Fusarium clavum (F. incarnatum-equiseti species complex 5) causes sugar beet seedling root rot in Wyoming, USA

Authors: KHAN, MOHAMED - North Dakota State University; BHUIYAN, ZIAUR - North Dakota State University; Lakshman, Dilip; LUIS, DEL RIO MENDOZA - North Dakota State University; ZHONG, SHAOBIN - North Dakota State University; LIU, ZHAOHUI - North Dakota State University; AZIZI, ABDOLBASET - North Dakota State University; AMEEN, GAZALA - North Dakota State University

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2024
Publication Date: 2/2/2024
Citation: Khan, M., Bhuiyan, Z., Lakshman, D.K., Luis, D., Zhong, S., Liu, Z., Azizi, A., Ameen, G. 2024. Fusarium clavum (F. incarnatum-equiseti species complex 5) causes sugar beet seedling root rot in Wyoming, USA. Canadian Journal of Plant Pathology. https://doi.org/10.1080/07060661.2024.2303650.
DOI: https://doi.org/10.1080/07060661.2024.2303650

Interpretive Summary: Sugar beet is an economically important crop in the USA. In a disease survey conducted in 2022 in Wyoming, sugar beet seedlings with water-soaked brown to blackish lesions in the hypocotyl and poor root systems were observed in the cultivated fields. The percent disease incidence of the sugar beet cultivar SX 1361 was estimated at 26% in the growing fields. Through molecular and morphological analysis, the disease was identified to be caused by the soilborne fungal pathogen Fusarium equiseti. The pathogenicity of the fungus was proven by artificial inoculation on healthy sugar beet seedlings. To the best of our knowledge, this is the first report of the fungus causing seedling death in Wyoming. Those findings will be useful to farmers, plant pathologists and extension agents to formulate effective management practices to contain the dispersal of the pathogen to other sugar beet-growing states.

Technical Abstract: Sugarbeets (Beta vulgaris L.) are a mainstay crop in Wyoming, which ranked 8th in the USA sugarbeet production. In April 2022, 26% of sampled sugarbeet seedlings (cv. SX 1361) from Snyder farms (4305518 N, 10800249 W) in Wyoming had water-soaked brown to blackish lesions in hypocotyl with poor root systems. The growth and appearances of the isolated fungal colonies from diseased plants were uniform, showing a whitish to light orange color and thick mycelia. Hyphae were simple to branched, smooth, and septate. Conidiophores were slender, septate, produced laterally from hyphae, and contained macroconidia. Microconidia were ovoid, and single-celled, measuring 10.5 to 15.2 X 2.8 to 5.2 µm (n=20). Round to oval-shaped, chlamydospores grew singly or in pairs. Based on morphological features, the isolates were identified as Fusarium equiseti (Leslie and Summerell 2006). Molecular identification carried out by homology searches with genome sequences amplified from the internal transcribed spacer (ITS), translation elongation factor (TEF-1a), RNA polymerase II (RPB-2), and ß-tubulin regions. The deposited NCBI Accessions are OP347117 (ITS), OP331329 (RPB-2), OP345186 (ß-tubulin), and OP345184 (TEF-1a) showed 100% homologies with MK168567 (ITS), MK077113 (RPB-2), and MN125494 (ß-tubulin), and 99.41% identity with MW362069 (TEF-1a) of F. equiseti. Pathogenicity assays were conducted by conidial root-dip method (1x106 conidia/ml) (Hanson 2006) on 15 sugarbeet seedlings and repeated twice, the inoculated seedlings developed symptoms identical to the field symptoms. The re-isolated fungi from artificial inoculations were morphologically identical to the fungus isolated from field samples. F. equiseti was previously reported to cause root rot on sugarbeet in Minnesota, USA (Khan et al. 2021). To our knowledge, this is the first report of F. equiseti causing a similar disease on sugarbeet in Wyoming, USA. This finding will help to formulate the effective management practice to control this pathogen before its widespread occurrence.