Evaluation location: North Dakota, United States
A commercial field site near St. Thomas (Pembina County) in northeastern North Dakota was selected to evaluate Beta vulgaris germplasm accessions for potential resistance to sugarbeet root maggot (SBRM), Tetanops myopaeformis, feeding injury. Plots were planted on 11 May, 2017, and no insecticide was applied to any plots. Individual treatment plots were single rows that were 28 ft (8.5 m) long and spaced 22 inches (55.9 cm) apart. Experimental design was a randomized complete block with four replications of 39 treatments. Treatments included 20 accessions of B. vulgaris vulgaris and two accessions of B. v. maritima that were obtained from the NPGS Beta collection (courtesy of the USDA-ARS Western Regional Plant Introduction Station [Pullman, WA]). Seventeen additional entries (i.e., ACH-817 (a commercial hybrid), PI-590659, PI-176424, PI-179180, PI-181718, PI-355957, PI-372278, PI-467873, PI-535818, PI-546511, PI-546513, PI-546525, PI-546526, PI-605413, PI-608437, PI-658654, PI-676971) were included for comparative purposes. Larval feeding injury was assessed on up to ten sugarbeet roots per plot and rated in accordance with a 0 to 9 scale (0 = no damage and 9 = 75% or more of root surface blackened with feeding scars or a dead plant) on 3 August. Sugarbeet root maggot fly activity occurred at nearly average timing compared to historical records, with activity peaking on June 11. Fly activity levels in the plot area were considered moderate, which was largely due to a hail storm that occurred on June 9 and killed an estimated 40 to 60% of the SBRM fly population in the plot area. As such, resulting larval feeding injury (RI) levels in the plot area were considered moderate. The lowest overall SBRM feeding injury in the test (i.e., 1.75) was recorded for PI-676971 (F1043). Other entries that incurred low levels of feeding injury that were not significantly different from those recorded for PI-676971 included PI-658654 (F1024), PI-179180, PI-608437 (F1016), and Ames 2662, which had respective average root ratings of 2.23, 2.35, 2.7, and 2.78. Additional entries for which relatively low (i.e., RI < 3.3) levels of root injury were recorded included PI-504177, PI-546525, PI-605413 (F1015), PI-518383, Ames 2659, PI-531253, PI-590659 (FC704), and PI-181718.