cross-like appearance.
Plasmodiophorids are traditionally considered slime mould
s, because of the plasmodial stage. Thus they are often classified as fungi
, and given names such as the Plasmodiophoromycota. However, genetic and ultrastructural studies indicate they belong to a diverse group of protists called the Cercozoa
, or are closely related to them.
Protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
s that are parasites of plants. A more common name for them is the plasmodiophorids, but this does not always include Phagomyxa. 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 powdery scab
Powdery scab
Powdery scab, is a disease that happens to tubers. It is caused by the cercozoan Spongospora subterranea, is widespread in potato growing countries. Symptoms of powdery scab include small lesions in the early stages of the disease, progressing to raised pustules containing a powdery mass. Powdery...
in potatoes. These are caused by species of Plasmodiophora and Spongospora, respectively.
The vegetative form is a multinucleate cell
Syncytium
In biology, a syncytium is a large cell-like structure; filled with cytoplasm and containing many nuclei. Most cells in eukaryotic organisms have a single nucleus; syncytia are specialized forms used by various organisms.The term may also refer to cells that are connected by specialized membrane...
, called a plasmodium
Plasmodium (slime mold)
A plasmodium is the macroscopic form of the protist known as a slime mold....
. This ultimately divides to form new spores, which are released when the host's cells burst. Both resting spores and motile zoospores, which generally have two smooth flagella
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
, are produced at different stages. Within the plasmodium, dividing nuclei have a distinctive cross-like appearance.
Plasmodiophorids are traditionally considered slime mould
Slime mould
Slime mold or mould is a broad term describing protists that use spores to reproduce. Slime molds were formerly classified as fungi, but are no longer considered part of this kingdom....
s, because of the plasmodial stage. Thus they are often classified as 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...
, 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
The Cercozoa are a group of protists. They are sometimes described as a kingdom.-Characteristics:The group includes most amoeboids and flagellates that feed by means of filose pseudopods. These may be restricted to part of the cell surface, but there is never a true cytostome or mouth as found in...
, or are closely related to them.
See also
- Spongospora subterranea f. sp. subterranea