| The experiment was conducted at the potting field of Yangzhou University College of Agriculture(1.19°22′ 22.688 ′E,32 ° 26 ′ 1.733 ′N)in 2020-2021.Nanjing 9108 and Fengjing 1606 were used as test materials and planted in pots.Four treatments of high temperature and drought combined stress(HD),high temperature conventional water management(HC),normal temperature drought(CD)and normal temperature conventional water(CK)were set up from 1 to 20 days after heading.The effects of high temperature and drought combined stress on rice yield and its components,panicle characteristics,dry matter production,leaf photosynthetic characteristics,chlorophyll fluorescence characteristics,rice quality and starch physicochemical properties were studied in order to provide theoretical reference for high yield and high quality stress resistance cultivation of high quality rice.The main results are as follows:1.The number of panicles per pot,1000-grain weight,seed setting rate,yield,harvest index and the number of filled grains,filled grain weight,1000-grain weight and seed setting rate on primary and secondary branches showed HD<HC<CD<CK among all treatments,the number of grains per panicle and the proportion of filled grains and the proportion of filled grain weight on primary branches showed the opposite trend,yield,seed setting rate and the seed setting rate on primary and secondary branches were significantly different among all treatments,1000-grain weight and the number of filled grains,filled grain weight on primary and secondary branches was not significantly different between HD and HC,but both of them were significantly different from CD and CK.In addition,the direct and indirect coefficients of grain indexes on primary branch to rice yield were greater than those on secondary branch,and the direct and indirect effects of grain weight on primary branch on yield were the largest.The above-ground dry matter accumulation of each treatment at different periods after heading showed HD<HC<CD<CK,and the dry matter accumulation of the two varieties increased fastest at 10-20 days after heading,and the increase was gentle at 30-50 days after heading.The dry matter accumulation rate of panicle under each treatment decreased with the delay of time after heading and had the greatest influence on 1-20 d after heading,which was HD<HC<CD.Among them,the difference between HD and HC treatments was not significant and was extremely significant with CD and CK,and most of the differences between CD and CK were not significant.In 2020,HD treatment was significantly or extremely significantly lower than CK at 21-30 days after heading,and there was no significant difference between 30-50 days after heading in each stress during the two years.The dry matter transport,transport rate and contribution rate after heading showed the tread of HD<HC<CD<CK among different treatments.The difference between CD and CK was extremely significant,and both were extremely significant with HD and HC,but the difference between HD and HC was not significant.2.At each stage of the filling stage after the beginning of the treatment,the SPAD value of the flag leaf was increased by the three stress treatments.At 30 days and 40 days after heading,the overall trend among the treatments was HD>HC>CD>CK.There was no significant difference between HD and HC,but both of them were significantly different from CD and CK.There was no significant difference between the stresses at other times.From the perspective of photosynthetic indicators,the net photosynthetic rate(Pn),stomatal conductance(Gs),intercellular CO2 concentration(Ci),and transpiration rate(Tr)of the flag leaf decreased over time.The performance between different stress treatments was HD<HC<CD<CK.Among them,there is significant difference between HD and HC on Pn,and both treatments have significant differences compared to CD and CK,and most of CD and CK also have significant differences.From the perspective of stress effect among varieties,under the combined stress of high temperature and drought,the net photo synthetic rate of flag leaves of Nanjing 9108 decreased more than that of Fengjing 1606.At 10 days after heading,Gs was significantly different between HD and HC,and was significantly different from CD and CK.There was no significant difference between CD and CK,but Ci and Tr were not significantly different among treatments.At 20 d and 30 d after heading,there was no significant difference in Ci and Tr between HC and CD treatments,but there was significant difference between HC and HD.At 40 d and 50 d after heading,there was no significant difference between HD and HC treatments,both of them were significantly different from CD and CK,and there was no significant difference between CD and CK.From the perspective of fluorescence parameters,the maximum photochemical efficiency of PSⅡ(Fv/Fm),the actual photochemical quantum efficiency of PSⅡ(Y(Ⅱ))and the photochemical quenching coefficient(qP)of flag leaf decreased with the growth period,and the performance among different treatments was HD<HC<CD<CK.There were significant differences between HD and HC,and both of them were were extremely different between CD and CK.Compared with Nanjing 9108,Fengjing 1606 decreased more slowly.The non-photochemical quenching coefficient NPQ of flag leaves in each treatment after heading showed a trend of increasing first and then decreasing,reaching a peak at 30 days after heading,and showing HD>HC>CD>CK among different treatments.the difference between HD and HC was significant,the difference between the two treatments and CK was significant,and the difference between HC and CD was not