Evaluation location: Idaho, United States
Thirty Plant Introductions (PIs) from the USDA-ARS National Plant Germplasm System (NPGS) (garden beet, sugar beet, leaf beet, fodder beet, and wild beet) were evaluated for resistance to the beet curly top virus in an artificially inoculated nursery, managed by the Beet Sugar Development Foundation in Kimberly, ID. The field was planted on 9 through 10 June. Planting was late to maximize the number of viruliferous leafhoppers available to transfer to the sugar beets while they are in the 8- to 10-leaf stage. Plots consisted of two, 12-ft long rows with a 22 in. between-row spacing. Plots were replicated twice. After the beets emerged, rows were trimmed to a length of 8ft and thinned to an in-row spacing of one foot, and cultivated. Viruliferous leafhoppers were released on 17 and 18 July 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 approximately leafhoppers uniformly throughout the field at a rate of approximately 1.2 leafhoppers per plant and then spreading the leafhoppers four times daily for the next week by dragging a 12-foot tarp across the field. The field was sprayed 11 August to kill the leafhoppers. Plots were visually evaluated and rated on a Disease Index (DI) scale of 0 to 9 (no symptoms to dead) September 2. The summer was very hot and dry and the epiphytotic severe.