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Fungi Associated with Postemergence Seedling Disease of Cotton in Three Soils. L. F. Johnson, Professor of Plant Pathology, Department of Agricultural Biology, University of Tennessee, Knoxville, TN 37901; D. D. Baird(2), A. Y. Chambers(3), and N. B. Shamiyeh(4). (2)Biologist, Air Quality Research, Tennessee Valley Authority, Muscle Shoals, AL 35660; (3)Associate Professor, Department of Agricultural Biology West Tennessee Experiment Station, Jackson, TN 38301; (4)Research Associate, Department of Agricultural Biology, University of Tennessee, Knoxville, TN 37901. Phytopathology 68:917-920. Accepted for publication 15 December 1977. Copyright © 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-917.

Soil samples were collected from 12 sites of three soils (Vicksburg fine sandy loam, Memphis silt loam, and Dexter loam) during a 12-mo period. Fungi were isolated from discolored or necrotic hypocotyls of cotton seedlings grown in the three soils at 19 C. More diseased hopocotyls occurred in soils not cropped to cotton than in soils cropped to cotton for 4 yr. The most frequently isolated fungi were Pythium spp., followed in descending order of frequency by Fusarium spp., Rhizoctonia solani, and Thielaviopsis basicola. The Pythium spp. isolated, in order of their frequency, were P. ultimum, nonsporulating “mycelial” isolates, P. sylvaticum, P irregulare, and P. heterothallicum. In pathogenicity tests, isolates of Pythium caused the most severe disease on cotton hypocotyls, followed by isolates of Rhizoctonia, Thielaviopsis, and Fusarium. Fewer diseased hypocotyls occurred on cotton grown in soils collected in February than in June, August, or November. In November, Pythium spp. were most prevalent; Fusarium spp., R. solani, and T. basicola were more prevalent in June and August than in February or November. Rhizoctonia solani and T. basicola were more prevalent in the Vicksburg fine sandy loam than in the Memphis or Dexter soils. Pythium spp. and Fusarium spp. were isolated more frequently from plants grown in soils not cropped to cotton and R. solani and T. basicola in soils cropped to cotton.

Additional keywords: cotton seedling blight, cotton damping-off.