Plant Disease: Soybean Mosaic Virus

Taxonomy:

Distribution:

• Occurs in all soybean-producing areas of the world.

Vector:

• SMV is transmitted by several aphid species, including the soybean aphid.


• Aphids can transmit the virus soon after acquiring it, but are unable to transfer the virus to its offspring.


• The primary source of inoculum is infested seedlings derived from infect seeds.


• Seed transmission is typically 5% or less in most commercial soybean varieties.

Impact:

• Surveys conducted in Nebraska in 2002, indicated that SMV is not as common as bean pod mottle virus.


• Yield losses due to SMV generally range from 8 to 35 %, however losses as high as 94 % have been reported.


• SMV infection will reduce oil content, seed germination, and seed quality due to seed coat mottling.

Symptoms:

• Varies with variety, virus strain, environment, and age of plant at infection.


• Most varieties will be stunted and have fewer pods.


• Trifoliate leaves will have a mosaic of light and dark green areas that may become blistered or raised with time.

Plant infected with SMV

Foliar signs of SMV

• Leaves may appear distorted similar to bean pod mottle virus , generally with the leaf margins curling downward.

• Seed from infected plants can be mottled black or brown depending on hilum color.


• Not all infected plants produce mottled seed and seed mottling does not indicate that the virus in present in the seed.


• SMV and bean pod mottle virus can infect the same plants and act synergistically.


• Yield losses associated with combined infection can be as high as 66 - 86%.


• The combined infection also increases the level of seed transmission of SMV.

Conditions Favorable for Development:

• Symptoms are most severe during cool weather and infection is rarely evident during Nebraska summers.

Host Range:

• Soybean is the most economically important host.


• Hosts are limited to six plant families: Fabaceae, Amaranthaceae, Chenopodiaceae, Passifloraceae, Schropulariaceae, and Solanaceae.


• Most of the hosts are legumes.

Management:

• Management of SMV is based on the use of virus free seed and avoiding late planting of soybean to minimize aphid transmission.


• There are currently three SMV resistance genes that have been identified, but they are not affective against all strains of the virus.


• There are currently nine strains of the virus known to occur in the U.S. at this time and the strains that occur in Nebraska are not known.