DEVELOPMENT OF SPORES AND CHARACTERS OF MYCORRHIZAE

OF THE GENUS APPENDICISPORA

In PVLG

Species of the genus Appendicispora Spain, Oehl & Sieverd. are dimorphic fungi, producing both acaulosporioid and glomoid spores, i. e., spores originating similarly to those of Acaulospora and Glomus spp., respectively (Morton and Redecker 2001; Spain et al. 2006). The acaulosporioid spores occur singly in the soil, and the glomoid ones are formed singly or in loose clusters in the soil and develop terminally from thin-walled hyphae grown from either the wall of a pedicel or branched germ tubes (Spain et al. 2006). In contrast to the sessile acaulosporioid spores of the genus Acaulospora Gerd. & Trappe emend. S.M. Berch and Archaeospora J.B. Morton & D. Redecker, those of Appendicispora spp. develop blastically at the tip of a short branch formed at the distal end of the neck of a sporiferous saccule. This branch is called “appendix” or “pedicel”. The sporiferous saccules of Appendicispora spp. originate terminally from mycorrhizal extraradical hyphae by their swelling.

In PVLG
In PVLG+Melzer's reagent
In PVLG

The spores of the known species of the Appendicispora are globose to subglobose and coloured. Their subcellular structure consists of a 3-layered, coloured spore wall and two inner, colourless germination walls. The outermost spore wall layer, forming the spore surface, is short-lived and rarely occurs in mature spores. The other two layers also more or less deteriorate with age and, thereby, occasionally completely expose the surface of the first inner germination wall (Błaszkowski, pers. observ.; Morton 2002; Morton and Redecker 2001). This first inner germination wall is permanent and consists of two, usually tightly adherent layers. The second innermost germination wall comprises three layers, of which the middle one is finely laminate and much thicker than the outer and the lower layers. Both these layers always tightly adhere to the middle layer and are difficult to observe.

The outer spore wall completes development subsequent to the formation of the outer layer of the first inner germination wall.

The spore wall and the outer layer of the first inner germination wall of spores of Appendicispora spp. are continuous with the pedicel wall layers.

The acaulosporioid spores of Ap. appendicula (Spain, Sieverd. & N.C. Schenck) Spain, Oehl & Sieverd., the only species in which germination was recognized, germinate with a none- or branched germ tube emerging from the second inner germination wall and exiting through the pore of the pedicel. A germination structure formed between the first and the second germination walls of spores of Ap. appendicula was found, but its morphological characters differ from those of the germination structures known in acaulosporioid spores of members of the Acaulospora and Ar. trappei (R.N. Ames & Linderman) J.B. Morton & D. Redecker (Spain 2003; Spain et al. 2006). The germ tubes produced frequently branch and the branches swell at their tips to form single or loose clusters of glomoid spores.

The mycorrhizae of species of the Appendicispora consist of arbuscules, vesicles, as well as intra- and extraradical hyphae. All these structures stain faintly in trypan blue (Spain et al. 2006).

At present, the genus Appendicispora includes three species, i. e., (1) Ap. appendicula, originally described as Acaulospora appendicula Spain, Sieverd. & N.C. Schenck (Schenck et al. 1984) and erroneously synonymized with A. gerdemannii N.C. Schenck & T.H. Nicolson (Spain et al. 2006) to establish the acaulosporioid morph of Ar. leptoticha (N.C. Schenck & G.S. Sm.) J.B. Morton & D. Redecker (Morton et al. 1997), (2) Ap. gerdemannii (S.L. Rose, B.A. Daniels & Trappe) Spain, Oehl & Sieverd., the former Glomus gerdemannii S.L. Rose, B.A. Daniels & Trappe (Rose et al. 1979), later renamed Ar. gerdemannii (S.L. Rose, B.A. Daniels & Trappe) J.B. Morton & D. Redecker (Morton and Redecker 2001), and (3) Ap. jimgerdemannii (N.C. Schenck & T.H. Nicolson) Spain, Oehl & Sieverd. of its first name A. gerdemannii N.C. Schenck & T.H. Nicolson (Nicolson and Schenck 1979).

