''Allomyces'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of fungi in the family Blastocladiaceae. It was circumscribed by British mycologist Edwin John Butler in 1911. Species in the genus have a polycentric

thallus Thallus (: 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. A thallus usually names the entir ...

and reproduce sexually or asexually by

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion in aqueous or moist environments. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Certain zoospores are ...

s that have a whiplash-like

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

. 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) 283x283px Anisogamy is a form of sexual reproduction">egg cell">oogamy (egg cell and sperm cell), C) anisogamy of non-motile cells (egg cell and spermatia).">283x283px Anisogamy is ...

alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the predominant type of life cycle in plants and algae. In plants both phases are multicellular: the haploid sexual phase – the gametophyte – alternates with a diploi ...

between a

haploid Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Here ''sets of chromosomes'' refers to the num ...

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 se ...

and a

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Here ''sets of chromosomes'' refers to the number of maternal and paternal chromosome copies, ...

sporophyte A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...

. 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 Carotenoids () are yellow, orange, and red organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips, corn, tomatoes, cana ...

. 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 that 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 that 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 () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...

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'', 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 that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

, but ''Cystogenes'' is

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

. Moreover, 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

External links

Blastocladiomycota Fungus genera {{Blastocladiomycota-stub