Influence of tannin on sorghum seed germination.

The presence of phenolic substances in the seed coat may inhibit the germination of sorghum seeds, however, it is not known whether during the storage the reduction of these compounds occurs or if a break of dormancy occurs at low temperatures. So, with the interest of verifying the relationship between tannin and seed dormancy, it was intended in this study to evaluate the biochemical, physiological and physical alterations occurred during the development of sorghum seeds with different concentrations of tannin. Seeds of cultivars BR 305 and BR 310, collected at seven development stages (100, 103, 107, 113, 119, 121, 127 days after sowing) according to water content were used. The seeds collected at each stage were divided into two lots, one subjected to drying at 35º C, up to the moisture of 12% and the other lot with out drying. Seed quality was evaluated by the tests of germination, electric conductivity and enzyme activity. Further, the concentration of tannins in the seeds at each development stage was also determined. Beneficial effect of drying on germination in seeds with higher water content is found. In the seeds evaluated without no drying, the percentage of dormancy is higher when compared to those of seeds subjected to artificial drying. For cultivar BR 305, drying favors the concentration of tannins in seeds collected at different development stages. The same occurred for cultivar BR 310, in seeds collected at 100, 103 and 119 days after sowing. The polyphenoloxidase activity was greter in seeds submitted to the drying of lots with low tannin concentration at both 100 and 103 dasy after sowin. g.