A method to effect rapid, near-synchronous colonization of tomato root systems by a vesicular arbuscular mycorrhizal fungus was developed. This procedure was used to compare the time course of colonization in roots of tomato that were grown under varying phosphate conditions. It was found that the primary symbiotic interaction developed through a series of regularly timed stages. Furthermore, the formation of intercellular hyphae, arbuscules and vesicles was significantly reduced in plants grown with high soil phosphate. These results show that this method is ideal for the production of material for molecular biological studies of VAM symbiosis, including investigation of the regulatory role of phosphate in the symbiosis and the processes that control the fungal life cycle.