Abstract
Soybean vein necrosis virus (SVNV; genus Tospovirus; Family Bunyaviridae) is a negative-sense single-stranded RNA virus that has been detected across the United States and in Ontario, Canada. In 2013, a seed lot of a commercial soybean variety (Glycine max) with a high percentage of discolored, deformed and undersized seed was obtained. A random sample of this seed was planted in a growth room under standard conditions. Germination was greater than 90% and the resulting seedlings looked normal. Four composite samples of six plants each were tested by reverse transcription polymerase chain reaction (RT-PCR) using published primers complimentary to the S genomic segment of SVNV. Two composite leaflet samples retrieved from seedlings yielded amplicons with a size and sequence predictive of SVNV. Additional testing of twelve arbitrarily selected individual plants resulted in the identification of two SVNV positive plants. Experiments were repeated by growing seedlings from the same seed lot in an isolated room inside a thrips-proof cage to further eliminate any external source of infection. Also, increased care was taken to reduce any possible PCR contamination. Three positive plants out of forty-eight were found using these measures. Published and newly designed primers for the L and M RNAs of SVNV were also used to test the extracted RNA and strengthen the diagnosis of viral infection. In experiments, by three scientists, in two different labs all three genomic RNAs of SVNV were amplified in these plant materials. RNA-seq analysis was also conducted using RNA extracted from a composite seedling sample found to be SVNV-positive and a symptomatic sample collected from the field. This analysis revealed both sense and anti-sense reads from all three gene segments in both samples. We have shown that SVNV can be transmitted in seed to seedlings from an infected seed lot at a rate of 6%. To our knowledge this is the first report of seed-transmission of a Tospovirus.
Highlights
In 2014, the U.S harvested over 33 million ha of soybean with a total value of over $40 million dollars [1]
We have shown that Soybean vein necrosis virus (SVNV) can be transmitted in seed and systemically transmitted to the emerging seedlings at a rate of approximately 6%
SVNV might interact with other viruses in the same soybean plant to cause synergistic reactions that could result in increased damage to soybean
Summary
In 2014, the U.S harvested over 33 million ha of soybean with a total value of over $40 million dollars [1]. Many diseases cause production issues for soybean throughout the U.S, including several viruses. In other countries Tospoviruses have been more readily identified on soybean and include TSWV, Tomato yellow ring virus, Groundnut ringspot virus, and Groundnut bud necrosis virus [6]. All viruses within the Tospovirus genus fall in these two sub-groups with the exception of SVNV and another closely related virus species, Bean necrotic mosaic virus (BeNMV) [7, 8]. SVNV was not identified as a pathogen of soybean until 2008 when it was documented in Tennessee, Arkansas, and several other southern states More recently it has been found in north central U.S states such as Wisconsin and Iowa [9]. SVNV can be transmitted by soybean thrips (Neohydatothrips variabilis) [4], but it is not known if other thrips species occurring on, or reproducing upon soybean can transmit the virus, or if there are other means of transmission
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