VIEW ARTICLE

Ecology and Epidemiology

Population Dynamics of Two Vesicular-Arbuscular Endomycorrhizal Fungi and the Role of Hyperparasitic Fungi. J. P. Ross, Plant Pathologist, Agricultural Research Service, U. S. Department of Agriculture, and Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607; Rosalie Ruttencutter, Plant Pathologist, Agricultural Research Service, U. S. Department of Agriculture, and Department of Plant Pathology, North Carolina State University, Raleigh, NC 27607. Phytopathology 67:490-496. Accepted for publication 17 September 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-490.

Populations of Glomus macrocarpus var. geosporus and Gigaspora gigantea, based on numbers of chlamydospores in roots and azygospores in soil, respectively, were followed through two growing seasons in small plots in which peanuts and soybeans were grown. During the second growing season, root infection data also were obtained. Populations of G. macrocarpus increased rapidly during the first season only in plots without G. gigantea which may indicate either that G. macrocarpus does not compete well with G. gigantea, or that other factors such as hyperparasites inhibit the former more than the latter. The inhibitory effect of high soil phosphorus on the percentage of root infection was less in doubly-infected roots than in roots infected with G. macrocarpus alone. Two hyperparasites, a species of Phlyctochytrium and a ‘Pythium-like’ fungus, were found attacking G. macrocarpus at the end of the second season. The hyperparasites were associated with a decline in chylamydospore production in soybean roots growing in soil from the plots. Hyperparasites of endotrophic mycorrhizal fungi are postulated to play an important role in limiting populations of certain of these beneficial fungi.