Verticillium dahliae:A Causal Agent of Root Discoloration of Horseradish in Illinois

In a survey of horseradish roots taken from commercial production fields in southwestern Illinois over 3 yr, Verticillium dahliae was found to be the primary pathogen associated with symptoms of root discoloration. The pathogen was isolated from 75% of roots showing symptoms of vascular discoloration, and from 55 and 56% of roots with symptoms of localized internal necrosis and rotting, respectively. V. dahliae was isolated from only one of the 54 asymptomatic roots that were assayed. Other species of bacteria and fungi, including Fusarium solani, also were isolated from horseradish roots, but none were consistently associated with specific symptoms