Member of phylum Chytridiomycota known as the most primitive fungi as per there fossil record. They are also known as Chytrids.
Traditionally, the Chytridiomycota have been regarded as aquatic fungi, but this is a misnomer.
They usually found wherever they are searched for, from the dry valleys of Antarctica to water held in tropical bromeliads.
On all continents and on remote islands in marine, acidic, neutral, and basal water. Many are parasitic on microflora and microfauna such as algae and rotifers, and some are parasitic on vascular plants.
The plat pathogens, with very few exceptions, cause little damage to the host.
They are mainly found in 4 habitats
1) Aquatic Species of Chytridiomycota
Much of the early literature dealt with aquatic species on freshwater algae, but little was known about the presence of chytrids in the ecosystem until the pioneering work of Canter and Lund.
Canter reported on Chytrids on planktonic algae, including many new species for 40 years. And he demonstrated that the population in English lakes is controlled during epidemics.
Many chytrids are also parasitic on invertebrates and there is considerable interest in the use of Coelomycetes, a genus of obligate parasites, in the body of insects and in the biological control of mosquitoes.
2) Halophytic species in Chytridiomycota
A number of chytrids have been found from saline sites but it is uncertain how many species are truly marine.
For example, Sparrow (1960) thought Olpidium maritimum, a chytrid described from brackish water, was probably an adaptive form of Olpidium pendulum.
In a series of pure culture experiments on species from coastal, saline soils, in 1971 Booth concluded that within species there where ecotypes with various tolerance to salinity, corresponding to the habitat, but that, in general, chytrids are facultatively marine.
Nonetheless, chytrids from estuarine habitats are obligate halophytes even though the minimum salinity is low, and there is a specific requirement of sodium.
In exhaustive observations in coastal areas of Europe, Ulken (1974) concluded that at high salinities and low temperatures thraustochytrids dominated, whereas at low salinities and higher temperatures chytrids dominated.
These observations were supported by laboratory testes which indicated that tolerance to salinity was a determining factor.
These have been many reports of chytrids occurring on seaweeds, including records from the Indian coast.
Reghukumar reported that Chytridium polysiphoniae Cohn. A parasite on the red alga, Centroceras clavulatum, grew best in the laboratory at 25% salinity, but rather poorly at 35%.
That is approximately the salinity of the open ocean. It is thus likely that chytrids have become adapted to saline soils and the sea, and that some can withstand salinity approaching that found in the open ocean.
3) Soil-inhabiting Species of Chytridiomycota
Although many of the early observation was in aquatic habitats, it was soon realized that chytrids also occurred in soil.
For example, perhaps two of the better-known species from the soil, Rhizophlyctis rosea and Olpidium brassicae.
Were described in 1865 and 1878, respectively. However, it was not until work by German groups, and in England by Willoughby that chytrids were realized to be just as terrestrial as they were aquatic.
They are found not only in mud and soil from ditches and on pond banks, but also in soils with rain as the sole source of moisture.
They are found in arid canyons of the Arizona and Mexican deserts, from above permafrost in the high arctic, from acidic peat, and from highly alkaline soils.
Little is known about the role of chytrids in soil. Cultural studies show that many species are effective, decomposers of cellulose, hemicellulose, chitin, and keratin, but the relative importance of chytrids to other organisms in soil fertility remains to be investigated.
4) Phytopathogens and Vectors of Plant Viruses
Parasitic species on vascular plants are confirmed to four genera, Synchytrium, Physoderm, Olpidium, and Rhizophydium, but the only species of major economic importance as a phytopathogen is Synchytrium endobioticum, the cause of the potato wart disease.
Physoderma maydis occasionally reachease minor importance as a pathogen.
Rhizophydium is a genus of primarily aquatic species occurring in open water and mud, but one species, R. graminis is parasitic on roots of monocots and dicots.
It is widespread in its distribution but dose not cause any noticeable harm to crops.
Olpidium brassicae and Olpidium radicale are economically important as vectors of destructive plant viruses.
However, they do not cause much harm to the host plant except possibly in combination with other pathogens.