| In recent years,with the simultaneous promotion of structural reform of agricultural supply side and agricultural green development,the demand for rice varieties with high yield,high nitrogen efficiency and good quality is increasing.The eastern region of Jianghuai mainly includes Jiangsu,Anhui,Henan,Shanghai and other regions.It is the main planting area of medium-maturity japonica rice,also the important grain production base and grain net output area in China.Therefore,it is of great significance for guiding rice variety selection,ensuring food security and meeting people's needs to carry out research on the morphological and physiological characteristics of good quality,high grain yield and high nitrogen efficiency varieties of medium-maturity japonica rice in the eastern region of Jianghuai.Based on this,field experiments were conducted using 90 and 105 medium-maturity japonica rice varieties(lines)in 2017 and 2018 in this study,the differences of grain yield,nitrogen efficiency and rice quality among different varieties(lines)and their relationships were analyzed,and the varieties(lines)with good quality,high grain yield and high nitrogen efficiency were selected from the tested varieties(lines)based on taste value,grain yield and the comprehensive evaluation value of nitrogen efficiency,and then the morphological,dry matter production and accumulation,nitrogen uptake and transport,leaf photosynthesis,and physiological characteristics of carbon and nitrogen metabolism of varieties(lines)with good quality and high grain yield and high nitrogen efficiency were studied in 2018 and 2019.The results showed that:1.There were significant differences in grain yield,nitrogen efficiency and rice quality among medium-maturity japonica rice varieties(lines)in the eastern region of Jianghuai.The grain yield of the highest product variety(line)was 44.85%(2017)and 50.73%(2018)higher than that of the lowest yield variety(line).The differences of nitrogen agronomic efficiency(NAE)and nitrogen physiological efficiency(NPE)among tested varieties(lines)were great,and their coefficients of variation were more than 20%.The differences of nitrogen grain yield production efficiency(GYE)and nitrogen dry matter production efficiency(DME)among tested varieties(lines)were small,and their coefficients of variation was below 5%.The variation range of head milled rice rate was 39.22%?74.86%,and the mean value was 63.89%(2017)and 58.14%(2018),respectively.The variation range of chalkiness degree was 1.57%?46.07%,and the mean value was 9.75%(2017)and 9.89%(2018),respectively.Nearly 40%of the varieties(lines)had amylose content(AC)below 14%,but their taste value was generally higher than that of the varieties(lines)with amylose content above 14%.Correlation analysis among grain yield,nitrogen efficiency and rice quality showed that spikelet per panicle and grain yield were significantly positively correlated with panicle dry matter accumulation,total dry matter accumulation,nitrogen recovery efficiency(NRE),NAE,NPE,DME and GPE in both years,indicating that grain yield and nitrogen efficiency could achieve synergistic improvement.AC had no significant correlation with grain yield and its components,and nitrogen efficiency.However,PC was negatively correlated with spikelet per panicle,grain yield,dry matter accumulation in organs at maturity,and some of the correlations reached significant or extremely significant levels.The results indicated that the selection and improvement of AC had no effect on grain yield and nitrogen efficiency and could be carried out simultaneously.2.Based on the entropy weight fuzzy synthetic evaluation method,NRE,NAE,NPE,DME and GYE were taken as the evaluation indexes of nitrogen efficiency,and the comprehensive evaluation value of nitrogen efficiency(CEV)of each variety(line)was calculated.Then,the grain yield-nitrogen efficiency index(GYNEI)was calculated by using CEV and grain yield.According to the GYNEI,the tested varieties(lines)were divided into three types by used the method of cluster analysis:high grain yield and high nitrogen efficiency type(HGHNE),middle grain yield and middle nitrogen efficiency type(MGMNE),and low grain yield and low nitrogen efficiency type(LGLNE),According to the screening results,23 and 27 varieties(lines)were divided into HGHNE in 2017 and 2018,respectively,and 19 varieties(lines),such as Nanjing9108,Nanjing5718,Ningjing7,Sidaol5,Yangjing239 and so on,were classified into HGHNE in both years.In addition,compared with the LGLNE,HGHNE showed the characteristics of larger biomass,more spikelet per panicle,higher nitrogen uptake,especially higher panicle nitrogen uptake.3.The differences of rice quality between HGHNE and LGLNE were compared and analyzed.The results showed that:there was no significant difference in milling quality between HGHNE and LGLNE,however,the rice chalkiness of HGHNE was better than that of LGLNE,and the chalky degree of HGHNE was significantly lower than that of LGLNE.The protein content of HGHNE was significantly lower than that of LGLNE,but there was no significant difference in amylose content and rice taste value between HGHNE and LGLNE.Based on the taste value,varieties(lines)with good eating quality were screened from HGHNE and LGLNE by systematic clustering method.According to the classification results,rice varieties(lines)with good eating quality,high grain yield and high nitrogen efficiency mainly included Nanjing 5718,Nanjing 9108,Su 1795,Nanjing 5711 and so on.In addition,the classification results also showed that the