Relationships of Seedling Disease of Cotton to Characteristics of Loessial Soils in Tennessee

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Abstract
Forty-five samples of loessial soils in western Tennessee were collected at 15 sites in the fall of 1982 and again in 1983. Fungi were isolated from discolored or necrotic hypocotyls of cotton seedlings grown in the soil samples at 17.degree. C, and a disease severity index value for each sample was determined. The most frequently isolated fungi were Fusarium spp., Pythium spp., Rhizoctonia solani, and Thielaviopsis basicola. The soil samples also were characterized as to textural class, pH, and organic matter content. Cotton was planted in 1984 at the sites from which samples were taken previously, and seedling disease determinations were made. Isolations of Pythium spp. and disease indices obtained in the bioassay procedure were positively correlated with disease severity in the field plantings. A significant negative correlation was obtained between isolations of Fusarium spp. and disease severity. Soil clay content was inversely correlated with disease severity. Models were developed with a stepwise regression analysis to describe significant relationships of disease severity with soil biological and physical characteristics.