Suitability of Glomus intraradices in vitro produced spores and root segment inoculum for the establishment of a mycorrhizosphere in an experimental microcosm

Various experimental systems have been developed to study the mycorrhizosph ere. In this study, a microcosm experimental system was constructed and opt imized to simulate the environments of the mycorrhizosphere: the rhizospher e, the mycosphere, and the bulk soil, using beans (Phaseolus vulgaris L.) a s host plants. We investigated, in a time-course study, the effect of axeni cally in vitro produced spore inoculum and root segment inoculum of the arb uscular mycorrhizal fungus, Glomus intraradices Schenck & Smith, on extrara dical mycelium development, rapidity of mycorrhizal colonization, and plant growth under nonsterile soil conditions. Three concentrations of in vitro produced spores and three concentrations of root segment inoculum produced from open pot cultures were used. The two highest concentrations of spores used as inoculum resulted in faster and more abundant colonization than whe n root segments were used. A significant correlation was obtained between h yphal densities present in the rhizosphere and mycosphere compartments, and the amount of spore inoculum used. The densities of roots in the rhizosphe re compartment and hyphae in the rhizosphere and mycosphere compartments we re comparable with field-grown plants; thus, the system realistically mimic s a natural mycorrhizosphere. The use of the microcosm described in this st udy, in combination with the in vitro produced spore inoculum of G. intrara dices, represents an experimental approach well adapted for studying the mi crobial ecology of the mycorrhizosphere.