Sunlight Induces Black Color and Increases Flavonoid Levels in the Grain of Sorghum Line Tx3362
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Crop Science Society of America. The grain sorghum [Sorghum bicolor (L.) Moench.] line Tx3362 has a uniformly black pericarp color when produced under summer production conditions and it also contains high levels of 3-deoxyanthocyanidins (3-DOAs) in the bran layers of the grain. Consequently, Tx3362 has high levels of antioxidant activity and is a source of natural pigmentation that can be used as natural food coloring. However, prior research indicates that the black color is not fully penetrant in all environments. Specifically, black sorghum panicles shaded from sunlight between flowering and physiological maturity are dark red in color. The objective of this study was to determine if the time of light exposure affects pericarp color, 3-DOA production, and other grain composition traits. Three experiments were conducted that shaded developing Tx3362 black sorghum panicles for varying time intervals in two Texas environments. After harvest, samples were visually phenotyped, quantitatively measured for color via colorimeter, and analyzed using nearinfrared spectroscopy (NIR) to estimate grain composition values. Across both environments, increased shading reduced and, in some cases, eliminated the black color, resulting in red grain. In addition, increased shading reduced the concentration of 3-DOA, total phenols, tannins, and fiber but increased fat concentrations. Because of the strong association between visual score and 3-DOA concentration, field selection for the darkest pericarp should result in selection for the highest 3-DOA content. Additionally, maximum production of these beneficial compounds is environment-specific. Therefore, environments with high sunlight intensity are conducive to the production of darker grain and higher 3-DOA, tannin, and phenol content.
