Appendicispora gerdemannii

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Appendicispora gerdemannii

(S.L. Rose, B.A. Daniels et Trappe) Spain, Oehl & Sieverd.

SPORES formed singly in the soil; originating blastically at the tip of a hyphal branch (pedicel) on the neck of a sporiferous saccule. Spores pale yellow (4A3) to maize yellow (4A6); globose to subglobose; (150-)210(-250) µm diam; sometimes ovoid; 150-190 x 210-250 µm.

SUBCELLULAR STRUCTURE OF SPORES consists of a spore wall and two inner germination walls.

Germination wall 1 comprises two fragile, smooth, hyaline layers (gw1l1 and 2), (0.5-)1.1(-1.6) µm and (0.6-)1.4(-2.1) µm thick, respectively, usually tightly adherent to one another and readily cracking to form line slits or polygonal pieces in crushed spores.

In Melzer's reagent, only spore wall layer 1 stains orange (6A6) to pastel red (8C5).

PEDICEL 10-15 µm long, 15-27 µm wide at the spore base, positioned 80-120 µm from the base of the sporiferous saccule, consisting of a hyaline wall continuous with the wall of the saccule neck, the spore wall, and layer 1 of germination wall 1. Pore open. According to Spain et al. (2006), in young spores, the pore is closed by germination wall 1.

SPORIFEROUS SACCULE hyaline to yellowish white (4A2), globose to subglobose, (185-)200(-275) µm diam, occasionally ovoid, 160-200 x 210-260 µm, formed at the end of a funnel-shaped neck.

CICATRIX. A slightly raised collar when seen in a cross view, circular, 9.5-12.0 µm diam, or ellipsoidal, 9.5-12.0 x 12.0-14.0 µm when observed in a plane view.

MYCORRHIZAE. In the field, spores of Ap. gerdemannii occurred among vesicular-arbuscular mycorrhizal roots of Achillea millefolium L., Campanula polymorpha Witasek, Cardaminopsis neglecta (Schult) Hayek, Cerastium tatrae Borbás, Equisetum arvense L., Hypericum perforatum L., Juniperus communis L., Knautia kitaibelii (Schult.) Borbás, Leucanthemum waldsteinii (Sch.Bip.) Pouzar, Melamphyrum herbichii Wol., Sesleria tatrae (Degen) Deyl, Thuja occidentalis L., and Thymus sp. Additionally, they were recovered from some trap cultures established from mixtures of roots and rhizosphere soils of these plants and with P. lanceolata as the plant host. Unfortunately, many attempts to produce one-species cultures of Ap. gerdemannii failed.

According to Morton (2002) and Morton and Redecker (2001), mycorrhizae of Ap. gerdemannii consisted of only arbuscules and intraradical hyphae; no vesicles were found. All the structures were patchily distributed along roots and stained weakly or not at all in trypan blue. Percentage mycorrhizal colonization always was very low, below 10%.

DISTRIBUTION. In Poland, spores of Ap. gerdemannii were found in 19 samples of roots and rhizosphere soils of 14 species of uncultivated plants. None of the almost 1500 root and soil mixtures coming from cultivated sites of Poland contained spores of this fungus.

The average abundance of spores of Ap. gerdemannii in the samples examined was 4.7 and ranged from 1 to 29 in 100 g dry soil. The proportion of spores of this species in spore populations of all the arbuscular fungi recovered averaged 11.8% in a range of 2.1-66.7%. The average abundance of species of arbuscular fungi in samples in which spores of Ap. gerdemannii occurred was 2.7 and ranged from 1 to 6 in 100 g dry soil.

Although Ap. gerdemannii probably has a worldwide distribution, this species has been infrequently reported. Most reports of Ap. gerdemannii come from the United States of America (Allen and MacMahon 1985; An et al. 1990, 1993; An et al. 1993; An et al. 1993; Bever et al. 1996; Koske et al. 1977; Nicolson and Schenck 1979; Rose et al. 1979). Additionally, spores of this fungus have been isolated in Brazil (Moreira-Souza et al. 2003), Colombia (Dodd et al. 1990), and Australia (Morton and Redecker 2001). In southern Poland, Turnau et al. (2001) recovered spores of a morphotype named Glomus sp. HM-CL4 of molecular properties close (71%) to those of Gl. gerdemannii, the basionym of Ap. gerdemannii (Spain et al. 2006). However, the authors did not show any morphological characters of the spores isolated and did not determine which of the two morphotypes of this fungus was found.

NOTES. The unique properties of Ap. gerdemannii are its fragile bi-layered germination wall 1 and the mode of differentiation of spores of this fungus. Additionally, Ap. gerdemannii is a dimorphic fungus producing two morphotypes, acaulosporioid (as in Acaulospora spp.) and glomoid (as in Glomus spp.), a phenomenon rarely occurring in other species of arbuscular fungi.

