Evaluation location: Colorado, United States
Forty sugar beet germplasm lines released over the past 30 years, or under development by the USDA-ARS Sugar Beet Research Unit located in Fort Collins, CO were evaluated for resistance to Rhizoctonia root rot. 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 23 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 17 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 3 through 6 Sept. 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 high temperatures in the summer of 2002 and a moderate inoculum load. The Rhizoctonia epidemic progressed quickly, becoming severe by the beginning of September. Differences in DIs among entries were highly significant (P < 0.001). Mean DIs across all tests in the 2002 nursery for highly resistant FC705-1, resistant FC703, and highly susceptible FC901/C817 controls were 1.89, 2.24, and 4.40 respectively. Percentages of healthy roots were 39.3, 35.9, and 10.0% for these controls. Percentages of roots in disease classes 0 thru 3 were 91.2, 86.3, and 37.1%, respectively. There was a significant difference between all the resistant germplasm and the susceptible control with two exceptions. A 1993 seed increase of FC704 was significantly more susceptible than the susceptible control and a FC702, and early release (1968) was not significantly different from the susceptible control.
View 2002 (B) Rhizoctonia data as an Excel spread sheet (.xls).