Evaluation location: Idaho, United States
Thirty sugar beet (Beta vulgaris L.) lines from the USDA-ARS National Plant Germplasm System plant introductions were screened for resistance to Beet severe curly top virus (BSCTV) and other closely related Curtovirus species in 2012. Commercial cultivars Monohikari and HM PM90 were included as susceptible and resistant checks, respectively. 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 alfalfa in 2011. The field was plowed in the fall and in the spring, fertilized (90 lb N and 110 lb P2O5/A) on 16 Apr 12, sprayed with Ethotron (2 pt/A), and roller harrowed. The germplasm was planted (density of 142,560 seeds/A) on 21 May. The plots were two rows 10 ft long with 22-in row spacing and arranged in a randomized complete block design with three replicates. The fields were sprinkler irrigated and hand weeded as necessary. Plant populations were thinned to about 47,500 plants/A on 19 June. Plants were inoculated at the four to six leaf growth stage on 22 June with six viruliferous beet leafhoppers per plant. The beet leafhoppers were moved twice a day (right after sunrise and just before sunset) for one week by dragging a tarp through the field. The plants were sprayed with Lorsban 4E (1.5 pints/A) on 4 July to kill the beet leafhoppers. The plots were rated for foliar symptom development on 10 July using a scale of 0-9 (0 = healthy and 9 = dead; Mumford 1974). Disease development was uniform and other disease problems were not evident in the plot area. The disease pressure in the test was severe with good disease development in the more susceptible lines.