Fine Mapping And Genetic Dissection Of QTL For Yield Traits On The Short Arm Of Rice Chromosome 6

In the previous study, quantitative trait loci (QTL) controlling yield traits were dissected using an F2:3 population segregated in interval RM587-RM19784 on the short arm of rice chromosome 6, which was derived from an residual heterozygous line (RHL) selected from Zhenshan 97B/ Milyang 46 recombinant inbred lines. Within the target interval, a QTL for number of grains per panicle (NGP), number of spikelets per panicle (NSP) and grain yield per plant (GY) is located in the upper region RM587-RM6119, while one or more QTL for yield and its components might located in the central region RM6119-RM402. In this study, four stepwise RHLs carrying heterozygous segments in intervals RM587-RM19410, RM587-RM225, RM19410-RM6119 and RM6119-RM402, respectively, were selected from F3 population. Four F2:3 populations were subsequently developed, from which two sets of secondary F2 populations, five sets of near isogenic lines (NILs) and six chromosome segment substitute lines (CSSLs) were further developed. These populations were used in fine mapping of QTL detected in the upper region and dissection of QTL detected in the central region. The main results are summarized as following:1. A QTL conditioning NGP, NSP and GY was delimited to a 26.3-kb region flanked by RM19410 and Si2940.QTL analysis was performed in three F2 and F3 populations, which were derived from three stepwise RHLs with overlapping-heterozygous segments in the target interval RM587-RM6119. The QTL for NGP, NSP and GY was mapped in each of populations showing additive genetic action mode and having the increasing allele from the maternal line Zhenshan 97B. It was also consistent with the QTL detected in the previous study in the genetic action mode and the allelic direction. It was suggested that a QTL was located in interval RM587-RM6119, regulating rice yield by controlling NGP and NSP. By comparing the herterozygous regions and crossing-over regions shared in the three RHLs, the QTL was mapped to a 125.1-kb interval RM19407- RM19417. One SSR and four InDel markers were newly developed and used to narrow down the location in two sets of secondary F2 populations with the smaller overlapping- heterogenous regions. Finally, the QTL was delimited to a 26.3-kb interval RM19410-Si2940 that contains three annotated genes according to the genome sequence of japonica rice Nipponbare.2. The QTLs for yield traits were verified using a RHL-F2:3 population and four QTL were further dissected to intervals ranging from 96.1 kb to 860.5 kb using five sets of NILs and six CSSLs which differed with each other in the interval RM6119-RM6779.QTL for yield traits were mapped in the F2 and F3 populations segregated in interval RM6119-RM402. The QTL showed no effect on heading date but the significant effects on NSP and GY. Five stepwise RHLs were selected from the F2 population and selfed to develop F2 populations. From the F2 progenies, five sets of NILs and six CSSLs were further constructed. The analysis was carried out based on the phenotype differences among the three genotype groups in each set of five NILs and the overlapping chromosome segments of six CSSLs. It was revealed that four QTL, including 1 for GY, 1 for NSP, NGP and GY, 1 for NSP and 1 for NSP and NGP were clustered in the target interval RM1163-RM19652. The region, where QTL were located, ranged from 96.1 kb to 860.5 kb. All QTL showed additive genetic action mode but differed in allelic direction. The enhancing allele of the QTL controlling for NSP, NGP and GY was from Milyang 46, and the others were from Zhenshan 97B.