Evaluation of USDA-ARS sugar beet germplasm for resistance to rhizomania and storage rot in Idaho, 2022

Authors: Dorn, Kevin; Strausbaugh, Carl; Majumdar, Raj

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2023
Publication Date: 8/30/2023
Citation: Dorn, K.M., Strausbaugh, C.A., Majumdar, R. 2023. Evaluation of USDA-ARS sugar beet germplasm for resistance to rhizomania and storage rot in Idaho, 2022. Plant Disease Management Reports. 17. Article eV153.

Interpretive Summary: Sugar beet yield loss caused by pests and pathogens is an ongoing threat to American sugar production. These yield losses can be caused before harvest by viral pathogens like Beet necrotic yellow vein virus, which causes the disease rhizomania. Post-harvest sugar loss can also be caused by fungal and bacterial pathogens that cause storage rot. USDA-ARS researchers in Fort Collins, CO and Kimberly, ID screened sugar beet breeding lines for resistance to both rhizomania and storage rot. In a panel of 30 lines, the researchers found two promising lines with resistance to both rhizomania and storage rot, with many other lines showing varying levels of resistance. The resistance data from this panel is being used to identify the region of the genome controlling resistance to rhizomania. The results of this research will enable sugar beet breeders to develop varieties that are more resistance to both rhizomania and storage rot.

Technical Abstract: Thirty sugar beet (Beta vulgaris L.) lines from the USDA-ARS Ft. Collins sugar beet program and five check cultivars were screened for resistance to Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania, and to storage rot. The rhizomania evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID. The germplasm was planted on 3 May in one row 10 ft plots with 22-in. between-row spacing and arranged in a randomized complete block design with 6 replicates. The trial relied on endemic field inoculum for rhizomania and storage rot development. The plots were rated for rhizomania foliar symptom development on 15 Aug. The plants were mechanically topped and hand harvested on 11-12 Oct. At harvest, ten roots per plot were rated for rhizomania symptom development using a scale of 0 to 9 (0 = healthy and 9 = dead. At harvest, eight roots per plot were also placed in a mesh-onion bag and kept in an indoor commercial storage facility (temperature set point 34°F) in Paul, ID on 13 Oct. On 14 Mar 23, after 152 days in storage, the roots were evaluated for the percentage of root surface area covered by fungal growth or rot. Except for root ratings, data were analyzed in SAS using the general linear model (Proc GLM) procedure, and Fisher’s protected least significant difference (a = 0.05) was used for mean comparisons. The root ratings were analyzed in a nonparametric analysis. Rhizomania symptom development was uniform and other disease problems were not evident in the plot area. The BNYVV susceptible check plots (Check 1 and Red beet) had 100% foliar symptoms and high root disease ratings. Resistant checks 3 and 4 had 0% foliar symptoms and a low root rating, which indicates that resistance based on these genes is holding up. Single gene resistance in Check 2 had foliar ratings of 8% indicating single gene resistance is not completely effective, but the root ratings were still good. The germplasm panel tested here represent a selected set of pre-breeding lines aimed at isolating the genomic region harboring the Rz1 resistance gene. Selection of germplasm for this panel targeted half of the panel to lack any known rhizomania resistance, with the other half of the panel harboring only Rz1-based resistance (by pedigree). FC1036, FC1028, FC1020, and FC705/1 from the Fort Collins pre-breeding program had a level of BNYVV resistance similar to the resistant checks based on the root ratings, but foliar ratings were higher than those for the resistant checks. FC1037, CR933, C869, FC1022, FC221, and FC1038 had foliar ratings similar to the resistant checks and root ratings similar to some of the resistant checks. FC1036, FC1028, and FC1020 performed well for rot in storage along with having good root ratings, but only FC1037 and FC1038 performed well for all three variables. Of the 14 most resistant entries based on root ratings, all but one (FC705/1) are predicted to possess Rz1-based resistance. The only entry with Rz1-based resistance falling outside of this grouping was FC221, however, this line had excellent foliar ratings. BNYVV resistance data from these lines may serve as a starting point for developing molecular markers for Rz1. Some of these entries may also serve as a starting point for improving resistance to storage rots.