Spain et al. (2006) concluded that the glomoid morph of A. appendicula is not synonymous with either Gl. leptotichum N.C. Schenck & G.S. Sm. or Gl. fecundisporum N.C. Schenck & G.S. Sm. as Morton and Redecker (2001) considered. Consequently, the latter two species were excluded from the Appendicispora and returned to the genus Glomus Tul. & C. Tul.

Spain et al. (2006) used seven arguments to separate the species listed above and to erect the new genus Appendicispora. First, although Ar. trappei, the only species remained in the genus, also is a dimorphic fungus, its spores origin directly on the neck of the sporiferous saccule and, hence, are sessile, whereas those of Appendicispora spp. develop at the tip of a pedicel. Second, in Ap. appendicula and Ap. gerdemannii, the wall of the pedicel is continuous with both the spore wall and the outer layer of the first inner germination wall of their spores, a unique feature in the attachments between spores and hyphae in all mycorrhizal species of the Glomeromycota. Third, the spore wall of Appendicispora spp. completes its differentiation after the full formation of the outer layer of the first inner germination wall. In contrast, in spores of Ar. trappei, the origination of the inner germination wall precedes the full synthesis of the spore wall (Morton and Redecker 2001). Forth, the walls of the neck and saccule of the sporiferous saccule of members of the Appendicispora consist of two to three layers continuous with the wall layers of their spores, and those of Ar. trappei are continuous with only the outermost spore wall spore wall layer (Błaszkowski 2003; Morton and Redecker 2001). Fifth, germination of the acaulosporioid morph of Ap. appendicula, the only species of the Appendicispora in which this property was recognized, is by regrowth of the germ tube through the pore of the pedicel, and not through the spore wall as in Ar. trappei (Spain 2003). Additionally, the morphological characters of the germination structure of Ap. appendicula differ from those of the germination structure formed inside spores of Ar. trappei (Spain 2003; Spain et al. 2006). Sixth, the mycorrhizae of Appendicispora spp. stain faintly in trypan blue, similarly to those of Ar. trappei (Morton 2003; Morton and Redecker 2001). However, Appendicispora spp. form mycorrhizae with both arbuscules and vesicles, whereas the mycorrhizae of Ar. trappei lack vesicles at all or they form rarely (Morton and Redecker 2001). Seventh, the published results of molecular analyses of Ap. jimgerdemannii (as A. gerdemannii), Ap. gerdemannii (as Gl. gerdemannii), and Gl. leptotichum showed them to be related with each other, but different from Ar. trappei (Redecker et al. 2000).

Apart from the morphological characters listed above, Appendicispora spp. and Ar. trappei also differ in their range of adaptation to various environmental conditions. While literature data indicate Appendicispora spp. to occur rather rarely in the world (Morton and Redecker 2001; Spain et al. 2006), Ar. trappei has a worldwide distribution and is one of the most frequently found species of Glomeromycota in different ecosystems (Błaszkowski 2003; Błaszkowski et al. 1999; Morton and Redecker 2001).

REFERENCES

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

Błaszkowski J., Tadych M., Madej T., Adamska I., Czerniawska B., Iwaniuk A. 1999. Acaulospora mellea and A. trappei, fungi new to the Mycota of Poland. Acta Mycol. 34, 41-50.

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

Morton J. B., Bever J. D., Pfleger F. L. 1997. Taxonomy of Acaulospora gerdemannii and Glomus leptotichum, synanamorphs of an arbuscular mycorrhizal fungus in Glomales. Mycol. Res. 101, 625-631.

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.

Redecker D., Morton J. B., Bruns T. D. 2000. Ancestral lineages of arbuscular mycorrhizal fungi (Glomales). Mol. Phylogenet. Evol. 14, 297–301.

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

Schenck N. C., Spain J. L., Howeler R. H. 1984. Several new and unreported vesicular-arbuscular mycorrhizal fungi (Endogonaceae) from Colombia. Mycologia 76, 685-699.

Spain J. L. 2003. Emendation of Archeospora and its type species, Archaeospora trappei. Mycotaxon 87, 109-112.

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.