SPORES occurring in corymbiform aggregates when formed from branched sporophores, rarely single in the soil when produced from straight sporophores. Spores pastel yellow (3A4) to orange (6A8); globose to subglobose; (50-)142(-220) µm diam; sometimes ovoid or pyriform; 110-125 x 120-200 µm; with a single subtending hypha.
Aggregates globose to subglobose; (180-)336(-490) µm diam; sometimes ovoid; 180-350 x 210-500 µm; composed of 2-13 (av. 6) spores enveloped individually by hyphal mantle.
Mantle (20-)47.5(-90) µm thick; consisting of a network of hyphae branching dichotomously three to four times at more or less right angles; hyphae thin-walled, hyaline to yellowish white (3A2), septate; length and diameter of branches diminishing with each successive dichotomy; initial hypha (9.8-)17.7(-27.2) µm long, (4.2-)4.9(-6.9) µm wide; developing from spore wall 1; final branch (13.5-)19.4(-25) µm long, (1.2-)1.8(-2.9) µm wide; distance between septa (14.5-)25.7(-31.4) µm; mantle frequently absent in mature spores.
Sporophore coenocytic to sparsely septate; hyaline to yellow (5A6); (10.3-)14.7(-17.5) µm wide; with a wall (1.5-)1.6(-1.7) µm thick; usually with two to three main monopodial branches, rarely straight; main branches frequently with one to ten (av. 4) monopodial second branches sometimes brunched monopodially one to two times; main, second and third branches slanted at 30-45o towards their parent hyphae; straight and branched sporophores bearing spores by swelling hyphal tips.
Layer 1 permanent, rigid, smooth, hyaline to deep yellow (4A8), (0.7-)1.1(-1.7) µm thick, closely attached to layer 2.
Layer 2 laminate, pastel yellow (3A4) to orange (6A8), (3.9-)7(-10) µm thick.
Layer 3 flexible, hyaline, (0.5-)0.9(-1.2) µm thick, usually tightly adherent to layer 2.
Wall of subtending hypha cream (4A3) to deep orange (5A8); (2.2-)6.5(-13.7) µm thick; composed of two layers (shwl1 and 2) continuous with spore wall layers 1 and 2.
Pore occluded by ingrowth of spore wall layer 3, a septum, ca. 0.7 µm wide, continuous with the innermost lamina of spore wall layer 2, and occasionally by thickening of spore wall layer 2.
Mantle and spores not reacting in Melzer's reagent.
GERMINATION. Not observed.
MYCORRHIZAE. In the field, Gl. corymbiforme has been associated with vesicular-arbuscular mycorrhizal roots of different dune plant species (Blaszkowski 1995, pers. observ.; Blaszkowski et al. 2001, 2002a, b; Tadych and Blaszkowski 2000). This fungus produced not numerous spores in trap cultures. However, with age of the cultures, the sporulation disappeared. Many attempts to establish one-species cultures of Gl. corymbiforme failed.
DISTRIBUTION. In Poland, Gl. corymbiforme has originally been found associated with roots of plants colonizing maritime dunes adjacent to Swinoujscie (53o55'N, 14o14'E; Blaszkowski 1995). The plant species under which Gl. corymbiforme spores occurred were Ammophila arenaria (L.) Link, Hieracium umbellatum L., and Petasites spurius (Retz.) Rchb. Later, this fungus has been revealed in maritime dunes of the Slowinski National Park (54o45’N, 17o26’E; Tadych and Blaszkowski 2000), the Vistula Bar (54o21’N, 19o14’E; Blaszkowski et al. 2002a), and in inland dunes of the Bledowska Desert (50o22’N, 19o34’E; Blaszkowski et al. 2002b).
Glomus corymbiforme has also been present among spores of arbuscular fungi isolated from dunes of the Mediterranean Sea adjacent to Karabucak-Tuzla (36o43'N, 34o59'E), Turkey, and Tel Aviv (32º4’N, 34º46’E), Israel (Blaszkowski et al. 2001; Blaszkowski, pers. observ.).
NOTES. The distinctive features of Gl. corymbiforme are the hyphal mantle enveloping individual spores and the clustered, corymbiform organization of spores in sporocarps.
