Ambispora appendicula

(Spain, Sieverd. & N.C. Schenck) C. Walker

A dimorphic fungus, producing acaulosporioid and glomoid spores. Acaulosporioid spores formed singly, and glomoid ones either singly or in loose aggregates in the soil.

ACAULOSPORIOID SPORES origin blastically at the tip of a short branch (pedicel) of the neck of a sporiferous saccule continuous
In PVLG

 

with a thick-walled, often rigid, persistent, 12-20(-25) µm wide mycorrhizal extraradical hypha. Spores pale yellow (4A3) to butter yellow (4A5); globose to subglobose; (170-)250(-390) µm diam.

 

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

Spore wall composed of three layers (swl1-3).
In PVLG
In PVLG+Melzer's reagent

Layer 1, forming the spore surface, evanescent, short-lived, hyaline, 0.5-1.0 µm thick, usually highly degraded or completely sloughed in even young spores.

Layer 2 friable, pale yellow (4A3) to butter yellow (4A5), (6.9-)12.9(-21.8) µm thick, of the upper surface somewhat roughened and with an irregular crazed pattern of fine cracks, usually highly degraded in mature and older spores.

Layer 3 flexible to semi-flexible, hyaline, ca. 0.5-1.0 µm thick, always tightly adherent to the lower surface of layer 2, and, thereby, difficult to see.

Germinal wall 1 comprises two semirigid to rigid, fragile, hyaline ornamented layers (gw1l1 and 2), usually separating from one another in crushed spores.
In PVLG
In PVLG+Melzer's

Layer 1 (2.0-)3.0(-5.7) µm thick, of the lower surface ornamented with knobby processes, 4.9-10.0 µm wide and 1.0-4.5 µm high, directed towards the spore centre.

Layer 2 (2.0-)4.9(-6.7) µm thick, of the upper surface ornamented with pits fitting in size, shape, and distribution the processes of the lower surface of layer 1. When layers 1 and 2 are adherent, the processes of layer 1 tightly fill the pits of layer 2.

Germinal wall 2 hyaline, (3.2)4.7(-8.3) µm thick, probably consisting of three, tightly adherent layers: two very thin, <0.5 µm
In PVLG

thick, layers (gw2l1 and 3) overlaying a markedly thicker, finely laminate middle layer (gw2l2). Layers 1 and 3 rarely visible in water mounted specimens, but almost imperceptible in spores crushed in PVLG (Błaszkowski, pers. observ.; Spain et al. 2006).

In Melzer's reagent, only the spore wall layer 2 stains orange (6A8) to high red (10A8).

PEDICEL hyaline to yellowish white (4A2); straight to recurved, cylindrical to slightly funnel-shaped; 30-100 µm long, 20-50 µm wide at the spore base, tapering up to 10-25 µm wide at the distal end from the spore; positioned 340-400 µm from the base of the saccule; consisting of a hyaline to yellowish white (A2), 2-layered wall (phwl1 and 2) continuous with the sporiferous saccule hyphal neck, the spore wall, and layer 1 of the germinal wall 1.
In PVLG

 

 

 

In PVLG

PORE closed by a septum positioned at or up to 5 µm below the spore base, formed by layer 1 of the germinal wall 1. Occasionally a second septum and less often a third one forms 20-50 µm below the spore base.

 

 

GERMINATION ORB hyaline, subcircular, with deep incisions separating clavate lobes of an arched top when seen in a plane view, positioned between the germinal walls 1 and 2 (Spain et al. 2006).

GERMINATION by a single or branched germ tube, 6-12 µm diam, emerging from the germinal wall 1 or the germination orb and exiting through the pore of the pedicel (Spain et al. 2006).
In PVLG

SPORIFEROUS SACCULE hyaline; globose to subglobose; (190-)250(-380) µm diam; rarely ellipsoid; 270-300 x 410-430 µm; frequently associated with young spores and usually not collapsing when detached from nature spores.

Wall of sporiferous saccule flexible to semiflexible, composed of three hyaline layers (sswl1-3): a (0.5-)1.0(-2.0) µm thick outermost layer, occasionally difficult to detect, a (2.9-)3.3(-3.7) µm thick middle layer, consisting of overlapping plate-like structures, and a thin, <0.5 µm thick, flexible innermost layer.

Saccule neck hyaline; 500-800 µm long, 45.0-57.5 µm wide at the base of the saccule, 22.5-30.0 µm wide at the spore base, then gradually tapering up to 12.5-10.0 µm wide.

