Glomus lamellosum Dalpé, Koske & Tews

SPORES single in the soil; pale yellow (2A3-3A3); yellowish white (4A2) to light yellow (4A4-6); globose to subglobose; (60-)100(-140) µm diam; sometimes ovoid; 80-110 x 120-160 µm; with a single subtending hypha.

SUBCELLULAR STRUCTURE OF SPORES composed of one wall with three layers (swl1-3).

In PVLG

Layer 1 hyaline, (2.2-)5.3(-10.5) µm thick, forming a halo under reflected light when not deteriorated, slowly decomposing beginning from its outer surface, present in most mature spores.

In PVLG+Melzer's reagent
Layer 2 laminate, pale yellow (2A3-3A3) to light yellow (4A4-6), (2.0-)4.2(-5.6) µm thick.

Layer 3 flexible, hyaline, 0.2-0.5 µm thick, sometimes separating from layer 2 in vigorously crushed spores, usually attached to the surface of the lumen of subtending hypha, staining pinkish white (7A2) to pastel red (9A4) in Melzer’s reagent.

The wall of most juvenile spores consists of layer 1 only. Layers 2 and 3 form successively with spore maturation, the termination of which determines the staining reaction of layer 3 in Melzer’s reagent.

In PVLG
SUBTENDING HYPHA hyaline to light yellow (4A4-6); straight or recurved; mostly flared, sometimes cylindrical, rarely constricted; (8.3-)13.0(-15.2) µm wide at the spore bases.

Wall of subtending hypha hyaline to light yellow (4A4-6); (3.9-)5.6(-8.3) µm thick at the spore base; composed of two layers (shwl1 and 2), continuous with spore wall layers 1 and 2.

Pore (1.5-)4.7(-10.3) µm wide, occluded by an invagination formed by spore wall layer 3.

GERMINATION. Not observed.

In roots of P. lanceolata
MYCORRHIZAE. In Poland, spores of Gl. lamellosum have been associated in the field with vesicular-arbuscular mycorrhizal roots of Ammophila arenaria (L.) Link, Corynephorus canescens (L.) P. Beauv., Elymus arenarius L., and Hieracium pilosella L. (Błaszkowski et al. 2002b). The mycorrhizae formed in single-species cultures of this fungus with Plantago lanceolata L. as the plant host consisted of arbuscules, vesicles, as well as intra- and extraradical hyphae. Arbuscules were irregularly distributed and had fine branches difficult to see. Vesicles were 21.8-34.3 x 51.7-83.4 µm and usually occurred in conglomerations highly scattered along roots. Intraradical hyphae were 3.4-5.9 µm wide and grew parallel to the root axis. These hyphae sometimes formed coils, 18.4-20.3 x 33.8-46.6 µm and Y-shaped branches. Extraradical hyphae were 5.1-6.9 µm wide. In 0.1% trypan blue, arbuscules stained violet grey (18B2-18C3), vesicles greyish violet (18B3), intraradical hyphae, coils, and extraradical hyphae greyish violet (18B4, 18B3-18E5, and 18B4-18C6, respectively).

DISTRIBUTION. In Poland, spores of Gl. lamellosum have so far been found in two field-collected rhizosphere soils coming from maritime dunes adjacent to Swinoujscie (53o55'N, 14o14'E) and 10 trap cultures with soil-root mixtures that did not harbour spores of this fungus in the field (Błaszkowski et al. 2002b). The mixtures came from dunes of Swinoujscie (4 samples), the Vistula Bar (54o21’N, 19o14’E; 2 samples; Błaszkowski et 2002a), and inland dunes of the Bledowska Desert (50o22'N, 19o34'E; 4 samples; Błaszkowski et al. 2002c).

Glomus lamellosum has earlier been known only from the sites listed in its original description (Dalpé et al. 1992). This fungus was associated with Ammophila breviligulata Fern colonizing a sandy shore of Nottawasaga Bay in Georgian Bay, Ontario, Canada and sand dunes of Bailey’s harbor, Wisconsin, U.S.A.

NOTES. The properties most distinguishing spores of Gl. lamellosum are their thick, hyaline, relatively permanent outermost wall layer (layer 1) producing a halo in reflected light and the flexible innermost wall layer (layer 3) staining pinkish white to pastel red in Melzer’s reagent.

