Taxonomy and Ecology Of Inland Sand Dune ... - Mycorrhizae

9germination shield is formed, andgermination is by direct growth of one ormore germ tubes through the spore wall(Walker and Sanders, 1986; Walker,1987).The term chlamydospore includes thespores of the anamorphic spore stage ofGlomus and Sclerocystis species.Powell and Bagyaraj (1984) defined achlamydospore as a terminal (rarelyintercalary), thick-walled spore formedasexually and usually formed on a singlesubtending hypha. A truechlamydospore has an inner wall(usually laminated) and an outer wallcontinuous with the hyphal wall. Aunispored sporangium contains a sporethat develops from a modification of thehyphal wall via plastic expansion. Aunispored sporangium usually has athinner wall than does a chlamydospore(Hammill, 1981). In contrast tounispored sporangia (considered primaryspores because of their function infungal distribution), chlamydosporesmay be involved more in dormancy thanin dispersion (Griffiths, 1974). Perhapsthe anamorphic spores of Glomus andSclerocystis are intermediate formsbetween chlamydospores and sporangia(Morton, 1988).a. SPORE MORPHOLOGYDissecting, light, and electronmicroscopes are used to determine sporesize, shape, color, and wall structure. Ofall known species of VAM fungi, G.tenue (Greenall) Hall is the smallest;spores average 10-12 µm in diam. Incontrast, Gigaspora gigantea (Nicolsonand Gerdemann) Gerdemann and Trappeis the largest; spores range from 183-500x 291-812 µm. Morton (1988)suggested that variation in spore shapemay be the result of environmentalstress. Thin-walled spores produced inthe root cortex often are ellipsoid, as inG. intraradices Schenck and Smith, G.diaphanum Morton and Walker, andScutellospora pellucida (Nicolson andSchenck) Walker and Sanders. Sporesthat are produced with a large thick wallare mostly globose or subglobose, as inG. clarum Nicolson and Schenck and G.manihot Howeler, Sieverding andSchenck. Ovoid, obovoid, pyriform,