Glomus insculptum Błaszk.

SPORES borne singly in the soil; yellowish white (2A2) to golden yellow (5B8); globose to subglobose; (50-)71(-85) µm diam; sometimes ovoid; 55-60 x 80-85 µm; with a single subtending hypha.

SUBCELLULAR STRUCTURE OF SPORES consists of one wall with two layers ( swl1 and 2).

In PVLG
In PVLG+Melzer's
In PVLG
Juvenile spore in PVLG+Melzer's

Layer 1 hyaline, ca. 0.5 µm thick, continuous with a one-layered subtending hypha of the most juvenile spores, then darkening to pale yellow (3A3) and thickening to (0.9-)1.1(-1.5) µm.

Layer 2 laminate, yellowish white (2A2) to golden yellow (5B8), (3.2-)4.4(-6.1) µm thick, with a smooth outer surface and an evenly pitted inner surface; pits round, (1.2-)1.6(-2.0) µm diam, 1.2-2.0 µm deep, separated by ridges, (0.7-)1.1(-1.7) µm wide; in the most juvenile spores, the inner surface frequently is smooth; in young spores, it contains shallow pits that may be difficult to see.

 

In PVLG
In PVLG+Melzer's reagent
SUBTENDING HYPHA hyaline to pale yellow (3A3); straight or recurved; cylindrical or slightly flared, rarely constricted; (2.9-)5.2(-6.9) µm wide at the spore base.

Wall of subtending hypha hyaline to pale yellow (3A3); (0.8-)1.3(-1.8) µm thick; consisting of two layers (shwl1 and 2) continuous with spore wall layers 1 and 2; layer 2 of spore wall is highly thinned at the spore base and then either further thins to 0.7 µm or forms a recurved septum.

Pore open or occluded by a recurved septum continuous with spore wall layer 2; the septum is 1.5-2.7 µm wide, 0.5-0.7 µm thick, and is positioned 1.0-6.0 µm in the hyphal lumen.

GERMINATION. Not observed.

In roots of P. lanceolata
MYCORRHIZAE. Mycorrhizae of this fungus formed in one-species cultures with Plantago lanceolata L. as the plant host consisted of arbuscules, intra- and extraradical hyphae. Arbuscules appeared as granular structures in cortical cells. Fine branches were difficult to see. Arbuscules were numerous, but unevenly distributed in roots. The intraradical hyphae were (4.2-)6.2(-7.4) µm wide and grow parallel to the root axis. They were straight or slightly curved, sometimes dichotomously branched and frequently coiled; the coils were 20.8-34.6 x 10.5-22.3 µm. No vesicles were present in roots of plants up to 8-month-old. Extraradical hyphae were (1.7-)3.2(-3.5) µm wide and frequently associated with young and mature spores. In 0.1% trypan blue, arbuscules stained violet white (17A2), intraradical hyphae violet white (17A2) to pastel violet (17A4), and extraradical hyphae pale violet (17A3).

DISTRIBUTION. In Poland, spores of Gl. insculptum have been revealed in seven field-collected soil samples and 10 trap pot cultures with rhizosphere soils of five plant species colonizing inland sand dunes of the Bledowska Desert (50o22’ N, 19o34’ E) located in south of Poland (Błaszkowski et al., in press). The plant species colonized by Gl. insculptum in the field have been Corynephorus canescens (L.) P. Beauv., Festuca rubra L. s. s., Holcus mollis L., Juniperus communis L., and Plantago major L.

There is no report of the presence of this fungus in the other regions of both Poland and the world.

NOTES. When observed under a dissecting microscope, spores of Gl. insculptum most resemble small-spored isolates of Gl. aggregatum N.C. Schenck & G.S. Sm. emend. Koske, Gl. arenarium Blaszk. at al., Gl. etunicatum W.N. Becker & Gerd., Gl. intraradices N.C. Schenck & G.S. Sm., Gl. pustulatum Koske et al., Gl. trimurales Koske & Halvorson, and Gl. versiforme (P. Karsten) S.M. Berch. All eight species form globose to subglobose and yellow-coloured spores, whose size range partly overlaps (Becker and Gerdemann 1977; Berch and Fortin 1983; Błaszkowski 1991; Błaszkowski et al. 2001, 2003, 2004; Koske 1985; Koske and Halvorson 1989; Koske et al. 1986; Morton 2000; Schenck and Smith 1982; Stürmer and Morton 1997).

