Symptom Severity, Yield, Seed Mottling and Seed Transmission of Soybean Mosaic Virus in Susceptible and Resistant Soybean: The Influence of Infection Stage and Growth Temperature

The effect of soybean mosaic virus (SMV) infection on symptom severity, yield, seed mottling and seed transmission in soybean in relation to the growth stage at infection and subsequent temperature was investigated using a susceptible (Harosoy), a moderately resistant (Evans) and a highly resistant (Merit) cultivar. Disease symptoms were more severe with early infection. A greater reduction in plant growth and seed yield, and higher percentages of mottled seeds and seed transmission of SMV also occurred with early infection. Virus titer was higher in younger plants than in older ones and also higher in plants infected at the ealier stage than at the later stage of growth. Merit (a highly resistant cultivar previously reported to be immune to seed mottling) inoculated at the early stage of plant growth resulted in infection and production of some mottled seeds. Temperature affected all parameters investigated. The effect of temperature was greater in the susceptible cultivar than in the resistant one. The optimal temperature for symptom severity, yield, seed mottling and seed transmission was 20 °C. Virus titer was highest at 30 °C in all three cultivars. Maturity of susceptible cultivar was delayed by infection.