Diagnosing Nebraska soybean viruses
We have five soybean viruses in Nebraska. Bean Pod Mottle (BPMV) is by far the most common. In fact reports of soybean mosaic are almost invariably BPMV. Soybean Mosaic (SMV) is occasionally found especially in Lancaster County commonly in mixed infection with BPMV. Alfalfa Mosaic (AMV) is rare and sporadic. AMV infected leaves have bright yellow areas. Plants with bud blight are rare and are associated with Tobacco Streak (TSV). TRSV was recovered late in the season from plants with "atypical" symptoms. See Plant Health Initiative site for general information.
Bean Pod Mottle
BPMV (comovirus) is beetle transmitted and commonly gives mosaic symptoms although symptoms vary and can be virtually invisible. BPMV gives local lesions on Pinto 111 beans. BPMV is easily diagnosed by minipurification. Tissue is loaded with virions that contain both large and small proteins. The small protein is normally a doublet; proteolysis converts the larger doublet protein to the smaller. BPMV is acid stable. Nebraska BPMV infects C. quinoa systemically; both local and systemic symptoms develop much slower than for AMV or TSV. PHI site. - see Nebraska BPMV page - good photo of field symptoms
SMV (potyvirus) is aphid and seed transmitted. SMV symptoms typically differ from those of BPMV. Minipurified samples contain a protein of about 34Kd which is resistant to chymotrypsin. SMV also infects C. quinoa. PHI site - see Nebraska soybean mosaic page
Alfalfa is commonly grown in Nebraska and is almost universally infected with AMV. It is surprising that AMV is not more common in soybean. Like SMV it is nonpersistently aphid transmitted. I have found AMV only in soybean plants showing bright yellow symptoms. Minipurified AMV has a characteristic 28K protein similar in size to TSV cp. AMV produces small amounts of a distinctive dsRNA. AMV systemically infects both C. quinoa and C. amaranticolor. Researchers in other states are beginning to find AMV in apparently symptomless plants.
TSV (Ilarvirus) protein cannot be detected by minipurification directly from field samples with bud blight symptoms. Inoculate samples to C. quinoa; symptoms appear very quickly (about 2 days). Local lesions (irregular) exhibit sunken areas and the virus goes systemic often killing the growing tip of the plant. Capsid protein is readily detected after minipurifying from C. quinoa and migrates (like AMVcp) at about 28K. TSV dsRNA is also similar to that of AMV. Nebraska TSV infects neither tobacco, nor N. benthamiana but will infect soybean in the greenhouse.
TRSV was recovered very late in the year from short, brown plants with small pods (see symptoms). Virus could not be detected by minipurification from field tissue, but minipurified samples were inoculated to C. quinoa and from systemically infected quinoa tissue back to soybean. TRSV coat protein was readily detected by minipurification from systemically infected quinoa. TRSV gave local lesions on quinoa and spread systemically, but more slowly than TSV or AMV. The virus gives brown lesions on inoculated cowpea leaves and kills the upper part of the plant. It gives local lesions on tobacco, it spreads very slowly ultimately giving " "local" lesions" and eventually systemic invasion on upper leaves. Symptoms on greenhouse soybean are dwarfing and bud proliferation, not bud blight. The virus is acid and protease stable. The capsid protein "size" on SDS gels distinguishes it from other nepoviruses in my greenhouse.