SPOROCARPS

COLOR: Orange (0-40-80-0) when immature, becoming orange-brown (0-60-100-0) to
dark orange-brown (20-60-100-0) when mature.

SHAPE:  Globose, subglobose, occasionally pulvinate; irregular surface due to
protruding spores covered by a dense peridium.

SIZE DISTRIBUTION: 200-360 µm; mean = 273 µm (n = 104)

PERIDIUM

A dense layer of tightly interwoven hyphae, 9-19 µm thick, covering all spores to keep them tightly packed.  To see spores clearly, this peridium must be cut with a scalpel before sporocarps are mounted on a slide.  Hyphae are 2.5-7 µm in diameter with walls 0.5-1 µm thick.

In PVLG		In PVLG and Melzer's reagent

 The peridium appears to develop from a "monohyphal stalk" (Wu, 1993) and is profuse even in immature sporocarps (see photos below)

Young sporocarp (in Melzer's)	Mature sporocarp (in PVLG)

SPORES

Spores usually were clavate, but sometimes obovate to elliptical; organized in a "single layer from a central plexus of hyphae" (Gerdemann and Bakshi, 1976); orange-brown in color; 28-63 x 50-95 µm (w x l) in size.  

In PVLG

SUBCELLULAR STRUCTURE OF SPORES

SPORE WALL: One layer (L1) surrounded by dense peridial hyphae (see photos above).

L1: Pale orange-brown (0-10-60-0 to 0-20-80-0) sublayers (or laminae) that always are adherent. Thickness varies considerably on a single spore, 1.5-6 µm, being thickest at base.  In some older spores, the apex also will thicken more than the sides of elliptical or clavate spores. 

SUBTENDING HYPHA

SHAPE: Cylindrical to slightly flared, although shape at the spore often is hard to detect because of sometimes profuse side branching connected to the central plexus hyphae (see photos above).

WIDTH: 4-8 µm

WALL STRUCTURE: A single layer continuous with the spore wall layer, concolorous, 2-4.2 µm thick.

OCCLUSION: Usually a thin septum, but occasionally by thickening of the spore wall sublayers (see photos above).

GERMINATION

Not observed, but apparently germination occurs frequently from the central hyphal plexus of sporocarps sampled by others (Almeida and Schenck, 1990; Wu, 1993a).   Reports indicate germ tubes produce extramatrical vesicle-like structures.

MYCORRHIZAE

Mycorrhizal development in corn is very patchily distributed.  No sporocarps are evident where intensive arbuscule development is observed.  They are associated with roots containing mostly loose intraradical hyphae and some vesicles. 

Arbuscules in 90-day-old corn plants			Mycorrhizae in 90-day-old corn		Sporocarps linked by hyphae to roots

NOTES

This species reportedly was established in monospecific pot culture by Almeida and Schenck (1990), but the one culture of this fungus tranferred from Florida to West Virginia contained only spores of Paraglomus occultum.  It took almost two years to establish a culture from sporocarps (many were heavily parasitized) and this reference culture is maintained constantly by reseeding at six month intervals.  Sporocarps and spores closely resemble those of type specimens and those pictured by Almeida and Schenck (1990) and Wu (1993a, b).

Stages of sporocarp development are difficult to establish because a dense aggregate of sinuous hyphae form almost immediately on the "monohyphal stalk".  Wu (1993a) attempts to compare development amongst related sporocarpic species, but his interpretations were indirect and based only on field-collected specimens.   Interestingly, the spores appear to form concurrently from the central plexus, after which the spore walls differentiate and thicken together as well.

The data collected thus far on this culture do not change our view that this species deserves placement in a genus separate from Glomus.  Sporocarp formation is more complex than that in Glomus but the various differences among species form an unbroken continuum.  Moreover, spore development and differentiation are not unique.

With this culture, we now have living healthy material for anyone who wants to examine molecular properties of this species.

REFERENCES

Almeida, R. T. and N. C. Schenck. 1990. A revision of the genus Sclerocystis (Glomaceae, Glomales). Mycologia 82:703-714.

Gerdemann, J. W. and B. K. Bakshi.  1976. Endogonaceae of India: two new species.   Trans. Br. Mycol. Soc. 66:340-343.

Wu, C-G. 1993a.  Glomales of Taiwan: III. a comparative study of spore ontogeny in Sclerocystis (Glomaceae, Glomales). Mycotaxon 47:25-39.

Wu, C-G. 1993b. Glomales of Taiwan: IV. A monograph of Sclerocystis (Glomaceae).  Mycotaxon 47:327-349.