Submitted to: Biological and Cultural Tests for Control of Plant Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/12/2004
Publication Date: 5/3/2004
Citation: Hanson, L.E., Panella, L.W. 2004. Rhizoctonia root rot resistance of Beta Pis from the USDA-ARS-NPGS, 2003. Biological and Cultural Tests for Control of Plant Diseases. (online) 19:FC012. DOI:10.1094/BC19. Interpretive Summary: Rhizoctonia root and crown rot is the most serious 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 control. In 2003, 36 Plant Introductions from the USDA-ARS National Plant Germplasm System were tested for resistance to Rhizoctonia root rot. Due to a hot summer and a moderate level of fungal inoculum, the disease progressed quickly and was severe. Seven of the Plant Introductions had disease levels that were not significantly different from that of the resistant control, of which four had percentages of healthy roots not significantly different from the resistant control.
Technical Abstract: Thirty-six Plant Introductions (PIs) 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 (dead). Analyses of variance were performed on disease indices (DIs), 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 arcsin-square root to normalize the data for analyses. Due to high temperatures in the summer of 2002, combined with a moderate inoculum load, a severe root rot epidemic developed. Differences in DIs 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 DIs for the PIs were 6.9 and 3.0, respectively. Seven PIs had DIs that were not significantly different from the resistant control, of which four were not significantly different from the resistant control for the percent of healthy roots.