First Report of Rottboellia yellow mottle virus Infecting Sorghum Sudangrass Hybrid (Sorghumbicolor x Sorghumbicolor var. sudanense) in North America.
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2016, American Phytopathological Society. All rights reserved. Poor or no regrowth of a sorghum-Sudangrass hybrid (Sorghum bicolor (L.) Moench Sorghum bicolor var. sudanense) grown for hay in nine fields (approximately 45 ha total) in Williamson Co., TX, was observed in September and October 2014. Most plants within the fields had chlorotic mosaic and mottling foliar symptoms and were severely stunted. Symptomatic plants tested positive for Maize dwarf mosaic virus (genus Potyvirus) via RT-PCR, cloning, and sequencing (data not shown). Following the recent characterization of Rottboellia yellow mottle virus (RoMoV), a novel grass-infecting Sobemovirus (Somera and Truve 2015), total RNA extracts from two plants showing symptoms consistent with those described for RoMoV from one of the affected fields were subjected to a two-step RT-PCR using three sets of newly designed and published RoMoV-specific primers. The primer pairs RoMoV662 (5-CRCACCATGAAGTGGTTAGA) and RoMoV1002 (5-CTTCTTCCCTCTCCTGCTTTAC) (this study) and RoMoV2702 and RoMoV3037 (Somera and Truve 2015) were capable of amplifying 360 bp each from the N- and C-termini of the polyprotein P2a2b cistron, respectively, while the primer pair RoMoV3314 (5-CACAAACGCAATGACCAAGAG) and RoMoV3972 (5-GACGACGTACTGCACCATAAT) (this study) could amplify a 679-bp fragment specific to the coat protein (CP) gene of RoMoV. DNA amplicons of the expected sizes were obtained with each primer pair, cloned, sequenced, and analyzed as described previously (Alabi et al. 2015). The two plant-tissue samples tested positive with all three pairs of RoMoV-specific primers described above. A BLASTn analysis of obtained sequences (KU306532-49) showed that they are specific to RoMoV. In pairwise comparisons, the N-terminal P2a2b polyprotein cistron sequences (KU306544 to KU306549) shared 99 to 100% nucleotide (nt) and 99 to 100% amino acid (aa) identities among themselves and 89% and 92 to 93% nt and aa identities, respectively, with corresponding sequences of RoMoV DSM:PV-0496 (KC577469). The C-terminal P2a2b polyprotein cistron (KU306538 to KU306543) shared 98 to 100% nt and 100% aa identities among themselves and 92 to 93% and 99% nt and aa identities, respectively, with corresponding sequences of RoMoV DSM:PV-0496. The CP-specific sequences (KU306532 to KU306537) shared 99 to 100% nt and 100% aa identities among themselves and 91 to 92% and 93% nt and aa identities, respectively, with corresponding sequences of RoMoV DSM:PV-0496. To the best of our knowledge, the results represent the first report of the occurrence of RoMoV in North America and the first record of a sorghum-Sudangrass hybrid as a natural host of the virus, thus expanding its host range.
