Evaluation location: North Dakota, United States
A field site near St. Thomas, ND was selected to evaluate Beta germplasm accessions for potential resistance to sugarbeet root maggot (SBRM) feeding injury. The experiment was planted on 22 May, 2008 without any insecticidal root protection into 28-ft (8.5 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. Thirty B. vulgaris accessions were obtained from the NPGS Beta collection, courtesy of the USDA-ARS Western Regional Plant Introduction Station (Pullman, WA). Six additional entries (i.e., PI-504204, PI-608437, PI-658654, Tst-2 (an experimental hybrid with a susceptible female (cms) pollinated by PI 658654, Beta 2084, and FC704) were included in the experiment for comparative purposes. 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 a 0 to 9 scale (0 = no damage and 9 = 75% or more of root surface blackened with feeding scars or a dead plant). Root maggot fly activity in the plot area began considerably later than average, with the first flies being detected on 20 June and activity peaking on 25 June at a very high rate of 110 flies captured per trap per day. Relatively high levels of SBRM root-feeding injury in this trial were also observed. The lowest mean SBRM feeding injury in the test (i.e., 0.38 on the 0 to 9 rating scale) was recorded for PI-608437 (F1016). Root injury incurred by PI-658654 (F1024) was also very low (mean = 0.93), which was not statistically different from the average feeding injury in plots planted with PI-608437. Other entries that incurred low levels of SBRM feeding injury (i.e., mean < 2.0) that were not significantly different from those in plots planted with PI-658654 included FC704 and PI-546411. The highest levels of SBRM feeding injury in this study (i.e., rating > 5.0) occurred in plots planted with PI-562588 and PI-540563, for which mean root injury ratings were 5.03 and 5.33, respectively.