Rhizophagus irregularis explained

Rhizophagus irregularis (previously known as Glomus intraradices^{[1] [2]}) is an arbuscular mycorrhizal fungus used as a soil inoculant in agriculture and horticulture. Rhizophagus irregularis is also commonly used in scientific studies of the effects of arbuscular mycorrhizal fungi on plant and soil improvement. Until 2001, the species was known and widely marketed as Glomus intraradices, but molecular analysis of ribosomal DNA led to the reclassification of all arbuscular fungi from Zygomycota phylum to the Glomeromycota phylum.^[3]

Description

Spores

• Color — white, cream, yellow-brown ^[4]
• Shape — elliptical with irregularities ^[4]
• Size — generally between 40–140 μm ^[4]

Hyphae

• Shape — Cylindrical or slightly flared ^[4]
• Size — Width: 11–18 μm ^[4]

Identification

Rhizophagus irregularis colonization peaks earlier than many of the other fungi in Rhizophagus. There tends to be extensive hyphal networking and intense intraradical spores associated with older roots of host plants.

At times the spores are densely clustered or patchily distributed, depending on the host species. When the spores are heavily clustered, mycorrhizologists and others will tend to mistake R. irregularis for G. fasciculatum.^[4]

Reproduction

Rhizophagus irregularis (previously known as Glomus intraradices) has been found to colonise new plants by means of spores, hyphae or fragments of roots colonized by the fungus ^[5]

Meiosis and recombination

Arbuscular mycorrhiza (AM) fungi were thought to have propagated clonally for over 500 million years because of their lack of visible sexual structures and thus were considered to be an ancient asexual lineage.^[6] However, homologs of 51 meiotic genes, including seven genes specific for meiosis were found to be conserved in the genomes of five AM species including Rhizophagus irregularis (referred to by its synonym designation Glomus irregulare).^[6] This observation suggests that the supposedly ancient asexual AM fungi are likely capable of undergoing a conventional meiosis.^[6] R. irregularis dikaryons also appear to be capable of genetic recombination.^[7]

Ecology and distribution

Distribution

Rhizophagus irregularis can be found in almost all soils, especially those populated with common host plants and in forests and grasslands.

This is a brief list of some common host plants. Most agricultural crops will benefit from Rhizophagus irregularis inoculation. Generally host plants must be vascular plants, but not always.^[8]

• Onion — Allium cepa L.^[9]
• Soapbush Wattle — Acacia holosericea^[10]
• Flax — Linum usitatissimum L.^[11]
• Cowpea — Vigna unguiculata ^[12]
• Tomato Plant — Lycopersicon esculentum ^[13]
• Albaida — Anthyllis cytisoides ^[14]

Conservation and status

Rhizophagus irregularis is not of conservation concern; however, individual populations could be harmed by agricultural chemicals and tillage.

Relevance

In numerous scientific studies R. irregularis has been shown to increase phosphorus uptake in multiple plants as well as improve soil aggregation due to hyphae.^[15]

Because of these qualities, R. irregularis is commonly found in mycorrhizal based fertilizers.

In a 2005 study, R. irregularis was found to be the only arbuscular mycorrhizal fungi that was able to control nutrient uptake amounts by individual hyphae depending on differing phosphorus levels in the surrounding soil.^[11]

External links

• Formey D, Molès M, Haouy A, etal . Comparative analysis of mitochondrial genomes of Rhizophagus irregularis — syn. Glomus irregulare - reveals a polymorphism induced by variability generating elements . The New Phytologist . 196 . 4 . 1217–27 . December 2012 . 22967288 . 10.1111/j.1469-8137.2012.04283.x.
• JGI Mycorrhizal Genomics Initiative on Rhizophagus irregularis DAOM 181602 v1.0

