QTL Analyses For Main Agronomy Traits Using Segregation Populations Derived From Different Maize Hybrids In China

Maize flowering time,plant height and kernel-related traits,not only mainly determine the grain yield,but are also associated with the adaptive of the hybrid to local climate factors.In the long term maize breeding,these agronomy traits have been main breeding targets that screened by breeders.Givenin their importance in maize development and production,researchers have conducted numerousof genetics and molecular studies in these traits on different levels.However,associated regulatory mechanisms underlying them werenot fully understood.Employing QTL mapping to dissect these important agronomy traits,will be in favor for identifying their possible regulatory genes.In the present study,seven elite hybrids in Chinese modern maize breeding were selected to construct RIL populations.Then,these seven RIL populations were used for identifying QTL for maize flowering time,plant height/ear heiht and kernel related traits.Additionally,a time-related QTL mapping method was employed to study the development of kernel-related traits in depth.1.In the present study,seven hybrids,including Zhongdan2,Danyu13,Yedan2,Yedan13,Pionner335,Zhengdan958 and Xundan20,were employed as the basic materials.And,GBS was used to genotype each line of the seven RIL populations.Then,the linkage maps,constructed by genotypic informations of the seven RIL populations,contain 2241～3217 reconbination bins withtotal length ranging from 1959.6～2781c M.Moreover,the genetypic data of seven populations is also used for constructing a joint map that can be employed for joint linkage mapping.2.Phenotypic analysis of the measured triats revealed that anthesis silking interval grandually reduced,and kernel weight and volume grandually tended to be stablewith the application period moving on.However,other traits measured in the seven RIL populations have not shown special trends.3.Using different QTL mapping methodologies,a great number of QTL were identified for days to anthesis,days to silking and anthesis silking interval,many of them distributing on chromosome 1,3,6,8,and 9.Compared the results of different mapping methods,several conserved QTL were identifed as major-effect QTL for flowering time traits,including Jq DA1-3,Jq DA2-2,Jq DA8-1,Jq DA10,Jq DS8-2,Jq DS9-2,Jq DS10 and Jq ASI9-2.Of them,Jq DA1-3and Bif2 were co-mapped at Bin1.06;Jq DA8-1 was consistent with two mutant genes that were mapped at Bin8.05;Jq DA10 and Jq DS10 wereconsistent with the location of zfl1 at Bin10.06.4.A certain number of QTL were detected for plant height and ear height by SLM and JLM QTL mapping,many of them clustered at several chromosomal regions,such as Bin1.05 ～ 1.08,Bin3.05,Bin3.06 ～ 3.07,Bin8.03 and Bin 8.06.Major effect QTL identified for plant height and ear height,Jq PH1-3,Jq EH1-3 and Jq EH8-2,all were consistent with QTL/genes for same traits reported in previous studies.Additionally,Jq EH1-5 and Dwarf8 were co-mappedwith the same chromosomal region at Bin1.09.5.For six kernel-related traits,a great deal of QTL were identified by SLM and JLM analysis,they distributed on the ten chromosomes of whole maize genome.And,a number of different methods conserved QTL were clustered at Bin1.08 ～ 1.10,Bin4.05 ～ 4.06,Bin5.03 ～ 5.04,Bin8.03 ～ 8.04,Bin10.02 ～ 10.03 and Bin10.06 ～ 10.07.Among the QTL identified at these hotspots,many of them were consistent with the QTL/genes for kernel-related traits reported in previous studies.Several QTL,Jq KL10-3,Jq KW10,Jq KV10-2,Jq KV10-3,Jq KT10-2and q KWID10-1,located at Bin10.06 ～ 10.07 were consistent with the locationsof QTL for kernel length and kernel density in previous studies.And,Jq KL4-3～4-7 have been uncovered in this study were consistent with the same locations of QTL for kernel weight,kernel density and kernel volume.In addition,our results imply that KD is largely determined by KW,not KV.6.Of the major-effect QTL detected for flowering time traits,the candidate gene of Jq DA10 encoding an F-box protein and Jq ASI9-2 encoding a NAD dependent epimerase/dehydrataseare probably two components in flowering regulatory network.An ear height major effect QTL,Jq EH1-3,whose candidate gene encodes Gibberellin 20 oxidase 2 that plays important role in GAssynthesis.And,GAs is an important plant hormone for plant height regulation.Of the major QTL for maize kernel-related traits,the candidate gene of Jq KL4-7 encodes an ubiquitin conjugating enzyme,whose orthologue in rice plays important roles in kernel weight and kernel width determination.And,the candidate gene of Jq KW4-2 encode a kind DCL chloroplast precursor,its rice orthologue takes part in copper ion metabolism pathway in photosynthesis.7.In time-related QTL analysis for kernel development,a great number of unconditional QTL at different kernel development stageswere uncovered for KW,KV and KD.Of them,q KW6 b,q KW7 a,q KW7 b,q KW10 b,q KW10 c,q KV10 a,q KV10 b and q KV7 were identified under multiple kernel developmental stages and environments.q KW7 a,q KW7 b and q KV7 weremapped at Bin7.02 ～ 7.03 with the QTL for grain filling rate,kernel weight and kernel desiccation rate in previous studies.And,q KW10 b,q KW10 c,q KV10 a,q KV10 b provided consistented locations at Bin10.06～10.07 with the QTL for kernel length,kernel weight,kernel volume and kernel width.8.In conditional QTL analysis,total of 26 QTL were identified for three developmental kernel traits.Of them,conq KW7 a,conq KV7 a,conq KV10 a,conq KD2,conq KD7 and conq KD8 a were conserved between the two mapping methodologies.Furthermore,most of these QTL were consistent with QTL and genes for kernel development/grain filling reported in previous studies.For example,conq KD2 provides same chromosomal location with mn1 and rgfl at Bin2.04 ～ 2.05.