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Inoculation of Soybean Seedlings With Zoospores of Phytophthora megasperma var. sojae for Pathogenicity and Race Determination. Linda L. Eye, Department of Botany & Plant Pathology, Michigan State University, East Lansing, MI 48824; B. Sneh(2), and J. L. Lockwood(3). (2)(3)Department of Botany & Plant Pathology, Michigan State University, East Lansing, MI 48824. Phytopathology 68:1769-1773. Accepted for publication 17 July 1978. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1769.

Severe root disease resulted when 2-day-old soybean seedlings growing in vermiculite were inoculated with 104 zoospores per plant and incubated at 20–30 C. Severe disease also resulted when 2-day-old soybean seedlings were placed in petri dishes containing 10–20 g of steamed soil that had been flooded with 30 ml of distilled water containing 2 × 102 zoospores per plant and were incubated at 20–30 C. Nine differential cultivars of soybean were inoculated with zoospores of six races of the pathogen in vermiculite or flooded soil. Results in either case generally corresponded with those obtained by placing mycelia in wounded hypocotyls. Larger numbers of zoospores than those stated resulted in infection of some “resistant” cultivars. Two-day-old soybean seedlings baited the pathogen from flooded samples of several naturally infested soils.

Additional keywords: Isolation, detection, Phytophthora root and stem rot.