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Laminar Necrosis, Growth Inhibition, and Death of Tobacco Plants Caused by Toxic Extracts of Phytophthora cryptogea. Alex Csinos, Department of Plant Pathology, University of Kentucky, Lexington, KY 40506; James W. Hendrix, Department of Plant Pathology, University of Kentucky, Lexington, KY 40506. Phytopathology 67:434-438. Accepted for publication 26 October 1976. Copyright 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-434.

Extracts of oat cultures and of mycelium of Phytophthora cryptogea grown on glucose-glutamate liquid medium in shake cultures were toxic to tobacco plants. The severity of growth inhibition and foliar necrosis increased with time of exposure of the roots to extracts. Long (60 min) exposures of the roots to the extracts often resulted in death of tobacco plants. Burley and flue-cured tobacco types, either resistant or susceptible to the black shank disease, were affected by the extracts. Even though the black shank pathogen, P. parasitica var. nicotianae, reduced growth and killed plants transplanted into infested soil, extracts of oat cultures of this fungus were not toxic. Growth inhibition of tobacco seedlings caused by these two fungi appears to be caused by different mechanisms.