The objective of this study was to determine the effects on the yield of two soybean cultivars caused by two strains of Soybean mosaic virus (SMV) and of the age of plants at the moment of inoculation. Two experiments were conducted in a greenhouse. Plants of the cultivars BRS 183 and UFV-16 Capinópolis were mechanically inoculated with strains G1 or G5, at three different ages. The experiments were conducted in a completely randomized design, with five replications. Differents characteristics related to yield and seed quality were evaluated. The conclusions were: (i) the two SMV strains cause significant losses in soybean yield and seed quality; (ii) the SMV G1 strain causes more losses than the G5 strain; (iii) plant age at inoculation affects the level of losses; (iv) the percentage of mottled seeds and the level of mottle in seeds were affected by the environment, cultivar, virus strain and age of plants at the moment of inoculation. The characteristics of each combination, plant dry weight and seed weight, root weight and volume, percentage of mottle seeds and level of mottling, showed a significant correlation in both cultivars, thus allowing the use of one characteristic from each pair to evaluate losses.