Spores of Gl. corymbiforme are initiated from thin-walled vesicles produced terminally from straight or branched sporophores swelling at their tips. At times, the vesicle layer becomes thicker due to the formation of a laminated layer first and then an innermost flexible layer. Straight, thin-walled hyphae grow from the vesicles and the outermost layer of immature spores. Small pores connecting the spore inside with the hyphal lumen are visible in young but mature specimens when seen in a plan view. These hyphae branch dichotomously and become thinner with each successive dichotomy. The hyphae of each spore intertwine with those of neighbouring spores, forming a common mantle enveloping an aggregate. This mantle detaches from mature spores.
The surface of most mature spores seen in a cross-sectional view is somewhat roughened, although spore wall layers 1 and 2 tightly adhere to each other. These roughenesses probably are a result of deformations of layers 1 and 2 originated during both the development of initial mantle hyphae and the process of occlusion of the pores connecting these hyphae with the spore contents. The latter likely interrupts physiological first and then physical unity between the spore and hyphae. Formation of occlusion also is a reason of detachment of hyphal sporiferous saccule from spore in many species of the genus Acaulospora and Archaeospora (Morton 2000).
Apart from Gl. corymbiforme, other species of the genus Glomus forming spores enveloped by a hyphal mantle are Gl. convolutum Gerd. & Trappe, Gl. globiferum Koske & C. Walker, Gl. mosseae (Nicol. & Gerd.) Gerd. & Trappe, Gl. mortonii Bent. & Hetrick, Gl. pubescens (Sacc. & Ellis) Trappe & Gerd., Gl. sinuosa (Gerd. & B.K. Bakshi) R.T. Almeida & N.C. Schenck, and Gl. tortuosum N.C. Schenck & S.M. Smith. The ontogeny of the hyphal mantle of Gl. corymbiforme is most similar to that of the mantle of Gl. globiferum spores. Both species form a mantle from initial hyphae growing from thin-walled vesicles or young spores (Wu and Sylvia 1993). However, in Gl. globiferum, these hyphae bear vesiculate swelling that are absent in Gl. corymbiforme. According to Koske and Walker (1986), the mantle hyphae of Gl. globiferum also are darker (yellow-brown vs. hyaline to yellowish white in G. corymbiforme) and wider [5-50 µm vs. (1.2-4.2-)1.8-4.9(-2.9-6.9) µm]. Additionally, spores of the former species occur singly in the soil, whereas the latter fungus mainly produces spores in sporocarps. The sinuous mantle hyphae of Gl. mortonii, Gl. sinuosa, and Gl. tortuosum (Bentivenga and Hetrick 1991; Gerdemann and Bakshi 1976; Schenck and Smith 1982) readily distinguish the three species from Gl. corymbiforme with its mantle composed of dichotomously branched hyphae. The hyphae enclosing spores of Gl. convolutum, Gl. mosseae, and Gl. pubescens are irregularly branched (Gerdemann and Trappe 1974) and, thereby, unlike those enveloping Gl. corymbiforme spores. Additional features separating Gl. corymbiforme from Gl. pubescens and Gl. sinuosa are the size and shape of spores (Gerdemann and Bakshi 1976; Gerdemann and Trappe 1974). Spores of Gl. corymbiforme are larger (av. 142 µm diam; range 50-220 µm diam) than those of both Gl. pubescens (20-48 x 18-45 µm) and Gl. sinuosa (45-118 x 30-83 µm). Glomus sinuosa produces obovate to clavate spores, whereas most Gl. corymbiforme spores are globose to subglobose.
Regardless of whether the hyphal mantle is present, the uniquely clustered (corymbiform) organization of Gl. corymbiforme sporocarps readily distinguishes this species from all other described species of Glomus.
Single mature spores of Gl. corymbiforme may be confused with those of Gl. globiferum in which the hyphal mantle is occasionally poorly developed and difficult to see (Koske and Walker 1986). Both species have spores similar in size, shape, and wall structure. However, spores of the latter fungus are darker (orange-brown to red-brown or occasionally black) than those of the former fungus, being typically orange. Other fungal species producing spores with three wall layers of the same types as in Gl. corymbiforme are Gl. fasciculatum (Thaxt.) Gerd. & Trappe emend. C. Walker & Koske and Gl. pustulatum Koske et al. (Koske et al. 1986; Walker and Koske 1987). However, spores of Gl. fasciculatum are lighter (pale yellow to yellow-brown vs. pastel yellow to orange), smaller [(50-)60-95(-149) x 55-90(-149) µm vs. (50-)142(-220) µm diam], and stain in Melzer's reagent (vs. not reacting in G. corymbiforme). Glomus pustulatum has a spore surface ornamented with blister-like thickenings, whereas all spore wall layers in Gl. corymbiforme are smooth.
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