Glomeromycetes
| Glomeromycota | |
|---|---|
 |
|
| Gigaspora margarita in association with Lotus corniculatus | |
| Scientific classification | |
| Kingdom: | Fungi |
| Division: |
Glomeromycota C.Walker & A.Schuessler (2001) |
| Class: |
Glomeromycetes Caval.-Sm. (1998) |
| Orders | |
Glomeromycota (informally glomeromycetes) is one of eight currently recognized divisions within the kingdom Fungi, with approximately 230 described species. Members of the Glomeromycota form arbuscular mycorrhizas (AMs) with the roots or thalli (e.g. in bryophytes) of land plants. Geosiphon pyriformis forms an endocytobiotic association with cyanobacteria, and is the only member of the Glomeromycota known not to form arbuscular mycorrhiza in association with plants. AM formation has not yet been shown for all species. The majority of evidence shows that the Glomeromycota are symbionts with land plants (Nostoc in the case of Geosiphon) for carbon and energy, but there is recent circumstantial evidence that some species may be able to lead an independent existence. The arbuscular mycorrhizal species are terrestrial and widely distributed in soils worldwide where they form symbioses with the roots of the majority of plant species (>80%). They can also be found in wetlands, including salt-marshes, and associated with epiphytic plants.
The Glomeromycota have generally coenocytic (occasionally sparsely septate) mycelia and reproduce asexually through blastic development of the hyphal tip to produce spores (Glomerospores) with diameters of 80–500 μm. In some, complex spores form within a terminal saccule. Recently it was shown that Glomus species contain 51 genes encoding all the tools necessary for meiosis. Based on these and related findings, it was suggested that Glomus species may have a cryptic sexual cycle.
New colonization of AM fungi largely depends on the amount of inoculum present in the soil. Although pre-existing hyphae and infected root fragments have been shown to successfully colonize the roots of a host, germinating spores are considered to be the key players in new host establishment. Spores are commonly dispersed by fungal and plant burrowing herbivore partners, but some air dispersal capabilities are also known. Studies have shown that spore germination is specific to particular environmental conditions such as right amount of nutrients, temperature or host availability. It has also been observed that the rate of root system colonization is directly correlated to spore density in the soil. In addition, new data also suggests that AM fungi host plants also secrete chemical factors which attract and enhance the growth of developing spore hyphae towards the root system.
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