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Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 6/9/2016 Publication Date: 9/5/2016 Citation: Padilla, J.T., Vagher, T.O., Fenwick, A.L. 2016. Rhizoctonia crown and root rot resistance evaluation of Beta PIs in Fort Collins, CO, 2015. Plant Disease Management Reports. 10:FC167. Interpretive Summary: Thirty beet accessions of either cultivated beet or sea beet (Beta vulgaris subsp. vulgaris or Beta vulgaris subsp. maritima (L.) Arcang) from the Beta collection of the USDA-Agricultural Research Service National Plant Germplasm System were screened for resistance to Rhizoctonia crown and root rot (Rcrr) at the Colorado State University ARDEC facility in Fort Collins, CO. Sugar beet seed was planted on June 9. The crop was managed according to standard cultural practices. An inoculum of dry, ground, hulless-barley grain, infested with Rcrr was applied on July 28. Roots were harvested on September 8 with a single row lifter (pulled and cleaned by hand), 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 with a Disease Index (DI) based on the average of the roots. Statistical analyses were performed. All entries were compared to the highly resistant controls (FC709-2 and FC705/1) and the most susceptible plant introduction accession (PI 518325). Disease progression was excellent and, at harvest, severe levels of rhizoctonia crown and root rot were evident in our plots. There were highly significant differences among entries for DI in this year’s test and there was a very good separation between resistant and susceptible entries. FC709-2 was significantly more resistant than all other entries. Of the five entries not significantly different from the other highly resistant check (FC705/1), FC 707(4x) and FC 702/7 were developed by ARS at Fort Collins for resistance to Rcrr and F1004 at Fargo by ARS for resistance to storage rot – their performance was not surprising. L 3T and FC604 were developed for Cercospora leaf spot resistance, and PI 169024 is a land race accession from Turkey. Although not significantly different from FC705/1, they did not perform as well as the germplasm developed for Rcrr resistance at Fort Collins, and will not be used in the germplasm enhancement program for Rcrr resistance. None of the sea beet accessions tested were significantly different the most susceptible entry. These results will be accessible to interested parties through the USDA-ARS, NPGS GRIN database (http://www.ars-grin.gov/npgs/index.html). Technical Abstract: Thirty beet accessions of either cultivated beet or sea beet (Beta vulgaris subsp. vulgaris or Beta vulgaris subsp. maritima (L.) Arcang) from the Beta collection of the USDA-Agricultural Research Service National Plant Germplasm System 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 germplasms, one resistant germplasm, and one susceptible germplasm used as controls. The 2015 Rhizoctonia screening nursery was a completely randomized design with five replicates in one-row plots. In 2015, the field was not fertilized due to available nitrogen and was bedded. Sugar beet seed was planted on June 9. The crop was managed according to standard cultural practices. 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 28 at a rate of 7.0 g/m 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. Roots were harvested on September 8 with a single row lifter (pulled and cleaned by hand), 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 with the Disease Index (DI) treated as a continuous variable for each replicate of each entry. Statistical analyses were 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). All entries were compared to the highly resistant controls (FC709-2 and FC705/1) and the most susceptible plant introduction accession (PI 518325). Disease progression was excellent and, at harvest, severe levels of rhizoctonia crown and root rot were evident in our plots. There were highly significant differences among entries for DI in this year’s test and there was a very good separation between resistant and susceptible entries. FC709-2 was significantly more resistant than all other entries. Of the five entries not significantly different from the other highly resistant check (FC705/1), FC 707(4x) and FC 702/7 were developed by ARS at Fort Collins for resistance to Rcrr and F1004 at Fargo by ARS for resistance to storage rot – their performance was not surprising. L 3T and FC604 were developed for Cercospora leaf spot resistance, and PI 169024 is a land race accession from Turkey. Although not significantly different from FC705/1, they did not perform as well as the germplasm developed for Rcrr resistance at Fort Collins, and will not be used in the germplasm enhancement program for Rcrr resistance. None of the sea beet accessions tested were significantly different the most susceptible entry. These results will be accessible to interested parties through the USDA-ARS, NPGS GRIN database (http://www.ars-grin.gov/npgs/index.html). |
