Glomus (fungus)

Taxobox
name = "Glomus"
regnum = Fungi
phylum = Glomeromycota
classis = Glomeromycetes
ordo = Glomerales
familia = Glomeraceae
genus = "Glomus"
subdivision_ranks = Species
subdivision ="Glomus aggregatum"
"Glomus etunicatum"
"Glomus fasciculatum"
"Glomus intraradices"
"Glomus microaggregatum"
"Glomus mosseae"
("ca." 90 species described)

"Glomus" is a genus of arbuscular mycorrhizal (AM) fungi, and all species form symbiotic relationships (mycorrhizas) with plant roots. "Glomus" is the largest genus of AM fungi, with "ca." 90 species described, but as currently defined is non-monophyletic. [ [http://www.lrz-muenchen.de/~schuessler/amphylo/amphylogeny.html AMF-phylogeny.com] ]

Classification

"Glomus" is the only genus in the family Glomeraceae, in the division Glomeromycota. Some members of the genus were originally described as "Sclerocystis" species, but this genus has been entirely transferred to "Glomus". However, further taxonomic changes are likely as the phylogeny of AM fungi becomes better understood.

"Glomus" is likely related to the fossil fungus "Glomites", discovered in the Rhynie chert deposits from the Early Devonian (400 million years ago).

Ecology

As with other AM fungi, all "Glomus" species are thought to be obligate symbionts, dependent on their mycorrhizal association with plant roots to complete their life cycle. They cannot be cultured in the laboratory in the absence of a plant host. "Glomus" species are found in nearly all terrestrial habitats, including arable land, deserts, grasslands, tropical forests, and tundras.

Arbuscular mycorrhizal fungi can provide numerous benefits to their plant hosts, including improved nutrient uptake, drought resistance, and disease resistance. However, the symbiosis is not mutualistic in all circumstances and may often be parasitic, with a detrimental effect on plant growth. Rarely, some plant species can parasitise the fungi.cite journal
author=Bidartondo, M.I., Redecker, D., Hijri, I., Wiemken, A., Bruns, T.D., Dominguez, L., Sersic A., Leake, J.R., Read, D.J.
year= 2002
title= Epiparasitic plants specialized on arbuscular mycorrhizal fungi
journal= Nature
volume= 419
pages= 389–392
doi= 10.1038/nature01054]

Life cycle

"Glomus" species are entirely asexual. Spores are produced at the tips of hyphae either within the host root or outside the root in the soil. Thought to be chlamydospores, these spores germinate and the germination tube that is produced grows through the soil until it comes into contact with roots. The fungus then penetrates the root and grows between root cells, or it may penetrate the cell wall and grow within root cells. Inside the root, the fungus forms arbuscules, which are highly branched hyphal structures that serve as sites of nutrient exchange with the plant. Arbuscules are formed within plant cell walls but are surrounded by an invaginated cell membrane, so remain within the apoplast. The fungus may also form vesicles, swollen structures which are thought to function as food storage organs.

Agricultural significance

Several species of "Glomus", including "G. aggregatum", are cultured and sold as mycorrhizal inoculant for agricultural soils. One species, "G. macrocarpum" (and possibly also "G. microcarpum"), causes tobacco stunt disease.cite journal
author=Modjo, H.S., Hendrix, J.W.
year= 1986
title= The mycorrhizal fungus "Glomus macrocarpum" as a cause of tobacco stunt disease
journal= Phytopathology
volume= 76
pages= 688–691]

References

* [http://annual.sp2000.org/browse_taxa.php?path=0,16963400,16964022,16964023,16964032,16964033,17008904&selected_taxon=17008904 "Genus "Glomus" at the Catalogue of Life Checklist]
* [http://invam.caf.wvu.edu/index.html International Culture Collection of (Vesicular) Arbuscular Mycorrhizal Fungi]
* [http://www.biologie.uni-hamburg.de/b-online/library/steur/engrhyn/eglomit.html Symbiotic Fungi]