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Ecology and Epidemiology

Factors Affecting In Vitro Growth and Zoospore Production by Aphanomyces raphani. H. S. Humaydan, Former Graduate Research Assistant, Department of Plant Pathology, University of Wisconsin, Madison, WI 53706, Present address of senior author: Joseph Harris Seed Company, Moreton Farm, Rochester, NY 14624; P. H. Williams, Professor, Department of Plant Pathology, University of Wisconsin, Madison, WI 53706. Phytopathology 68:377-381. Accepted for publication 29 July 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-377.

A partially selective medium containing 150 μg/ml streptomycin sulfate and 10 μg/ml benomyl in radish agar facilitated the isolation of Aphanomyces raphani from infected radish roots. Oospores and zoospores formed readily on radish agar, but were completely suppressed in the presence of streptomycin sulfate or peptone. Maximum numbers of motile zoospores (5 × 10⁴/ml) were produced 24 hr after transferring 2-day-old mycelial mats grown at 24 C in radish peptone broth into sterile distilled water; water at 20 C and pH 4.0-5.3 provided optimum conditions. Washing the mycelial mats reduced the number of zoospores produced. Zoospore production and mycelial growth was reduced by boron and inhibited by tap water.