Rice Varieties With Synergy Between High Yield And High Quality And The Underlying Mechanism

Rice is the staple food for more than half of population in China,continuous increase in rice production is important to ensure national food security.Furthermore,the demand of quality rice ha substantially increased due to population growth and changing debit.Although rice self-sufficient has been successfully achieved in China,in which the production of quality rice is relatively low and insufficient for growing demand in the future.There is an urgent need to simultaneously achieve high grain yield and rice quality,i.e.yield-quality synergy（YQS）,for the improvement of the productivity of quality rice.However,limited information was available on the approaches to achieving YQS and related agronomic mechanism.Therefore,the study was conducted in 2020 and 2021using the major rice varieties with high quality from various regions in China,including inbred rice varieties Yuzhenxiang,Meixiangzhan2,Huangkexiang1,Xiadao1,Efengsimiao（EFSM）,Ezhong5,and Huanghuazhan（HHZ,check variety）,and hybrid rice varieties Quanyouefengsimiao,Jingliangyou534（JLY534）,Longliangyouhuazhan,Quanliangyouefengsimiao,and Yangliangyou6（YLY6,check variety）.The objectives of this study were to select suitable varieties with high grain yield and quality,and clarify the mechanism for achieving YQS in rice by comparing the grain yield,rice quality,lodging resistance,and nitrogen（N）use efficiency of different varieties.This work will provide an insight for the breeding and cultivation of rice varieties with high yield and quality.The main results are as follows:（1）The highest grain yield of 9.07 t ha^-1and 8.77 t ha^-1were obtained in EFSM and JLY534 among inbred and hybrid rice varieties,respectively,which were 10.9%and11.0%higher than that of check variety,respectively.Yield improvement of EFSM and JLY534 were mainly attributed to improved spikelets m^-2due to the increase in spikelets panicle^-1and panicles m^-2in comparison with check variety,respectively.On average,the spikelets m^-2of EFSM and JLY534 were 16.4%and 33.0%higher than that of check variety,respectively.Furthermore,EFSM and JLY534 exhibited higher total dry weight（TDW）and harvest index compared with check variety.There were significant and positive correlations of grain yield with spikelets m^-2,TDW,and harvest index.Therefore,the increase in spikelets m^-2,TDW,and harvest index were critical to improve the grain yield of quality rice varieties.（2）Increasing post-heading dry matter weight associated to higher crop growth rate mainly contributed to the increase in TDW of EFSM and JLY534 at maturity.Correlation analysis revealed that grain yield significantly and positively correlated with crop growth rate in post-heading.Furthermore,there was a significant quadratic correlation between grain yield and leaf area index at heading,indicating that grain yield only increased with the increase in leaf area index within a suitable range,and much higher leaf area index could not contribute to the further increase in grain yield of quality rice varieties.（3）The lodging index（LI）of EFSM and JLY534 were 88.4%and 94.1%,which was significantly lower than or comparable to check variety（83.7%and 135.5%）.Lower LI of EFSM and JLY534 were mainly due to the increase in breaking resistance and the decrease in bending moment,respectively.Furthermore,the length of N4 internode of EFSM and JLY534 was lower than that of corresponding check variety,which was also responsible for relatively lower LI of EFSM and JLY534.Correlation analysis showed that LI was significantly and positively correlated with the length of N4 internode and plant height,implying that the reduction of the length of N4 internode and plant height improved the lodging resistance of quality rice varieties.In addition,hybrid rice resulted in no significant difference in LI from inbred rice,which was primarily attributed to higher breaking resistance and bending moment of hybrid rice than inbred rice.（4）For the rice quality,EFSM had higher head rice rate and lower crude protein content than HHZ among inbred rice varieties.Similarly,JLY534 exhibited higher head rice rate and lower chalky rice rate,chalkiness,amylose content,and crude protein content than YLY6.The rice quality of EFSM and JLY534 achieved 3^rddegree or above according to the standards of NY/T 593-2013（2013）‘quality edible rice’,which were better than other varieties.In addition,compared with inbred rice,hybrid rice exhibited higher processing quality but lower appearance quality,and slight differences in cooking and nutrient quality were observed between them.（5）The N use efficiency for grain production（NUE_g）of EFSM and JLY534significantly increased by 14.2%-14.9%and 11.7%-17.1%compared with HHZ and YLY6,respectively.However,no significant differences were observed in total N uptake and N harvest index between EFSM and HHZ and between JLY534 and YLY6.Correlation analysis showed that there was a significant quadratic correlation between grain yield and NUE_g.Furthermore,all of head rice rate,amylose content,and crude protein content were significantly correlated with NUE_g.These results suggest that NUE_gcould be used for the evaluation of the ability of YQS in rice.In present study,the suitable NUE_gfor maximizing YQS ranged from 41.2 kg kg^-1to 47.7 kg kg^-1,which was confirmed by the fact that the NUE_gof EFSM and JLY534 suitable for achieving YQS were also in this range.In conclusion,EFSM and JLY534 exhibited better comprehensive performance in grain yield,lodging resistance,and rice quality in comparison of other varieties among inbred and hybrid rice,respectively,which were suitable varieties for achieving YQS.Furthermore,NUE_gis closely related to grain yield and rice quality,and can be used as an effective indicator to evaluate the ability of YQS,and the increase in NUE_gwithin suitable rage is critical to improve the ability of YQS in rice.