Koske, Friese, C. Walker & Dalpé
SPORES borne singly in the soil or in roots; deep orange (5A8); globose to slightly ovoid; (85-)100(-110) µm diam; with a single subtending hypha.
SUBCELLULAR STRUCTURE OF SPORES composed of one wall with three layers (swl1-3).
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In PVLG
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Layer 1 permanent, greyish-yellow (1B4) to butter yellow (4A5), of a basic thickness of (1.0-)1.7(-2.7) µm, ornamented with blistery, cup- or irregularly shaped outgrowths, 2.0-5.9 µm high, 2.0-11.8 µm wide at the base, circular, elliptic to irregular in a plan view, unevenly distributed on the spore surface.
Layer 2 laminate, smooth, deep orange (5A8), (3.2-)5.4(-10.3) µm thick.
Layer 3 flexible, hyaline, 0.8-1.0 µm thick, tightly adherent to layer 2, usually separating in vigorously crushed spores.
None of the spore wall layers stains in Melzer’s reagent.
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In PVLG |
SUBTENDING HYPHA pale yellow (3A3) at the spore base, lighten to hyaline distally; straight or recurvate; cylindrical or flared; (5.4-)6.5(-7.1) µm wide at the spore base.
Wall of subtending hypha pale yellow (3A3) at the spore base; (0.2-)1.3(-2.0) µm thick; composed of two layers (shwl1+2), continuous with spore wall layers 1 and 2.Pore occluded by thickening of spore wall layer 2 or a recurved septum continuous with spore wall layer 2.
GERMINATION. Spores germinate by a germ tube penetrating the spore wall.
MYCORRHIZAE. In Poland, in the field, Gl. pustulatum has been found associated with vesicular-arbuscular mycorrhizal roots of different dune plant species (Blaszkowski 1994, 1995; Tadych and Blaszkowski 2000a, b). Attempts to produce mycorrhizae of this fungus in one-species cultures failed. According to Koske et al. (19860, Gl. pustulatum formed mycorrhizae with arbuscules and vesicles in a pot culture with Lathyrus japonicus Willd. subsp. maritimus (L.) P. W. Ball.
DISTRIBUTION. In Poland, Gl. pustulatum has been recorded in dune sands of the Slowinski National Park (54º45’N, 17º26’E; Blaszkowski 1994; Tadych and Blaszkowski 2000a), Swinoujscie (53º55’N, 14º14’E; Blaszkowski 1995), and the Bledowska Desert (50º22’N, 19º34’E; Blaszkowski et al. 2002). Additionally, spores of this fungus have been isolated from soils of the Tuchola Forests (53º46’N, 17º42’E-53º40’N, 17º54’E; Tadych and Blaszkowski 2000b).
Other reports of this fungus are those from maritime dunes of Madras (Mohankumar et al. 1988), Canada (Dalpé 1989), and the USA (Koske et al. 1986).
NOTES. The distinctive feature of Gl. pustulatum is the ornamentation of the outermost spore wall layer. The predominate structures forming the ornamentation are blister-like outgrowths. In a cross view, they are most frequently circular or arched. The size of these structures seems to be inversely related to their frequency of occurrence on the spore surface. Cup-shaped and irregular outgrowths occur rarely and mainly on spores densely covered with blister-like thickenings. In a few specimens, both the number of pustules and their size are very low and, hence, such spores are almost smooth. The pustules are solid, not fatty, and do not disappear when spores are mounted in lactic acid-based mountants.
The spore wall layer 2 easily separates into single laminae or their groups, especially in vigorously crushed spores. The outer laminae are usually darker than the inner ones, which sometimes are almost hyaline. The spore wall layer 3 is most difficult to see, as it always tightly adheres to layer 2 and is hyaline. Even vigorous crushing of spores does not separate it completely from the laminae layer. However, numerous wrinkles on the inner surface of layer 2 and small areas of this layer separated from layer 2 supports its presence.
Most spores of Gl. pustulatum recovered by the author of this website possess a straight and cylindric or slightly flared subtending hypha. Its wall is thin and usually lighter coloured than the spore wall. The pore in the subtending hypha is usually closed by the thickened spore wall layer 2; in a few spores, a curved septum continuous with the innermost lamina of spore wall layer 2 is also present. According to Koske et al. (1986), the pore in Gl. pustulatum is closed only by ingrowth of spore wall layer 2. Alternative occlusion of a subtending hyphal pore either by wall thickening or a septum has been described in other species of the genus Glomus (Morton 1988).