Examination of subcellular structure and phenotypic properties of layers in the spore wall of specimens crushed in Melzer’s reagent readily separates these species. Only Gl. insculptum forms spores in which the laminate spore wall layer is regularly pitted. However, in young spores, the inner surface either is smooth or the pits are very shallow and difficult to see. Even then, Gl insculptum is distinguishable from other species. Although Gl. etunicatum, Gl. insculptum, and Gl. versiforme have a spore wall composed of two layers, the outer layer of each differs. In Gl. etunicatum the layer sloughs as spores mature (Stürmer and Morton 1997), while in Gl. versiforme it is semi-permanent (Morton 2000) and in Gl. insculptum it is permanent. Additionally, the outer spore wall layer of Gl. insculptum and Gl. versiforme (Morton 2000) is nonreactive in Melzer’s reagent but stains dark pinkish red to reddish-purple in Gl. etunicatum (Stürmer and Morton 1997). Glomus versiforme also differs from Gl. insculptum in the occasional production of spores arranged in epigeous sporocarps (Berch and Fortin 1983; Morton 2000) vs. only single, hypogeous spores in Gl. insculptum and in that the mean diameter of globose spores of the former fungus is almost twice that of spores of the latter species. In contrast to the two-layered subcellular spore wall structure of Gl. insculptum, that of Gl. arenarium, Gl. pustulatum, and Gl. trimurales consists of three layers.

The only other species of arbuscular fungi forming spores with an ornamented inner surface of their innermost wall layer are Gl. kerguelense Dalpé & Strullu and Gl. verruculosum Blaszk. However, compared with Gl. insculptum, spores of the two species are much larger (mean diameter = 71 µm in Gl. insculptum vs. 186.3 µm and 189.0 µm in Gl. kerguelense and Gl. verruculosum, respectively) and the ornamentation of the innermost layer of their wall consists of fine granules (Gl. kerguelense) or warts (Gl. verruculosum; Błaszkowski and Tadych 1997; Dalpé et al. 2002) vs. pits in Gl. insculptum.

REFERENCES

Becker W. N., Gerdemann J. W. 1977. Glomus etunicatus sp. nov. Mycotaxon 6, 29-32.

Berch S. M., Fortin J. A. 1983. Lectotypification of Glomus macrocarpum and proposal of new combinations: Glomus australe, Glomus versiforme, and Glomus tenebrosum (Endogonaceae). Can. J. Bot. 61, 2608-2617.

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

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

Błaszkowski J., Adamska I., Czerniawska B. 2003. Glomus trimurales, an arbuscular mycorrhizal fungus (Glomerales) new for Poland and Europe. Mycotaxon 87, 425-436.

Błaszkowski J., Adamska I., Czerniawska B. 2004. Glomus insculptum, a new arbuscular mycorrhizal species from Poland. Mycotaxon 89, 225-234.

Błaszkowski J., Tadych M., Madej T. 2001. Glomus arenarium, a new species in Glomales (Zygomycetes). Acta Soc. Bot. Pol. 70, 97-101.

Dalpé Y., Plenchette C., Frenot Y., Gloaguen J. C., Strullu D. G. 2002. Glomus kerguelense sp. nov., a new Glomales species from sub-Antarctic. Mycotaxon 84, 51-60.

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

Koske R. E., Halvorson W. L. 1989. Scutellospora arenicola and Glomus trimurales: two new species in the Endogonaceae. Mycologia 81, 927-933.

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. 2000. International Culture Collection of Arbuscular and Vesicular-Arbuscular Mycorrhizal Fungi. West Virginia University.

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

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