Location: Soil Management and Sugarbeet ResearchTitle: Evaluation of Beta PIs from the USDA-ARS, NPGS for Rhizoctonia crown and root rot resistance, 2021
Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2022
Publication Date: 8/9/2022
Citation: Dorn, K.M., Metz, N.J., Fenwick, A.L., Yeater, K.M., Nielson, A.L., Floyd, B.A., Sowder, B.M. 2022. Evaluation of Beta PIs from the USDA-ARS, NPGS for Rhizoctonia crown and root rot resistance, 2021. Plant Disease Management Reports. 16. Article eV161.
Interpretive Summary: Fungal pathogens in the soil are an ongoing threat to root crops like sugar beet, and can cause significant yield losses. Genetic resistance to these below ground pathogens, like Rhizoctonia, offer a highly effective way for farmers to protect sugar beet crop production. USDA-ARS scientists in Fort Collins, Colorado screened two germplasm panels from the National Plant Germplasm System to identify lines with resistance to Rhizoctonia. The scientists identified 14 lines in one panel with resistance to Rhizoctonia, and 11 lines with resistance in the second panel. Ongoing genetic experiments will re-screen and incorporate these lines into the Fort Collins pre-breeding program to improve sugar beet genetic resistance to Rhizoctonia.
Technical Abstract: Two panels of Beta vulgaris subsp. vulgaris (beet) and Beta vulgaris subsp. maritima (sea beet) accessions from the Beta collection of the USDA-Agricultural Research Service National Plant Germplasm System (NPGS) 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. Panel #1 consisted of 26 cultivated beet NPGS accessions, where the second panel consisted of 17 cultivated beet and 7 sea beet accessions from the NPGS collection. Both tests (each panel) also included used two resistant germplasm and two susceptible germplasm as controls. Each nursery was planted in a completely randomized design with 5 replications per entry in one-row plots (76 cm row spacing) 3.7 m long. Plots were planted on 3 Jun with 1.9 cm of irrigation applied on 9 Jun. An inoculum of dry ground hulless barley grain infested with Rhizoctonia solani isolate R-9 (AG-2-2 IIIB) was applied to the crown of the plants on 15 Jul (8 to 12 leaf growth stage) at a rate of 8.8 g m-1 of row. A Gandy® electrically driven applicator was used to apply the inoculum and the field was cultivated afterwards to place soil onto the plant crowns. Roots were defoliated and harvested Aug 17 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 index for each entry. The root ratings were rank transformed prior to analysis with the mixed linear models (Proc MIXED) procedure in SAS. The Dunnett’s one-tailed t-test (P = 0.05) option in the LSMEANS statement was used to compare entries to the resistant check FC709-2 and susceptible check 20151020, based on the rank of DI. Disease progression was excellent with severe and uniform levels of RCRR in the nursery. In Panel #1, the resistant check (FC709-2) had the lowest disease index rating. A total of 14 entries were statistically similar to FC709-2, including the second resistant check FC901xC817, however all of these entries were not statistically different compared to the susceptible check. These 14 entries represent improved cultivars donated to NPGS over the past several decades. In Panel #2, FC709-2 again had the lowest disease index rating, and 11 entries were statistically similar to FC709-2. Of note, Ames 4331, PI 611062, and Ames 10837 had statistically better levels of resistance compared to the susceiptble check. A total of 23 entries were not statistically different than the susceptible check 20151020. Lines identified in both panels will be retested in greenhouse RCRR screenings to select resistant individuals for potential incorporation into the USDA-ARS RRCR resistance breeding program at Fort Collins, CO to enhance sugar beet pre-breeding germplasm. These results will be accessible to interested parties through the USDA-ARS, NPGS GRIN database http://www.ars-grin.gov.