Effects Of Low Temperature And Weak Light During The Early Grain Filling Stage On Yield And Quality And Starch Physicochemical Properties Of Rice

The experiments were carried out in the pot farm of Agricultural College of Yangzhou University,artificial Intelligence Climate Room and Liuyuan Village,Jiangdu District,Yangzhou in 2021 and 2022.Nanjing 9108 and Huidao 5 were used as experimental materials.In the pot experiment,the temperature gradient was set within 24 hours to simulate the dynamic decline of temperature during the early grain filling stage(from heading to 20 days after heading),the dynamic low temperature and weak light treatment were set during the early filling stage,and the outdoor temperature and light were used as CK.In the field experiment,by setting sowing date and shading after heading(from heading to 20 days after heading),different light and temperature compound treatments were formed during the early filling stage,which were CK,slight low temperature and weak light,low temperature and weak light.The purpose of this study was to study the effects of low temperature and weak light during the early filling stage on yield and its composition,dry matter production,rice quality,starch RVA profile characteristics,antioxidant enzyme activities and starch structure and characteristics of japonica rice,and to clarify the response characteristics of rice yield and rice quality to low temperature and weak light during the early grain filling stage,so as to provide theoretical basis and technical support for high yield and stress-resistant cultivation of japonica rice.The main results are as follows:1.Pot and field experiments showed that compared with CK,rice yield and seed setting rate decreased,1000-grain weight increased under low temperature and weak light treatment during the early filling stage,and 1000-grain weight decreased under low temperature and weak light treatment(the performance was different in two years in field experiment).In field experiment,1000-grain weight decreased significantly under low temperature and weak light treatment in 2021,and increased under low temperature and weak light treatment in 2022.In the field experiment,the yield decreased under the low temperature treatment of 2021 and increased in 2022.The effect of low temperature and weak light on the yield of the two varieties was greater than that of low temperature,and the total dry matter weight of rice decreased under low temperature and weak light treatment,mainly due to the decrease of panicle dry weight.The analysis of dry matter accumulation ratio of each organ showed that compared with CK,the proportion of stem and sheath accumulation in low temperature treatment and low temperature and weak light treatment increased,while that in panicle decreased.Low temperature and low temperature and weak light treatment during the early filling stage decreased the transport of stem and sheath dry matter to ear.2.Pot and field experiments showed that compared with CK,the processing quality and appearance quality of rice treated with low temperature during the early filling stage were better,while the processing quality of rice under low temperature and weak light treatment became worse.,and the appearance quality varied from year to year.Chalky grain percentage and chalkiness degree increased under low temperature and weak light treatment in 2021,while chalky grain percentage and chalkiness degree decreased slightly in 2022.Under low temperature treatment,amylose content increased,gel consistency decreased and protein content decreased.Under low temperature and weak light treatment,amylose content decreased,gel consistency decreased and protein content increased.Both treatments decreased the eating quality of rice.In the field experiment,the taste quality was different in the two years under light low temperature treatment.2021 young low temperature cooking quality decreased,while 2022 young low temperature treatment improved.3.The pot experiment showed that compared with CK,the SPAD values of 1st leaf,2nd leaf and 3rd leaf increased under low temperature and weak light during the early filling stage,which showed the order of low temperature and weak light>low temperature>CK.Compared with CK,the activities of CAT,POD and SOD in flag leaves of the two varieties increased at first and then decreased under low temperature and weak light treatment.MDA content increased continuously during the treatment period,showing that low temperature and weak light>low temperature>CK.With the passage of low temperature and weak light treatment time,H2O2 content increased,APX activity increased significantly.4.Pot and field experiments showed that compared with CK,the surface of starch grains was sunken,underdeveloped and irregular under low temperature and weak light during the early filling stage.Low temperature and low light did not change the crystal structure of rice starch in the early filling stage,compared with CK,the relative crystallinity,maximum scattering intensity,starch ordering,gel enthalpy,retrogradation enthalpy and retrogradation degree were decreased under low temperature treatment during the early filling stage,while the relative crystallinity,maximum scattering intensity,starch ordering degree,gel enthalpy,retrogradation enthalpy and retrogradation degree were increased under low temperature and weak light treatment.To sum up,under low temperature treatment,rice yield decreased,rice processing quality and appearance quality were improved,cooking and eating quality became worse,nutritional quality decreased,rice yield decreased under low temperature and weak light treatment.Rice processing quality,appearance quality and cooking and eating quality became worse,and nutritional quality improved.The relative crystallinity,maximum scattering intensity,starch ordering,gel enthalpy,retrogradation enthalpy and retrogradation degree were decreased under low temperature treatment during the early filling stage,while the relative crystallinity,maximum scattering intensity,starch ordering degree,gel enthalpy,retrogradation enthalpy and retrogradation degree were increased under low temperature and weak light treatment.