Submitted to: Biological and Cultural Tests for Control of Plant Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2005
Publication Date: 5/1/2005
Citation: Hanson, L.E., Panella, L.W. Rhizoctonia root rot resistance of Beta Pis from the USDA-ARS NPGS, 2004. Biological and Cultural Tests for Control of Plant Diseases. (online) 20:FC016. DOI: 10. 1094/BC20. The American Phytopathological Society, St. Paul, MN. 2005. Interpretive Summary: Rhizoctonia root and crown rot is the most serious fungal root disease of sugar beet in the United States. Rhizoctonia root rot is difficult to control, and development of sugar beet cultivars with resistance to the disease is important for disease management. In 2004, 43 Plant Introductions from the USDA-ARS National Plant Germplasm System were tested for resistance to Rhizoctonia root rot. Due to mild summer temperatures and a moderate level of fungal inoculum, the disease progressed slowly and was rated in early September. Two of the Plant Introductions had disease levels that were not significantly different from the resistant control.
Technical Abstract: Forty-three Plant Introductions (PI) from the USDA-ARS National Plant Germplasm System were evaluated for resistance to Rhizoctonia root rot. Materials were planted at the Crops Research Lab-Fort Collins Research Farm in CO and inoculated with dry, ground, barley-grain inoculum of Rhizoctonia solani isolate R-9. Immediately after inoculation, a cultivation was performed to throw soil into the beet crowns. At harvest, each root was rated for rot on a scale of 0 (no damage) to 7 (completely rotted). Analyses of variance were performed on disease indices (DI), percent healthy roots (undamaged classes 0 and 1 combined), and percentage of roots in classes 0 thru 3 (those most likely to be harvested and taken to the factory). Percentages were transformed using arcsine-square root to normalize the data for analyses. Due to mild temperatures in the summer of 2004, combined with a low inoculum load, a moderate root rot epidemic developed. Differences in DI among entries were highly significant (P < 0.001). Mean DI across all tests in the 2004 nursery for highly resistant FC705-1, resistant FC703, and highly susceptible FC901/C817 controls were 2.1, 2.4, and 3.5 respectively. Percentages of healthy roots were 36.1, 32.1, and 12.3% for these controls. Percentages of harvestable roots in disease classes 0 thru 3 were 88.9, 80.1, and 40.7%, respectively. The highest and lowest DI for the PIs were 6.8 and 3.0, respectively. Two PIs had DI that were not significantly different than the resistant control.