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Epidemiology of Rhizoctonia solani Preemergence Damping-Off of Radish: Survival. D. M. Benson, Former Research Assistant, Colorado State University, Fort Collins 80521, Present address of senior author: San Joaquin Valley Agricultural Research and Extension Center, University of California, Parlier 93648; Ralph Baker, Professor of Botany and Plant Pathology, Colorado State University, Fort Collins 80521. Phytopathology 64:1163-1168. Accepted for publication 29 March 1974. DOI: 10.1094/Phyto-64-1163.

When survival of Rhizoctonia solani was followed after infesting natural soil, a brief increase in density occurred occasionally during the first 1-2 days but, in most instances, this increase was followed by a rapid decrease in detectable propagules. Twelve days after infestation population counts were consistently low. Rates of inoculum survival following repeated planting of diseased radish seeds and seedlings in soil, or the addition of cultures of either cornmeal-sand mixture or chopped potato tubers to soil were not significantly different. Rates of population decline were similar at initial high (127 propagules/g), medium (85 propagules/g), or low (37 propagules/g) inoculum densities; the actual number of propagules surviving for 8-80 days being proportional to the amount of original inoculum added to soil. Survival of R. solani was greatest in cool dry soil. Soil pH had no significant effect on survival. Extrapolations for 50% survival (TS₅₀) and rate of decline were complementary when log-probit and semilogarithmic transformations were used. Quantitative analyses of the major epidemiological factors determining disease incidence for Rhizoctonia damping-off of radish are now possible.