First report of Fusarium equiseti causing seedling death on sugar beet in Minnesota, USA

Authors: KHAN, M - North Dakota State University; BHUIYAN, M - North Dakota State University; LIU, Y - North Dakota State University; Lakshman, Dilip; LIU, Z - North Dakota State University; ZHONG, S - North Dakota State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2021
Publication Date: 2/18/2021
Citation: Khan, M.F., Bhuiyan, M.Z., Liu, Y., Lakshman, D.K., Liu, Z., Zhong, S. 2021. First report of Fusarium equiseti causing seedling death on sugar beet in Minnesota, USA. Plant Disease. https://doi.org/10.1094/PDIS-10-20-2102-PDN.
DOI: https://doi.org/10.1094/PDIS-10-20-2102-PDN

Interpretive Summary: Minnesota is the top sugar beet (Beta vulgaris L.) producing state in the United States. In May 2019, we discovered sugar beet plants in fields in Moorehead, MN, with stunted growth, and root tip tissue discoloration. A fungus was isolated from roots of infected seedlings and found to cause similar stunting and root tip discoloration symptoms upon inoculation to healthy sugar beet seedlings in the greenhouse. Based on morphological and molecular tests, the pathogen was identified as Fusarium equiseti. To our knowledge, this is the first report of F. equiseti causing disease on sugar beet seedlings in Minnesota. There are reports of other Fusarium species (e.g., F. oxysporum and F. secorum) causing significant economic damage to sugar beet. The presence of this new pathogenic species of Fusarium (F. equiseti) in sugar beet in Minnesota will require further monitoring for its prevalence and investigation of commercial cultivars for resistance to the pathogen.

Technical Abstract: In May 2019, sugar beet (Beta vulgaris L.) seedlings were observed in Moorhead (46.5507° N, 96.4208° W), Minnesota, USA with stunted growth and yellowing of leaves, and dying seedlings had root tip tissue discoloration. The isolated fungus produced white to yellow aerial mycelia. Macroconidia (18.9 to 30.3×2.5 to 3.6 µm, 5-7 septate) exhibited dorsoventrally curvature. No microconidia were found. Chains of chlamydospores were observed in three-week-old culture. The morphological features of the isolates were consistent with Fusarium equiseti. Amplification of a segment of the RNA polymerase (RPB2) from genomic DNA of two isolates, sequencing (GenBank Accession MW048778) and BLAST analysis revealed that the fungal sequences from both isolates had 100% homology with F. equiseti (Accession MK077037.1). In the Koch’s postulate analysis for confirmation of pathogenicity, the isolated fungus produced symptoms identical to those present on sugar beets in the field. Although the association of F. equiseti was reported on freshly harvested beet in the USA, its pathogenicity on sugar beet was demonstrated for the first time in this investigation. The presence of a new pathogenic species of Fusarium (F. equiseti) in sugar beet in Minnesota will require further monitoring its prevalence and investigation of commercial cultivars for resistance to the pathogen.