Submitted to: Biological and Cultural Tests for Control of Plant Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 27, 2001
Publication Date: May 7, 2001
Citation: Panella, L.W., Hanson, L.E. 2001. Rhizoctonia root rot resistance of beta pis from the usda-ars npgs, 2000. Biological and Cultural Tests for Control of Plant Diseases. 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 2000, 28 Plant Introductions from the USDA-ARS National Plant Germplasm System were tested for resistance to Rhizoctonia root rot. Due to an unusually hot summer and a high level of fungal inoculum, the disease progressed quickly and was severe. A few of the Plant Introductions had disease levels that were not significantly different from the resistant controls, and one had very low disease levels.
Technical Abstract: Twenty-eight Plant Introductions (PIs) from the USDA-ARS National Plant Germplasm System were evaluated for resistance to rhizoctonia root rot. Materials were planted in Windsor, 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 sAt 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 unusually high temperatures in the summer of 2000, combined with a high 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 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 PIs were 6.2 and 2.5, respectively. A few PI accessions had DIs not significantly different from the resistant checks, and one performed extremely well (PI 590766).