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Soybean Vein Necrosis Virus Detected In South Dakota Soybeans

Sep 22, 2017
By Emmanuel Byamukama
Assistant Professor & SDSU Extension Plant Pathologist
 
A new soybean virus called Soybean vein necrosis virus (SVNV) was detected in South Dakota soybean fields in Davison and Union counties. Symptomatic plants were sporadic and found along the field borders. Infected plants showed mild to moderate severity. It is possible this virus is occurring in other counties but at very low incidence within the field making it difficult for the plants to be easily observed.
 
Symptoms
 
Soybean vein necrosis virus symptoms start as light yellow lesions between the veins (Figure 1). These expand out over time but are limited to within the leaf veins. The yellow lesions eventually turn to reddish brown lesions (Figure 2). Infected leaf tissues may die but do not fall out (Figure 3). Infected plants may have only a few leaves showing symptoms or the entire plant may show symptoms (Figure 4).
 
Fig. 1. Initial Soybean vein necrosis symptoms. 
 
Fig. 2. Typical symptoms of Soybean vein necrosis virus. Notice the yellow, reddish-brown discoloration between the main veins.
 
Fig. 3. Advanced symptoms of SVNV showing tissue necrosis.
 
Transmission
 
Soybean vein necrosis virus is transmitted by thrips. Several species are thought to transmit SVNV but so far soybean thrips (Neoydatothirps variabilis) have been confirmed as the vector of this virus. The immature stage of this insect, the nymph, is the only stage that can feed on infected plants and acquire the virus. Adults that did not acquire the virus at the nymph stage do not transmit the virus, nor do they pass on the virus to their eggs. It is thought that SVNV overwinters in broadleaf weeds where thrips acquire it and transmit it to soybeans. Recently, seed transmission of this virus was reported to be around 6%.
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