Effects Of Shading At Different Growth Stages With Various Shading Intensities On The Grain Yield,Anthocyanin Content And Antioxidant Capacity Of Colored Rice(Oryza Sativa L.)

Rice(Oryza sativa L.)as a staple food for the world’s people,occupies a vital position in food production,feeding approximately 50%of the world’s population.However,the motivation of farmers to plant rice is seriously affected by the shortage of rural labor,deteriorating labor structure,excessive growth in production costs and declining production efficiency.In addition,with the deterioration of the environment and the change in human dietary habits,various chronic diseases have increased year by year,and the proportion of human beings in sub-healthy conditions has increased,which has placed great pressure on society and the national health care system.Therefore,it is imperative to transform rice into colored rice with high efficiency,high quality and high added value.Growing colored rice is one of the most popular ways to improve the quality of rice and increase its added value and market competitiveness.However,the synthesis and distribution of anthocyanins in colored rice are susceptible to environmental factors,especially the effect of light on anthocyanins.Meanwhile,there are few studies on the effects of shading at different growth periods with various shading intensities on the grain yield,anthocyanin content and antioxidant capacity of colored rice.Therefore,field experiments were conducted in a split-split plot design with four replications in Guangji Village,Nanbao Town,Lingao County,Hainan Province in 2020 and 2021.The red rice cultivars Youxianghongdao(YXHD)and the black rice culticars 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 response mechanism of light intensity affecting the grain yield,anthocyanin content and antioxidant capacity of colored rice was initially investigated by measuring the relationship between colored rice yield and its components,anthocyanin content and its antioxidant capacity with different shading periods and different shading intensities treatments.The main results are as follows:1.The grain yields of both colored rice varieties decreased as the shading intensity increased for the three shading periods.Compared to CK,the grain yield of YXHD and SXHN decreased by 0.3%-46.7%and 1.0%-58.7%due to shading treatment across the two years,respectively.Therein,no significant impact on grain yield and its components were observed in either variety at S1.Shading at S2 significantly decreased the number of spikelets per m~2in both colored rice varieties.However,compared to CK,shading at S3period,the filled grain rates decreased resulted in decreases in the grain yield of YXHD and SXHD of 6.2%-58.7%和4.6%-46.2%in 2020 and 2021,respectively.2.Inconsistent responses of grain anthocyanin content to shading period and shading intensity in two colored rice cultivars.The grain anthocyanin content of YXHD decreased as the shading intensity increased under shading during S1 and S2,while under S3 shading,the grain anthocyanin content increased as the shading intensity increased.However,for the SXHN,the anthocyanin content in grains showed the opposite trend with the change in shading intensity.Shading at different growth periods on the anthocyanin content of YXHD and SXHN was in the sequence of S3>S1>S2 and S2>S1>S3,respectively.3.The variation trends of flavonoid content,total antioxidant capacity and hydroxyl radical scavenging capacity of two colored rice varieties under shading at different growth stages were consistent with the variation trend of anthocyanin content.Further analysis showed that,a significant positive correlation(P<0.001)was observed between the anthocyanin content,flavonoid content,total antioxidant capacity and hydroxyl radical scavenging capacity of YXHD and SXHN.Therefore,the higher the content of anthocyanin in colored rice,the higher its antioxidant capacity.Above results indicated that both colored rice varieties were most sensitive to shading treatment during S3 among the three shading periods.Meanwhile,our 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.