''Allomyces'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of fungi in the family Blastocladiaceae. It was

circumscribed In geometry, the circumscribed circle or circumcircle of a polygon is a circle that passes through all the vertices of the polygon. The center of this circle is called the circumcenter and its radius is called the circumradius. Not every polyg ...

by British mycologist

Edwin John Butler Sir Edwin John Butler (13 August 1874 – 4 April 1943) was an Irish mycologist and plant pathologist. He became the Imperial Mycologist in India and later the first director of the Imperial Bureau of Mycology in England. He was knighted in 1 ...

in 1911. Species in the genus have a polycentric

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...

and reproduce sexually or asexually by

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 ...

s that have a whiplash-like flagella. They are mostly isolated from soils in tropical countries, commonly in ponds, rice fields, and slow-moving rivers.

Morphology

''Allomyces'' thalli consist of a cylindrical trunk-like basal cell that gives rise to well-developed, highly branched rhizoids that anchor the thallus to the substrate. The trunk-like basal cell also gives rise to numerous dichotomously branched side branches that terminate as either resistant sporangia, zoosporangia, or gametangia depending on the life cycle stage. Septa are sometimes present, especially at the base of reproductive organs. Allomyces germling 6-14-11

Life cycle and mating

There are three distinct life cycles in ''Allomyces'', and some authors delineate the subgenera ''Euallomyces'', ''Cystogenes'', and ''Brachyallomyces'' based on the life cycles while others do not. Euallomyces and Brachyallomyces are known to be classified as polyphyletic but Cystogenes is monophyletic. The ''Euallomyces'' life cycle is an

anisogamous Different forms of anisogamy: A) anisogamy of motile cells, B) egg_cell.html"_;"title="oogamy_(egg_cell">oogamy_(egg_cell_and_sperm_cell),_C)_anisogamy_of_non-motile_cells_(egg_cell_and_spermatia)..html" ;"title="egg_cell_and_sperm_cell.html" ;" ...

alternation of generations between a haploid

gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the ...

and a diploid sporophyte. In this life cycle, the two stages are indistinguishable until reproductive organs are formed. Gametophytes produce colorless female gametangia and orange male gametangia; the orange coloration is transferred to the male gametes and is due to the presence of gamma carotenoid. Formation of male gametes is faster than of female gametes. Both male and female gametangia release motile gametes, but the male gametes are smaller and orange. Female gametangia and gametes release a

pheromone A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

called sirenin that attracts the male gametes. Male gametes produce a pheromone called parisin. Female gametes are sluggish and stay close to the female gametangia, which sets up a strong concentration gradient of sirenin. Fertilization of female gametes by male gametes appears to be near 100% efficient. Fertilization takes place when two gametes contact one another. The plasma membranes fuse to form a binucleate cell with nuclear fusion quickly following. The resulting zygote is initially biflagellate, but it soon encysts and germinates. It grows into a dichotomously branched sporophyte, which forms two types of sporangia: thin-walled zoosporangia that may be colorless or orange and thick-walled resting sporangia that are reddish-brown due to the presence of melanin pigments. The thin-walled zoosporangia give rise to motile zoospores that germinate and grow into another sporophyte. The resting sporangia undergo

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately r ...

at germination and give rise to haploid zoospores that will germinate and grow into gametophytes. In ''Cystogenes'' life cycle the resting sporangia (from the sporophyte) give rise to biflagellated, bi-nucleated zoospores that will encyst, undergo meiosis, and germinate to yield motile gametes. These gametes will then fuse in pairs and the resulting zygotes germinate and grow into new sporophytes. In the ''Brachyallomyces'' life cycle, the gametophytic stage is missing altogether.

Ecology

''Allomyces'' species seem to have a global distribution and are readily isolated from soils and waters by baiting with a sterile seed. Species of ''Allomyces'' can be parasitized by '' Catenaria allomycis'', ''

Rozella allomycis ''Rozella'' is a fungal genus of obligate endoparasites of a variety of hosts, including Oomycota, Chytridiomycota, and Blastocladiomycota. ''Rozella'' was circumscribed by French mycologist Marie Maxime Cornu in 1872. Considered one of the ear ...

'', and '' Olpidium allomycetos''.

Taxonomy

The genus was circumscribed in 1911 by Butler and numerous species have been described. Based on type of life cycle, Emerson delineated three subgenera: ''Euallomyces'', ''Cystogenes'', and ''Brachyallomyces''. Based on a molecular phylogeny using portions of the nuclear ribosome, it appears ''Euallomyces'' and ''Brachyallomyces'' are

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

but ''Cystogenes'' is monophyletic. As well, it appears several species in the genus are polyphyletic.

Species

*'' Allomyces anomalus'' R.Emers. 1941 *'' Allomyces arbusculus'' E.J.Butler 1911 *'' Allomyces catenoides'' Sparrow 1964 *'' Allomyces cystogenus'' R.Emers. 1941 *'' Allomyces javanicus'' Kniep 1929 *'' Allomyces macrogynus'' (R.Emers.) R.Emers. & C.M.Wilson 1954 *'' Allomyces moniliformis'' Coker & Braxton 1926 *'' Allomyces neomoniliformis'' Indoh 1940 *'' Allomyces reticulatus'' R. Emers. & J.A.Robertson 1974 *'' Allomyces strangulata'' Minden 1916

References

6. Allomyces. Phillip W. Miller,... W. James Nelson, in Current Topics in Membranes, (2013). Journals & Books. https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/allomyces

External links

Blastocladiomycota Fungus genera {{Blastocladiomycota-stub