What might cause “bleeding hilum” in soybeans?
The most common cause of a bleeding hilum in soybeans is infection by the soybean mosaic virus. Seed infected with SMV is usually smaller than normal with a mottled brown or black seed coat as well as the bleeding hilum symptom. The virus is vectored by many species of aphids which obtainthe virus by feeding on an infected plant. As they move about the field, they easily transmit the virus. Seed transmission is also known and the virus can remain viable for up to two years in seeds. The extent of seed transmission depends on the strain of the virus and the genotype of the host. No consistent relationship has been found between virus-infected seed and the location of seed within a pod or on the plant. The reaction of a plant to SMV infection depends on the genotype, virus strain, age of plant at time of infection, and environmental conditions. Severity of symptoms on plants also varies with the same conditions. Symptoms tend to be less severe at higher temperatures. I have also noticed
