Genetic Dissection Of Major QTL Associated With Kernel Width And Kernel Weight In Maize

As an important crop for grain,economy and feed,maize occupies a crucial role in grain production and ensuring food security in the world.Kernel related traits in maize are important factors to determine yield of maize.Kernel related traits contain kernel length,kernel width,kernel thickness and hundred kernel weight,in which kernel length,kernel width and kernel thickness are strongly related to kernel size.Additionally,hundred kernel weight is closely related to kernel s ize.Therefore,it is essential to study the genetic mechanism of kernel width and hundred kernel weight,which has important theoretical value for high yield breeding by molecular design and the cultivation of excellent new varieties.In this study,a secondary separation population was developed by crossing B73（recurrent parent）with NIL-1041A（one of the near-isogenic lines from the B73×CML277 population）,which have significant difference in kernel-related traits.The major effective QTL qKW2.04 associated with kernel width and kernel weight was selected as target for fine mapping and analyzing the genetic basis of kernel traits in maize,providing soild theoretical support for the fine mapping of major loci.The main results are as follows:1.QTL mapping for kernel related traits in mazie based on high-density genetic map.Constructing RILs containing 182 recombinant inbred lines by crossing important inbred line B73and CML277,QTL were detected for kernel length（KL）,kernel width（KW）,hundred kernel weight（HKW）and kernel row number（KRN）.Based on GBS（genotyping-by-sequencing）technology,a high-density genetic map containing 2141 bin markers w as constructed,which was 1264.26 cM in linkage length,with an average interval of 0.59 cM between adjacent markers.Using the average value of multiple environmental phenotype,a total of 16 QTL were detected containing 2 QTL for KW,3QTL for KW,4 QTL for HKW and 7 QTL for KRN,and all the QTL distributed on chromosome 1、2、3、4、5、8、9、10,with phenotypic variation explanation from 3.58%to 23.36%by single marker.In addition,qKW-2-1 and qHKW-2-1 were mapped to the same interval（m1403-m1420）located in bin2.04on chromosome 2 with the LOD score 9.65 and 7.59 separately,and with PVE（phenotypic variation explanied）20.34%and 15.84%respectively.Therefore,bin2.04（m1403-m1420）on chromosome 2 was considered as an important interval for genetic dissection,and record qKW-2-1 and qHKW-2-1 as qKW2.04.2.Identification of introgressed segments in NIL-1041A and decomposition of major QTL qKW2.04High-density MaizeSNP50 chips were used to identify the chromosome segments that CML277introgressed into B73 in near isogenic line NIL-1041A,with B73 as the genetic background.Result showed that there were totally two introgressed segments distributing in chromosome 2 and chromosome 3,and the segment length were 182.63 Mb and 133.97 Mb,respectively.Using the ICIM（inclusive composite interval mapping）algorithm,the QTL analysis associated with KW and HKW was conduct in the F₂ separation population derived from B73×NIL-1041A.As the result showed,there were two major QTL detected in the introgressed segment on chromosome 2.Among the two major QTL,one consistent QTL flanking by InDel23.32-umc1448 associated with KW and HKW,with PVE from13.97%to 22.45%and synergistic variation originated from NIL-1041A.Another QT L flanking by InDel47.09-InDel57.06 associated with KW and HKW,with PVE 12.22%,and the synergistic variation of this QTL also originated from NIL-1041A.Furthermore,the two major QTL in introgressed segment mentioned above were all mapped to the bin2.04 on chromosome 2,with their PVE all greater than 10%.Thus,the first major QTL was recorded as qKW2.04-1,and the second major QTL was recorded as qKW2.04-2,and qKW2.04-1 and qKW2.04-2 will be the main loci for further genetic dissection.3.Genetic dissection for major QTL qKW2.04-1 and qKW2.04-2Continually constructing F₃-F₆ separation population derived from B73×NIL-1041A,dense markers were designed in the target region,and heterozygous individuals of the target region were screened for planting,meanwhile,the genetic background was also purified,apply ICIM algorithm to major QTL qKW2.04-1 and qKW2.04-2 for QTL analysis.Homozygous lines which span and overlap with each other in the target segment were constructed in F₇-F₈,apply group t test to major QTL qKW2.04-1 and qKW2.04-2 for QTL analysis.Finally,the major QTL qKW2.04-1 and qKW2.04-2 was limited to the interval of 4.13 Mb（InDel23.73-InDel27.86）and 3.18 Mb（InDel41.76-InDel44.94）,respectively.Based on the linkage analysis result,association analysis was applied to the target region through both GLM（general linear model）and MLM（mixed linear model）algorithm in association panel comprising 627 mazie inbred lines.As the result demonstrated,significant SNPs were only detected in major QTL qKW2.04-2.The possible reason was inferred that CML277 as one of the parent belonged to tropical maize,and the association panel belonged to temperate maize,resulting in the rare allele in tropical maize couldn’t be detected in the association panel.