Evaluation location: Colorado, United States
The trial was a randomized, complete-block design. One-row plots, replicated five times were planted in Windsor, CO, on 16 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 AG 2-2 isolate R-9 was performed on 12 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 31 Jul through 2 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 (DIs). We had unusually high temperatures in the summer of 2000 which, combined with a high inoculum load, contributed to a severe root rot epidemic. The Rhizoctonia epidemic progressed very quickly, becoming severe by the end of July. Differences in DIs among entries were highly significant (P < 0.001). Mean DIs across all tests in the 2000 nursery for highly resistant FC705-1, resistant FC703, and highly susceptible FC901/C817 controls were 2.5, 2.7, and 4.4 respectively. Percentages of healthy roots were 16.0, 16.3, and 3.9% for these controls. Percentages of roots in disease classes 0 thru 3 were 79.9, 67.1, and 28.7, respectively. The highest and lowest DIs for the evaluated lines were 6.4 and 1.7, respectively. A few PI accessions had DIs not significantly different from the resistant checks, and one performed extremely well (PI 590766).
View 2000 Rhizoctonia data as an Excel spread sheet (.xls).