Evaluation location: Idaho, United States
Thirty sugar beet (Beta vulgaris L.) Plant Introduction (PI) Lines from the USDA-ARS National Plant Germplasm System (NPGS), and four 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 which has Portneuf silt loam soil and had been in barley in 2016. In the spring the field was plowed and then fertilized (90 lb N and 110 lb P2O5/A) and roller harrowed on 11 Apr 17. The germplasm was planted (density of 142,560 seeds/A) on 4 May. The plots were one row 10-ft long with 22-in. row spacing and arranged in a randomized complete block design with 6 replicates. The crop was managed according to standard cultural practices for southern Idaho. Plant populations were thinned manually to 47,500 plants/A on 3 Jun. 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 21 Aug. The plants were mechanically topped and hand-harvested on 10 Oct. At harvest, ten roots per plot were rated for symptom development using a scale of 0 to 9 (0 = healthy and 9 = dead; Plant Disease 93:632-638), with disease index (DI) treated as a continuous variable. At harvest, eight roots per plot were also placed in a mesh-onion bag and placed in an indoor commercial storage facility (temperature set point 34°F) in Paul, ID on 10 Oct. On 21 Feb 18, after 133 days in storage, the roots were evaluated for the percentage of root surface area (0 to 100%) covered by fungal growth and rot. Data were analyzed in SAS (Ver. 9.4) using the general linear models procedure (Proc GLM), and Fisher’s protected least significant difference (α = 0.05) was used for mean comparisons.
Rhizomania symptom development was uniform and other disease problems were not evident in the plot area. Entries 1, 3, 24, and 30 were dropped from the study because of poor stand. The BNYVV susceptible check (Check 1) had 97% foliar symptoms and a high root disease severity rating. The three resistant checks (2, 3, and 4) had 0 to 6% foliar symptoms and the lowest root ratings. Based on root ratings, all PI Line entries were more susceptible than the resistant checks and 14 entries were not different from the susceptible check. However, entry 2 had both the lowest foliar rating of the PI lines and ranked first among all entries for the lowest storage rot. The root rating for entry 2 may have been affected by poor inherent root shape and may not necessarily represent a lack of resistance to BNYVV. The foliar rating and resistance to storage rot both suggest entry 2 should be reevaluated for resistance to BNYVV. Entry 2 may serve as a starting point for identifying additional sources of resistance to BNYVV and storage rots.
Root Disease Index (DSI) scores were converted to 0-9 scale for loading into Grin-Global 0-9 coded ratings
link to the 2017 Rhizomania article