HOST-RANGE OF VERTICILLIUM-DAHLIAE FROM HORSERADISH AND PATHOGENICITY OF STRAINS

The pathogenicity of Verticillium dahliae isolated from horseradish (Armoracia rusticana) was evaluated on nine herbaceous plant species. A range of disease reactions, from highly susceptible to highly resistant, was observed following root-dip inoculation, and foliar symptoms developed on China aster, eggplant, horseradish, potato, and sunflower, No external symptoms were seen on brussels sprouts, but root and/ or stem tissues had slight to moderate vascular discoloration. Pepper, tomato, and watermelon were asymptomatic, but the pathogen was recovered from roots and/or basal stem areas from each of them. Eleven strains of V. dahliae isolated from a wide range of hosts were also evaluated for their ability to cause symptoms on a susceptible cultivar of horseradish. On the basis of root and foliar symptoms, the strains ranged from highly virulent to nearly avirulent. The time from inoculation to symptom appearance ranged from 35 to 110 days, depending on the strain of V. dahliae. The shortest incubation (35-40 days) was observed for the horseradish strain.