First Report of Soybean vein necrosis virus in Soybean Fields of Oklahoma.

Soybean vein necrosis virus (SVNV) causes a new emerging disease of soybean that has been recorded in more than 10 states (1,2,3,4) of the United States, but so far no information is available about its presence in soybean crops of Oklahoma. Surveys of commercial soybean fields were conducted for soybean viruses during summer of 2012. A total of 327 samples were randomly collected from soybean fields in 11 counties. Symptoms typical of SVNV infections including leaf chlorosis and leaf-vein necrosis were observed on some soybean plants in the field (4). All soybean leaf samples were tested against SVNV polyclonal antisera obtained from AC Diagnostics, Inc. (Fayetteville, AR) by dot-immunobinding assay (DIBA) (1). Fifty-three samples reacted positively with SVNV antisera. Total RNA was extracted from three DIBA-positive samples collected from soybean plants in Choctaw County and tested by reverse transcription (RT)-PCR using SVNV-specific primers (forward primer 5'-ATGTTCTCTCTATAATAGCCA and reverse primer 5'-ACCCATAACAATTGATCAAGA-3') that were designed from the available sequence in the GenBank (Accession No. GU722317.1) to amplify a fragment from RNA1. A band of the expected size of 344 bp was observed on a 1% agarose gel in all three samples. The PCR products were purified using QIAquick PCR Purification Kit (QIAGEN, Valencia, CA), cloned (pGEM-T Easy Vector, Promega, Madison, WI) and sequenced in both directions. The consensus sequence of the 344-bp fragment was 99% identical with the corresponding region of RNA 1 of SVNV isolate 'Milan_TN' (Accession No. GU722317.1). These results confirmed the presence of SVNV in soybean fields, which are mostly located in Criage, Choctaw, Hughes, LeFlore, Mayes, Muskogee, McCurtain, Okmulgee, Ottawa, Rogers, and Sequoyah counties of Oklahoma. None of the samples collected from north central or western parts of the state were positive against SVNV. To our knowledge, this is the first report of SVNV in soybean crops in Oklahoma. Soybean is one of the major oil seed crops cultivated on approximately 200,000 hectares annually in Oklahoma and the presence of SVNV could pose a potential threat to the production of soybean in the future. References: (1) J. L. Jacobs and M. I. Chilvers. Plant Dis. 97:1387, 2013. (2) J. Han et al. Plant Dis. 97:693, 2013. (3) D. L. Smith et al. Plant Dis. 97:693, 2013. (4) J. Zhou et al. Virus Genes 43:289, 2011.