The effects of selected arbuscular mycorrhizal (AM) fungi, Glomus mosseae, Glomus etunicatum, Glomus fasciculatum and Gigaspora margarita, on growth of pepper seedlings and Phytophthora blight caused by Phytophthora capsici and the role of the phytoalexin, capsidiol were investigated. Root colonization by AM fungi reached between 61.3% and 68.1% in roots of pepper 4 weeks after transplanting. All tested AM fungi increased the shoot height between 23.4% and 31.7% and fresh and dry weights of shoots and roots of plants were enhanced by G. etunicatum, G. fasciculatum and Gigaspora margarita compared to uninoculated plants in pot experiments. G. fasciculatum increased yield significantly by 22% under greenhouse conditions. G. mosseae reduced the disease severity of P. capsici by 91.7%, 43.0% and 57.2% under pot, greenhouse and field conditions, respectively. Compared to the control, the capsidiol level was increased by preinoculation with G. mosseae and in the necrotic stems of P. capsici-inoculated pepper plants. In conclusion, AM fungi, especially G. mosseae enhanced the development of plants and reduced Phytophthora blight of pepper. (c) 2007 Elsevier Ltd. All rights reserved.