The differentiation of spore wall of Gl. lamellosum comprises successive formation of discrete layers, beginning from the outermost layer 1. This pattern correspond with that found in all Glomus spp. investigated ontogenetically to date (e. g., Błaszkowski and Tadych 1997; Stürmer and Morton 1997).

With age, layer 1 gradually deteriorates, beginning from its outer surface and, thereby, looses transparency. However, it is present in most even old spores.

Spore wall layer 2 consists of tightly adherent, very thin sublayers (laminae). It forms de novo after the formation of layer 1 is completed.

The innermost spore wall layer 3 always tightly adheres to the laminate layer 2. Only vigorous crushing of spores sometimes separates layer 3 from layer 2. However, the presence of layer 3 most reveals its staining reaction in Melzer’s reagent. The intensity of staining of layer 3 in Melzer’s reagent varies in different spores and probably depends on the stage of development of this layer, as found in, e. g., Entrophospora colombiana Spain & Schenck (Stürmer and Morton 1999).

The arbuscular mycorrhizal fungi most resembling Gl. lamellosum are Gl. claroideum Schenck & Smith, Gl. clarum Nicolson & Schenck, and Gl. luteum Kennedy, Stutz & Morton. All these fungi form yellow-coloured spores of a more or less overlapping size range (Dalpé et al. 1992; Kennedy et al. 1999; Morton 2000; Schenck and Smith 1982; Stürmer and Morton 1997).

The main differences between the four fungal species are the number and properties of the spore wall and subtending hyphal wall components. The spore wall of Gl. lamellosum consists of three layers, whereas that of Gl. claroideum and Gl. luteum contains four layers (Kennedy et al. 1999; Stürmer and Morton 1997). Glomus lamellosum does not differentiate a mucilaginous outermost layer staining in Melzer’s reagent as do the letter two species. Additionally, the outer hyaline layer of Gl. lamellosum spores is much more persistent than that of the two outer hyaline spore wall layers of Gl. claroideum and Gl. luteum. It is especially evident in Gl. claroideum, in which these layers usually are completely sloughed in mature spores.

The most important structure grouping Gl. lamellosum with Gl. claroideum and Gl. luteum is the flexible innermost wall layer of their spores. Although it is phenotypically identical in the three fungi, it stains in Melzer’s reagent only in Gl. lamellosum (Kennedy et al. 1999; Morton 2000; Stürmer and Morton 1997). The reactivity of a flexible innermost spore wall layer infrequently occurs in other Glomus spp. (Morton 2000; Błaszkowski, pers. observ.). Additionally, the degree of adherence of this layer to the laminate structural spore wall layer highly differs in these species: it adheres to the laminate layer in most crushed spores of Gl. lamellosum, but separates readily from it in the other two species.

Although spores of Gl. clarum also have a three-layered wall and a halo in reflected light, those of Gl. lamellosum neither possess the mucilaginous outermost wall layer (staining in Melzer’s reagent) nor their halo is produced by a hyaline, laminate wall layer as found in Gl. clarum (Stürmer and Morton 1997).

Differences between the four Glomus spp. compared here also reside in the structure of wall of their subtending hyphae. The wall of subtending hypha of Gl. lamellosum is two-layered, whereas it consists of three layers in the other fungal species considered.

Finally, the mycorrhizae of Gl. lamellosum, Gl. claroideum, and Gl. luteum are similar: they stain darkly in trypan blue, and vesicles are formed sporadically. In contrast, despite the mycorrhizal structures of Gl. clarum that also stain intensively in trypan blue, this fungus frequently forms intraradical vesicles (Morton 2000).

REFERENCES

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. 2002a. Arbuscular mycorrhizal fungi (Glomeromycota) of the Vistula Bar. Acta Mycol. 37, 39-62.

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

Błaszkowski J., Tadych M., Madej T. 2002c. Arbuscular mycorrhizal fungi (Glomales, Zygomycota) of the Bledowska Desert, Poland. Acta Soc. Bot. Pol. 71, 71-85.

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

Kennedy L. J., Stutz J. C., Morton J. B. 1999. Glomus eburneum and G. luteum, two new species of arbuscular mycorrhizal fungi, with emendation of G. spurcum. Mycologia 91, 1083-1093.

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.

Stürmer S. L., Morton J. B. 1999. Taxonomic reinterpretation of morphological characters in Acaulosporaceae based on developmental patterns. Mycologia 91, 849-857.