Sclerotinia sclerotiorum (Lib) deBary causes root rot and necrosis in sugar beet in Moorhead, MN USA

Authors: BHUIYAN, ZIAUR - North Dakota State University; Lakshman, Dilip; MENDOZA, LUIS DEL RIO - North Dakota State University; MOSHER, PRESLEY - North Dakota State University; KHAN, MOHAMED - North Dakota State University

Submitted to: Journal of Plant Protection Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/4/2021
Publication Date: 12/20/2021
Citation: Bhuiyan, Z.M., Lakshman, D.K., Mendoza, L., Mosher, P., Khan, M.F. 2021. Sclerotinia sclerotiorum (Lib) deBary causes root rot and necrosis in sugar beet in Moorhead, MN USA. Journal of Plant Protection Research. 61(4):384-391. https://doi.org/10.24425/jppr.2021.139247.
DOI: https://doi.org/10.24425/jppr.2021.139247

Interpretive Summary: Minnesota is a leading sugar beet producing states in the US, and together with North Dakota contributes 57% of domestic production, which results in more than $5 billion in economic activities. A disease of sugar beet with typical rot symptoms along with whitish mycelial growth and blackish sclerotia on the external surface of the root was detected in growers’ fields in Moorhead, MN in September 2020. The disease-causing agent was pathologically, morphologically, and molecularly characterized and identified as the soilborne fungus, Sclerotinia sclerotiorum. This is the first report on the occurrence of this disease in Minnesota. Our findings have important implications for improved sugar beet disease management in the state. The information generated in this manuscript will be useful for mycologists, plant pathologists and agricultural extension workers.

Technical Abstract: Sugar beet is a major sugar yielding crop in the US states of Minnesota (MN) and North Dakota. Sugar beet root samples collected from Moorhead, MN in September 2020 had typical rot symptoms along with whitish mycelia growth and blackish sclerotia on the external surface of the root. Pure cultures were obtained from infected roots through sterile technique. Sclerotinia sclerotiorum was identified based on morphological features and further confirmed molecularly by sequencing of the Internal Transcribed Spacers (ITS) region and matching homology with reported ITS of the fungus. Pathogenicity of S. sclerotiorum was confirmed through mycelial inoculation of seeds and roots in laboratory and greenhouse conditions. Inoculated seeds showed a range of symptoms that included pre- and post-emergence damping off, wilting, black discoloration of root, constricted collar region and stunted seedling growth. In laboratory conditions, roots were artificially wounded using a cork borer and inoculated by mycelial plug. This resulted in noticeable root decay and growth of whitish, cottony mycelia and sclerotia externally. Transverse sections of the diseased root showed brown to black discoloration and rotting of internal tissue. Root inoculation of 4-weeks old sugar beet plants was achieved by depositing pathogen colonized barley grains near roots in the greenhouse, resulting in brown to black lesions and necrosis of root tissue when evaluated at 28 days post inoculation. The S. sclerotiorum was re-isolated from inoculated roots showing infection and was found identical to pure isolates of the pathogen recovered from the field samples. These findings could be useful for sugar beet growers in Minnesota, allowing better management of this pathogen in field and storage conditions before its widespread future occurrence.