Several viruses cause disease on soybeans in the United States. The viruses, their major symptoms, and vectors are summarized in Table 3. The viruses can not be identified by the foliar and stem symptoms produced on soybeans, because symptoms for the same virus and virus combinations will appear different on different soybean varieties. In addition, dual infections or combinations of viruses in plants may contribute to different symptoms and increase severity of some virus diseases. The identity of a specific virus causing the problem needs to be determined with either greenhouse or serological laboratory assays. All of these soybean viruses are mechanically transmitted, each has characteristic natural vectors, and three of the viruses show agronomically significant seed transmission.
| Table 3. Some Properties of Viruses That Infect Soybeans in the North Central United States. | |||
| Virus | Symptoms | Vectors | |
| Bean Pod Mottle | BPMV | Leaf mosaic Pod/seed mottling Green stem |
Beetle |
| Soybean Mosaic | SMV | Leaf mosaic, seed mottling Stunting |
Aphid |
| Tobacco Ring Spot | TRSV | Bud blight Nematode Thrips Mites Flea beetles |
Multiple |
| Tobacco Streak | TSV | Systemic necrosis | Thrips |
| Alfalfa Mosaic | AMV | Leaf mottle/mosaic | Aphid |
| Bean Yellow Mosaic | BYMV | Leaf mottle/mosaic | Aphid |
| Symptoms caused by soybean viruses. Soybean viruses, as can be seen in these photographs, cause a wide variety of symptoms: | ||
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| Figure 34. Misshapen leaves. | Figure 35. Mosaic symptoms. | Figure 36. Small, misshapen, turned-up pods. |
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| Figure 37. Dark necrosis and curling down of stems. | Figure 38. Small, misshapen, turned-up pods. | Figure 39. Yellow mosaic. |
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| Figure 40. Dark necrosis and curling down of stems. | Figure 41. Yellow mosaic. | Figure 42. Soybean virus nursery at Virginia Polytechnic Institute and State University. |
Bean pod mottle (BPMV) is transmitted by several species of beetles, including the bean leaf beetle, Certoma trifurcata. BPMV has a fairly narrow host range infecting only legumes, principally common bean (Phaseolus vulgaris) and soybean. On soybeans, BPMV infection causes moderate to severe mosaic and mild puckering of leaves, and mottled pods and seed coats and has been associated with the soybean green-stem syndrome. In this syndrome, soybean stems remain green after pods mature, and leaf petioles remain attached to stems.
Soybean mosaic virus (SMV) is non-persistently transmitted by various aphid species, which means that the aphids will acquire the virus then immediately transfer the virus the next time it feeds. In addition, SMV is seed transmitted. Seed transmission is an important source of the virus in the soybean crop. The virus has a broad host range of about 30 dicotyledonous plant species. On soybeans, SMV causes mosaic symptoms on leaves, rolling or distortion of younger leaves, seed mottling, plant stunting, reduced pod set, and malformed or seedless pods.
The virus is transmitted by a broad range of vectors including a nematode (Xiphinema americanum), thrips (Thrips tabaci), spider mites (Tetranychus spp.), grasshoppers (Melanoplus app.), and possibly the tobacco flea beetle, (Epitrix hirtipennis). The virus is also seed-transmitted with up to 10% efficiency. Tobacco ringspot nepovirus (TRSV) has a wide host range that includes more than 17 dicot and monocot families. On soybean, TRSV causes bud blight of soybean, where the tips of branches turn a dark black and are curled down. This can be a severe disease and is associated with substantial losses of yield.
This virus is efficiently transmitted in seeds. Tobacco streak ilarvirus (TSV) causes a systemic necrosis in soybean resembling bud blight
Alfalfa mosaic alfamovirus (AMV) is transmitted by a number of different aphid species including Mysus persicae. It is not seed transmitted. AMV has a very broad host range that includes more than 430 dicot species, but virus infection is frequently symptomless. The virus incites variable mosaic and mottle symptoms on soybean. These infections may be latent, and recovery often occurs.
Like SMV and AMV, bean yellow mosaic potyvirus (BYMV) is transmitted by aphids. It is not transmitted in seed. BYMV hosts include legumes and non-legumes. Like SMV, BYMV has a fairly narrow host range. The virus causes mottle or mosaic symptoms similar to those incited by mild strains of SMV in soybean.
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