Submitted to: Plant Disease Management Reports
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/26/2007
Publication Date: 4/9/2007
Citation: Hanson, L.E., Panella, L.W. 2007. Rhizoctonia root rot resistance of Beta PIs from the USDA-ARS NPGS, 2006. Plant Disease Management Reports. (online) 1:V023. DOI: 10.1094/PDMR01. The American Phytopathological Society. St. Paul, MN. 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 2006, 30 Plant Introductions from the USDA-ARS National Plant Germplasm System were tested for resistance to Rhizoctonia root rot. Due to irrigation problems and a low level of fungal inoculum, the disease progressed slowly and was moderate. Three of the Plant Introductions had disease levels that were not significantly different from the highly resistant and resistant controls, and one additional Plant Introductions was not significantly different from the resistant control, although it had significantly greater disease than the highly resistant control.
Technical Abstract: Thirty 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 inability to control the timing of irrigation, combined with a low inoculum laad, a mild root rot epidemic developed. Differences in DIs among entries were highly significant (P<0.001). Mean DIs accross all tests in the 2006 nursery for highly resistant FC705-1, resistant FC703, and highly susceptible FC901/C817 controls were 1.7, 1.8, and 3.5 respectively. Percentages of healthy roots were 51.5, 43.7, and 21.3% for these controls. Percentages of roots in disease classes 0 thru 3 were 97.4, 91.5, and 50.9%, respectively. The highest and lowest DIs for the PIs were 6.3 and 2.3, respectively. Three PIs had DIs that were not significantly different than the highly resistant and resistant controls, and one additional PI had a DI that was not significantly different than the resistant control, but was significantly greater than the highly resistant control.