Difference In Response Of Grain Quality To Nitrogen Application Rates Among Japonica Rice Varieties And Its Causes

With the improvement in living standard,people need good rice quality for their better life.Fertilizer-nitrogen(N),as a key factor in rice production,plays an important role in the regulating grain quality.However,over-use of fertilizer-N accompanied by low N use efficiency(NUE)is a serious problem in the rice production of China,which could not only increase the production cost,but also pollute environment and reduce the grain quality.Breeding and selecting rice varieties with high yield,good quality and high NUE is an important way to develop rice production with green,high efficiency and good quality.To elucidate the difference in response of grain quality among Japonica rice varieties to N application rates(NARs)and its causes would have great significance in breeding and selecting rice varieties with high yield,good quality and high NUE.In this study,three Japonica rice varieties that differ in spikelet-forming abilities and are suitable for planting in Jiangsu Province were field-grown,with three NARs,0 kg N hm-2(0N),180 kg N hm-2(180N)and 360 kg N hm-2(360N),during the rice growing season,and the difference in response of grain quality among Japonica rice varieties to NARs and its causes were investigated.The main results are as follows.1.Difference in response of grain yield and NUE to NARs among Japonica rice varietiesThe grain yield of all test varieties was increased with the increase in NARs,but the increase varied with the varieties.From 0N to 180N,the grain yield was increased by 36.58%,45.09%,and 35.33%respectively,and from 180N to 360N,the grain yield was increased by 38.39%,17.99%,and 16.49%,respectively,for Yangfujing 8,Nanjing 9108,and Yongyou 2640.Although the yield of Yongyou 2640 was increased slightly after nitrogen application,the total spikelets and grain yield of Yongyou 2640 were the highest among the three varieties under the same nitrogen application rate.Among the three tested varieties,Yongyou 2640 showed the highest total N uptake,partial factor productivity of N,and N harvest index,but had a lower internal NUE under the high N application rate(3 60N).Under all NARs,the N uptake,partial factor productivity of N,internal NUE,and N harvest index of Nanjing 9108 were significantly higher than those of Yangfujing 8.Increasing NARs increased the N uptake,and decreased the agronomic NUE,partial productivity of N,internal NUE,and N harvest index for all the rice varieties.2.Difference in response of grain quality to NARs among Japonica rice varietiesAmong the three varieties,Yangfujing 8 had the best rice processing quality under the three NARs.Proper N application(180N)increased milled rice rate and head rice rate for Yangfujing 8,but had no significant effect on the processing quality of Nanjing 9108 and Yongyou 2640.Under all NARs,the chalkiness degree of Nanjing 9108 was the lowest,and that of Yongyou 2640 was the highest among the three varieties.The eating taste showed that Nanjing 9108>Yangfujing 8>Yongyou 2640.Proper N application(180N)improved the eating taste of Nanjing 9108,but less affected on that of Yongyou 2640 and Yangfujing 8.Under the three NARs,The content of essential amino acids of Yangfujing 8 was the highest under 0N,and that of Yongyou 2640 was higher under 180N or 360N than under 0N,while the difference in content of essential amino acids of Nanjing 9108 was not significant between 180N and 360N.The increase of N application increased contents of amino acids and proteins in the rice grain.Among the three varieties,Yongyou 2640 had the highest contents of microelements,such as B,Cu,Fe,Mn,Zn,in the grain under the three NARs.The contents of microelements of Yangfujing 8 were significantly lower than those of Nanjing 9108 under both 0N and 180N,but the contents of microelements of Yangfujing 8 were significantly higher than those of Nanjing 9108 under 360 N.Altogether,Nanjing 9108 had the characteristics of higher yield,better quality and higher NUE under a medium N application rate(180N)3.Difference in response of fine structure and physicochemical properties of starch to NARs among Japonica rice varietiesThe highest crystallinity,less starch