DEVELOPMENT OF SPORES AND CHARACTERS OF MYCORRHIZAE

OF THE GENUS GLOMUS

In PVLG
Spores of Glomus spp. develop blastically at the end of a sporogenous hypha, although intercalarily spore formation has also been reported (e. g, Declerck et al. 2000). In most species, the sporogenous hypha develops from extraradical hyphae of mycorrhizal roots. Spores of some species, e. g., Gl. aggregatum N.C. Schenck & G.S. Sm. emend. Koske, Gl. intraradices N.C. Schenck & G.S. Sm., frequently occur inside roots (Schenck and Smith 1982). Glomus aggregatum and Gl. microaggregatum Koske et al. additionally produce inner spores from a sporogenous hypha arising from the subtending hypha of the parent spore (Błaszkowski 1991; Koske 1985; Koske et al. 1986a; Schenck and Smith 1982).

The surface of spores of Glomus spp. may be smooth (in most species) or differently ornamented (e. g., Gl. multiforum Tadych & Blaszk., Gl. pustulatum Koske et al.; Błaszkowski 1994a; Błaszkowski and Tadych 1997; Koske et al. 1986b). Some species produce spores enveloped in a hyphal mantle consisting of interwoven (e. g., Gl. mortonii Bentiv. & Hetrick, Gl. fuegianum (Speg.) Trappe & Gerd.; Bentivenga and Hetrick 1991; Błaszkowski et al. 1998) or dichotomously branched (Gl. corymbiforme Blaszk.; Błaszkowski 1995) hyphae.
In water
SEM
Most species of the genus Glomus produce spores singly in the soil. Other taxa form more or less compact spore aggregates (e. g., Gl. minutum Blaszk. et al., Gl. aggregatum; Błaszkowski et al. 2000; Błaszkowski 1991; Koske 1985) or sporocarps (e. g., Gl. coremioides (Berk. & Broome) D. Redecker & J.B. Morton, Gl. fuegianum, Gl. mosseae (Nicol. & Gerd.) Gerd. & Trappe; Almeida and Schenck 1990; Błaszkowski et al. 1998; Gerdemann and Trappe 1994) consisting of spores and a peridium. The formation of the peridium may precede the spore origination or the peridium expands together with the developing spores, as e. g. in Gl. mosseae and Gl. coronatum Giovann. (Giovannetti et al. 1991). Some spores of Gl. gibbosum Blaszk. develop within a hyphal mantle without an opening (Błaszkowski 1997).

Although fungi of the phylum Glomeromycota, except for Geosiphon pyriformis (Kütz.) Wettst. emend. Schüßler, are considered to form obligatorily arbuscular mycorrhizae in mutualistic associations with living plants (Morton and Benny 1990; Schüßler et al. 2001), the formation of spores associated with both mycorrhizal roots and non-root habitats by, e. g., Gl. fuegianum (Błaszkowski et al. 1998; Pegler et al. 1993), Gl. fasciculatum (Thaxt.) Gerd. & Trappe emend. C. Walker & Koske, and Gl. sinuosum (Gerd. & B.K. Bakshi) R.T. Almeida & N.C. Schenck (Gerdemann and Trappe 1974; Koske, pers. comm.) indicate that some species are facultative symbionts (Błaszkowski et al. 1998).

All members of the genus Glomus form spores with only one wall including at least two layers, of which the structural layer consists of many sublayers (laminae). The outer layer or layers adherent to the laminate layer frequently slough(s) with age. In some species, e. g., Gl. claroideum N.C. Schenck & G.S. Sm. and G. etunicatum W.N. Becker & Gerd., the outermost layer stains red in Melzer’s reagent (Stürmer and Morton 1997). A few species, e. g., Gl. claroideum, Gl. lamellosum Dalpé et al. and Gl. gibbosum, produce an inner flexible layer developing from the subtending hypha; this layer frequently is adherent to the inner surface of the laminate layer and, therefore, it usually is difficult to see (Błaszkowski 1997; Błaszkowski et al. 2002; Dalpé et al. 1992; Stürmer and Morton 1997). Of the described species, the inner flexible spore wall layer of only Gl. lamellosum stains in Melzer’s reagent (Błaszkowski et al. 2002); however, this property also occurs in some other undescribed species (Błaszkowski, pers. observ.).
In PVLG

The wall layers of a subtending hypha are continuous with spore wall layers. During ontogeny, they differentiate at the same time and rate. At the end of spore development, the lumen of the subtending hypha usually becomes closed by either (1) a curved septum continuous with the innermost lamina of the laminate spore wall layer, (2) an invaginated flexible innermost layer, (3) an amorphous plug, (4) thickening subtending hyphal wall, or (5) a combination of the structures mentioned.