varieties(lines)with good eating quality were dominated by the soft rice type under both HGHNE and LGLNE.Therefore,choosing soft rice varieties under HGHNE is an effective way to achieve synergistic improvement of grain yield,nitrogen efficiency and eating quality in this region.4.The differences in plant morphology,dry matter production and accumulation,nitrogen uptake and transport,leaf photosynthesis,carbon and nitrogen metabolism between HGHNE varieties and LGLNE varieties under the types with good quality were compared and analyzed in 2018-2019.The results showed that:(1)Among the varieties with good quality,compared with LGLNE,the tiller number per unit area of HGHNE was not superior,but its productive tiller rate was significantly higher than that of LGLNE.Leaf area index at key growth stages,high effective leaf area ratio,top three leaves widths,and single stem-sheath weight of HGHNE increased significantly.Before elongating,there was no significant difference in dry matter accumulation between HGHNE and LGLNE.After elongating,HGHNE began to show their advantages of dry matter accumulation due to their higher leaf area index,higher population growth rate and lower decreasing rate of leaf area.The dry matter accumulation dynamics of HGHNE showed the characteristics of "stable in the front,increase in the middle and high in the back".The stem and leaf dry matter transfer amount of HGHNE was significantly higher than that of LGLNE during the grain filling period,which may be one of the reasons for HGHNE to have a higher proportion of dry matter allocation in panicle.Correlation analysis showed that dry matter accumulation,stem and leaf dry matter transfer,population growth rate,leaf area index,leaf length and leaf width of efficient leaves were positively correlated with grain yield,nitrogen efficiency index and taste value.(2)Among the varieties with good quality,compared with LGLNE,the nitrogen absorption rate of HGHNE had a significant advantage after elongating,which made the total nitrogen accumulation at heading and maturity stage significantly higher than that of LGLNE.Due to the higher nitrogen transport amount and efficiency of stem and leaf,the nitrogen distribution ratio of stem and leaf at maturity stage of HGHNE was significantly lower than that of LGLNE,while the nitrogen distribution ratio of panicle was significantly higher than that of LGLNE.HGHNE can maintain higher nitrogen absorption rate and amount during grain filling stage,which can be directly transported to panicle,so that the contribution rate of nitrogen transfer from stem and leaf to grain nitrogen increase was lower than that of LGLNE.Correlation analysis showed that the amount and proportion of nitrogen accumulation at heading and maturity stage,the amount and rate of nitrogen transport in stem and leaf were positively correlated with grain yield,nitrogen efficiency index,and taste value.(3)Among the varieties with good quality,the SPAD value of flag leaf of HGHNE was higher than that of LGLNE at each period after full heading stage,and the SPAD value of leaves of HGHNE was significantly higher than that of LGLNE at 30d and 40d after full heading stage due to the longer decreasing period of chlorophyll content of HGHNE.Compared with LGLNE,HGHNE had higher net photosynthetic rate,especially in the middle and late stage of grain filling period,also had a longer duration of high value of photosynthetic rate.(4)Among the varieties with good quality,the activities of ribulose 1,5-bisphosphate carboxylase(Rubisco)and sucrose phosphate synthase(SPS)of HGHNE were higher than those of LGLNE at all stages after heading.The activities of sucrose synthetase(SS)of different grain yield and nitrogen efficiency types was significantly different from 30 days after heading,and the activity of HGHNE was higher.There was no significant difference in the activity of sucrose decomposing enzyme(SD)between HGHNE and LGLNE.The activities of nitrate reductase(NR),glutamate synthase(GOGAT)and glutamine synthase(GS)involved in nitrogen metabolism increased firstly and then decreased during the filling period,and the activities of the three nitrogen metabolism enzymes of HGHNE were higher than those of LGLNE at each stage after heading.In conclusion,there were significant genotypic differences in grain yield,nitrogen efficiency and rice quality of medium maturity japonica rice in the eastern region of Jianghuai.Among the soft rice types,choosing the varieties with larger biomass and more grains per panicle is an effective way to realize synergistic improvement of grain yield,nitrogen efficiency and rice quality in this region.Higher single stem-sheath weight,larger efficient leaf width and smaller efficient leaf angle,higher leaf area index and higher ratio of efficient leaf area were the important morphological characteristics of medium maturity japonica rice varieties with good quality,high grain yield and high nitrogen efficiency.However,the important physiological characteristics of medium maturity japonica rice varieties with good quality,high grain yield and high nitrogen efficiency mainly showed that they had higher photosynthetic rate and nitrogen absorption rate during grain filling stage,which could promote photosynthetic production and nitrogen absorption.At the same time,they had higher activities of key enzymes of carbon and nitrogen metabolism,such as SPS,SS,GOGAT and GS,which promotes the efficient transfer and reuse of carbon and nitrogen from vegetative organs to panicle. |
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