Combined Effects Of Low Temperature And Weak Light At Grain-filling Stage On Rice Yield And Grain Quality

The experiment was conducted in Crop Planting Physiology Laboratory,Yangzhou University in 2017-2018.The experiment sets potted plants and two rice varieties,Nanjing 9108 and Huaidao 14,were used as materials,Single low temperature,single weak light and low temperature and weak light combined stress were conducted at different time periods(1-7 d,8-14 d,15-21 d,22-28 d,29-35 d)during the grain filling stage.The study defined the effects of different treatments on rice yield,quality,photosynthetic physiological characteristics,activities of key enzymes in starch synthesis,and starch physical and chemical characteristics,in order to provide a reference for the stress-resistant cultivation and regulation of low temperature and weak light combined stress in grain filling stage of Jiangsu rice production.The main results were as follows:1.The yield between different treatments in all time periods after heading showed the trend of LW<LN<NW<NN,the difference between LW treatment and NN treatment was significant.The reason for the significant decrease in yield is the decrease in the 1000-grain weight and seed setting rate.For 1000-grain weight,1?7 d and 8?14 d after heading,LW treatment and LN treatment were significantly or extremely significantly lower than control treatment;after 14 days after heading,there was no significant difference between the stress treatments.The seeding rate decreased the most,in 2018,the japonica rice nanjing 9108 had 74.7%and 78.1%,and huaidao14 had 72.9%and 75.3%under LW treatment at 1-7 days and 8-14 days after heading,that low temperature,weak light and combined stress in the early stage of grain filling have a great influence on the seed setting rate,among which LW treatment has the greatest influence.From the characteristics of spike,The seed setting rate of the first and second branches is LW<LN<NW<NN,and the seed setting rate of the second branch is greatly affected,the LW treatment is significantly lower than the NN treatment in all time periods,and is significantly or very significantly different from the LN and NW treatments.Within 14 days after heading,NW treatment was significantly or extremely significantly lower than the control,and within 28 days after heading,LN treatment was significantly or extremely significantly lower than the control.Each stress treatment has influence both on the inserted filled grain number of primary and secondary branches,whose trend is in general accord with the seed setting rate of primary and secondary branches2.Each stress treatments at different time periods after heading all increased the chalkiness degree,chalkiness rate,and chalkiness size of the two varieties,and the performance was LW>LN>NW>NN between different treatments,among them,compared with the control,the difference of LW treatment was significant or extremely significant,and the difference of NW and LN treatment reached a significant level in some time periods.The stress treatment at different time periods reduced brown rice rate,milled rice rate,and head milled rice rate to different degrees,which made the processing quality worse,the degree of influence of LW treatment on the processing quality is head milled rice rate,milled rice rate and brown rice rate,of which the treatment within 21 days after heading has a greater impact.The LW treatment significantly or very significantly reduced the rice amylose content,gel consistency,appearance,viscosity and taste value,and significantly or very significantly increased the protein content and hardness,LN,NW treatment and LW treatment have the same trend.From the characteristic value of RVA spectrum,LW treatment and NW and LN treatments all cause the peak viscosity,trough viscosity and break down of rice to decrease,while final viscosity,set back and peak time increase.The results showed that single low temperature,single weak light and combined stress in different time periods after heading caused the rice quality to decrease to varying degrees,and the combined stress had a greater effect within 21 days after heading.3.At the end of the stress treatment at different time periods after heading,the SPAD values of flag leaves under different stress treatments showed LW<LN<NW<NN,and then the difference gradually decreased.Immediately after the stress treatment at different periods after heading,the net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO2 concentration(Ci),and transpiration rate(Tr)of flag leaves all showed a downward trend,showing LW<LN<NW<NN,and the treatment time passes,the difference gradually decreases,and the influence in the early treatment is greater.The LW treatment resulted in a marked increase in SOD enzyme activity in the flag leaves of the two varieties of rice in a short period of time,and decreased rapidly after returning to normal growth;The CAT activity of Nanjing 9108 showed a significant downward trend,Huaidao 14 significantly increased in the short term,and then decreased;the POD activity of two varieties of flag leaves was lower than NN from the end of stress to the maturity period,and the trend of different stress treatments was LW<LN<NW<NN.In the first two periods of grain filling(1-7 days,8-14 days after heading),the MDA content of the combined stress treatment continued to rise,and in the late grain filling(22-28 days,29-35 days after heading)MDA content has little effect.Single stress also basically has the similar rules,but the degree of influence is lower than combined stress4.During each period after heading,the activities of SSS,ADPG,and GBSS under NW,LN,and LW were lower than NN from the end of treatment to maturity.The decline degree of SSS,ADPG,and GBSS activities among the three stress methods showed the trend of LW>LN>NW,which were significantly different from NN,the effect of treatments during the first three periods after heading were greater,in the late two time periods,the enzyme activity of each stress treatment was little different from NN.At the end of each stress treatment during each period after heading,the DBE activity in grains increased,and that under LW increased most largely.However,from 7 d after the potted plants were restored to normal environment to maturity,the DBE activities in grains under NW,LN and LW were significantly lower than NN.LW,LN and NW treatment affected SBE activities in grains throughout the whole grain filling stage which were significantly higher than NN,LW affected most greatly among different stresses.In general,the combined stress at the grain filling stage decreased the activities of antioxidant enzymes in the flag leaf and SSS,ADPG and GBSS in grains and decreased the DBE activity after a brief rise,and increased SBE activity in grains,and it is not beneficial for starch synthesis and accumulation,especially LW during the first three periods after heading5.In structural characteristics,LW treatment starch granule development is not full,part of the starch is irregular and the surface of the starch has depressions.and within 21 days after heading,the effect was greater,it has little effect on single stress.Each stresses at different time periods after heading all caused a decrease in amylose content and an increase in amylopectin content and there was a significant difference between the total starch content of the LW treatment and the control in the first three stages after the heading,and the single stress was not significantly different from the control.LW,LN and NW treatment increased the content of large starch granules and decreased the content of medium and small granules of starch.The crystal structure of the starch remained unchanged in each treatment,but the relative crystallinity and the order degree of the surface layer of the starch increased.In starch gel properties,The different stress treatments at grain-filling stage increased the gelatinization enthalpy,retrogradation enthalpies and retrogradation percentage of starch,and the most obvious was combined stress.The starting temperature,peak temperature,and ending temperature of starch have a downward trend under stress treatments,and the basic performance is LW<LN<NW<NN.From the perspective of influence degree,the effect was larger within 21 days after heading,and the effect was the smallest from 29 to 35 days after heading.This study showed that low temperature and weak light combined stress and single stress at different time periods after heading can change the starch structural characteristics of rice,and then affect the physicochemical characteristics of starch,which will increase the aging tendency of starch and deteriorate the cooking quality and taste of starch.