Evaluations of Ft. Collins sugar beet germplasm for rhizomania and storage rot resistance in Idaho, 2016

Fifty sugar beet (Beta vulgaris L.) lines from the USDA-ARS Fort 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 to fungal growth in storage, which is related to storage rot. The rhizomania (RZ) evaluation was conducted at the USDA-ARS North Farm in Kimberly, ID, which had been in barley in 2015. The field was fall plowed, fertilized and roller harrowed before plant to a density of 142,560 seed/A. The plots were single row 10-ft long with 22-in. row spacing and arranged in a randomized complete block design with 6 replications. The crop was managed according to standard cultural practices for southern Idaho and plants were thinned to 47,500 plants/A . The trial relied on endemic field inoculum for rhizomania and storage rot development. The plots were rated for foliar symptom (percentage of plants with yellow, stunted, upright leaves) development on August 18th, were mechanically topped and hand harvested on October 13th. At harvest, ten roots per plot were rated for rhizomania symptom development using a scale of 0 to 9 (0 = healthy and 9 = dead), with disease index (DI) treated as a continuous variable. At harvest, eight of the evaluated roots per plot also were placed in a mesh-onion bag and put on top of the pile in an indoor commercial storage facility (temperature set point 34°F) in Paul, ID. On February 9, 2017, after 118 days in storage, the roots were evaluated for the percentage of root surface area covered by any fungal growth. Data were analyzed in SAS using the general linear models procedure (Proc GLM), and Fisher’s protected least significant difference (a = 0.05) was used for mean comparisons. The foliar data were square root transformed prior to analysis. Rhizomania symptom development was uniform and no other disease symptoms were evident in the plot area. The BNYVV susceptible check plots (Check 1) had 81% foliar symptoms and a high root disease severity rating of 46. The three resistant checks (2, 3, and 4) had 0 to 7% foliar symptoms and low root disease severity ratings (18 to 24). Based on root ratings, all but three entries had some resistance, because these were the only entries not different from the susceptible check. Four entries (20141007, 20141009, 20131010H11, and 20131010H10) had good rhizomania resistance based on both root symptoms and foliar ratings because these did not significantly differ from more of the resistant checks. A number of entries performed well in storage, four entries only had single digit fungal growth and 20 others were not significantly different from these four, although these were not always the same entries that showed resistance to BNYVV. Some of these entries may serve as a starting point for identifying additional sources of resistance to BNYVV and storage rots