Effects of shading at different growth stages with various shading intensities on the grain yield and anthocyanin content of colored rice (Oryza sativa L.)

Colored rice is a high-quality and high-added-value rice that has attracted increasing attention in recent years. Therein, the main functional substance in colored rice is anthocyanin, which plays an important role in anti-aging, inhibiting adipocyte accumulation, preventing cancer and treating cancer. However, there are few studies on the effects of shading at different growth periods with various shading intensities on the grain yield and anthocyanin content of colored rice. Field experiments were conducted in Hainan Province in 2020 and 2021, and two inbred rice cultivars, Youxianghongdao (YXHD) and Suixiangheinuo (SXHN), were adopted. Shading treatments were conducted at three different growth periods: shading from the regreening stage to the mid-tillering stage (S1), shading from the mid-tillering stage to the full heading stage (S2), and shading from the full heading stage to the maturity stage (S3). Based on the treatment of these three shading growth stages, three shading intensities were incorporated, including shading 20% (D1), 40% (D2) and 60% (D3) light intensities. No shading during the whole growth stage was used as a control (CK). The results indicated that the grain yield and anthocyanin content of both colored rice varieties were most sensitive to shading treatment during S3 among the three shading periods. The grain yields of both colored rice varieties decreased as the shading intensity increased for the three shading periods. In addition, the grain anthocyanin content of the red rice variety (YXHD) decreased as shading intensity increased under S1 and S2, while under S3, the grain anthocyanin content increased as shading intensity increased. However, for the black rice variety (SXHN), the anthocyanin content in grains showed an opposite trend with the changes in both shading intensity and shading period. Above results suggested that SXHN was more suitable for planting in the rainy season with low light intensity than YXHD based on low grain yield loss, strong shade tolerance and high anthocyanin content. However, it is necessary to explore the effects of light intensity on the anthocyanin synthesis mechanism in the near future.