disordered structure,lowest solubility and swelling were observed in Yangfujing 8,whreas the results were reversed in Nanjing 9108 at the same N rate.The increase of nitrogen application increased the crystallinity and decreased the starch disordered structure in Yangfujing 8 and Yongyou 2640 while Nanjing 9108 had the lowest crystallinity and more starch disordered structure.Nanjing 9108 had the highest breakdown and lowest setback value,the breakdown value of Yongyou 2640 was significantly higher than that of Yangfujing 8,but the setback value was reversed.The increase of nitrogen application decreased the breakdown value of Yongyou 2640 and Yangfujing 8 while increased the setback value.Furthermore,Nanjing 9108 had the highest breakdown value and lowest setback value at the N rate of 180 kg N hm-2.Yangfujing 8 had the highest enthalpy value while Nanjing 9108 had the lowest,whereas the tendency of mid-short chain content in amylopectin was reversed.The increase of nitrogen application increased the enthalpy value of Yongyou 2640 and Yangfujing 8 while decreased the mid-shour chain in amylopectin.Nanjing 9108 had the highest mid-short chain value and lowest enthalpy value at 180N level.Correlation analysis showed that mid-short chain in amylopectin was positively and significantly correlared with breakdown value,starch disorderes structure,solubility and swelling degree,negaticvely correlated with enthalpy value,setback value and crystallinity.The results suggested that the higher mid-shor chain in amylopectin accounted for the better cooking and eating rice quality in Nanjing 9108.4.Difference in response of dry matter production,activities of key enzymes involved in starch synthesis,and hormonal contents to NARs among Japonica rice varieties during grain fillingAmong the three varieties and under the three NARs,Yongyou 2640 had the highest dry matter accumulation,crop growth rate,and leaf area duration after heading.The above traits were higher for Nanjing 9108 than for Yangfujing 8 under 0N and 180N,but they showed no significant difference between the two varieties under 360N.Nanjing 9108 had the highest,whereas Nanjing 9108 had the lowest,activity of starch branching enzyme(SBE)during grain filling among the three varieties under all the NARs.A proper N application(180N)increased SBE activity of Nanjing 9108 and decreased SBE activity of Yangfujing 8 and Yongyou 2640.Under the three NARs and when compared with Yangfujing 8 or Yongyou 2640,Nanjing 9108 had a lower activity of adenosine diphosphate glucose pyrophosphorylase(ADPG)at the early grain filling stage.The ADPG activity was intermediate between Yangfujing 8 and Yongyou 2640 at the mid and late grain filling stages.The ADPG activity showed no significant difference between Yangfujing 8 and Yongyou 2640 in the early and middle grain filling stages,and it was higher for Yongyou 2640 than for Yangfujing 8 at the late grain filling stage.Under the three NARs,the activity of bound starch synthase(GBSS)was the lowest for Nanjing 9108,the highest for Yongyou 2640,and intermediate for Yangfujing 8.The activities of ADPG and GBSS were increased with the increase of N application for all the varieties.Under the three NARs and compared with either Yangfujing 8 or Yongyou 2640,Nanjing 9108 produced a lower content of abscisic acid(ABA)in the grain at the early and middle stages of grain filling,and a higher ABA content at the late stage of grain filling.The ABA content showed no significant difference between Yangfujing 8 and Yongyou 2640.Increase of N application decreased ABA content for all the varieties.Under the same N rate,the contents of cytokinin(zeatin+zeatin riboside)and indole 3-acetic acid(IAA)in the grain showed that Yongyou 2640>Nanjing 9108>Yangfujing 8,and they were increased with the increase of NARs.The activities of key enzymes in starch synthesis and the contents of Z+ZR and IAA in the grain during grain filling were closely associated with the grain quality traits,such as gel consitency,head rice rate,and contents of amino acids and proteins,indicating that the differences of hormonal contents and the activities of key enzymes in starch synthesis are the important physiological reasons for the difference of rice quality in response to NARs.