Effects Of Shading Stress After Flowering On Grain Yield,Dry Matter Transport And Quality Of Indica Japonica Hybrid Rice

The grain yield advantage of indica-japonica hybrid rice(I-JR)over indica hybrid rice(IR)has been studied extensively.Compared with other types of rice,I-JR has the stronger characteristics of photosynthetic production capacity,photosynthetic validity period,dry matter accumulation capacity and grain yield increasing capacity.Due to its grain yield and quality advantages,the planting area of I-JR are expanding year by year at this stage,but there are few studies on the growth characteristics and grain yield performance of I-JR under shading stress.Experiments were conducted in 2019-2021 at the agricultural science and technology industrial park of Yangtze University.Two I-JR(Yongyou 1540 and Yongyou 538)were used as test materials,and two IR(Y-liangyou 900 and Quanyouhuazhan)that have been widely grown in China were used as the control.Compare the grain yield,total dry weight(TDW),and radiation use efficiency(RUE)of I-JR and IR under shading stress after flowering(FL)in four key reproductive periods.To study on the changes of grain quality of I-JR after shading in Jianghan Plain and its effects on the grain yield of I-JR.The main results are as follows:(1)Under normal conditions,I-JR had a 10.13%grain yield advantage over the IR.The grain yield of rice decreased significantly with the shading stress after FL and there were differences among varieties.The average decline rate of I-JR in three years was 44.0%,which was significantly lower than 57.7%of IR.Shading after FL led to a significant reduction in the grain filling percentage of all tested rice varieties,which was the main reason for the decline of rice yield.(2)Shading after FL resulted in a significant decrease in aboveground dry matter accumulation of rice.Under shading,the average TDW of I-JR decreased by 25.8%,while that of IR decreased by 34.0%in 2019-2020.Shading stress significantly increased apparent exportation and apparent exportation rate.I-JR had stronger dry matter accumulation ability than IR,but the photosynthetic compounds accumulated in stems and leaves before anthesis had a poor ability to export to grains.The study on the dry matter distribution ratio of panicle showed that shading after FL reduced the dry matter distribution ratio of panicle,and the reduction range of I-JR was significantly less than that of IR.In general,I-JR still had strong dry matter accumulation,transport and distribution capacity under shading.(3)There were significant differences in RUE of rice varieties at the grain filling stage under shading.Compared with IR,I-JR had higher and more stable RUE at grain filling stage.Shading after FL reduced RUE of different type of rice.The average RUE of I-JR decreased by 26.5%,while that of IR decreased by 71.7%.Through the correlation analysis between grain yield and RUE of rice under shading after FL,compared with IP(R2=0.0005)increasing the interception of photosythetically active radiation(R2=0.50)of I-JR could alleviate the yield loss caused by shade stress.(4)Shading increased nitrogen accumulation in various organs,and the increase of nitrogen in various organs of IR was significantly greater than that of I-JR.There were significant differences in the changes of soluble sugar in stems and leaves of different types of rice under shading.The soluble sugar content in stems of I-JR decreased by 11.3%,while that of IR increased by 18.8%;Shading significantly reduced the soluble sugar content in the leaves of IR,but had no significant effect on I-JR.Shading increased the activities of glutamate synthase and nitrate reductase,decreased the activities of sucrose synthase and sucrose phosphate synthase,and the activities of various enzymes in I-JR were less affected by shading.Shading stress delayed the senescence rate of rice leaves,but significantly reduced the net photosynthetic rate(Pn)of rice.The Pn of I-JR decreased by 20.2%and that of IR decreased by 32.1%in 2019-2020.The changes of stomatal conductance(Gs)and specific leaf weight(SLW)were consistent with the net photosynthetic rate,which were lower than normal,and the decline of I-JR was less than that of IR.I-JR had more stable carbon and nitrogen metabolism and photosynthetic characteristics than IR.(5)Shading caused the decline of rice appearance and processing quality.The content of nitrogen increased significantly,the content of carbon decreased significantly,the content of amylose in rice decreased,the protein increased,and the eating quality decreased.Shading after FL significantly reduced rice grain yield and quality,but there were significant differences among varieties.The shading tolerance of I-JR was significantly better than that of IR.By analyzing the correlation between the characteristics of RUE and rice quality traits of different types of rice varieties,it was found that compared with IR,I-JR had stronger correlation between the characteristics of RUE and rice quality.