Soybean vein necrosis virus

The genome of SVNV is a negative sense single stranded RNA virus (Group V) that has three segments (S, M, and L segments). The L segment is 9010 nt and encodes for the RNA-dependent RNA polymerase (RdRp). The M segment is 4955 nt and to encode for NSm and GN/GC proteins. The S segment is 2603 nt and encodes the N and NSs proteins. This virus codes proteins from the M and S segments in an ambisense manner, meaning that proteins are translated from both positive and negative sense RNA. There is preliminary evidence to suggest low diversity within SVNV. The NSm protein is a non-structural protein (not present in mature virion) and is critical to cell-to-cell movement within plant cells (8). The NSs protein is also a non-structural protein and contributes to suppression of RNA silencing during plant infection. The N protein contributes to viral replication, and coats the genomic RNA within the virion. ==Transmission==

Presently the soybean thrips (Neohydatothrips variabilis) is the only known vector of SVNV. Research needs to be done to verify if this is the only thrips species capable of transmitting this new and widespread virus. This virus is believed to have a transmission cycle similar to other members of the Tospovirus genus. In TSWV, acquisition of the virus by the thrips vector can only occur during the larval stage of development by the thrips. From the larval stage the virus is passed transstadially to the adult stage. Adult thrips are then able via feeding to transmit the virus to the plant host. It is important to keep in mind with this pathogen, as with all vectored pathogens, that behavior of the vector can contribute to the potential spread of the disease. ==Agricultural importance==

Agricultural importance remains to be assessed. Typically thrips feeding alone on soybean plants does not cause economic damage, however it may if the plant is under some other form of stress. The impact of SVNV in terms of yield loss has not yet been determined. Presently no other agronomic crops are known hosts for SVNV. ==Diagnosis==

Symptoms associated with SVNV infection begin with vein clearing and then yellowing (chlorosis) in areas near veins. Chlorotic areas eventually can turn into red-brown lesions (necrotic lesions). If the disease is severe enough leaves can fall off. If a farmer believes they have SVNV in their field, they should send samples to their local extension office. To verify SVNV presence laboratories will likely use an ELISA or PCR method. == Epidemiology ==

SVNV was first identified in Tennessee in 2008. Presently it has been detected in: AL, DE, IA, IL, KS, KY, MD, MS, MO, NY, PA, TN and WI. Portions of the virus that are believed to be critical for the spread of this virus, based on what is known for other members of the genus Tospovirus are the movement protein (NSm) and the glycoproteins (GC/GN). The Nsm protein is critical for cell-to-cell movement within plants. The glycoproteins (GC/GN) have been found to be necessary for thrips transmission. ==Management==

Presently, there are no management recommendations. This is a relatively new disease and as such whether or not there is a significant yield impact remains to be determined. Thrips themselves do not typically cause economic damage on soybeans. Insecticide application targeting thrips for control of the pathogen is not presently recommended. Land Grant universities’ extension (agricultural extension) websites should be monitored for new developments in management as this pathogen undergoes continued study. ==References==