Evaluation location: North Dakota, United States
This research was carried out in a commercial sugarbeet production field site near St. Thomas, ND during the 2006 growing season to screen Beta germplasm accessions for potential resistance to sugarbeet root maggot (SBRM) feeding injury. Plots were planted on 8 May, 2006 without any insecticidal root protection into 35-ft (10.7 m) long single-row plots spaced 22 inches (55.9 cm) apart. Experimental design was a randomized complete block with four replications. A total of 36 entries were tested. Twenty-nine accessions of B. vulgaris maritima were obtained from the NPGS Beta collection, courtesy of the USDA-ARS Western Regional Plant Introduction Station (Pullman, WA). Seven additional entries (i.e., PI-221436, PI-285595, PI-658654, 04N0064, PI-608437, PI-590659, and Beta 2084 [a commercial hybrid]) were included in the experiment for comparative purposes. Sugarbeet root maggot larval feeding injury was assessed on up to ten sugarbeet roots per plot on 14 August. Each root was washed, examined for SBRM feeding injury, and rated in accordance with the 0 to 9 scale (0 = no damage and 9 = 75% or more of root surface blackened with feeding scars or a dead plant. The onset of SBRM adult fly activity in the plot area occurred slightly earlier than average, with the first flies being detected early in the last week of May, and activity peaking around 4 June at over 80 flies per trap per day. This was considered a high level of SBRM fly activity in comparison to most previous years of testing. Accordingly, the overall levels of SBRM feeding injury in this trial were also relatively high. The lowest mean SBRM root-feeding injury (i.e., DR) in the test (DR = 1.43 on the 0 to 9 rating scale) was recorded for PI-608437 (F1016). Entries PI-658654 (F1024), PI-590659 (FC704), and 04N0064 also incurred low levels of injury (DR = 1.47, 2.38, and 2.76, respectively), and were not significantly different from PI-608437. Other accessions that sustained moderately low levels of SBRM feeding injury (mean < 4.0) included the following (in ascending order of root injury): PI-540660 (DR=3.43), PI-540667 (DR=3.48), Beta-2084 (DR=3.50), PI-518433 (DR=3.60), PI-546407 (DR=3.62), PI-546403 (DR=3.85), PI-285595 (DR=3.85), PI-540657 (DR=3.95), PI-540654 (DR=3.95), and PI-540664 (DR=3.98). The highest levels of injury in this study (i.e., rating > 5.0) occurred in plots planted with PI-504272, PI-546413, PI-546379, PI-504264, PI-504248, PI-546422, PI-546418, and PI-504235, which respectively averaged 5.05, 5.14, 5.15, 5.29, 5.43, 5.76, 6.00, and 7.00 on the 0 to 9 scale.