significant.The NPQ coefficient of Fengjing 1606 was significantly higher than that of Nanjing 9108.3.The brown rice rate,milled rice rate and head rice rate showed HD<HC<CD<CK among different stress treatments.The head rice rate was significantly different among different stress treatments.The difference of brown rice rate and milled rice rate between CD and CK was not significant,both were significantly or extremely significantly different from HD and HC,and there was no significant difference between HD and HC.The chalkiness rate,chalkiness size and chalkiness degree showed HD>HC>CD>CK.Among them,the difference between HC and CD was not significant,both were significantly different from HD,and the three were significantly different from CK.All stress treatments reduced gel consistency,amylose content and taste value,and there was no significant difference between CD and CK in most indexes,but significant difference between CD and HD,HC.From the texture characteristics of rice,the hardness value of rice under each stress treatment was HD>HC>CD>CK,and the elasticity and viscosity showed the opposite trend.There was no significant difference in taste balance value among the three stress treatments,but they were significantly lower than CK.There were significant or extremely significant differences in hardness among all treatments.There was no significant difference in elasticity and viscosity between HD and HC,but extremely significant difference with CD and CK.There was no significant difference in elasticity and viscosity between CD and CK.It can be seen that stress leads to deterioration of texture characteristics,with the greatest impact of compound stress,followed by single high temperature.Each stress treatment increased the contents of gliadin,glutelin and total protein,which showed HD>HC>CD>CK among different treatments.The total protein content was significantly or extremely significantly different among different treatments.There was no significant difference in the contents of gliadin and glutelin between HD and HC,which were significan tly or extremely significantly different from CD and CK,there was no significant difference in albumin and globulin among different treatments,gliadin and glutelin were greatly affected by stress.The peak viscosity,hot paste viscosity,final viscosity,disintegration value and peak time showed HD<HC<CD<CK among different stress treatments,and the reduction value and gelatinization temperature showed the opposite trend.HD and HC were significantly different from CD and CK.Among them,HD and HC were significantly different in some treatments.The difference between CD and CK was not significant in most of treatments.4.The gaps and voids between starch granules treated with HD and HC were significantly larger than those treated with CD and CK.Although the starch granules treated with CD were still compact,there were obvious holes,cracks and irregular shapes.There was no significant difference in starch granule size ratio and average particle size between HD and HC treatments.Compared with CD and CK,the proportion of large starch granules and average particle size were significantly increased,and the proportion of small and medium granules was significantly reduced.Except Fengjing 1606 in 2020,there was no significant difference in starch granule size ratio and average particle size between CD and CK.In the two years,the starch diffraction patterns of the two varieties under different treatments were all A-type,and each stress caused an increase in relative crystallization and at 1045/1022cm-1,which showed HD>HC>CD>CK among different treatments,1022/995cm-1 showed the opposite trend.There was no significant difference between HD and HC treatments,which was significantly or extremely significantly different from CD and CK,there was no significant difference between CD and CK.The swelling potential and solubility of good taste quality japonica rice starch increased under different stress treatments,and the order was HD>HC>CD>CK.The difference between HD and HC was significant or extremely significant,which was extremely significant compared with CK.Among them,the difference between the two and CD was also significant,and the difference between CD and CK was not significant.The thermodynamic properties of starch showed that the gelatinization enthalpy,initial temperature,peak temperature,termination temperature,retrogradation enthalpy and retrogradation value of different stress treatments were HD>HC>CD>CK.Except for the termination temperature,there was no significant difference in each index between HD and HC treatments.The initial temperature,retrogradation enthalpy and retrogradation value of HD and HC were significantly or extremely significantly different from those of CD and CK.Among them,HD was also significantly different from CK in the gelatinization enthalpy and peak temperature of the two varieties,and there were significant differences between CD and CK.The total starch content and amylose content between different stress treatments showed HD<HC<CD<CK,and the amylopectin content and the ratio of amylopectin to amylose showed the opposite trend.The total protein content of HD was significantly or extremely significantly different from that of CK which had no significant difference among the stresses.There was no significant difference between HD and HC in amylose content,amylopectin content and ratio of amylopectin to amylose.The difference between HD and HC was extremely significant or significant compared with CD and CK,and the difference between CD and CK was not significant. |
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