In July 2013, soybean (Glycine max) plants at the research field in Daegu, South Korea, showed virus-like symptoms, such as mosaic, mottle, yellowing, and stunting. Overall, there were approximately 1% of soybean plants that showed these symptoms. Sixteen soybean samples were collected based on visual symptoms and subjected to laboratory characterization. Total RNA was extracted from each sample with the Tri Reagent (Molecular Research Center, Cincinnati, OH) and cDNA was synthesized using random N25 primer with RevertAid Reverse Transcriptase (Thermo Scientific, Waltham, MA), according to the manufacturers' instructions. All samples were tested by PCR with Prime Taq Premix (2X) (GeNet Bio, Daejeon, Korea) and primer sets specific to Soybean mosaic virus (SMV; 5′-CATATCAGTTTGTTGGGCA-3′ and 5′-TGCCTATACCCTCAACAT-3′), Peanut stunt virus (PSV; 5′-TGACCGCGTGCCAGTAGGAT-3′ and 5′-AGGTDGCTTTCTWTTGRATTTA-3′), Soybean yellow mottle mosaic virus (SYMMV; 5′-CAACCCTCAGCCACATTCAACTAT-3′ and 5′-TCTAACCACCCCACCCGAAGGATT-3′), and Soybean yellow common mosaic virus (SYCMV; 5′-TTGGCTGAGAGGAGTGGCTT-3′ and 5′-TGCGGTCGTGTAGTCAGTG-3′). Among 16 samples tested, five were positive for SMV and two for SYMMV. Three samples were found infected by both SMV and SYMMV and four by both SMV and PSV. Since two of the symptomatic samples were not infected by viruses described above, a pair of primers specific to Peanut mottle virus (PeMoV; 5′-GCTGTGAATTGTTGTTGAGAA-3′ and 5′-ACAATGATGAAGTTCGTTAC-3′) was tested (1). All 16 samples were subjected to RT-PCR with primers specific to PeMoV. Four were found positive for PeMoV. Two of them were already found infected with SYMMV. In order to identify the complete nucleotide sequences of PeMoV coat protein (CP), another primer set (5′-TGAGCAGGAAAGAATTGTTTC-3′ and 5′-GGAAGCGATATACACACCAAC-3′) was used. RT-PCR product was cloned into RBC TA Cloning Vector (RBC Bioscience, Taipei, Taiwan) and the nucleotide sequence of the insert was determined by Macrogen (Seoul, Korea). CP gene of the PeMoV (GenBank Accession No. KJ664838) showed the highest nucleotide sequence identity with PeMoV isolate Habin (KF977830; 99% identity), and the highest amino acid identity with GenBank Accession No. ABI97347 (100% identity). In order to fulfill Koch's postulates, several G. max cv. Williams 82 were inoculated with the extracts of PeMoV-infected leaf tissue. At 14 days post-inoculation, plants showed systemic mottle symptoms. These symptomatic plants were subjected to RT-PCR, and the nucleotide sequences of the PCR product were found identical to that of the virus in the inoculum. To our knowledge, this is the first report of soybean-infecting PeMoV, a member of the genus Potyvirus in the family Potyviridae, in South Korea.
Reference: (1) R. G. Dietzgen et al. Plant Dis. 85:989, 2001.
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