Effects Of Nitrogen Managements On Lodging Resistance Of Direct-seeded Rice And QTL Analysis For Lodging Resistance-Related Traits Of Rice

Lodging in rice production is a major problem that results in decreased grain yield and deteriorated grain quality.Direct-seeded rice(DSR)is a traditional rice cultivation method,which leaves out the tedious nursery and transplanting work of transplanted rice.Although DSR alleviates the current situation of agricultural labor shortage,the occurrence of lodging has always been an important factor restricting the development of direct seeding in rice production.The continuous heavy rainfall is often accompanied in the late rice growing seasons due to the special ecological conditions in Sichuan,which is easy to cause a large area of rice lodging.In addition,the current nitrogen management adopted in DSR is mostly the same as that in transplanted rice.It is still unclear whether nitrogen management in transplanted rice can meet the needs of the growth and development of DSR.Thus,it is necessary to further clarify the difference in lodging resistance related traits between DSR and transplanted rice,and the difference in lodging resistance of DSR among the different nitrogen management,and the closely related traits to lodging resistance of DSR.Then,the quantitative trait loci(QTL)of traits related to lodging resistance of rice were identified by using the quantitative genetics research methods,which lay a foundation for the discovery and identification of related control genes.It is expected to provide new ideas for breeding high yield and quality rice varieties with strong lodging resistance.In this study,two indica hybrid rice with large difference in lodging resistance varieties(F-you-498 and De-you-4923)were used as materials to study the effects of nitrogen managements on the dry matter production capacity,nitrogen absorption and utilization capacity,lodging resistance and yield components of DSR,and to illuminate the major factors of culm lodging in DSR.In addition,the difference in the traits related to lodging resistance of two high-yielding rice varieties between DSR and transplanted rice was systematically compared.Finally,two recombinant inbred lines(RILs)constructed by parents with different genetic backgrounds were used as materials to identify the QTLs associated with lodging resistance in rice under DSR or transplanted rice.The main results are as follows:1.Two different indica hybrid rice varieties were used to compare the effects of nitrogen managements on the dry matter production capacity,nitrogen absorption and utilization capacity,lodging resistance,grain yield and its components of DSR.The results showed that hybrid rice F-you-498 had a higher dry matter accumulation in each organ and the total dry matter accumulation of the rice plants,redistribution amount of pre-anthesis stored dry-matter from vegetative organs to grain(RPG),percentage of redistribution of reallocated pre-anthesis stored dry-matter from vegetative organs to grain(PRPG),contribution of RPG to grain yield(CRPG),nitrogen accumulation in each organ and the total nitrogen accumulation of the rice plants,nitrogen transport capacity of stem(sheath)and leaf,nitrogen use efficiency for biomass production(NUEBP),nitrogen use efficiency for grain production(NUEGP),apparent nitrogen recovery efficiency(ANRE),and partial factor productivity for applied nitrogen(PFPAN)than hybrid rice De-you-4923.Moreover,the effective panicle number and filled grain number per panicle of F-you-498 were 4.92%?13.53%and 12.25%?13.53%higher than that of De-you-4923,respectively,which turn out the grain yield of F-you-498 increased by 1.97%?3.88%.However,the nitrogen harvest index(NHI),agronomic nitrogen use efficiency(ANUE),physiological nitrogen use efficiency(PNUE)and soil nitrogen dependent rate(SNDR)of hybrid rice De-you-4923 were higher than that of hybrid rice F-you-4923.In addition,compared to hybrid rice De-you-4923,F-you-498 in DSR had the higher bending moment at breaking(M),bending stress(BS),lignin content,cellulose content,hemicellulose content and non-structural carbohydrates content(NSC),the lower plant height,gravity center height,fresh weight from broken point to panicle top and length from broken point to panicle top,the shorter internode length of culm,which makes hybrid rice F-you-498 have strong lodging resistance in DSR.With the increase of nitrogen application level or the earing nitrogen application,the dry matter accumulation in each organ and the total dry matter accumulation of rice plant,RPG,PRPG,CRPG,the nitrogen accumulation in each organ and the total nitrogen accumulation of rice plant at the maturity stage,filled grain number