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Ecology and Epidemiology

Parasitism of Oospores of Phytophthora megasperma var. sojae, P. cactorum, Pythium sp., and Aphanomyces euteiches in Soil by Oomycetes, Chytridiomycetes, Hyphomycetes, Actinomycetes, and Bacteria. B. Sneh, Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824; Susan J. Humble(2), and J. L. Lockwood(3). (2)(3)Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824. Phytopathology 67:622-628. Accepted for publication 23 November 1976. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-622.

Oospores of Phytophthora megasperma var. sojae, P. cactorum, Pythium sp., and Aphanomyces euteiches in natural soil were infected with oomycetes, chytridiomycetes, hyphomycetes, actinomycetes, and bacteria. The oomycetes were Pythium sp. and Leptolegnia sp. The hyphomycetes were Dactylella spermatophaga, Diheterospora chlamydosporia, Humicola fuscoatra, Fusarium oxysporum, Cephalosporium sp., and Alternaria alternata. One isolate with nonseptate sterile mycelia was not identified. The chytrids were identified as Rhizidiomycopsis japonicus, Canteriomyces stigeoclonii, and Hyphochytrium catenoides. The actinomycete was Actinoplanes missouriensis. Two bacterial isolates were identified as Pseudomonas spp. In flooded soils, oospores were parasitized primarily by chytrids, oomycetes, A. missouriensis, and bacteria, whereas in soil with moisture levels below water-holding capacity, hyphomycetes predominated. Parasitism may have a significant potential for reducing populations of oospores in soil.