Dissection And Validation Of Three QTLs In The QTGW1.2 Region On Chromosome 1 In Rice(Oryza Sativa L.)

Thousand-grain weight(TGW) is one of the three component traits of grain yield in rice(Oryza sativa L), which is mainly determined by grain length(GL) and grain width(GW). Grain shape itself is an importance factor influencing the appearance quality and milling quality of rice. Identification of quantitative trait loci(QTLs) controlling TGW, GL and GW could facilitate the understanding of genetic mechanism underlying these traits and the application of molecular breeding for rice vaireities with high-yielding potential and good grain quality. In previous studies, populations were derived from the indica rice cross Zhenshan 97(ZS97)///ZS97//ZS97/Milyang 46(MY46) for the dissection of QTLs for TGW in a 12.0 Mb region on the long arm of chromosome 1. Two QTLs linked in repulsion phase, qTGW1.1 and qTGW1.2, were detected. One of them, qTGW1.2 was later separated into two QTLs, including qTGW1.2a located in the 934 kb interval RM11730-RM11762, and qTGW1.2b in the 2.1 Mb interval RM11800-RM11885. In the present study, near isogenic lines(NILs) and NIL-F2 populations with smaller segregating regions overlapped in the 3.96 Mb interval RM11703-RM11885 harboring qTGW1.2a and qTGW1.2b were constructed. Mapping resolution or qTGW1.2a and qTGW1.2b was increased and one new QTL for GL was detected between them. Main results are summarized as the followings.A plant carrying a heterozygous segment extending from RM212 to RM265 on the long arm of chromosome 1 of rice was selected from the ZS973/MY46 BC2F8 population. The resulting BC2F9 population was assayed with DNA markers. Two plants were identified,carrying heterozygous segments covering the intervals RM212-RM11787 and RM11787-RM265 which were previously found to harbor qTGW1.2a and qTGW1.2b, respectively. Two BC2F10 populations were produced, from which three plants with sequential heterozygous regions were identified, respectively. Using the six BC2F11 populations derived, a QTL for GL was detected in the interval RM11730-RM11800, and the regions for qTGW1.2a and qTGW1.2b were narrowed down to the 580 kb interval RM11730-Wn33304 and 2.0 Mb interval RM11807-RM11885, respectively. In the meantime, five plants with smaller heterozygous regions were selected, from which five BC2F12 populations were constructed. A QTL for GL was detected in each of the five populations. The additive effect ranged from 0.03 mm to 0.06 mm with the enhancing alleles derived from Milyang 46. Based on comparison of the segregating regions among the five populations, qGL1.2 for GL was delimited to a 372 kb region flanked by RM11781 and Wn34526. This QTL had the additive genetic action mode and may simultaneously affect TGW, GL and GW.NILs in BC2F10:11 were also developed to validate the effects of qTGW1.2a, qTGW1.2b and GL1.2. Six plants carrying heterozygous segments which were sequentially located in the interval RM212–RM265 were selected from the BC2F9 populations. In the resultant BC2F10 populations, plants showing no recombination in the segregating regions, including ZS97 homozygote, MY46 homozygote and the heterozygote, were identified. Selfing seeds of these plants resulted in the development of six sets of NILs with sequential segregating regions extending from RM212 to RM265. SAS procedure GLM was used to analyze the phenotypic variation among different genotypic groups. In each of the six NIL populations, significant variation among the three genotypic groups was detected for TGW. Significan variariations were also found for GL and/or GW. The qTGW1.2 was separated into three QTLs, which were found to be corresponding to qTGW1.2a, qGL1.2 and qTGW1.2, respectively. While qTGW1.2a and qTGW1.2b displayed the genetic action mode of negatively partial dominance, qGL1.2 appeared to have a positively dominance effect as large as its additive effect.