NPIPM:Soybean mosaic virus on soybean
Authors: Buyung Hadi, Loren Giesler, Dean Malvick and Lawrence Osborne
Causal Organism
Soybean mosaic is caused by Soybean mosaic virus (SMV), a pathogen from family Potyviridae. Soybean mosaic virus infect other leguminous plants with soybean as the most economically important host.
Symptoms
Typical symptom of SMV infection range is leaf mottling and deformation. Mottling appears as light and dark green patches on leaf surface. Infected leaves may appear puckered and curled downward. Symptoms may not appear when infected plants are subjected to temperatures above 90˚F (32.2˚C).
Disease Impacts
Infected plants are stunted and may produce fewer seeds. Infections during early growth phases affect yield more severely than infections that occur later. Seeds produced by SMV-infected plants are of lesser weight and can sometimes show seed mottling. Not all infected plants produce mottled seed. On the other hand seed mottling can be caused by other factors, thus the presence of mottled seeds does not indicate that the virus is present in the seed.
Life Cycle and Epidemiology
Soybean mosaic virus can not survive outside a living cell and its spread is not assisted by wind, water, soil or plant debris. The virus survive in seeds and is introduced to the field through usage of infected seeds. Seed transmission can be as high as 75% in the most susceptible varieties. The rates of seed transmission in modern soybean varieties range between 0-5%. Once introduced to the field via infected seeds, aphids can transmit the disease from plant to plant. Over 30 species of aphids have been reported to transmit SMV. Soybean aphid has been shown to transmit this virus.
Soybean mosaic virus and Bean pod mottle virus act synergistically. Infection by both viruses induce severe symptoms and terminal death may occur. Co-infection of both viruses increased the yield loss to as high as 86% and increase the rate of SMV seed transmission.
Management Approaches
Cultural Methods
Because SMV introduction depend largely on the usage of infected seeds, usage of virus-free seeds is fundamental in SMV management. In operations where seeds are saved for next season, seeds should be checked for viral infection if significant proportion of the seeds from aphid infested fields are mottled.
Late planting exposes young plants to aphid colonization period. In the presence of SMV-infected plants in the field, soybean that are planted late have an increased risk of SMV early infection.
Host Plant Resistance
Most commercial soybean cultivars are susceptible to SMV. Nevertheless, three SMV resistance genes have been identified. None of these genes are affective against all strains of the virus. Growers are encouraged to inquire their seed dealers for virus resistance.
