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

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