Kimberly sugar beet germplasm evaluated for rhizomania and storage rot resistance in Idaho, 2022

Rhizomania caused by Beet necrotic yellow vein virus (BNYVV) and storage losses are serious sugar beet production problems. To identify sugar beet germplasm lines with resistance to BNYVV and storage rots, seven Beta vulgaris lines and five check cultivars were screened. The lines were grown in a sugar beet field infested with BNYVV during the 2022 growing season in a randomized complete block design with 6 replications. At harvest on 12 October, roots were dug and evaluated for rhizomania symptoms and then placed in an indoor commercial sugar beet storage building. After 152 days in storage, samples were evaluated for the percentage of root surface area covered by fungal growth or rot. Rhizomania symptom development in the field was uniform and other disease problems were not evident in the plot area. The BNYVV susceptible sugar and red beet checks both had 100% foliar symptoms and a high root disease severity ratings. The resistant check with two resistance genes, Rz1 + Rz2 (check 3), had no foliar symptoms and low root rating. The resistant checks with only one resistance gene had foliar symptoms ranging from 0 to 8%, but their root ratings were still within an acceptable range. Foliar symptoms indicate single gene resistance for BNYVV is becoming marginal. Based on the root ratings, all entries had some level of BNYVV resistance since they were all better than the susceptible checks. Entry 3 (KEMS12; PI672570) had a level of BNYVV resistance similar to resistant checks based on both foliar and root ratings. Although entries 1, 2, 6, and 7 all had poor foliar ratings, their root ratings were better than those for the susceptible checks. Both entries 1 (KEMS09) and 3 were described as containing some rhizomania resistance in their release notes, but entry 1 appears to have lost some of its resistance, while entry 3 remains resistant. All the entries had some resistance to fungal rots in storage, but only entry 3 performed well for all three variables. Thus, some entries will serve as genetic sources for identifying additional resistance to BNYVV and storage rots, which will aid the sugar beet industry in improving sucrose yield and retention in commercial sugar beet cultivars