Evaluation location: Colorado, United States
The trial was a randomized, complete-block design. One-row plots, replicated five times were planted at the Crops Research Lab-Fort Collins Research Farm, CO, on 15 May. Plots were 4.5 m long with 56 cm between rows and 20 to 25 cm within-row spacing. Inoculation with dry, ground, barley-grain inoculum of Rhizoctonia solani isolate R-9 (AG 2-2) was performed on 10 Jul. Immediately after inoculation, a cultivation was performed to throw soil into the beet crowns. The field was thinned by hand and irrigated as necessary. Beets were harvested 27 Aug. Each root was rated for rot on a scale of 0 (no damage) to 7 (dead). Analyses of variance were performed on disease indices (DI). We had high temperatures in the summer of 2003 and a high inoculum (3 g/m) load. The Rhizoctonia root rot epidemic progressed quickly, becoming severe by the end of August. Differences in the DI among entries were highly significant (P < 0.001). Mean DIs across all tests in the 2003 nursery for highly resistant FC705-1, resistant FC703, and highly susceptible FC901/C817 controls were 3.2, 3.3, and 5.5 respectively. Percentages of healthy roots were 12.2, 8.7, and 1.4% for these controls. Percentages of roots in disease classes 0 thru 3 were 57.4, 50.5, and 7.0%, respectively. The highest and lowest DI for the evaluated lines was 6.9 and 2.9, respectively. The highest and lowest DI for the PI accessions was 6.8 and 3.0, respectively. Seven PIs had DIs that were not significantly different from the resistant control.
View 2003 Rhizoctonia data as an Excel spread sheet (.xls).