Draft of Glomus etunicatum Becker & Gerdemann [as ‘etunicatus’] for 2010/2011 EOL University Species Pages Initiative by ostn

Title: Draft For 2010/2011 Eol University Species Pages Initiative By Ostn (Public)
Name: Glomus etunicatum Becker & Gerdemann [as ‘etunicatus’]
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 Draft For 2010/2011 Eol University Species Pages Initiative By Ostn (Public) [Edit]

Description status: Approved
 (Latest review: 2010-12-17 08:21:33 PST (-0800) by Anne Pringle)

Taxonomic Classification:

Domain: Eukarya
Kingdom: Fungi
Phylum: Glomeromycota
Class: Glomeromycetes
Order: Glomerales
Family: Glomeraceae


General Description:

Glomus etunicatum is an arbuscular mycorrhizal fungus (hereafter referred to as an AM fungus). In general, AM fungi are obligate symbionts that participate in mutualistic relationships with various kinds of plants. The basis of the mutualism is nutrient exchange between the two partners. AM fungi are distinguished from the ectomycorrhizal fungi by a characteristic structure called an arbuscule, a tree-shaped hyphal structure that penetrates the walls of cortical cells in the roots of host plants. The arbuscule provides the interface between the two partners in the symbiosis.

Glomus etunicatum has large, multinucleate spores, like many other AM fungi. It produces round, thick-walled spores (chlamydospores) that are 68-144 μm in diameter. These spores have two layers, and the outer layer is ephemeral due to decomposition by soil microorganisms. This is why Glomus etunicatum has its name: ‘etunicatus’ is Latin for ‘deprived of its coat’. The outer wall is rarely found intact in mature spores. The inner wall darkens as the spore ages.

Once the spore germinates, hyphal growth ensues and the fungus begins looking for a suitable autotrophic plant whose roots to colonize. Hyphae are capable of anastomosis, or fusion, with closely related indidivuals.

AM fungi are thought to be one of the most ancient multicellular lineages with no evidence of sexual reproduction. There is no known sexual reproduction in Glomus etunicatum.

Debate swirls around the genetic organization of Glomus etunicatum (and of AM fungi generally). Evidence indicates that each spore contains hundreds of nuclei. There is debate about whether the spores contain haploid nuclei or polyploid nuclei. There is also debate as to whether the spores contain nuclei that are genetically different, or whether all nuclei in a spore are genetically identical. According to Jany and Pawlowska (2009) the population of nuclei in a particular spore is the result of an inundation of nuclei from the mycelium at large. Thus, spores are not populated by nuclei that derive from the mitotic division of a single nuclear progenitor. There is still much to be learned about the genetics and reproductive habits of Glomus etunicatum and of AM fungi in general.


Diagnostic Description:

The spores of Glomus etunicatum are similar to spores of G. caledonius, which are are larger and which have an outer wall that tends to persist longer. Additionally, hyphae of G. etunicatum are thin-walled, and so spores tend to break off from the hyphae immediately under the spore. Thus, spores do not cluster in this species when wet-sieved. This distinguishes G. etunicatum from G. fasciculatus and G. macrocarpus var. macrocarpus, both of which cluster when wet-sieved. G. macrocarpus var. geosporus spores are also found in singles when wet-sieved, but tend to be darker, larger, and to possess a thicker hyphal wall than spores of G. etunicatum.


Distribution:

Glomus etunicatum is apparently quite common. The fungus has been found in Illinois, Missouri, Florida, and in the Chihuahuan and Sonoran Deserts in North America. Becker and Gerdemann suggest that G. etunicatum is widespread in the Eastern United States. It has also been found in the Namib Desert in Africa, which suggests that the fungus is indeed widespread. More data about the distribution of this fungus are required to provide an exhaustive account, however.


Habitat:

Glomus etunicatum participates in mycorrhizal symbioses with various plants. A list of plant associates is as follows (and is surely incomplete): Acer saccharum Marsh, Andropogon gerardii Vitman, Andropogon scoparius Michx., Allium cepa L., Allium sativum L., Capsicum frutescens var. longum Sendt., Gleditsia triacanthos var. inermis Willd., Sorghum vulgare (Piper) Hitch., Trifolium repens L., Zea mays L., The wide variety of plant associates suggests that G. etunicatum is found in a variety of habitats, though more data are needed.


References:

Daniels Hetrick, B.A. et al. Effects of Drought Stress on Growth Response in Corn, Sudan Grass, and Big Bluestem to Glomus etunicatum. New Phytol. (1987), 105, 403-410

Hijri, M. & Sanders, I.R. Low gene copy number shows that arbuscular mycorrhizal fungi inherit genetically different nuclei. NATURE, 433 (7022): 160-163 JAN 13 2005

Jany, J. & Pawlowska, T.E. Multinucleate Spores Contribute to Evolutionary Longevity of Asexual Glomeromycota. Vol. 175, No. 4, The American Naturalist, April 2010

Pawlowska, T., et al. In vitro propagation and life cycle of the arbuscular mycorrhiza fungus Glomus etunicatum. Mycol. Res. 103 (12): 1549-1556 (1999)

Smith, S.E. & Read, D. Mycorrhizal Symbiosis (Academic, San Diego, 2008)

Stutz, J.C., et al. Patterns of species composition and distribution of arbuscular mycorrhizal fungi in arid regions of southwestern North America and Namibia, Africa. Can. J. Bot. 78(2): 237–245 (2000)

Yawney, W.J. & Schultz, R.C. Anatomy of a vesicular-arbuscular endomycorrhizal symbiosis between sugar maple (Acer saccharum Marsh) and Glomus etunicatum Becker & Gerdemann. New Phytol. (1990), 114, 47-57


Notes:

Glomus etunicatum was introduced as Glomus etunicatus. However, the former name appears to be used exclusively to refer to this species.


Description author: ostn (Request Authorship Credit)


Created: 2010-12-09 07:24:37 PST (-0800) by ostn
Last modified: 2010-12-09 08:53:48 PST (-0800) by ostn
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