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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Soil Management and Sugarbeet Research » Research » Publications at this Location » Publication #316337
Title: USDA-ARS germplasm evaluated for resistance to Rhizoctonia crown and root rot in Fort Collins, CO, 2014

Author
item Panella, Leonard
item Vagher, Travis
item FENWICK, ANN - Beet Sugar Development Foundation

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2015
Publication Date: 8/1/2015
Citation: Panella, L.W., Vagher, T.O., Fenwick, A. 2015. USDA-ARS germplasm evaluated for resistance to Rhizoctonia crown and root rot in Fort Collins, CO, 2014. Plant Disease Management Reports. 9:FC138. Online doi:10.1094/PDMR09:FC138.

Interpretive Summary: Thirty-six sugar beet germplasm developed by the USDA-Agricultural Research Service pre-breeding program at Fort Collins, Colorado were screened for resistance to Rhizoctonia crown and root rot (RCRR) in Fort Collins, CO. There were two highly resistant germplasm, one resistant germplasm, and one susceptible germplasm used as controls. Sugar beet seed was planted on May 29 and irrigated as needed with an overhead linear irrigation system. Betamix (2 oz acre-1) was applied on June 12 and 19. Inoculum was applied to the crown of the plants on July 21 (at the 8-12 leaf stage). Beets were harvested on September 16, and each root was rated for rot on a scale of 0 (no disease) to 7 (dead plant, leaves brown with root completely rotted). Average disease severity per plot was determined (on a continuous scale between 0 and 7) to create a disease index (DI) for each entry. Disease index, percent of healthy roots (classes 0 and 1 combined) and percent of the roots in classes 0 through 3 (harvestable roots) were analyzed. There were significant differences among entries for all three characteristics. The DI was 1.7 in the highly resistant control and 4.9 in the most susceptible entry. Entries a DI of 2.9 or below were not different from the highly resistant control and entries with a DI of 3.8 or higher were not different from the most susceptible entry. Entries with a DI between 2.9 and 3.8 were moderately resistant. All germplasm developed by the USDA-ARS pre-breeding program at Fort Collins are screened for RCRR before release; even if they have not been selected primarily for RCRR-resistance, this is useful information for other plant breeders wishing to incorporate the germplasm into their breeding programs.

Technical Abstract: Thirty-six sugar beet (Beta vulgaris subsp. vulgaris) germplasm from the USDA-Agricultural Research Service pre-breeding program at Fort Collins, Colorado were screened for resistance to Rhizoctonia crown and root rot (RCRR) at the Colorado State University ARDEC facility in Fort Collins, CO. There were two highly resistant germplasm, one resistant germplasm, and one susceptible germplasm used as controls. The 2014 Rhizoctonia screening nursery was a randomized complete-block design with five replicates in one-row plots (76 cm row spacing) 3.7 m long. Sugar beet seed was planted on May 29 May to moisture and irrigated as needed with an overhead linear irrigation system. Betamix (2 oz acre-1) was applied on June 12 and 19 Jun. An inoculum of dry, ground, hulless-barley grain, infested with Rhizoctonia solani isolate R-9 (AG-2-2), was applied to the crown of the plants on July 21 (at the 8-12 leaf stage) at a rate of 6.01 g m-1 of row. An electrically driven applicator was used to apply the inoculum and the field was cultivated afterwards to place soil onto the plant crowns. Beets were harvested on September 16 , and each root was rated for rot on a scale of 0 (no disease) to 7 (dead plant, leaves necrotic with root completely rotted). Average disease severity per plot was determined (on a continuous scale between 0 and 7) to create a disease index (DI) for each entry. Analyses of variance (PROC GLM) was performed on disease indices, percent of healthy roots (classes 0 and 1 combined) and percent of the 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). Disease progression was good, and at harvest there was moderate disease pressure. There were significant differences among entries for all three variables. The DI was 1.7 in the highly resistant control and 4.9 in the most susceptible entry. An analyses of variance (PROC MIXED) was performed on DI, and Dunnett’s one-tailed t-test (p = 0.10) adjusted for sample size was used to compare all entries to the highly resistant control (FC709-2) and the most susceptible germplasm (20121023HO) for DI. Entries a DI of 2.9 or below were not different from the highly resistant control and entries with a DI of 3.8 or higher were not different from the most susceptible entry. Entries with a DI between 2.9 and 3.8 were moderately resistant. All germplasm developed by the USDA-ARS pre-breeding program at Fort Collins are screened for RCRR before release; even if they have not been selected primarily for RCRR-resistance, this is useful information for other plant breeders wishing to incorporate the germplasm into their breeding programs.