First Report of Soybean vein necrosis virus on Soybeans in Michigan.

Soybean vein necrosis virus (SVNV) is associated with an emerging disease in soybean producing regions of the United States. Soybean leaves with necrotic vein symptoms were initially noted in 2008 or 2009 in fields across Arkansas, Kansas, Missouri, Illinois, Mississippi, Tennessee, and Kentucky and SVNV was determined to be the causal agent (2). In 2012, widespread reports of SVNV were made across most soybean (Glycine max) producing states including the recent confirmation of SVNV in Iowa and Wisconsin (1). Foliar symptoms similar to those reported for SVNV were observed at approximately 1 to 10% incidence in soybean fields across Michigan in late August and September of 2012, including fields located in Cass, Ingham, Midland, Saginaw, and Van Buren counties. Symptoms included chlorosis and necrosis which initiated on the veins with subsequent spread across the leaf. An initial sample collected from the East Lansing Agricultural Research Station was confirmed to have SVNV with a polyclonal antibody using double antibody sandwich (DAS)-ELISA at AC Diagnostics, Inc. (Fayetteville, AR) and with reverse transcription PCR by Ioannis Tzanetakis, University of Arkansas, Fayetteville. Additional samples from five fields were subsequently collected from Cass, Ingham, and Van Buren counties. Duplicate leaf tissue samples were tested with DAS-ELISA using the SVNV test kit (AC Diagnostics). All symptomatic leaf samples exhibited a strong positive reaction based on the optical density reading at 405 nm. Absorbance reading that exceeded the healthy soybean tissue by a standard deviation of +3× were considered positive. Total RNA was also extracted from each sample using the RNeasy Plant Mini Kit (Qiagen, Germantown, MD). Complementary DNA (cDNA) was generated using virus-specific LdetR and SdetR primers (2) with the High Capacity RT cDNA kit (Life Technologies; Carlsbad, CA). The cDNA was used as template for PCR with the SVNV-specific primers that amplify regions of the L (LdetF/LdetR) and the S (SdetF/SdetR) RNAs (1). Amplification products of the expected 297 and 861 bp size, respectively, were detected in all symptomatic samples while no amplification products were generated from healthy soybean plant tissues grown under greenhouse conditions. Significantly, this is the first documentation and confirmation of the widespread prevalence of SVNV across the state of Michigan in 2012. References: (1) D. L. Smith et al. Plant Dis. http://dx.doi.org/10.1094/PDIS-11-12-1096-PDN . (2) J. Zhou et al. Virus Genes 43:289, 2011.