Sugar beet activities of the USDA-ARS East Lansing conducted in cooperation with Saginaw Research & Extension Center during 2019

Authors: Hanson, Linda; MCGRATH, J MITCHELL - Retired ARS Employee; CORDER, HOLLY - Michigan State University; Goodwill, Tom; JAYAWARDANA, MALINI - Michigan State University; MINIER, DOUG - Michigan State University

Submitted to: Saginaw Valley Bean and Beet Farm Report
Publication Type: Research Technical Update
Publication Acceptance Date: 3/1/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Evaluation and rating plots were planted at the Saginaw Valley Research & Extension Center (SVREC) in Frankenmuth, MI in 2019 focusing on Cercospora leaf spot, (CLS) and Rhizoctonia root and crown rot (RRCR) disease performance of a range of Beta vulgaris materials and developing inoculation method for Alternaria leaf spot (ALS). CLS and RRCR trials were conducted in conjunction with the Beet Sugar Development Foundation (BSDF) and CLS trials included USDA-ARS cooperator germplasm. All trials were planted following normal fall and spring tillage operations. The BSDF CLS nursery was planted on May 6, the BSDF RRCR nursery on May 7, 2019, and the USDA RRCR, CLS, and ALS trials were planted on May 8, 2019. The CLS nurseries were inoculated on July 9 with a liquid spore suspension (approximately 1 x 103 spores/ml) of Cercospora beticola. Inoculum was produced from a mixture of leaves collected from the 2018 inoculated leaf spot nursery at SVREC and naturally infected leaves. For ALS, two inoculation times were tested, early June, and late August. Inoculum was produced from a culture in the lab and applied as a liquid spore suspension (approximately 1 x 104 spores/ml). Visual evaluations of the plots were conducted with a disease index (DI) on a scale from 0-10 where 0=no symptoms and 10=all leaves dead. CLS severity peaked in late August, after which regrowth started to outpace new disease development. Powdery mildew was present in the field unusually early (usually not observed until mid to late September), and caused difficulties in rating CLS and ALS in some plots. USDA entry ratings ranged from 3.5 to 7.0 at the last rating. The overall mean for the USDA materials was 5.5 (LSD 0.05 = 0.9) with the checks susceptible and resistant checks scored at 4.5 and score 7.5, respectively at the final rating. For RRCR, the nursery was inoculated on July 11 with a dry ground barley inoculum of Rhizoctonia solani anastomosis group 2-2. Roots were dug August 14-20 (part of harvest was delayed due to rain. Each root was rated for disease severity using a 0-7 scale where 0=no visible lesions and 7=root completely rotted. A weighted disease index was calculated for each replicate. The disease index means for the 2019 nursery ranged from 3.3 to 5.1 (avg. ~4.3), with controls averaging 4.3 and 4.9 for the moderately resistant and susceptible varieties respectively. Samples taken from the CLS nursery fields and used in genetic analysis showed evidence of largely clonal populations, with some similar, but none identical to the strain used in the RRCR nursery inoculations. A high level of diversity was found with variability between fields sampled. This can help to ensure appropriate materials are used for inoculations to make sure they represent diversity in the growing regions, and that good practices can help limit the spread of strains used for artificial inoculations.