Date of Award:

5-1968

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Plant Pathology

Committee Chair(s)

Orson S. Cannon

Committee

Orson S. Cannon

Committee

J. LaMar Anderson

Committee

Gerald M. Baker

Abstract

The effect of temperature and inoculum density on the incidence of disease on radish caused by Rhizoctonia solani Kühn was studied. The fungus attacks radish at one or more stages during host development and causes pre- and pose-emergence damping-off, root rot, and storage-organ decay. The isolate of the fungus used in the study was obtained from infected radishes grown in Salt Lake County, Utah.

To determine the effect of temperature on the pathogenicity of R. solani on radish, soil temperatures of 15, 20, 25, and 30 C were used. Varying inoculum densities of 1360, 816, 408, 136, and 0 grams inoculum per million grams soil-peatmoss mixture were used to determine the effect of inoculum density on the incidense of disease at the various temperatures.

The optimum temperature for the growth of this strain of R. solani on potato dextrose agar was determined to be near 24 C, with a maximum of about 33 C and a minimum below 6 C. Pre-emergence damping-off of radish was found to be determined by the soil temperatures as it affects the relative growth of the host and pathogen, and by the inoculum density. Post-emergence damping-off increases with an increase in inoculum density, and at a given inoculum density is greatest at the optimum temperature for growth of the pathogen. It was not possible to devise an experiment to determine the effect of inoculum density on mature radish because the radishes succumbed to damping-off before the radishes could develop. Rot of mature radishes was determined to be greatest at the optimum temperature for growth of the pathogen.

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