Evaluation location: North Dakota, United States
A grower-owned field site near St. Thomas, North Dakota was selected to evaluate Beta germplasm accessions for potential resistance to sugarbeet root maggot (SBRM) feeding injury. Plots were planted on 6 May, 2005, and no planting-time or postemergence insecticide protection used for any of the treatments. Individual treatment plots consisted of single rows that were 28 ft (8.5 m) long and spaced 22 inches (55.9 cm) apart. Forty treatments were arranged in a randomized complete block design with four replications. Treatments included 30 accessions of B. vulgaris maritima that were obtained from the NPGS Beta collection, courtesy of the USDA-ARS Western Regional Plant Introduction Station (Pullman, WA). Ten additional entries (i.e., PI-179180, PI-181718, PI-221436, PI-285596, PI-605413, PI-608437, 04N0063, PI-658654, Beta 6600, and PI-590659 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 23 August. Due to extended periods of cold weather during April and May, SBRM fly activity in 2005 began later than normal and peaked on 22 June at a relatively low level of 51 flies per trap per day. However, fly activity persisted for a relatively long period of nearly three weeks. Accordingly, root maggot larval feeding injury rating means in the more susceptible entries of this trial (i.e., PI-504202, PI-504249, and Ames 4436) were moderately high, ranging from 5.45 to 6.85 on the 0 to 9 scale. The lowest SBRM feeding injury in the test (i.e., mean = 0.28) was recorded for roots of PI-590659 (FC704) plants. Other entries that also incurred very low levels of feeding injury (i.e., 0.40 to 2.23) that were not statistically different from that recorded for PI-590659 included the following (in ascending order of injury): PI-181718, PI-179180, PI-285596, PI-658654 (F1024), PI-540616, PI-540620, PI-608437 (F1016), PI-221436, PI-518421, PI-540629, PI-540643, PI-540619, PI-540615, and PI-540630.