Evaluation location: Colorado, United States
Accessions were evaluated for resistance to the beet curly top virus in an artificially inoculated nursery, managed by the Beet Sugar Development Foundation (BSDF) in Kimberly, ID. The field was planted on 14 and 15 Jun. Planting was late to maximize the number of viruliferous leafhoppers available to transfer to the sugarbeets while they are in the 8- to 10-leaf stage. Plots were 12 ft long, two-rowed with 22 in between rows and replicated twice. After the beets emerged, plots were trimmed to 8 ft in length, thinned to one foot between beets, and cultivated. Viruliferous leafhoppers were released on 22 Jul to cause an artificial epiphytotic. One week before the leafhoppers were released in the nursery, they had been transferred onto curly top-infested beets to assure that they were viruliferous when placed in the field. Uniform infection was achieved by placing 530 small cages, each with 175 to 200 leaf hoppers, uniformly throughout the field for release, and then spreading the leafhoppers daily for the next week by dragging a 12-foot tarp across the field. The field was sprayed 9 Aug with parathion to kill black bean aphid (and not harm the leaf hoppers) and then with an insecticide on 9 Sep to kill the leafhoppers. Plots were visually evaluated and rated on a Disease Index (DI) scale of 0 to 9 (no symptoms to dead) on 22 Sep. An analysis of variance (PROC ANOVA - SAS) on the disease indices (visual evaluation scores) determined that there were highly significant differences (P=0.05) among entries.