Ontogeny of Glomus clarum in Ri T-DNA transformed roots

The spore ontogeny of Glomus clarum was monitored during the nonsymbiotic growth phase and after the colonization in transformed roots of clover (Trifolium repens) and carrot (Daucus carota). The germinated spore in water agar produced sporelike vesicles during the nonsymbiotic phase. It has been shown that these structures were in fact juvenile spores, that after root colonization were able to form mature spores. G. clarum began the spore formation in its nonsymbiotic phase. However, the juvenile spore structures senesced without establishment of an effective symbiosis. Spores of the genus Glomus are assumed to form terminally from sporogenic hyphae, but the ontogeny of G. clarum in transformed roots demonstrates that sporogenesis can also involve intercalary sporelike vesicles formed along the sporogenic hyphae. Using root organ culture system, all steps of spore formation can be followed in vivo without disturbing the system. This technique provides a better way to visualise events that occur during the pre- and postcolonization phase of arbuscular mycorrhiza, allowing the comprehension of full life cycle of this fungi. There are morphological variations in the ontogeny of G. clarum spores which differentiate its pattern from other Glomus species.