IN soils containing little available phosphate mycorrhizal plants often grow much better than non-mycorrhizal ones because they can absorb more phosphate from the soil1–4. In many tropical soils, such as the “campos cerrados” soils covering large areas of Brazil, shortage of available phosphate is a main factor limiting plant growth and there is no response to nitrogen until the phosphate deficiency is relieved5. In such soils inoculation with a mycorrhizal fungus may be beneficial, even though most soils naturally contain some fungi that form vesicular-arbuscular (VA) mycorrhiza. The indigenous mycorrhizal fungi can be killed by irradiation and VA mycorrhiza can then be re-established by inoculation with species of Endogone. Several different strains exist and effects of four strains on the growth of the tropical grass Paspalum notatum var. Batatai were compared in two Brazilian soils.