Effects of Vesicular-Arbuscular Mycorrhizal Fungi on the Development of Verticillium and Fusarium Wilts of Alfalfa. S. F. Hwang, Alberta Environmental Centre, Vegreville, Alberta, Canada T0B 4L0. K. F. Chang, and P. Chakravarty. Alberta Tree Nursery and Horticulture Center, Edmonton, Alberta, Canada T5B 4K3; and Alberta Environmental Centre, Vegreville, Alberta, Canada T0B 4L0. Plant Dis. 76:239-243. Accepted for publication 8 September 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0239.

Interactions of vesicular-arbuscular (VA) mycorrhizal fungi and two wilt pathogens of alfalfa (Medicago sativa), Verticillium albo-atrum and Fusarium oxysporum f. sp. medicaginis, were investigated under controlled conditions over a 6-mo period. The four × two factorial design used included four treatments of mycorrhizal fungi (Glomus spp., G. fasciculatus, G. mosseae, and nonmycorrhizal control) and two levels of pathogen inoculum (with and without) of either V. albo-atrum or F. o. medicaginis. Shoot dry weights of alfalfa plants inoculated with VA mycorrhizal fungi significantly exceeded those of nonmycorrhizal plants. Inoculation with V. albo-atrum or F. o. medicaginis significantly reduced the shoot dry weights of alfalfa. Seedlings inoculated with VA mycorrhizal fungi had a lower incidence of wilt than nonmycorrhizal ones. Propagule numbers of both pathogens were lower in the soil inoculated with VA mycorrhizal fungi than in the nonmycorrhizal soil.