 

In PVLG

Spores of the genus Glomus germinate by emergence of the germ tube through either the lumen of the subtending hypha (most species) or the spore wall. Germination by both the lumen and spore wall was also observed.

The mycorrhizae of Glomus spp. consist of arbuscules, vesicles (not always formed), and intra- and extraradical hyphae. Arbuscules have cylindrical or slightly flared trunks with branches progressively tapering in width toward tips. Vesicles usually are thin-walled and ellipsoid. Intraradical hyphae usually spread along roots and frequently form Y-shaped branches, H-shaped connections, and coils. Coils mainly occur at entry points.
In roots of Plantago lanceolata L.

REFERENCES

Almeida R. T., Schenck N. C. 1990. A revision of the genus Sclerocystis (Glomaceae, Glomales). Mycologia 82, 703-714.

Bentivenga S. P., Hetrick B. A. D. 1991. Glomus mortonii sp. nov., a previously undescribed species in the Glomaceae isolated from the tallgrass prairie in Kansas. Mycotaxon 42, 9-5.

Błaszkowski J. 1988. Four new species of the Endogonaceae (Zygomycotina) from Poland. Karstenia 27, 37-42.

Błaszkowski J. 1991. Polish Endogonaceae. IX. Glomus aggregatum with spores forming an evanescent outermost wall. Crypt. Bot. 2/3, 130-135.

Błaszkowski J. 1994. Polish Glomales 11. Glomus pustulatum. Mycorrhiza 4, 201-207.

Błaszkowski J. 1995. Glomus corymbiforme, a new species in Glomales from Poland. Mycologia 87, 732-737.

Błaszkowski J. 1997. Glomus gibbosum, a new species from Poland. Mycologia 89, 339-345.

Błaszkowski J., Adamska I., Madej T. 2002. Glomus lamellosum (Glomales, Zygomycota), an arbuscular mycorrhizal fungal species new for Poland and Europe. Mycotaxon 81, 281-292.

Błaszkowski J., Madej T., Tadych M. 1998. Entrophospora baltica sp. nov. and Glomus fuegianum, two species in the Glomales from Poland. Mycotaxon 68, 165-184.

Błaszkowski J., Tadych M. 1997. Glomus multiforum and G. verruculosum, two new species from Poland. Mycologia 89, 804-811.

Błaszkowski J., Tadych M., Madej M. 2000. Glomus minutum, a new species in Glomales (Zygomycetes) from Poland. Mycotaxon 76, 187-195.

Dalpé Y., Koske R. E., Tews L. L. 1992. Glomus lamellosum sp. nov.: a new Glomaceae associated with beach grass. Mycotaxon 43, 289-293.

Declerck S., Cranenbrouck S., Dalpé Y., Grandmougin-Ferjani A., Fontaine J., Sancholle M. 2000. Glomus proliferum sp. nov.: a description based on morphological, biochemical, molecular and monoxenic cultivation data. Mycologia 92, 1178-1187.

Gerdemann J. W., Trappe J. M. 1974. The Endogonaceae in the Pacific Northwest. Myc. Memoir 5, 1-76.

Koske R. E. 1985. Glomus aggregatum emended: A distinct taxon in the Glomus fasciculatum complex. Mycologia 77, 619-630.

Giovannetti M., Avio L., Salutini L. 1991. Morphological, cytochemical, and ontogenetic characteristics of a new species of vesicular-arbuscular mycorrhizal fungus. Canad. J. Bot. 69, 161-167.

Koske R. E. 1985. Glomus aggregatum emended: A distinct taxon in the Glomus fasciculatum complex. Mycologia 77, 619-630.

Koske R. E., Gemma J. N., Olexia P. D. 1986. Glomus microaggregatum, a new species in the Endogonaceae. Mycotaxon 26, 125-132.

Koske R. E., Friese C., Walker C., Dalpé Y. 1986. Glomus pustulatum: A new species in the Endogonaceae. Mycotaxon 26, 143-149.

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.

Pegler D. N., Spooner B. M., Young T. W. K. 1993. British truffles. A revision of British hypogeous fungi. Royal Botanic Gardens, Kew. 216 pp. + 26 plates.

Schenck N. C., Smith G. S. 1982. Additional new and unreported species of mycorrhizal fungi (Endogonaceae) from Florida. Mycologia 74, 77-92.

Schüßler A., Schwarzott D., Walker C. 2001. A new fungal phylum, the Glomeromycota: phylogeny and evolution. Myc. Res. 105, 1413-1421.

Stürmer S. L., Morton J. B. 1997. Developmental patterns defining morphological characters in spores of four species in Glomus. Mycologia 89, 72-81.