The germination wall 1 of Ap. gerdemannii resembles a hardened glass. In slightly crushed spores, linear cracks appear on the surface of this wall. However, in spores vigorously crushed, this wall almost always breaks into small pieces. Another characteristic of this wall not found in any species of arbuscular fungi is its glittering when seen in a polarized light.

The author of this website was unable to produced one-species cultures of Ap. gerdemannii, and spores of this fungus recovered from both field-collected samples and trap cultures did not make possible to investigate their whole ontogenetic development. According to Morton and Redecker (2001), the ontogenetic development of the acaulosporioid morphotype of Ap. gerdemannii starts the formation of a sporiferous saccule at the end of the sporiferous saccule neck continuous with an extraradical hypha of an arbuscular mycorrhiza, identically to that of members of the genus Acaulospora. Spores of this fungus originate from a hyphal branch called “a pedicel” positioned 180-260 µm from the base of the saccule. The wall of the pedicel consists of hyaline layers continuous with layers of the spore wall and layer 1 of germination wall 1. The pedicels of Polish specimens were much shorter (10-15 µm long) than those characterized by Morton and Redecker (2001; 50-90 µm long) and, thereby, undoubtedly formed a more persistent link between spores and sporiferous saccules than longer ones. All the specimens of Ap. gerdemannii found by the authors of this paper came from the field and probably only the sporiferous saccules with short pedicels remained associated with spores during their isolation. Sporiferous saccules rarely occur in field-collected spores of the families Acaulosporaceae and Archaeosporaceae because of their detachment or deterioration by soil microorganisms (Błaszkowski 2003). When spores begin to expand blastically at the end of the pedicel, spore wall layer 1 forms de novo. In young spores, it is smooth and best visible in specimens mounted in Melzer's reagent in which it stains orange (6A6) to pastel red (8C5). However, with age, it becomes friable, degrades, and sloughs partly in separated patches or completely. Hence, older spores are either covered with yellow brown remnants of layer 1 or are hyaline because of the prominence of the second hyaline spore wall layer. After the full differentiation of the outermost layer 1 and the innermost layer 3 of the spore wall, first the 2-layered germination wall 1 and then the 3-layered germination wall 2 probably successively origin, similarly as in spores of members of the genus Acaulospora. In fully mature spores, the germination wall 2 resembles a coriaceous wall sensu Walker (1986). However, by definition, a coriaceous wall is a uniform structure, whereas the germination wall 2 of Ap. gerdemannii consists of three layers, of which the middle one corresponds with properties of a laminate layer. Except for Appendicispora spp., no other species of the phylum Glomeromycota forms spores with a laminate layer of their innermost wall. Although Morton and Redecker (2001) also found the germination wall 1 (called layer 3) to be fragile and the germination wall 2 (called layer 4) to resemble a skin, they did not detect their 2- and 3-layered structure, respectively. According to Morton and Redecker (2001), layers 3 and 4 are uniform structures. Additionally, they concluded that these layers are components of the spore wall. However, only the outer layer of the germination wall 1 may arise from the pedicel wall with which layers of the spore wall are continuous (Spain et al., in press) and the germination wall 1 has no physical contact with the innermost germination wall 2. Moreover, all these walls usually markedly separate from each other in crushed spores. Thus, the location of these walls in relation to one another and to the spore wall highly resembles that of the spore walls and germination walls of spores of fungi of the genera Acaulospora, Entrophospora, Kuklospora, Pacispora, and Scutellospora (Błaszkowski 2003). The outer surface of the innermost germination wall of spores of the latter genera is the place on which pre-germination structures (called germination orb or germination shield) form with emerging germ tubes. Although no one of such structures were so far revealed in spores of Ap. gerdemannii, the formation of the germination wall 2 in spores of this species probably precedes the synthesis of a similar structure and, thereby, makes the fungus to be able to germinate.

When observed under a dissecting microscope, spores of Ap. gerdemannii may easily be confused with those of A. spinosa C. Walker & Trappe, A. thomii Blaszk., and Ap. appendicula (Spain, Sieverd. & N.C. Schenck) Spain, Oehl & Sieverd. All the fungi form yellow brown and dull spores of a similar size range.

Examination of the subcellular structure of spores and their ontogenetic development readily separates the species of Archaeospora from those of Acaulospora. Spores of Ap. gerdemannii and Ap. appendicula differ mainly in the properties of layers of the first germination wall. In the former species, both layers are smooth on both sides. In contrast, in the latter fungus, the under surface of layer 1 is ornamented with hemispherical protuberances, which impress hemispherical concave depressions on the upper surface of layer 2 during its differentiation (Morton and Redecker 2001). Additionally, in vigorously crushed spores, the germination wall 1 of Ap. gerdemannii usually disintegrates, and that of Ap. appendicula remains its integrity.

