Sieverd. & Oehl
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SPORES single in the soil; hyaline to white, glistening; globose to subglobose; (80-)130(-175) µm diam; sometimes ovoid; 80-120 x 90-170 µm; with a single subtending hypha.
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In PVLG+Melzer's reagent
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SUBCELLULAR STRUCTURE OF SPORES composed of a spore wall and one inner germination wall.
Spore wall consists of three layers (swl1-3).
Layer 1 permanent, semiflexible, smooth, hyaline, (0.5-)0.9(-1.1) thick, usually tightly adherent to layer 2, occasionally slightly separating from layer 2, especially in forcibly crushed spores.
Layer 2 laminate, smooth, hyaline to white (A1), (2.0-)3.8(-7.5) µm thick.
Layer 3 flexible to semiflexible, hyaline to white (A1), 0.5-0.8 µm thick, usually tightly adherent to layer 2.
Germination wall composed of three layers (gwl1-3).
Layer 1 flexible, hyaline, (0.3-)0.5(-0.9) µm thick, easily separating from layer 2.
Layer 2 flexible, coriaceous, hyaline, (0.9-)1.9(-3.1) µm thick.
Layer 3 flexible, hyaline, less than 0.5 µm thick, usually tightly adherent to layer 2, difficult to see.
Germination wall layers 2 and 3 stain dull red (9B4) to deep red (11B8) in Melzer's reagent.
GERMINATION SHIELD. Not observed.
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In PVLG |
SUBTENDING HYPHA hyaline; straight or slightly curved; cylindrical, sometimes constricted at the spore base; (6.2-)8.5(-12.5) µm wide at the spore base.
Wall of subtending hypha hyaline; (1.0-)1.5(-1.8) µm thick at the spore base, gradually thinning up to 0.5 µm thick distally; composed of two layers continuous with spore wall layers 1 and 2.Pore open or closed by a transverse septum positioned at the level of spore wall layer 2.
GERMINATION. Not observed.
MYCORRHIZAE. In Poland, P. franciscana was associated in the field with arbuscular mycorrhizae of Festuca rubra L. s.s., Lupinus luteus L., Malus domestica Borkh., Pisum sativum subsp. arvense (L.) Asch. et Graebn., Secale cereale L., Thuja occidentalis L., Triticum aestivum L., and Z. mays L. growing in Brzozowo, Dziadowo, Kamien Pomorski, Lipnik, Nowogard, Przelewice, Przybiernów (the Western Pomerania province), Chelm, and Zwierzyniec (the Lublin province). In Turkey, this fungus occurred among arbuscular mycorrhizal roots of Ammophila arenaria (L.) Link.
About 50 attempts to establish one-species cultures from both a single spore and many (ca. 20-50) spores of P. franciscana failed.
Pacispora franciscana has probably earlier been recorded as the white reticulate spore by Mosse and Bowen (1968) in Australia and as the white smooth-walled azygospore in Libyan soils and in the Negev Desert, Israel, by El Giahmi et al. (1976) and Dodd and Krikun (1984), respectively.
In Poland, P. franciscana has for the first time been found associated with roots of L. luteus cultivated in Lipnik (north-western Poland; 51o44'N, 15o41'E) in 1985. Later, spores of this fungus have been isolated from 12 other rhizosphere soil samples coming from under eight cultivated and uncultivated plant species growing in different regions of Poland (Blaszkowski, pers. observ.). Additionally, this fungus occurred among roots of A. arenaria colonizing sandy dunes of the Mediteranean Sea located near Karabucak-Tuzla (36o43'N, 34o59'E), Turkey.