per panicle and grain yield of hybrid rice in DSR mostly showed an increase first and then decrease,while nitrogen translocation amount,nitrogen translocation efficiency and the conversion rate of nitrogen translocation of stem(sheath)and leaf,the length of the basal internode,bending moment of the whole plant,the fresh weight from broken point to panicle top,the length from broken point to panicle top and lodging index were increased,and the bending moment at breaking of lower part of plant,section modulus,bending stress,the internode length of upper part of plant,the outer diameter of the major axis,the outer diameter of the minor axis,the inner diameter of the major axis,the inner diameter of the minor axis,culm diameter,lignin content,cellulose content,hemicellulose content and NSC were decreased However,the thickness of the cell wall showed no significant differenceFurthermore,the increase in nitrogen application level could also improve the effective panicle number but decrease nitrogen absorption efficiency and seed-setting rate of hybrid rice in DSR.With the increase of the earing nitrogen fertilizer,the NUEBP,NUEGP,PNUE,and SNDR showed a decrease first and then increase which contrary to the PFPAN,ANUE,ANRE and seed-setting rate.Taken together,the lodging resistance of culm of DSR under nitrogen management was mainly related to the bending moment at breaking(M),the fresh weight from broken point to panicle top,the gravity center height,the length of the basal intenode and plant height.In this study,both the nitrogen application level in DSR for hybrid rice F-you-498 and De-you-4923 at 150 kg/hm2 with the nitrogen applicated as earing fertilizer were 40%and 20%,respectively,which could obtain a higher grain yield,strong lodging resistance,and higher nitrogen absorption and utilization capacity.2.By comparing the difference in the traits related to lodging resistance between DSR and transplanted rice,the results showed that there were significant differences in culm breaking-type lodging,culm bending-type lodging and root-type lodging between DSR and transplanted rice.Moreover,the lodging resistance of DSR was inferior to that of transplanted rice.Compared with transplanted rice,the bending moment at breaking(M),section modulus,bending stress,flexural rigidity,the secondary moment of inertia,Young's modulus and pushing resistance of the two high-yielding rice varieties was smaller in DSR.Further analysis of culm morphology traits showed that the lodging resistance of DSR was inferior to that of transplanted rice mainly due to the elongated basal internode,the decrease of root number per stem,the decreased area of large vascular bundle and thickness of mechanical tissue,lignin content,cellulose content,hemicellulose content.3.QTL analysis for lodging resistance related traits in rice using two different RILs populations showed that five and nine QTLs associated with culm length,section modulus,outer diameter of the major axis,outer diameter of the minor axis,inner diameter of the major axis,cross sectional area and hemicellulose content in F6 and F7 populations derived from a cross between two high-yielding and superior lodging resistant rice cultivars Tachisugata and Hokuriku 193 under transplanted rice condition,respectively.Six QTLs control flag leaf angle,flag leaf length,flag leaf width,and flag leaf area,and seven QTLs related to spikelet number of secondary branch number,spikelet number per panicle,panicle number and grain width were also identified using the F7 populations.Interestingly,one stable QTL for the section modulus and the outer diameter of the major axis was detected on chromosomes(Chrs.)2 in both the F6 and F7 population,and the positive allele was derived from Tachisugata,which was also identified to control flag leaf length,spikelet number of secondary branch number and spikelet number per panicle.In addition,a total of 17 QTLs associated with lodging resistance were detected on Chrs.1,3,4,5,6,7,8 and 11 in an F5 population derived from a cross between Nekken 2 and Hokuriku 193 under DSR condition.Moreover,one QTL simultaneously control pushing resistance,the inner diameter of the major axis and inner diameter of the minor axis was identified on Chr.8,and the positive allele was derived from Hokuriku 193.In conclusion,the pleiotropic QTL detected on Chr.2 in transplanted rice and the QTL cluster detected on Chr.8 in DSR were expected to simultaneously improve several related traits of lodging resistance in rice,which lay a foundation for further research on the key genes that may be related to lodging resistance,leaf and panicle traits in rice,and the genetic mechanism of lodging resistance and high grain yield in rice.