USDA-ARS Plant Introduction lines evaluated for Rhizomania and storage rot resistance in Idaho, 2021

Authors: Dorn, Kevin; Strausbaugh, Carl

Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2022
Publication Date: 8/9/2022
Citation: Dorn, K.M., Strausbaugh, C.A. 2022. USDA-ARS plant introduction lines evaluated for rhizomania and storage rot resistance in Idaho, 2021. Plant Disease Management Reports. 16. Article eV126.

Interpretive Summary: Rhizomania and storage rot are global threats to sugar beet production, that threaten both yield potential and loss of recoverable sugar. Tapping the USDA National Plant Germplasm System sugar beet germplasm collection, Agricultural Research Service scientists evaluated 30 germplasm lines for resistance to both rhizomania and storage rot. For rhizomania resistance, the researchers identified four germplasm lines with below ground disease ratings equivalent to the resistant commercial checks which contain two known rhizomania resistance genes. However, three of these germplasm lines had substantially worse above ground symptoms compared to the checks, indicating these may contain new forms of resistance. For storage rot, the researchers identified 8 germplasm lines with statistically equivalent storage rot ratings compared to the commercial lines. This research continues the decades long screening effort by the USDA for resistance to important sugar beet diseases, and provides actionable information for sugar beet breeders to improve genetic resistance.

Technical Abstract: Thirty sugar beet (Beta vulgaris L.) USDA-ARS Plant Introduction (PI) lines 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 plots were one row 10-ft long 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 (percentage of plants with yellow, stunted, upright leaves) development on 19 Aug. The plants were mechanically topped and hand harvested on 18-19 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 19 Oct. On 28 Feb 22, after 132 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 rank transformed prior to analysis with the mixed linear models (Proc MIXED) procedure, but the non-transformed means have been presented in the table. Mean separation for root ratings was based on a PDIFF comparison with a probability cutoff of 0.05. Rhizomania symptom development was uniform and other disease problems were not evident in the plot area. The BNYVV susceptible check plots had 100% foliar symptoms and high root disease ratings. Resistant check 3 had 0% foliar symptoms and a low root rating which indicates that resistance based on two genes is holding up. Single gene resistance (Checks 2 and 4) had foliar ratings ranging from 2 to 4% indicating single gene resistance is not completely effective, but the root ratings were still good. Entry 27 had a level of BNYVV resistance similar to the resistant checks based on both foliar and root ratings. Entries 11, 12, 13, 14, 28, 30, and 31 had root ratings similar to the resistant checks but had higher foliar ratings. Entry 29 had a very good foliar rating and just missed being similar to the resistant checks for root rating. A number of the entries had resistance to fungal rots in storage, but only entry 29 performed well for all three variables. Entry 31 performed well in storage and had a good root rating, but this line had a high foliar rating. Some entries may serve as a starting point for identifying additional sources of resistance to BNYVV and storage rots.