Optimizing sowing date to enhance grain yield and quality formation of colored rice in tropical regions of China

Context: Colored rice is a high-quality yielding rice type with functional substances and gaining recognition among consumers, however, achieving synergistic increases in grain yield and quality is a serious challenge in production. Objective: The present study was conducted to assess how sowing dates (SO) simultaneously influence the formation of grain yield and functional substance content of colored rice. Methods: The experiments were conducted in Hainan Province, which consisted of two varieties, Youxianghongdao (YXHD) and Suixiangheinuo (SXHN) were sown on six sowing dates, i.e., March 5 (S1), April 5 (S2), May 5 (S3), June 5 (S4), July 5 (S5), and August 5 (S6) in 2022 and 2023. Results: Results revealed that the grain yield, anthocyanin, and flavonoid content (i.e., functional substance) of both colored rice under different SO treatments were significantly affected by temperature and solar radiation at the maturity stage. Compared with early-sown rice (S1-S3), both rice varieties showed lower yield under late- sown rice (S4-S6) that was mainly attributed to the reduction in the grain filling rate. In addition, the functional substances and total antioxidant capacity of variety YXHD were higher in early-sown rice than late rice, while the highest values were noticed in S2 and the lowest was in S6. Nevertheless, the functional substances and antioxidant capacity of SXHN showed the opposite trend as those of YXHD among the different SO. Further analysis indicated that higher temperatures and solar radiation were conducive to the accumulation of functional substances in YXHD grains, while lower temperatures and solar radiation are suitable for improving functional substance content in SXHN. Conclusions: The above results suggested that sowing from S1 to S2 contributed to the synergistic enhancement of grain yield and functional substance content for YXHD. For SXHN, it was observed that an appropriate sown (S2- S6) could diffidently improve the grain functional substance content. Therefore, sowing from S2 to S3 can ensure the highest grain yield of SXHN with a modest increase in grain functional substance content. Significance: Overall, sowing between March 5 and April 5 for red rice and between April 5 and May 5 for black rice is conducive to achieving a high grain yield and quality by synchronizing the required temperature and light resources for the production of colored rice.