First Report of Soybean dwarf virus on Soybean in Wisconsin.

Soybean dwarf virus (SbDV) causes widespread economic losses on soybean (Glycine max (L.) Merr.) in Japan (4), and has been reported on soybean in Virginia (2), in various legumes in the southeastern United States (1), and in peas in California (3). During late July and early August of 2003, soybean plants in Wisconsin were surveyed for SbDV. In 286 soybean fields at the R2-R4 growth stage, the uppermost fully unfurled leaf was collected from 10 plants at each of five sites. Samples were collected at random without regard to symptoms. SbDV symptom information was not recorded. Samples were stored on ice until frozen at -80°C. Five fields in four Wisconsin counties (Columbia, Lafayette, Sauk, and Waushara) tested positive for SbDV using double antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA). DAS-ELISA testing was conducted with reagents from Agdia, Inc (Elkhart, IN) following the manufacturer's protocol. Absorbance was read at 405 nm with a Stat Fax 2100 microplate reader (Awareness Technology, Inc., Palm City, FL) or visually evaluated. DAS-ELISA did not discriminate between strains of SbDV. The presence of SbDV was confirmed, and strain identity was inferred as dwarfing strain using reverse transcription-polymerase chain reaction (RT-PCR). Total RNA was extracted from homogenized leaf tissue, reverse transcribed, and amplified with the SuperScript One Step RT-PCR System (Invitrogen, Carlsbad, CA) and SbDV-specific primers (5'-CTGCTTCTGGTGATTACACTGCCG-3' and 5'-CGCTTTCATTTAACGYCATCAAAGGG-3'). Size of the RT-PCR products (110 bp) was consistent with the dwarfing strain, SbDV-D. All locations that tested positive for SbDV showed soybean aphids, Aphis glycines Matsumura (Homoptera: Aphididae), on 100% of soybean plants. Several aphid species have been reported to vector SbDV, but at this time, vector relations in the Wisconsin infections are unknown. To our knowledge, this is the first report of SbDV infecting soybean in Wisconsin. References: (1) V. D. Damsteegt et al. Plant Dis. 79:48, 1995. (2) A. Fayad et al. Phytopathology (Abstr.) 90(Suppl.):S132, 2000. (3) G. R. Johnstone et al. Phytopathology (Abstr.) 74:795(A43), 1984. (4) T. Tamada et al. Ann. Phytopathol. Soc. Jpn. 35:282, 1969.