The main differences between Ap. gerdemannii, A. spinosa, and A. thomii are (1) the continuity of the outermost spore wall layer with the wall of a sporiferous saccule in Acaulospora spp. (vs. the wall of a sporiferous saccule is continuous with spore wall layers 1-3 and layer 1 of germination wall 1 in Ap. gerdemannii) and (2) the presence of a beaded outer layer and a flexible to plastic, dextrinoid inner layer in the innermost germination wall in most Acaulospora spp. (vs. no such structures have been found in spores of Appendicispora spp.). Finally, only Ap. gerdemannii is a dimorphic fungus, forming both acaulosporioid and glomoid spores. The glomoid morphotype of Ap. gerdemannii has not so far been found in Poland and the only report of its existence is that of Morton and Redecker (2001).

Allen M. F., MacMahon J. A. 1985. Impact of disturbance on cold desert fungi: comparative microscale dispersion patterns. Pedobiol. 28, 215-224.

An Z.-Q., Grove J. H., Hendrix J. W., Hershman D. E., Henson G. T. 1990. Vertical distribution of endogonaceous mycorrhizal fungi associated with soybean as affected by soil fumigation. Soil Biol. Biochem. 22, 715-719.

An Z.-Q., Guo B. Z., Hendrix J. W. 1993. Mycorrhizal pathogen of tobacco: cropping history and current crop effects on the mycorrhizal fungal community. Crop prot. 12, 527-531.

An Z.-Q., Hendrix J. W., Hershamn D. E., Ferriss R. S., Henson G. T. 1993. The influence of crop rotation and soil fumigation on a mycorrhizal fungal community associated with soybean. Mycorrhiza 3, 171-182.

An Z. Q., Quo B. Z., Hendrix J. W. 1993. Populations of spores and propagules of mycorrhizal fungi in relation to the life cycles of tall fescue and tobacco. Soil Biol. Biochem. 25, 813-817.

Bever J., Morton J. B., Antonovics J., Schultz P. A. 1996. Host-dependent sporulation and species diversity of arbuscular mycorrhizal fungi in a mown grassland. J. Ecol. 84, 71-82.

Błaszkowski J. 2003. Arbuscular mycorrhizal fungi (Glomeromycota), Endogone and Complexipes spec ies deposited in the Department of Plant Pathology, University of Agriculture in Szczecin, Poland.http://www.agro.ar.szczecin.pl/~jblaszkowski/.

Dodd J. C., Arias I., Koomen I., Hayman D. S. 1990. The management of populations of vesicualr-arbuscular mycorrhizal fungi in acid-infertile soils of a savanna ecosystem. Plant and Soil 122, 241-247.

Koske R. E., Gemma J. N., Jackson N. 1977. Mycorrhizal fungi associated with three species of turfgrass. Can. J. Bot. 75, 320-332.

Moreira-Souza M., Trufem F. B., Gomes-da-Costa S. M., Cardoso E. J. B. N. 2003. Arbuscular mycorrhizal fungi associated with Araucaria angustifolia (Bert.) O. Ktze. Mycorrhiza 13, 211-215.

Morton J. B. 2002. International Culture Collection of (Vesicular) Arbuscular Mycorrhizal Fungi. West Virginia University: http://www.invam.caf.wvu.edu/.

Morton J. B., Redecker D. 2001. Two families of Glomales, Archaeosporaceae and Paraglomaceae, with two new genera Archaeospora and Paraglomus , based on concordant molecular and morphological characters. Mycologia 93, 181-195.

Nicolson T. H., Schenck N. C. 1979. Endogonaceous mycorrhizal endophytes in Florida. Mycologia 71, 178-198.

Rose S., Daniels B. A., Trappe J. M. 1979. Glomus gerdemannii sp. nov. Mycotaxon 8, 297-301.

Spain J. L., Sieverding E., Oehl F. 2006. Appendicispora: a new genus in the arbuscular mycorrhiza-forming Glomeromycetes, with a discussion of the genus Archaeospora. Mycotaxon 97, 163-182.

Turnau K., Ryszka P., Gianinazzi-Pearson V., Tuinen D. van 2001. Identification of arbuscular mycorrhizal fungi in soils and roots of plants colonizing zinc wastes in southern Poland . Mycorrhiza 10, 169-174.

Walker C. 1986. Taxonomic concepts in the Endogonaceae. II. A fifth morphological wall type in endogonaceous spores. Mycotaxon 25, 95-99.


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