Evaluation location: North Dakota, United States
A commercial field site near St. Thomas (Pembina County) in northeastern North Dakota was selected to evaluate Beta germplasm accessions for potential resistance to SBRM feeding injury. The experiment was planted on 6 May, 2004. No planting-time or postemergence insecticide protection was applied to any plots. Individual treatment plots were single rows that were 33 ft (10 m) long and spaced 22 inches (55.9 cm) apart. Experimental design was a randomized complete block with four replications of 36 treatments. Treatments included 26 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-285595, PI-658654, 02N0028, PI-605413, PI-608437, 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 18 August. Sugarbeet root maggot fly activity was delayed by cool spring weather conditions that prevailed during much of April and May. Despite later-than-average emergence, fly activity in the plot area peaked at a relatively high level of 113 flies per stake per day on June 30 (i.e., about two weeks later than normal). Root maggot larval feeding injury levels were also relatively high compared to other years of testing. For example, the highest average root rating in the trial (7.11 on the 0 to 9 scale) was recorded for PI- 504250. The lowest overall SBRM feeding injury in the test (i.e., 1.85) was recorded for PI-608437 (F1016). Other entries that incurred low levels of feeding injury that were not significantly different from those recorded for PI-608437 included PI-658654 (F1024), 02N0028, and PI-605413 (F1015), which had average root ratings of 2.45, 2.60, and 2.85, respectively. Root injury ratings for these four top-performing entries were all significantly lower than all other entries in the trial. All remaining entries incurred mean levels of root maggot feeding injury that exceeded 4.0 on the 0 to 9 rating scale.