Development of Gigaspora

DEVELOPMENT OF SPORES AND CHARACTERS OF MYCORRHIZAE

OF THE GENUS GIGASPORA


In PVLG

Spores of Gigaspora develop blastically from a bulbous sporogenous cell formed at the end of a fertile hypha connected with mycorrhizal roots (Bentivenga and Morton 1995; Walker and Sanders 1986). The wall of the most juvenile, expanding spores always consists of two layers of near equal thickness. Then, the inner layer thickens due to the synthesis of new sublayers (laminae). At the end of ontogeny, a warty or knobby one-layered germination wall is formed, from which germ tubes arise. This wall tightly adheres to the inner surface of the laminate spore wall layer. The outermost spore wall layer of all the Gigaspora spp. recognized is smooth.

Apart from spores, Gigaspora spp. also form clusters of auxiliary cells. They are echinulate with spines.

Interspecies differences in members of the genus Gigaspora reside in colour and size of spores (Bentivenga and Morton 1995). At present, this genus comprises only five species.

The mycorrhizae of Gigaspora spp. consist of only arbuscules and hyphae staining darkly in trypan blue or other stains; no vesicles are produced (Bentivenga and Morton 1995). Arbuscules generally form fine branches directly from a swollen basal hypha. Intraradical hyphae are straight to coiled and vary in diameter because of the presence knob-like projections and inflated areas.

REFERENCES

Bentivenga S., P., Morton J. B. 1995. A monograph of the genus Gigaspora, incorporating developmental patterns of morphological characters. Mycologia 87, 719-731.

Walker C., Sanders F. E. 1986. Taxonomic concepts in the Endogonaceae: III. The separation of Scutellospora gen. nov. from Gigaspora Gerd. & Trappe. Mycotaxon 27, 169-182.