First report of damping off and seedling rot of hemp (Cannabis sativa L.) caused by Fusarium solani (Mart.) Sacc. in North Dakota, USA

Authors: KHAN, MOHAMED - North Dakota State University; BHUIYAN, ZIAUR - North Dakota State University; Lakshman, Dilip; MOSHER, PRESLEY - North Dakota State University; KNOKE, SCOTT - North Dakota State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/23/2022
Publication Date: 5/25/2022
Citation: Khan, M.F., Bhuiyan, Z.M., Lakshman, D.K., Mosher, P., Knoke, S. 2022. First report of damping off and seedling rot of hemp (Cannabis sativa L.) caused by Fusarium solani (Mart.) Sacc. in North Dakota, USA. Plant Disease. https://doi.org/10.1094/PDIS-12-21-2681-PDN.
DOI: https://doi.org/10.1094/PDIS-12-21-2681-PDN

Interpretive Summary: Hemp (Cannabis sativa L.) is grown specifically for medicinal and industrial uses, and the US is the world’s third largest producer of hemp after China and Canada. Symptomatic hemp seedlings were received from a hemp grower in Towner County, North Dakota in July 2020. Seedlings grown in the greenhouse had damping off with brown to blackish root tips with about 8 to 10% infection. The disease-causing fungus was identified as Fusarium solani. The pathogen was been reported to cause damping off and root rot in several states in the U.S. To the best of our knowledge, this is the first report of the fungus causing seedling damping off and root rot on hemp in ND, and it warrants surveillance and development of management practices for the disease.

Technical Abstract: Hemp (Cannabis sativa L.) is grown specifically for medicinal and industrial uses, and the US is the world’s third largest producer of hemp after China and Canada. Symptomatic hemp seedlings were received from a hemp grower in Towner County (48.7486° N, 99.2761° W), North Dakota (ND), USA in July 2020. Seedlings grown in the greenhouse had damping off with brown to blackish root tips with about 8 to 10% infection. For pathogen isolation, infected root areas were surface disinfested in 1% sodium hypochlorite for 1 min, rinsed thrice with sterile distilled water, and blotted dry. About 1-cm sectioned root tips were plated both in water agar (WA) and acidified potato dextrose agar (PDA, pH: 4.8) media and incubated in 12-h photoperiod in florescent light at 25° C. After 7 days of incubation, single spores produced from emerging mycelia were isolated and sub-cultured on PDA and carnation leaf agar (CLA) media for morphological observations. Colonies had uniform appearances and produced white, thick and floccose mycelium. Conidiophores produced from lateral hyphae were simple to branched. Phialides were slender, smooth, hyaline and septate. Macro-conidia were 12.5 to 30.2 x 2.2 to 3.6 µm, septate (3-5), thick walled, hyaline and moderately curved shaped. Micro-conidia were oval to ellipsoid, smooth walled, no septa and measured 3.4 to 8.8 µm and 1.3 to 4.3 µm. Chlamydospores were round shaped, thick-walled, and produced singly or in pairs. Based on morphological characteristics, isolates were identified as Fusarium solani (Mart.). For molecular identification, genomic DNA of three representative fungal isolates were extracted using DNeasy Plant Mini Kit. PCR was carried out using primers and conditions specified for the translation elongation factor (TEF-1a) and RNA polymerase II (RPB 2) primer pairs 5F2/7cR and 7cF/11aR of Fusarium species. All three isolates had identical PCR product sequences for the respective primer sets. The DNA sequences were deposited to NCBI GenBank with accession No. OK880264 (TEF-1a), OK880266 (RBP 5F2/7cR), and OK880265 (RBP 7cF/11aR). The NCBI Megablast search of the OK880264, OK880266, and OK880265 showed 100% similarity with respective homologue sequences from F. solani species complex (GU170628, KC808344, and EU329608). Similar results were obtained by BLASTN search in the FUSARIUM ID database. A pathogenicity assay was conducted for three fungal isolates on the first true leaf stage of hemp seedlings. A conidial suspension (1 x 106 conidia/ml) was pipetted, without wounding roots, onto the soil around the base of the four plants. An equal number of plants inoculated with distilled water served as control. The test was conducted twice. At 10 days post inoculation (dpi), yellowing of leaves and damping off were observed; the infected seedlings dried and developed brown to black root rot symptoms with little or no lateral roots. The re-isolated fungi from the infected plant samples were identical to the isolate used for root inoculation. F. solani has been reported to cause damping off and root rot in several states in the U.S., Canada and Italy. To the best of our knowledge, this is the first report of F. solani causing seedling damping off and root rot on hemp in ND, and it warrants further study and surveillance for management of the disease.