Evaluation of Beta PIs from the USDA-ARS, NPGS for Rhizoctonia crown and root rot resistance, 2018.

Authors: Fenwick, Ann; Fall, Amy; Metz, Nicholas; Floyd, Bradley; Yeater, Kathleen; Dorn, Kevin

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary: Thirty sugar beet cultivars (Beta vulgaris subsp. vulgaris and Beta vulgaris subsp. maritima (L.) Arcang)were screened for resistance to Rhizoctonia crown and root rot (RCRR) at the Colorado State University Agricultural Research, Development, and Education Center in Fort Collins, Colorado. The Rhizoctonia screening nursery used two highly resistant cultivars, one resistant cultivar and one susceptible cultivar as controls. The nursery was planted in a completely randomized design with five replications in one-row plots. The test was planted on 23 May, with an initial irrigation on 01 June. An inoculum of dry ground hulless barley grain infested with Rhizoctonia solani was applied to the crown of the plants on 12 Jul (8 to 12 leaf growth stage) at a rate of 8.5 g m-1 of row. Following inoculation, the field was cultivated afterwards to place soil onto the plant crowns. Disease progression was excellent and at harvest we had severe levels of RRCR in the nursery. The disease pressure was uniform throughout the test. Roots were harvested 26 August with a single row lifter (pulled and cleaned by hand), and each root was rated for RRCR on a scale of 0 (no damage) to 7 (dead plant with root completely rotted). Average disease severity per plot was determined to create a disease rating index for each entry. There were significant differences among entries for disease index. The highest performing entries were the highly resistant checks FC705/1 and FC709-2, and the resistant check FC703. The next four most resistant entries, PI590664, PI232887, NSL31344, and PI408965 were not significantly different from the highly resistant check FC705/1. PI 504179, was the most susceptible in the test, and there were 19 entries not significantly different than it. These cultivars will be retested and, if resistance is confirmed, incorporated into the USDA-ARS RRCR resistance breeding program at Fort Collins, CO to enhance sugar beet germplasm. These results will be accessible to interested parties through the USDA-ARS, NPGS GRIN database http://www.ars-grin.gov.

Technical Abstract: Thirty beet (Beta vulgaris subsp. vulgaris and Beta vulgaris subsp. maritima (L.) Arcang) accessions 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 Agricultural Research, Development, and Education Center in Fort Collins, Colorado. The Rhizoctonia screening nursery used two highly resistant germplasm (FC705/1 and FC709-2), one resistant germplasm (FC703) and one susceptible germplasm (FC901/C817) as controls. The nursery was planted in a completely randomized design with five replications in one-row plots (76 cm row spacing) 3.7 m long. The soil is a Fort Collins loam, (0 to 1 % slope, pH 7.2). The test was planted on 23 May, with an initial irrigation on 01 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 12 Jul (8 to 12 leaf growth stage) at a rate of 8.5 g m-1 of row using a Gandy® electrically driven applicator. Following inoculation, the field was cultivated afterwards to place soil onto the plant crowns. Disease progression was excellent and at harvest we had severe levels of RRCR in the nursery. The disease pressure was uniform throughout the test. Roots were harvested 26 Aug with a single row lifter (pulled and cleaned by hand), and each root was rated for RRCR on a scale of 0 (no damage) to 7 (dead plant with root completely rotted) (Plant Dis. Rep. 63:518-522). Average disease severity per plot was determined to create a disease index (DI) for each entry and DI was treated as a continuous variable. Data are also represented as the percentage of sugar beet roots in classes 0 through 1, considered as healthy and in classes 0 through 3, considered harvestable. Data in classes 0-1 and 0-3 were transformed using arcsine square root to normalize the data for analyses %0-1 and %0-3. Dunnett’s one-tailed t-test (P = 0.05) was used to compare entries to the highly resistant control FC705/1 (19851032H) and the most susceptible line tested (PI504179). There were significant differences among entries for DI. The highest performing entries were the highly resistant checks FC705/1 and FC709-2, and the resistant check FC703. The next four most resistant entries, PI590664, PI232887, NSL31344, and PI408965 were not significantly different from the highly resistant check FC705/1. PI 504179, was the most susceptible in the test, and there were 19 entries not significantly different than it. These accessions will be retested and, if resistance is confirmed, incorporated into the USDA-ARS RRCR resistance breeding program at Fort Collins, CO to enhance sugar beet germplasm. These results will be accessible to interested parties through the USDA-ARS, NPGS GRIN database http://www.ars-grin.gov.