First report of leaf blight of sugar beet (Beta vulgaris L.) caused by Sclerotinia sclerotiorum in Minnesota, USA

Authors: KHAN, MOHAMMED - North Dakota State University; BHUIYAN, M - North Dakota State University; LIU, Y - North Dakota State University; Lakshman, Dilip; BLOOMQUIST, M - Southern Minnesota Beet Sugar Cooperative

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2021
Publication Date: 7/19/2021
Citation: Khan, M.F., Bhuiyan, M.Z., Liu, Y., Lakshman, D.K., Bloomquist, M. 2021. First report of leaf blight of sugar beet (Beta vulgaris L.) caused by Sclerotinia sclerotiorum in Minnesota, USA. Plant Health Progress. 22:149-150. https://doi.org/10.1094/PHP-02-21-0048-BR.
DOI: https://doi.org/10.1094/PHP-02-21-0048-BR

Interpretive Summary: Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In August 2020, we discovered for the first time a new leaf blight on sugar beet in fields in Hector, Minnesota. The infected plants showed light brown to dark brown necrotic lesions along with blight of leaves and a dark brown to blackish colored mid rib. A fungus was isolated from infected leaves and proven by inoculation testing to be the causative agent of the disease. Based on morphological and molecular tests, the pathogen was identified as Sclerotinia sclerotiorum. To our knowledge, this is the first report of S. sclerotiorum casing leaf blight in Minnesota. Several commercial fields sampled in different sugar beet production regions of Minnesota, including Ada, Waukon, and Andrea were also infected with S. sclerotiorum. The discovery of this pathogen in sugar beet fields of Minnesota will prompt future research to screen for resistant varieties, and initiate research to evaluate the disease impact on yield and quality.

Technical Abstract: In August 2020, sugar beet (Beta vulgaris L.) seedlings were observed with light brown to dark brown necrotic leaf lesions along with blighted leaf and dark brown to blackish colored mid rib regions in Hector (44°44'33'N 94°42'52'W), Minnesota, USA. Several commercial fields sampled in different sugar beet production regions of Minnesota, including Ada, Waukon and Andrea also had plants with similar symptoms. Symptoms appeared on the lowermost two to three leaves close to the soil surface and over 90% of the plants in the field were infected. The isolated fungus had creamy white mycelia and produced black sclerotia at the periphery of pure culture on potato dextrose agar (PDA) medium. Hard bodied sclerotia were blackish in color, globose to variable in shape and 3.9 to 4.5 mm in diameter and 4.2 to 5.1 mm in length. Genomic DNA from two isolates was amplified for the internal transcribe spacer (ITS1-5.8S-ITS2 rDNA) region, sequenced, and BLASTn searched for homology in the NCBI database. The nucleotide sequences of both isolates showed 100% homology with two GenBank accessions CP017820 and KY859158 of Sclerotinia sclerotiorum. Koch’s postulates assay confirmed pathogenicity with symptom development identical to the field symptoms. This is the first report of S. sclerotiorum causing leaf blight on sugar beet in Minnesota. Because of higher prevalence of this disease in wide geographic locations of Minnesota, trials will be required to identify cultivars for resistance to this pathogen, and to initiate research to evaluate the disease impact on yield and quality.