Evaluation location: North Dakota, United States
Several Beta germplasm accessions were assessed for potential resistance to sugarbeet root maggot (SBRM) feeding injury in a field trial near St. Thomas in northeastern ND. Plots were planted on 14 May, 2002, and none of the treatments received chemical insecticide protection. Individual treatment plots were single, 33-ft (10 m) long rows that were spaced 22 inches (55.9 cm) apart. Experimental design was a randomized complete block with four replications of 40 treatments. Treatments included one accession of Beta macrocarpa, two accessions of B. vulgaris, and 27 accessions of B. vulgaris maritima from the NPGS Beta collection, courtesy of the USDA-ARS Western Regional Plant Introduction Station (Pullman, WA). Ten additional entries (i.e., PI-608437, PI-605413, PI-179180, PI-181718, 01N0015, 01N0017, 01N0018, 01N0019, 01N0023, and PI-590659) were included for comparative purposes. Sugarbeet root maggot flies were first detected in the plot area on 28 May; however, the majority of fly activity occurred later than average for the area, and peaked on 28 June at a moderately high rate of 103 flies per trap per day. Larval feeding injury was assessed on up to ten sugarbeet roots per plot by rating them 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 19 August. Overall, root maggot larval feeding injury (i.e., RI) levels observed in the trial were moderate to moderately high in comparison to other years of testing. Roots of PI-608437 (F1016) plants incurred significantly lower levels of SBRM feeding injury (mean RI = 1.15 on the 0 to 9 scale) than all other entries in the trial. Other entries that sustained relatively low levels of feeding injury (i.e., RI < 4.00) included 01N0015, PI-590659 (FC704), PI-605413 (F1015), 01N0017, and 01N0019, for which the average root ratings were 2.43, 3.28, 3.80, 3.85, and 3.98, respectively. The experimental breeding program entry, 01N0015, incurred significantly lower levels of root injury than all other entries in the trial, except PI-608437 and PI-590659.