Evaluation location: Idaho, United States
Twenty-four sugar beet (Beta vulgaris L.) Plant Introduction (PI) Lines from the USDA-ARS National Plant Germplasm System (NPGS) were screened for resistance to Beet curly top virus (BCTV). The curly top evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID which has Portneuf silt loam soil and had been in barley in 2013. The field was plowed in the fall and in the spring, it was fertilized (90 lb N and 110 lb P2O5/A), sprayed with Ethotron (2 pt/A) for weed control, and roller harrowed on 11 Apr. The germplasm was planted (density of 142,560 seeds/A) on 19 May. The plots were two rows 10 ft long with 22-in row spacing and arranged in a randomized complete block design with three replications. The fields were sprinkler irrigated and hand weeded as necessary. Plant populations were thinned to about 47,500 plants/A on 14 June. Plants were inoculated at the four- to six-leaf growth stage on 23 June with approximately six viruliferous (contained three BCTV strains: Cal/Logan, severe, and Worland) beet leafhoppers per plant. The beet leafhoppers were redistributed three times a day during the first two days and then twice a day for five more days by dragging a tarp through the field. The plants were sprayed with Lorsban 4E (1.5 pints/A) on 7 July to kill the beet leafhoppers. Plots were rated for foliar symptom development on 16 July using a scale of 0 to 9 (0 = healthy and 9 = dead). Curly top symptom development was uniform and no other disease problems were evident in the plot area. The resistant and susceptible checks performed as expected for both the visual rating.