Validation Of QGS10, A Quantitative Trait Locus For Grain Size On The Long Arm Of Chromosome 10 In Rice(Oryza Sativa L.)

Rice(Oryza sativa L.) is one of the most important cereal crops. Grain yield in rice is determined by three components, i.e., number of panicles per plant, number of grains per panicle, and grain weight. Grain size is a major determinant of grain weight, and a trait having important impact on the appearance quality and market value of rice grain. The objective of this study is on the basis of the primary mapping of grain length and width in rice, to identify a candidate region and constructed populations with more isogenic genetic background. Then the effects of target QTL for grain length, grain width and grain weight were validated, as well as for other yield traits.In the primary mapping, using the linkage maps of the three sets of recombinant inbred line populations derived from indica rice crosses Teqing/IRBB lines(TI), Zhenshan 97/Milyang 46( ZM), and Xieqingzao/Milyang 46(XM), were utilized to analyze the QTLs for grain length and grain width using QTL Network 2.0, involving grain length and grain width traits of indica rice with the assistance of molecular linkage map and two years phenotypic data. In the TI, ZM and XM populations, 6, 8 and 4 QTLs for grain length as well as 7, 4 and 2 QTLs for grain width were detected, respectively. Among these QTLs, seven QTLs were shared by two populations, including four for GL and three for GW, and the remaining 17 QTLs found in one population. One of them, QTL qGW10.2 located on the long arm of chromosome 10 where QTL for grain weight and grain size had not been fine-mapping or cloned before, showed signif icant effects in the TI and ZM population. Therefore, this QTL was taken for further validation.According to the primary mapping results, two lines selected from the TI population with different genotypes in the qGW10.2 region were crossed to develop a F2 population. Assayed with DNA markers, one plant was selected, remained to be heterozygous in target region RM6100-RM228 on the long arm of chromosome 10, and identif ied to be heterozygous and homozygous at 19 loci and 103 marker loci in the background, respectively. The resultant RH- F2:3 families consisting of 307 individuals was used for QTL analysis on GL, GW, 1000-grain weight(TGW), number of panicle per plant(NP), number of grains per panicle(NGP), number of spikelet per panicle(NSP), and grain yield per plant(GY). In the target region, qGW10.2, qGL10 and qTGW10 associated with the three traits for GW, GL and TGW were detected, explaining 23.88, 14.35 and 11.58 % of the phenotypic variance, respectively. The enhancing alleles of the three QTLs were all derived from Teqing, hence, the three putative QTLs for grain size detected in this region were integrated as qGS10. Regarding the other four traits analyzed, GS10 was found to affect NGP only, with the enhancing allele derived from IR24.Three plants that were heterozygous in the interval RM6100-RM228 from RH-F2:3 population were selected. New RH-F2 populations were developed and assayed with the segregating markers. Selfing seeds of these plants resulted in the development of three sets of NILs, of which each consisted of two homozygous genotypic groups differing in the target region. Analyzed the genotypic difference in each NIL set on the seven traits described above with two repetition phenotypic data, it was found the qGS10 region had major effects on grain length, grain width and grain weight, and maybe minor effects on grain number, which are consistent in the results in the TI and RH- F2:3 populations. This region was also previously detected to affect grain chalkiness and endosperm transparency, indicated qGS10 signif icantly influenced appearance quality in rice, providing a good candidate for functional analys is and breeding utilization.