Submitted to: Plant Disease Management Reports
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/9/2016
Publication Date: 9/5/2016
Citation: Panella, L.W., Strausbaugh, C.A. 2016. Ft. Collins sugar beet germplasm evaluated for rhizomania and storage rot resistance in Idaho, 2015. Plant Disease Management Reports. 10:FC168.

Interpretive Summary: Fifty-seven sugar beet (Beta vulgaris L.) lines from the USDA-ARS Ft. Collins sugar beet program and four check cultivars were screened for resistance to Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania, and storage rot. The rhizomania evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID. Seed of the sugar beet germplasm lines was planted on April 21. The trial relied on natural infection for rhizomania and storage rot development. The plots were rated for leaf symptoms (percentage of plants with yellow, stunted, upright leaves) development on July 8 and 20. At harvest, roots in the plots were rated using a scale of 0 to 9 (0 = healthy and 9 = dead). At harvest, eight roots per plot were also collected in a mesh-onion bag and placed in an indoor commercial storage facility in Paul, ID on October 8. Following 126 days in storage, the roots were evaluated for the percentage of root surface area covered by fungal growth. Data were analyzed. Rhizomania symptom development was uniform and other disease problems were not evident in the plot area. The BNYVV susceptible check had 89 to 92% leaf symptoms and a high root disease severity rating. The three BNYVV resistant checks (2, 3, and 4) had no leaf symptoms and low root ratings. Most entries had fewer leaf symptoms and a better root rating than the susceptible check indicating they have some level of resistance. Based on BNYVV root ratings, the entries not different from the best performing entry (25) were checks (2, 3, 4), and entries 16, 20, 34, and 48). All of these had leaf ratings that were 4% 4% or less (not significantly different from the best performing entries with 0%). Entries 25, 16, and 20 were experimental hybrids with FC1740 or FC1741 . Entry 34 is a germplasm developed for resistance to root rot complexes. Storability is an important trait in harvested beet roots and beets were screened for surface rotting, which was frequently present. Entries 9, 11, 18, 31, 34, and 43 were not significantly different from the entry most resistant to fungal growth in storage (entry 18 with only 2%). Entries 14, 20, 21, 48, and 53 performed well for rhizomania resistance and resistance to storage rots. Some of these entries may serve as a starting point for identifying additional sources of resistance to both BNYVV and storage rots.

Technical Abstract: Fifty-seven sugar beet (Beta vulgaris L.) lines from the USDA-ARS Ft. Collins sugar beet program and four check cultivars were screened for resistance to Beet necrotic yellow vein virus (BNYVV), the causal agent of rhizomania, and storage rot. The rhizomania evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID. Seed of the sugar beet germplasm lines was planted on April 21. One-row plots, 10 ft long with 22-in row spacing between rows were arranged in a randomized complete block design with 4 replications. The trial relied on natural infection for rhizomania and storage rot development. The plots were rated for foliar symptom (percentage of plants with yellow, stunted, upright leaves) development on July 8 and 20. At harvest, roots in the plots were rated for symptom development using a scale of 0 to 9 (0 = healthy and 9 = dead). At harvest, eight roots per plot were also collected in a mesh-onion bag and placed in an indoor commercial storage facility in Paul, ID on October 8. Following 126 days in storage, the roots were evaluated for the percentage of root surface area covered by fungal growth. Data were analyzed using the general linear models procedure, and Fisher’s protected least significant difference (a = 0.05) was used for mean comparisons. Rhizomania symptom development was uniform and other disease problems were not evident in the plot area. The BNYVV susceptible check had 89 to 92% foliar symptoms and a high root disease severity rating. The three BNYVV resistant checks (2, 3, and 4) had no foliar symptoms and low root ratings. Most entries had fewer foliar symptoms and a better root rating than the susceptible check indicating they have some level of resistance. Based on BNYVV root ratings, the entries not significantly different from the best performing entry (25) were checks (2, 3, 4), and entries 16, 20, 34, and 48). All of these had foliar ratings that were 4% 4% or less (not significantly different from the best performing entries with 0%). Entries 25, 16, and 20 were experimental hybrids with FC1740 (entry 48 – Rz1Rz1Rz2Rz2, based on associated SNP markers) or FC1741 (entry 49 – rz1rz1Rz2Rz2, based on associated SNP markers). Entry 34 is a polycross population developed for resistance to root rot complexes. Storability is an important trait in harvested beet roots and beets were screened for surface rotting. The primary fungal growth was an Athelia-like Basidiomycete, but Botrytis sp. and Penicillium sp. were also frequently present. Entries 9, 11, 18, 31, 34, and 43 were not significantly different from the entry most resistant to fungal growth in storage (entry 18 with only 2%). Entries 14, 20, 21, 48, and 53 performed well for all variables. Some of these entries may serve as a starting point for identifying additional sources of resistance to both BNYVV and storage rots.