Abstract
The spread of mycorrhizal fungi through soil was estimated by transplanting clover plants infected with morphologically distinct mycorrhizal fungi into troughs of soil. Mycorrhizal fungi spread into non-mycorrhizal seedlings at rates of 0.6–1.5 m/year and into mycorrhizal seedlings at rates of 0.9–3.2 m/year. Mycorrhizal infestation of the trough soil greatly reduced the spreading rate of an introduced fungus. A precrop of kale or mustard grown in the trough soil repressed the soil's mycorrhizal infectivity and allowed an introduced fungus to spread rapidly.