DEVELOPMENT OF SPORES AND CHARACTERS OF MYCORRHIZAE
OF THE GENUS ENTROPHOSPORA
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Spores of Entrophospora baltica and E. infrequens, the only two representatives of the genus Entrophospora, occur singly in the soil or inside roots (Blaszkowski et al. 1988; Sieverding and Oehl 2006). The spores develop inside the neck of a sporiferous saccule directly at or at a short distance from the saccule and originate from the neck and saccule contents. The sporiferous saccules originate terminally from or intercalary inside mycorrhizal extra- and intraradical hyphae by their swelling.
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The spores of the two species listed above are globose to subglobose and coloured. Their subcellular structure consists of a 4-layered, coloured spore wall and one inner 3-layered, colourless germination wall, of which the middle layer is much thicker than the two other ones.
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The outermost sloughing layer of the 4-layered spore wall of E. baltica and the two outer evanescent layers of the 4-layered spore wall of E. infrequens are continuous with the layer(s) of their sporiferous saccules (Blaszkowski et al. 1988; Sieverding and Oehl 2006). The permanent layers of this wall usually are continuous with the wall of two short opposite stalks, of which one projects inward the saccule, and the second towards the end of the sporiferous saccule neck. The stalk directed to the saccule usually is funnel-shaped, and the second one is cylindrical.
The two opposite pores formed at the beginning of the spore origination inside the neck of the sporiferous saccule are closed by the material building the permanent spore wall layers after the full differentiation of the spore wall. In spores lacking the sporiferous saccules, two opposite cicatrices resembling small rings with a slightly raised border are visible. The cicatrices are frequently accompanied by stalks developed from the permanent spore wall layers.
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Entrophospora infrequens, the only species of this genus grown in one-species cultures, formed vesicular-arbuscular mycorrhizae staining intensively in trypan blue (Sieverding and Oehl 2006).
The genus Entrophospora has been erected from Glomus infrequens after the recognition of the origination of its spores inside the neck of a sporiferous saccule (Ames and Schneider 1979). The main reason of the erroneous accommodation of this fungus in the genus Glomus was the use in the establishment of this taxon incomplete spores with a short stalk (subtending hypha), making them, thereby, similar to spores of the genus Glomus .
The genus Entrophospora, initially placed in the family Endogonaceae Paoletti in the order Endogonales Moreau, has subsequently been transferred to the newly erected order and family Glomales (ortographically corrected to Glomerales by Schüßler et al. 2001) and Acaulosporaceae, respectively, the latter with the type genus Acaulospora (Morton and Benny 1990). Walker and Schüßler (2004) located the family Acaulosporaceae with the genera Acaulospora and Entrophospora in the new order Diversisporales, including the families Diversisporaceae with the genus Diversispora, Gigasporaceae with the genera Gigaspora and Scutellospora and Pacisporaceae with the genus Pacispora. In 2006, Sieverding and Oehl (2006) established the family Entrophosporaceae with the type genus Entrophospora, remaining in the family Acaulosporaceae representatives of the genus Acaulospora, as well as Kuklospora colombiana and K. kentinensis, species originally classified within the genus Entrophospora sensu Ames and Schneider (1979). The main reasons of the separation of Entrophospora spp. from the family Acaulosporaceae were (1) the formation of 2-walled spores by Entrophospora spp., and 3-walled by fungi of the Acaulosporaceae, (2) the presence of a relatively thick, coriaceous sensu Walker (1986), layer in the inner germination wall of spores of Entrophospora spp. and its lack in any inner germination wall of spores of the genera Acaulospora and Kuklospora, and (3) the production of an outer beaded layer in the innermost germination wall of spores of most known species of the Acaulosporaceae compared with the lack of such a layer in the inner germination wall of E. baltica and E. infrequens spores. Additionally, all available results of molecular analyses of members of the Acaulosporaceae and E. infrequens have indicated no relationship between these fungi (Sieverding and Oehl 2006).
REFERENCES
Ames R. N., Schneider R. W. 1979. Entrophospora, a new genus in the Endogonaceae. Mycotaxon 8, 347-352.
Blaszkowski J., Madej T., Tadych M. 1998. Entrophospora baltica sp. nov. and Glomus fuegianum, two species in the Glomales from Poland. Mycotaxon 68, 165-184.
Morton J. B., Benny G. L. 1990. Revised classification of arbuscular mycorrhizal fungi (Zygomycetes): a new order, Glomales, two new suborders, Glomineae and Gigasporineae, and two new families, Acaulosporaceae and Gigasporaceae, with an emendation of Glomaceae. Mycotaxon 37, 471-491.
Schüßler A., Schwarzott D., Walker C. 2001. A new fungal phylum, the Glomeromycota: phylogeny and evolution. Myc. Res. 105, 1413-1421.
Sieverding E., Oehl F. 2006. Revision of Entrophospora and description of Kuklospora and Intraspora, two new genera in the arbuscular mycorrhizal Glomeromycetes. J. Appl. Bot. Food Qual. 80, 69-81.
Walker C. 1986. Taxonomic concepts in the Endogonaceae. II. A fifth morphological wall type in endogonaceous spores. Mycotaxon 25, 95-99.
Walker C., Schüßler A. 2004. Nomenclatural clarifications and new taxa in the Glomeromycota. Mycol. Res. 108, 979-982.