The spore density of P. franciscana in the soil samples examined by the author of this website averaged 23.2 and ranged from 1 to 95 in 100 g dry soil. The participation of spores of this fungus in the spore populations of all the arbuscular fungi isolated averaged 20.8% and ranged from 0.2 to 82.9%. The arbuscular fungi accompanying P. franciscana in the soils examined were Acaulospora lacunosa J.B. Morton, Glomus aggregatum N.C. Schenck & G.S. Sm. emend. Koske, Gl. caledonium (Nicol. & Gerd.) Trappe & Gerd., Gl. constrictum Trappe, Gl. deserticola Trappe et al., Gl. etunicatum W.N. Becker & Gerd., Gl. fasciculatum (Thaxt.) Gerd. & Trappe emend. C. Walker & Koske, Gl. geosporum (Nicol. & Gerd.) C. Walker, Gl. macrocarpum Tul. & C. Tul., Gl. mosseae, Gl. przelewicensis Blaszk., P. scintillans (S.L. Rose & Trappe) Oehl & Sieverd., Paraglomus occultum (C. Walker) J.B. Morton & D. Redecker, Scutellospora dipurpurescens J.B. Morton & Koske, and S. pellucida (Nicol. & N.C. Schenck) C. Walker & F.E. Sanders.
NOTES. When observed under a dissecting microscope, spores of P. franciscana most resemble those of Gl. albidum C. Walker & L. H. Rhodes, Gl. diaphanum J.B. Morton & C. Walker, Gl. eburneum L.J. Kenn. et al., and Gl. viscosum Nicol. All are hyaline to white, as well as more or less overlap in size and shape (Kennedy et al. 1999; Morton 1985; Morton and Redecker 2001; Walker et al. 1995; Walker and Rhodes 1981). Another fungus producing spores reminiscent of those of P. franciscana at low microscope magnifications is P. scintillans, especially its isolates with indistinctly ornamented spores (Blaszkowski 2003; Walker et al. 2004).
The method readily separating the fungal species listed above is examination of their subcellular spore structure under a compound microscope. Only P. scintillans and P. franciscana have spores with two walls: an outer spore wall and an inner germination wall. However, the outermost layer of the spore wall of P. scintillans is ornamented with warts, blunt spines or ridges and, thereby, dull (Walker et al. 2004), whereas that of P. franciscana is smooth and glistening. The diversity of all the other species compared here hides only in the spore wall.
Pacispora franciscana has originally been accommodated in the family Glomeraceae Piroz. & Dalpé (Oehl and Sieverding 2004). Recently, this fungus has been transferred to the newly erected family Pacisporaceae C. Walker et al., whose molecular properties showed an ancestry with the family Gigasporaceae J.B. Morton et Benny (Walker et al. 2004). Additionally, the frequent co-occurrence of P. franciscana and P. scintillans (Blaszkowski, pers. observ.) suggests these fungi to represent one dimorphic species. Molecular analyses of spores of P. franciscana are needed to confirm the supposition.REFERENCES
Blaszkowski 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/.
El-Giahmi A. A., Nicolson T. H., Daft M. J. 1976. Endomycorrhiza fungi from Libyan soils. Trans. Br. Mycol. Soc. 67, 164-169.
Dodd J. C., Krikun J. 1984. Observations on endogonaceous spores in the Negev desert (Israel). Trans. Br. Mycol. Soc. 82, 536-540.
Kennedy L. J., Stutz J. C., Morton J. B. 1999. Glomus eburneum and G. luteum, two new species of arbuscular mycorrhizal fungi, with emendation of G. spurcum. Mycologia 91, 1083-1093.
Morton J. B. 1985. Variation in mycorrhizal and spore morphology of Glomus occultum and Glomus diaphanum as influenced by plant host and soil environment. Mycologia 77, 192-204.
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.
Mosse B., Bowen G. D. 1968. A key to the recognition of some Endogone spore types. Trans. Br. Mycol. Soc. 51, 469-483.
Oehl F., Sieverding E. 2004. Pacispora, a new vesicular arbuscular mycorrhizal fungal genus in the Glomeromycetes. J. Appl. Bot. 78, 72-82.
Walker C., Blaszkowski J., Schwazott D., Schüßler A. 2004. Gerdemannia gen. nov., a genus separated from Glomus, and Gerdemanniaceae fam. nov., a new family in the Diversisporales based on the former Glomus scintillans. Mycol. Res. 108(6), 707-718.
Walker C., Giovannetti M., Avio L., Citernesi A. S., Nicolson T. H. 1995. A new fungal species forming arbuscular mycorrhizas: Glomus viscosum. Mycol. Res. 99, 1500-1506.
Walker C., Rhodes L. H. 1981. Glomus albidus: a new species in the Endogonaceae. Mycotaxon 12, 509-514.