CICATRIX. A smooth pore or a slightly raised collar when seen in a cross view; circular; 27.5-35.0 µm diam; or ellipsoidal; 35.0-37.5 x 44.6-50.0 µm; when observed in a plane view.
In PVLG
In PVLG+Melzer's

 

 

 

 

GLOMOID SPORES origin blastically at the tip of thin-walled hyphae, 6-12 µm diam, branched from thick-walled hyphae bearing acaulosporioid sporiferous saccules. Spores hyaline to subhyaline; globose to subglobose; (170-)187(-210) µm diam; rarely ellipsoid; 110-210 x 130-220 µm; with one subtending hypha.
In PVLG

 

 

 

In PVLG

SUBCELLULAR STRUCTURE OF GLOMOID SPORES consists of a spore wall composed of two hyaline to subhyaline layers (swl1 and 2).

Layer 1, forming the spore surface, evanescent, (1.7-)2.5(-3.2) µm thick, frequently with adhering debris on its upper surface.

Layer 2 laminate, (4.9-)6.1(-7.3) µm thick.

In PVLG

SUBTENDING HYPHA hyaline to subhyaline; straight or recurvate; cylindrical or slightly funnel-shaped; (11.0-)17.0(-24.5) µm wide at the spore base.

Wall of subtending hypha hyaline to subhyaline; (2.2-)4.2(-5.6) µm thick at the spore base; composed of two layers continuous with spore wall layers 1 and 2.

Pore usually open, (8.8-)12.8(-18.9) µm wide, occasionally closed by a septum continuous with the inner layer of the subtending hyphal wall, positioned 5-12 µm below the spore base.

GERMINATION. By a germ tube developing from the subtending hypha (Spain et al. 2006).

MYCORRHIZAE. According to Spain et al. (2006), Am. appendicula formed mycorrhizae with arbuscules, vesicles, and intraradical hyphae staining pale blue in trypan blue.

PHYLOGENETIC POSITION. According to Walker et al. (2007a), Am. appendicula belongs in a monophyletic clade along with Am. callosa (the former Glomus callosum), Am. fennica, Am. gerdemannii (Archaeosporales) , and Geosiphon pyriformis (Geosiphonaceae) to which the clade containing Archaeospora trappei, the type species of the genus Archaeospora and the family Archaeosporaceae, is a sister linage.

DISTRIBUTION. The holotype of Am. appendicula (OSC 41495) comes from spores isolated from a pot culture with Pueraria phaseoloides (Roxb.) Benth. as the host plant (culture no. C-13-1) grown at Centro Internacional de Agricultura Tropical (CIAT), Cali, Colombia (Schenck et al. 1984). This culture has originally been established from spores isolated from native grasses and tropical kutzu (P. phaseoloides ) at Carimagua, Meta province, Colombia. Schenck et al. (1984) also found spores of this fungus in acid soils (pH 5-5.5) near Gainesville and Ona, Florida, USA. Additionally, Am. appendicula has been recorded in soils of Mexico, Brazil, Bolivia, Costa Rica, Venezuela, Switzerland, Germany, Namibia, Republic of Congo, Thailand (Spain et al. 2006), Argentina (Schalamuk et al. 2006), Great Britain (Merryweather and Fitter 1998), China (Gai et al. 2006), and Japan (Walker et al. 2007a). The only Polish finding of Am. appendicula is that from under ....... growing ............

NOTES. The description of the morphological and biochemical properties of spores of Am. appendicula presented above was prepared based on the revised description of this fungus (Spain et al. 2006) and examination of its specimens provided by Dr. F. Oehl, Institute of Botany, University of Basel, Switzerland). Additionally, a microscope slide with well preserved spores of Am. appendicula associated with roots of Sesleria tatrae (Degen) Deyl growing in the Mountain Botanical Garden of the Polish Academy of Sciences in Zakopane and collected by Dr. Sz. Zubek, Jagiellonian University, Kraków, Poland, was used.

Most characters of both acaulosporioid and glomoid spores of Am. appendicula examined by the author of this website generally agreed with those of the two morphotypes given by Spain et al. (2006), who combined results of their own observations with the data of the species published by Schenck et al. (1984), as results from the two protologues. Small differences were found in (1) size of the processes of layer 1 of the germinal wall 1 (4.9-10.0 µm wide x 4.5 µm high; Błaszkowski, pers. observ.; vs. 7-12 µm wide x 3-5 µm high; Spain et al. 2006), (2) thickness of layer 2 of the germinal wall 1 (3.2-8.3 µm thick vs. 2-10 µm thick), (3) size of glomoid spores [170-210 µm diam vs. 120-240(-280) µm diam], (4) thickness of the spore wall layers 1 and 2 [1.7-3.2 µm thick and 4.9-7.3 µm thick, respectively vs. 1.5-2.5 µm thick and 2-8(-12) µm thick, respectively], (5) width of the subtending hypha [11.0-24.5 µm wide vs. 7-16(-19) µm wide], and (6) width of its pore [8.8-18.9 µm wide vs. 5-10(-12) µm wide].

