NIL Development And Fine Mapping Of Three QTL For100-Grain Weight In Maize

Most of important agronomic traits in crops are quantitatively inheritedwith complex genetic basis. They are easily influence by environmental conditions.Followed with the completion of sequence for the whole maize genome, map-basedcloning has become one of the most important methods used in QTL cloning. Theconstruction of near-isogenic lines (NIL) and fine mapping of objective QTL is theprecondition for map-based cloning. In this stuty, three QTL-NILs for100-grainweight (qnpGW1, qqnpGW5and qnpGW7) were constructed using themarker-assisted selection (MAS) according to the primary QTL identified using theRIL population developed from the cross between a large grain maize inbred lineDan232and a small grain popcorn maize inbred line N04in our previous research.And qnpGW1and qnpGW7were fine mapped using the BC3F2populationsconstructed by the QTL-NILs, respectively. This result proved the primary mappedQTL for100-grain weight, and provided the important basis for further fine mapping,cloning and candidate gene mining of the target QTL.The main results of this study are listed as below:1. Using N04, a popcorn maize inbred line with small grain, as the recipient andrecurrent parent, the NIL of qnpGW1was constructed in N04background followingfour consecutive backcrosses and MAS. The of recovering ratio of geneticbackground (RRGB) for the selected target plant B8-28was95.0%in BC3F1generation. qnpGW1was mapped to the chromosome region,2.0cM from umc2145and7.1cM from umc2532, using the BC4F1population. This QTL could explain24.96%of the phenotypic variation with LOD7.78. The LOD value contribution tothe trait variance was higher than that of the corresponding QTL primarily mapped inthe RIL and F2:3population. And the distance between bilateral markers decreased to9.1cM. Plants with heterozygous target segment were grown. According to thesequence difference from the small-scale sequencing result between the two parentinbreds Dan232and N04, ten indel markers were developed and used to test plantswith different exchanges in the objective region in the BC4F2population.. Using thechromosome fragment substitution approach, qnpGW1was fine mapped to a14.62 Mb region between marker np1-1and umc2532.2. The NIL for qnpGW5was constructed using the same method asNIL-qnpGW1. The target plant B9-74with96.3%of RRGB was selected in the BC3F1generation. qnpGW5was mapped to a genetic region,1.2cM from umc1274and4.7cM from umc2296, using the BC4F1population, which could explain17.73%of thephenotypic variation with LOD about3.31. Its LOD value contribution to the traitvariance were higher than that of the corresponding QTL primarily mapped in the RILand F2:3populations, And the genetic distance between bilateral markers decreased to5.9cM.3. The NIL for qnpGW7was constructed using the same method asNIL-qnpGW1. The target plant B12-4was selected and95.0%of RRGB was obtainedin BC3F1generation. qnpGW7was mapped to a genetic region,2.0cM from umc2092and1.8cM from umc1393, using the BC4F1population. This QTL could explain16.43%of the phenotypic variation with LOD about3.87. Its LOD value andcontribution to the trait variance was higher than that of the corresponding QTLprimarily mapped in the RIL and F2:3populations. And the genetic distance betweenbilateral markers decreased to5.9cM. Six new indel markers were developed usingthe same method as for NIL-qnpGW1. qnpGW7was narrowed down a3.72Mb regionbetween marker np7-3and np7-5using the chromosome fragment substitutionapproach.