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Epidemiology of Rhizoctonia solani Pre-emergence Damping-off of Radish: Influence of Pentachloronitrobenzene. 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, Parlier, California 93648; Ralph Baker, Professor of Botany and Plant Pathology, Colorado State University, Fort Collins 80521. Phytopathology 64:38-40. Accepted for publication 25 June 1973. DOI: 10.1094/Phyto-64-38.

Curves for the inoculum density-disease incidence relationship of Rhizoctonia solani preemergence damping-off of radish (Raphanus sativus ‘Early Scarlet Globe’) were parallel for different concentrations of pentachloronitrobenzene (PCNB). Position of the curves was significantly different with an ID50 value (inoculum density required for 50% incidence of disease) of 5.2 propagules/gram of soil (p/g) for 0 µgPCNB/g soil, 11.0 p/g for 7.5 µgPCNB/g soil, 26.0 p/g for 12.5 µgPCNB/g soil and 50.0 p/g for 20 µgPCNB/g soil on a log-log basis. Synergism between R. solani propagules was suggested when transformations proposed for the inoculum density-disease incidence curve were used to analyze the data.

Additional keywords: infection court, spermosphere.