Notes and References

1. Web site: Home — Rhizophagus irregularis DAOM 181602 v1.0. genome.jgi.doe.gov.
2. Stockinger . H. . Walker . C. . Schußler . A. . 2009 . 'Glomus intraradices DAOM197198', a model fungus in arbuscular mycorrhiza research, is not Glomus intraradices . New Phytol . 183 . 4. 1176–87 . 10.1111/j.1469-8137.2009.02874.x. 19496945 . free .
3. Krüger. Manuela . Claudia Krüger . Christopher Walker . Herbert Stockinger . Arthur Schüßler. Phylogenetic reference data for systematics and phylotaxonomy of arbuscular mycorrhizal fungi from phylum to species level. New Phytologist. 2012. 193. 4. 970–984. 10.1111/j.1469-8137.2011.03962.x . 22150759.
4. Morton, J, & R Amarasinghe. Glomus intraradices.International Culture Collection of (Vesicular) Arbuscular Mycorrhizal Fungi. 2006. West Virginia University. 17 November 2009. http://invam.caf.wvu.edu/index.html .
5. Klironomos . JN . Hart . MM . Aug 2002 . Colonization of roots by arbuscular mycorrhizal fungi using different sources of inoculum . 10.1007/s00572-002-0169-6 . 12189472 . Mycorrhiza . 12 . 4. 181–4 . 19464409 .
6. Halary S, Malik SB, Lildhar L, Slamovits CH, Hijri M, Corradi N . Conserved meiotic machinery in Glomus spp., a putatively ancient asexual fungal lineage . Genome Biol Evol . 3 . 950–8 . 2011 . 21876220 . 3184777 . 10.1093/gbe/evr089 .
7. Mateus ID, Auxier B, Ndiaye MM, Cruz J, Lee SJ, Sanders IR . Reciprocal recombination genomic signatures in the symbiotic arbuscular mycorrhizal fungi Rhizophagus irregularis . PLoS One . 17 . 7 . e0270481 . 2022 . 35776745 . 9249182 . 10.1371/journal.pone.0270481 . free.
8. Book: Peterson, R.L. . H.B. . Massicotte . L.H. . Melville . [{{GBurl|lZ3En5HpHFkC|p=8}} Mycorrhizas: Anatomy and Cell Biology ]. NRC Research Press . Ottawa . 2004 . 978-0-85199-901-2 . 7–8 .
9. Toro M, Azcon R, Barea J . Improvement of Arbuscular Mycorrhiza Development by Inoculation of Soil with Phosphate-Solubilizing Rhizobacteria To Improve Rock Phosphate Bioavailability ((sup32)P) and Nutrient Cycling . Applied and Environmental Microbiology . 63 . 11 . 4408–12 . November 1997 . 10.1128/aem.63.11.4408-4412.1997 . 16535730 . 1389286 . 1997ApEnM..63.4408T .
10. Duponnois . R . Colombet . A . Hien . V . Thioulouse . J . 2005 . the mycorrhizal fungus Glomus intraradices and rock phosphate amendment influence plant growth and microbial activity in the rhizosphere of Acacia holosericea . Soil Biology & Biochemistry . 37 . 8. 1460–1468 . 10.1016/j.soilbio.2004.09.016.
11. Cavagnaro . T . Smith . F . Smith . S . Jakobsen . I . 2005 . Functional diversity in arbuscular mycorrhizas: exploitation of soil patches with different phosphate enrichment differs among fungal species . Plant, Cell and Environment . 28 . 5. 642–650 . 10.1111/j.1365-3040.2005.01310.x. free .
12. Augé . R . Stodola . A . Tims . J . Saxton . A . 2000 . Moisture retention in a mycorrhizal soil . Plant and Soil . 230 . 1 . 87–97 . 10.1023/a:1004891210871. 6174495 .
13. Cavagnaro . T . Jackson . L . Six . J . Ferris . H . Goyal . S . Asami . D . Scow . K . 2005 . Arbuscular mycorrhizas, microbial communities, nutrient availability, and soil aggregates in organic tomato production . Plant and Soil . 282 . 1–2. 209–225 . 10.1007/s11104-005-5847-7. 6935846 .
14. Requena . N . Perez-Solis . E . Azcón-Aguilar . C . Jeffries . P . Barea . J . 2000 . Management of indigenous plant-microbe symbioses aids restoration of desertified ecosystems . Applied and Environmental Microbiology . 67 . 2. 495–498 . 10.1128/aem.67.2.495-498.2001. 11157208 . 92612 . 10.1.1.334.4707 .
15. Cardoso . Irene M. . Kuyper . Thomas W. . 2006 . Mycorrhizas and tropical soil fertility . Agriculture, Ecosystems & Environment . 116 . 1–2 . 72–84 . 10.1016/j.agee.2006.03.011.