Verticillium dahliae resistance in horseradish germ plasm from the University of Illinois collection

A total of 113 horseradish cultivars from the University of Illinois germ plasm collection at Urbana were evaluated for their reaction to Verticillium dahliae in the greenhouse following a root-dip inoculation. Root discoloration was rated 2 months after inoculation on a scale of 0 to 3 as follows: 0 = no symptoms; 1 = trace to less than 10% of the root cross-section with vascular discoloration; 2 = 10 to 50% of the root cross-section with vascular discoloration; and 3 = more than 50% of the root cross-section with vascular discoloration. The cultivars exhibited a large amount of variation in response to V. dahliae infection, with mean root discoloration ratings ranging from 0.2 to 2.6. The frequency distribution of responses of the 113 cultivars was normal, with a mean and a standard deviation of 1.2 and 0.4, respectively. Six cultivars, 635A, 1236A, 769A, 125A, 761A, and 28A, were identified as resistant to V. dahliae. The existence of resistance to V. dahliae in horseradish germ plasm from the University of Illinois collection is a great resource for the breeding of improved horseradish cultivars that will combine resistance to V. dahliae with other desirable characters.