The spore base of many specimens found is obscured by germ tubes growing most frequently near the subtending hypha, although germinating spores with germ tubes developed at the opposite of the subtending hypha are also present. The germ tubes grow through a small hole seen in the spore wall layer 1. No spore germinating by regrowth of the subtending hypha was found. This kind of germination most frequently occurs in Glomus spp. (Morton and Benny 1990).
When observed under a dissecting microscope, spores of Gl. pustulatum resemble those of Gl. aggregatum N.C. Schenck & G.S. Sm. emend. Koske, Gl. arenarium Blaszk. et al., Gl. claroideum N.C. Schenck & G.S. Sm., Gl. etunicatum W.N. Becker & Gerd., and Gl. hoi S.M. Berch & Trappe. Spores of all these species are yellow-coloured and have a similar size (Berch and Trappe 1985; Blaszkowski et al. 2001; Schenck and Smith 1982; Stürmer and Morton 1997; Walker and Vestberg 1998).
Examination of the subcellular structure of the spores under a compound microscope readily separates them. Only Gl. pustulatum produces spores whose the outermost wall layer is permanent and ornamented with blister-like processes. In the other fungi, the outermost spore wall layer sloughs and rarely occurs at maturity.
Glomus trimurales Koske & Halvorson forms spores ornamented with blisters (Blaszkowski et al. 2003). However, in contrast to those of Gl. pustulatum, the blisters deteriorate and disappear with age.
REFERENCES
Berch S. M., Trappe J. M. 1985. A new species of Endogonaceae, Glomus hoi. Mycologia 77, 654-657.
Blaszkowski J. 1994. Polish Glomales 11. Glomus pustulatum. Mycorrhiza 4, 201-207.
Blaszkowski J. 1995. Glomus corymbiforme, a new species in Glomales from Poland. Mycologia 87, 732-737.
Blaszkowski J., Adamska I., Czerniawska B. 2003. Glomus trimurales, an arbuscular mycorrhizal fungus (Glomerales) new for Poland and Europe. Mycotaxon 87, 425-436.
Blaszkowski J., Tadych M., Madej T. 2001. Glomus arenarium, a new species in Glomales (Zygomycetes). Acta Soc. Bot. Pol. 70, 97-101.
Blaszkowski J., Tadych M., Madej T. 2002. Arbuscular mycorrhizal fungi (Glomales, Zygomycota) of the Bledowska Desert, Poland. Acta Soc. Bot. Pol. 71, 71-85.
Dalpé Y. 1989. Inventaire et repartition de la flore endomycorhizienne de dunes et de rivages maritimes du Québec, du Nouveau-Brunswick et de la Nouvelle-Ecosse. Naturaliste Can. (Rev. Ecol. Syst.) 116, 219-236.
Koske R. E., Friese C., Walker C., Dalpé Y. 1986. Glomus pustulatum: A new species in the Endogonaceae. Mycotaxon 26, 143-149.
Mohankumar V., Ragupathy S., Nirmala C. B., Mohadevan A. 1988. Distribution of vesicular-arbuscular mycorrhizae (VAM) in the sandy beach soils of Madras coast. Cur. Sci. 57, 367-368.
Morton J. B. 1988. Taxonomy of VA mycorrhizal fungi: classification, nomenclature, and identification. Mycotaxon 32, 267-324.
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.
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.
Tadych M., Blaszkowski J. 2000a. Arbuscular fungi and mycorrhizae (Glomales) of the Slowinski National Park, Poland. Mycotaxon 74, 463-483.
Tadych M., Blaszkowski J. 2000b. Arbuscular mycorrhizal fungi of the Brda river valley in the Tuchola Forests. Acta Mycol. 35, 3-23.
Walker C., Vestberg M. 1998. Synonymy amongst the arbuscular mycorrhizal fungi: Glomus claroideum, G. maculosum, G. multisubstensum and G. fistulosum. Ann. Bot. 82, 601-624.