First Report of Sweet potato chlorotic fleck virus Infecting Sweet Potato in Sichuan Province, China.

Sweet potato chlorotic fleck virus (SPCFV) is one of several viruses naturally infecting sweet potato (Ipomoea batatas L.), and it has recently been classified as a new member of the genus Carlavirus (family Flexiviridae) (1). However, SPCFV is distantly related to typical carlaviruses, as most of its putative gene products share amino acid sequence identities of <40% with those of typical carlaviruses (1). China is the largest sweet potato producing country in the world. So far, SPCFV has been reported in eastern China, such as Jiangsu, Anhui, Henan (3), and Guangdong (2) provinces, but no reports exist in western China. Sichuan Province, located in southwestern China, is the largest sweet potato producing area in the country. There are big differences between the environment and climate conditions between Sichuan and eastern China. During 2012, a survey was constructed to determine the genetic diversity and distribution of sweet potato viruses in Sichuan. Forty-seven sweet potato samples exhibiting virus-like symptoms were collected from four different geographic areas of the province. Western blotting using the antisera obtained from the International Potato Center showed that two samples were positive for SPCFV, whereas with reverse transcription (RT)-PCR, only one isolate of SPCFV was obtained from a sample exhibiting symptoms of chlorosis, leaf distortion, and vein clearing. Serological detection indicated that the plant was co-infected with SPCFV, Sweet potato feathery mottle virus (SPFMV), and Sweet potato virus G (SPVG). Total RNA was extracted from symptomatic leaves using Trizol reagent (Invitrogen) according to the manufacturer's protocol, and RT-PCR was performed by using primer pairs SPCFV-CP F (5′-ATGGCGGCGAAGGAGGCTGATA-3′) and SPCFV-CP R (5′-TCACTTGCACTTCCCATTAC-3′) corresponding to the entire coat protein (CP) gene of SPCFV. Expected DNA fragments of 900 bp were obtained from the symptomatic plant but not from control plants. The obtained fragments were purified and cloned into the PMD19-T vector (TaKaRa). Recombinant plasmids were then transformed into competent cells of Escherichia coli strain DH5α. Nucleotide BLAST analysis revealed that the 900-bp fragment (GenBank Accession No. KC414676) shared 87 to 91% nucleotide identities with other SPCFV isolates available in the GenBank database. To our knowledge, this is the first report of the co-infection between SPCFV and other sweet potato viruses including SPFMV and SPVG in China, and this is the first molecular report of SPCFV in Sichuan, western China. It shows that SPCFV is spreading to a new ecological area of China, and the spread of the virus may affect sweet potato crop yields in western China. Some measures must be carried out quickly to control the virus.