First Report of Sweet Potato Feathery Mottle Virus Infecting Chrysanthemum morifolium in China

Chrysanthemum (Chrysanthemum morifolium Ramat.) is one of the eight well-known traditional medicinal herbs (“zhe ba wei”) in China. Its flowers are used in the production of medicine for antitumor, antibiosis, anti-inflammatory, antioxidation, and hypolipidemic purposes in modern pharmacology (Cui et al. 2014; Lee et al. 2009; Lii et al. 2010; Wang et al. 2010). Tongxiang City in the Zhejiang Province of China is a major C. morifolium production region, with a cultivation area of 3,161 ha and an annual yield of 9,090 metric tons (Tongxiang Statistical Yearbook 2019, unpublished). In July 2018, chrysanthemum plants with symptoms of chlorotic blotches, mosaic, and mottle were observed in a greenhouse in Tongxiang City, where the disease incidence was estimated to be 100%. To reveal the possible agents responsible for these virus-like symptoms, a total of 18 plants were collected and tested first by RT-PCR for various viruses and viroids that have been reported in chrysanthemum in China in the past (Hu et al. 2018; Zhao et al. 2015), including chrysanthemum virus B, tomato aspermy virus, cucumber mosaic virus, tobacco mosaic virus, potato virus X, potato virus Y, tomato spotted wilt virus, chrysanthemum stunt viroid, and chrysanthemum chlorotic mottle viroid. Surprisingly, none of abovementioned viruses and viroids was detected. Nevertheless, a transmission electron microscopy (Hitachi H7650) assay on a representative sample detected flexuous filament-shaped virus-like particles of 600 to 900 nm in length after negative staining with phosphotungstic acid. The 18 samples were then tested using DAS-ELISA with antibodies (DSMZ, Germany) against sweet potato feathery mottle virus (SPFMV), zucchini yellow mosaic virus, and turnip mosaic virus. Only SPFMV was detected serologically in all screened samples. To confirm the ELISA results, the samples were again subjected to total RNA extraction using TRIzol Reagent (Takara) and followed by RT-PCR assay with the SPFMV-specific primer pair, SPFMV 1F (5′-TACACACTGCTAAAACTAGG-3′) and SPFMV 1R (5′-AGTTCATCATAACCCCATGA-3′) (Kwak et al. 2014). An amplicon of the predicted size (356 bp) was obtained from all the samples. The amplicon was then purified with the DNA Gel Extraction Kit (Tsingke, China), cloned into the pGEM-T Easy Vector (Promega, U.S.A.), and sequenced by the Sanger method. A consensus sequence obtained from more than eight clones originated from one sample was deposited in GenBank under accession number MH844809. BLASTn analysis indicated that the sequence shared 98.6% nucleotide identity with that of a Chinese isolate of SPFMV from Dendrobium candidum (MH508094) and a Korean isolate of SPFMV from sweet potato (KP115608). To our knowledge, this is the first report of SPFMV naturally infecting C. morifolium in China. In consideration of the wide planting area of C. morifolium in China, a SPFMV outbreak would cause serious economic losses to farmers. Therefore, it is worthwhile to prevent its spread to other chrysanthemum-cultivating regions.