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United States Department of Agriculture

Agricultural Research Service

Title: Rhizoctonia root rot resistance of Beta PIs from the USDA-ARS NPGS, 2007.

Authors
item Panella, Leonard
item Fenwick, Ann
item Hill, Amy
item McClintock, Mary
item Vagher, Travis

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 3, 2008
Publication Date: March 25, 2008
Citation: Panella, L.W., Fenwick, A.L., Hill, A.L., Mcclintock, M.E., Vagher, T.O. 2008. Rhizoctonia root rot resistance of Beta PIs from the USDA-ARS NPGS, 2007. Plant Disease Management Reports. (online) 2:V057.DOI:10.1094/PDMR02. The American Phytopathological Society. St. Paul, MN.

Interpretive Summary: Thirty-two plant introductions (PI) from the USDA-ARS National Plant Germplasm System (NPGS) (including garden beet, sugar beet, leaf beet, fodder beet, and wild beet) were evaluated for resistance to Rhizoctonia root rot. The trial was a randomized complete-block design with five replications in one-row plots at the ARS Fort Collins Research Farm, CO. Seed was planted on May 22, 2007 to moisture, and furrow irrigated as needed. (The first irrigation, on June 6, germinated the seed.) Inoculation with dry, ground, barley grain inoculum of Rhizoctonia solani isolate R-9 (AG-2-2) was applied to the crown of the plants on August 1, and again (due to heavy rainfall after initial inoculation) on August 10. Beets were harvested October 3, and each root was rated for rot on a scale of 0 (no damage) to 7 (dead plant with root completely rotted). Average disease severity was determined to create a disease index for each PI. Means of entries in all three tests were highly statistically significant (< 0.0001). There were six screening tests in the 2007 nursery, including Plant Introductions, experimental breeding material, and commercial cultivated varieties. Controls were included in all tests. The disease started slowly but, by the end of September, Rhizoctonia root rot reached severe levels in most of the nursery. The average DI across the six tests in the 2007 nursery for highly resistant FC705-1, resistant FC703, and susceptible FC901/C817 controls were 1.8, 2.6, and 4.6, respectively. The greatest and least DI for all of the lines evaluated in the nursery were 6.7 and 1.3, respectively. In all of the tests in 2007, there were highly significant differences among the entries for DI. Four of the PIs had a significantly small DI than the susceptible check, PI 552534, PI 504261, PI 552533, and PI 546420, and three of these were not significantly different from the highly resistant check.

Technical Abstract: Thirty-two plant introductions (PI) from the USDA-ARS National Plant Germplasm System (NPGS) (including garden beet, sugar beet, leaf beet, fodder beet, and wild beet) were evaluated for resistance to Rhizoctonia root rot. The trial was a randomized complete-block design with five replications in one-row plots (76 cm row spacing) 4 m long at the ARS Fort Collins Research Farm, CO. The field had been summer fallowed in 2004, 2005, 2006, and planted to barley in 2003. The soil (Garrett loam, 0 to 1 % slope, pH 7.8) was deep ripped in Nov 2006, and disked, roller harrowed and leveled in May prior to bedding and planting. The field was fumigated Apr 2006 with Telone II for control of potentially confounding soil borne diseases (esp. rhizomania) and insects. Seed was planted on 22 May to moisture, and furrow irrigated as needed. (The first irrigation, on 6 Jun, germinated the seed.) The plant population was thinned to 20-25 cm spacing by hand in late June. Inoculation with dry, ground, barley grain inoculum of Rhizoctonia solani isolate R-9 (AG-2-2) was applied to the crown of the plants on 1 Aug at a rate of 5.1 g/m row and again (due to heavy rainfall after initial inoculation) on 10 Aug at a rate of 2.4 g/m. A new Gandy electrically driven applicator with Hawkins Ditchers attached was used to apply the inoculum and place soil onto the plant crowns. Beets were harvested 3 Oct, with a single row lifter (pulled and cleaned by hand) and each root was rated for rot on a scale of 0 (no damage) to 7 (dead plant with root completely rotted). Average disease severity was determined to create a disease index for each PI. Analyses of variance (PROC GLM) were performed on disease indices (DI), % healthy roots (classes 0 and 1 combined) and % - roots in classes 0 through 3 (harvestable roots). Data in classes 0-1 and 0-3 were transformed using arcsine square root to normalize the data for analyses (AP 0-1 and AP 0-3, respectively). The LSD values in this trial were calculated with 3 missing plots using 5 as the number of replications. Means of entries in all three tests were highly statistically significant (< 0.0001). There were six screening tests in the 2007 nursery, including Plant Introductions, experimental breeding material, and commercial cultivated varieties. Controls were included in all tests. The disease started slowly but, by the end of September, Rhizoctonia root rot reached severe levels in most of the nursery. The average DI across the six tests in the 2007 nursery for highly resistant FC705-1, resistant FC703, and susceptible FC901/C817 controls were 1.8, 2.6, and 4.6, respectively. Percentages of healthy roots (those in disease classes 0 to 1) were 46.4, 35.8, and 12.6% for these controls, respectively. The percentages of harvestable roots (those in disease classes 0 through 3) were 77.5, 62.2, and 30.0% for these controls, respectively. The greatest and least DI for all of the lines evaluated in the nursery were 6.7 and 1.3, respectively. In all of the tests in 2007, there were highly significant differences among the entries for DI, percent healthy roots, and percent harvestable roots. Four of the PIs had a significantly small DI than the susceptible check, PI 552534, PI 504261, PI 552533, and PI 546420, and three of these were not significantly different from the highly resistant check.

Last Modified: 8/1/2014
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