Grain yield and functional substance content in colored ratoon rice system under low solar radiation stress in southern China

Context

Ratoon rice has great potential for agricultural development in China due to its enhancement of the multiple-cropping index and reduction in the costs of seeds, fertilizers, and land preparation. Currently, growing public health awareness has sparked increased consumers attention in colored rice owing to its high bioactive compounds.Therefore, integrating colored rice into the ratoon rice system could be a promising cultivation strategy. Even so, rice production often struggles with rainy and low light weather in southern China, which poses a challenge to crop growth and yield improvement. However, the effects of low solar radiation stress on the regeneration rate, grain yield, and functional substance content in colored ratoon rice system remain understudied.

Method

A two-factor field experiment was conducted in 2023 and 2024, involving two colored rice genotypes (Tiandaohongdao II and Suixiangheinuo) and four shading intensities (0 %, 20 %, 40 %, and 60 %) applied during both the main and ratoon seasons, to evaluate the effects of varying shading intensities on the regeneration rate, grain yield, and functional substance content in the colored ratoon rice system.

Results

The regeneration rate and ratoon-to-main crop yield ratio (RMYR) of both red and black rice varieties declined as shading intensity increased. Notably, across varying shading intensities, black rice exhibited higher regeneration rate (1.31) and RMYR (0.46) compared to red rice (1.23 and 0.38, respectively). However, grain anthocyanin, flavonoid, and total phenolic contents, and total antioxidant capacity in red rice grains decreased with increasing shading intensity, whereas in black rice grains, they were increased with the increase in shading intensity in both seasons. Therein, in the main and ratoon seasons, the grain anthocyanin content in black rice under 20 −60 % light shading was 28.51 %-52.72 % and 35.87 %-68.58 % higher than those without shading (971.59 μg g⁻¹ and 705.29 μg g⁻¹, respectively). Comprehensive analysis revealed that black rice exhibited a stronger regeneration rate, larger RMYR, and higher functional substance content under low solar radiation stress in the ratoon rice system.

Conclusion

It is suggested that black rice varieties were prioritized for adoption in colored ratoon rice systems under low solar radiation stress in southern China.