The soybean mosaic virus (SMV) is widespread in all soybean production areas. The mottled brown seed is the most characteristic symptom under our conditions, so in Brazil the disease was called "mancha-café" (coffee-spot). The mottling was the main limiting factor to the seed production in the certification system. The present paper had two objetives: screenning lines with different levels of mottled seeds, and to verify the interaction between selected genotypes and inoculation dates. During 1987, 131 F4:5 experimental lines from the cross IAC78-2318 x Santa Rosa, both susceptible to SMV, were evaluated under field conditions in Campinas (SP), Brazil. In the next year, seventeen selected lines plus the cultivars Santa Rosa, representing the five levels of mottling were planted again under field conditions in randomized complete-block design, with six replications. The results showed that the screenning realized in the field was efficient to identify the lines with different levels of mottled seeds. It was also observed that this characteristic was not much influenced by environmental effects as indicated by the positive and high correlation between diseases notes of both years, as well as the low value of the coefficient of variation. An additional study was carried out under greenhouse conditions to evaluate genotypes in distinct growth stages when mechanically inoculated with the virus. It consisted of a factorial experiment, involving a non-inoculated control, three inoculation times, and five lines representing notes from 1 to 5, plus the cultivars Santa Rosa, IAC-Santa Rosa PC and IAC-Santa Rosa DF. The genotypes were sowed in plastic bags and at the maturity, the following evaluations were made: the mottled seed rate, seed production (g/3 plants), mass (g) of 100 seeds and the rate of green stem. The line IAC87-5934, which scored one under field conditions, also showed the lowest mottled seed rate in all inoculation growth stages. It was also the only one that did not transmit the virus by the seeds in this experiment.
Glycine max; soybean mosaic virus (SMV); plant resistance