Of the three other described species of the genus Ambispora, Am. appendicula is morphologically most closely related to Am. jimgerdemannii. Spores of the two species are similar in appearance, colour, size, and their first inner germinal wall consists of two adherent layers of an identical ornamentation (Błaszkowski, pers. observ.; Spain et al. 2006). The main differences between these species reside in the phenotypic and biochemical properties of their spore wall. Although the number and properties of the spore wall components of Am. jimgerdemannii are not exactly known because of the poor condition of the specimens preserved and the lack of living spores of this fungus, the relatively thick (6.9-21.8 µm thick) friable spore wall layer 2 of Am. appendicula is overlaid with a thin (0.5-1.0 µm thick) hyaline evanescent layer, whereas the second spore wall layer of Am. jimgerdemannii is persistent, laminate, 1.0-1.5 µm thick, and covered with a thick (8-14 µm thick), brown layer of the upper surface ornamented with cerebriform folds, (6-)10-12 µm high, 4-6 µm wide, and spaced 1-3 µm apart from each other (Błaszkowski, pers. observ.; Spain et al. 2006). Additionally, the upper surface of the spore wall layer 2 of the former fungus is slightly roughened and crazed, and that of the latter fungus is smooth. Moreover, in contrast to the spore wall layer 2 of Am. appendicula staining orange (6A8) to high red (10A8) in Melzer's reagent, none of the spore wall layers of Am. jimgerdemannii reacts in this reagent.

Another less important character separating the fungi compared here is the thickness of their inner germinal walls. Both the germinal walls 1 and 2 of spores of Am. appendicula are much thicker (4.0-12.4 µm and 3.2-8.3 µm thick, respectively) than those of Am. jimgerdemannii spores (2-3.5 µm and 4-6 µm thick, respectively; Błaszkowski, pers. observ.; Spain et al. 2006). Finally, glomoid spores have so far been recognized only in Am. appendicula (Spain et al. 2006).

Compared with Am. fennica and Am. gerdemannii, the first germinal wall of spores of only Am. appendicula is ornamented (Błaszkowski 2003; Spain et al. 2006; Walker et al. 2007a). In the two former species, the first germinal wall is smooth.

According to Spain et al. (2006), Morton and Redecker (2001) mistakenly named Archaeospora leptoticha and its glomoid morph using spores of Acaulospora appendicula (now Am. appendicula) and the known glomoid morph of this species. Acaulospora gerdemannii has not been known from pot cultures and its glomoid morph remains unknown. Consequently, Ar. leptoticha has been excluded from the genus Archaeospora, and Glomus leptotichum, erroneously considered a synanamorph of Ar. leptoticha and a synonym of Gl. fecundisporum, has been returned with Gl. fecundisporum to the genus Glomus (Spain et al. 2006). In contrast, Walker et al. (2007b, 2008) considered Gl. fecundisporum and Gl. leptotichum to belong in the genus Ambispora and erected two new combinations, Am. fecundicispora and Am. leptoticha.

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/.

Gai J. P., Christie P., Feng G., Li X. L. 2006. Twenty years of research on biodiversity and distribution of arbuscular mycorrhizal fungi in China: a review. Mycorrhiza 16, 229-239.

Merryweather J., Fitter A. 1998. The arbuscular mycorrhizal fungi of Hyacinthoides non-scripta. I. Diversity of fungal taxa. New Phytol. 138, 117-129.

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.

Schalamuk S., Velazquez S., Chidichimo H., Cabello M. 2006. Fungal spore diversity of arbuscular mycorrhizal fungi associated with spring wheat: effect of tillage. Mycologia 98, 16-22.

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., 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.

Walker C. 2008. Ambispora and Ambisporaceae resurrected. Mycol. Res. 112, 297-298.

Walker C., Vestberg M., Demircik F., Stockinger H., Saito M., Sawaki H., Nishmura I., Schüßler A. 2007. Molecular phylogeny and new taxa in the Archaeosporales (Glomeromycota): Ambispora fennica gen. sp. nov., Ambisporaceae fam. nov., and emendation of Archaeospora and Archaeosporaceae. Mycol. Res. 111, 137-13.

Walker C., Vestberg M., Schüßler A. 2007. Nomenclatural clarifications in Glomeromycota. Mycol. Res. 111, 253-255.