First report of barley virus G in foxtail millet (Setaria italica) in Korea

Foxtail millet (Setaria italica) is an important cereal grain crop and has been used as a functional food for promoting human health in Korea. Until now, only Rice black-streaked dwarf virus (RBSDV) and Rice stripe virus (RSV) have been reported infecting S. italica in Korea (Choi et al. 1989; Yoon et al. 2014). To find unreported viral disease of S. italica, a nationwide virus survey in foxtail millet was conducted from 2015 to 2016. A total of 133 S. italica leaf samples showing necrotic spots, streaking, and yellowing stripe symptoms were collected and stored for future virus testing. To identify viruses associated with the symptoms, all collected symptomatic leaves were combined into one sample and total RNA was extracted from the pooled sample with an Easy-Spin total RNA extraction kit (iNtRON Biotechnology, Seoul, Korea). Next-generation sequencing (NGS) was performed using an Illumina HiSeq 2500 sequencer as described previously (Lim et al. 2015) and the whole NGS procedure was performed by Theragen Etex Bio Institute (Suwon, Korea). Among the analyzed contigs, 129 viral contigs (123 contigs matching RSV and six contigs matching Barley virus G [BVG]) were obtained in the range of 110 to 9,216 bp. The NGS result was confirmed by reverse transcription (RT)-PCR with primers encompassing the coat protein (CP) gene of BVG (Park et al. 2017). RT-PCR product (988 bp) from 10 BVG-positive samples was cloned and sequenced. Nucleotide BLAST search revealed that the BVG CP gene has 99% identity with BVG isolate Uiseong and Gimje (GenBank accession nos. LC159487 and KT962089). The sequence of the CP gene was deposited in GenBank under accession number LC159486 (BVG Jeju isolate). BVG is a proposed new species in the genus Polerovirus that was recently described in proso millet (Panicum miliaceum L.) and barley (Hordeum vulgare L.) from Korea (Park et al. 2017; Zhao et al. 2016). In the survey, 39 of the 133 collected samples were positive for BVG. Of the 39 BVG-positive samples, 10 samples were single infection with BVG and 29 samples were mixed infection with RSV and another unreported virus. The most common symptoms of BVG-positive samples were yellowing stripe and mosaic, but single infection with BVG or RSV and mixed infection with both BVG and RSV showed similar symptoms; thus, specific symptoms of BVG were unclear at the moment. Further research will be required to determine the natural host range, prevalence, and pathological properties of BVG. To our knowledge, this is the first report of BVG in S. italica in Korea and the world.