Validation Of QTLs Controlling Yield Traits On The Short Arm Of Rice Chromosome 6

A cross was made between maintainer line Zhenshan 97B and restorer line Milyang 46 of a major commercial F₁ hybrid rice Shanyou 10. An F₂ population and four recombinant inbred line (RIL) populations were each derived from a single F₁ plant. In previous studies, mapping of quantitative trait loci (QTL) conditioning grain yield and yield components were conducted by using the F₂ population of 171 individuals and an RIL population of 247 lines. It was shown that QTLs on the short arm of chromosome 6 contributed a considerable proportion to the phenotypic variance of the yield traits. From 612 RILs derived from other three F₁ plants, residual heterozygous lines (RHL) were selected in thisstudy and employed for QTL fine mapping.F_2:3 populations were derived from the RHLs with overlapping heterozygous segments on the short arm of chromosome 6. The F₃ populations, consisting of 221 lines for Ch6-1, 145 lines for Ch6-3, 154 lines for Ch6-4 and 192 lines for Ch6-5, were planted in two replications in Lingshui, Hainan Province, China from December 2004 to April 2005 and in Fuyang, Zhejiang Province from May to September, 2005. Twelve plants per replication were grown and the middle 10 plants were harvested. Six traits, grain yield per plant (GYD), number of panicles per plant (NP), number of filled grains per panicle (NFGP), total number of spikelets per panicle (TNSP), spikelet fertility (SF) and 1000-grain weight (TGWT), were measured. Mean values over the two replications were used for analysis.QTLs were determined with composite interval mapping and refined with multiple interval mapping of Windows QTL Cartergrapher 2.0. QTLs for yield traits were detected in the three populations showing significant effects for NFGP, TNSP, SF and GYD in CH6-3, for NP, NFGP, TNSP and TGWT in CH6-4 and for NFGP, SF and TGWT in CH6-5. Similar results were gained in the sub-populations that consisted of individuals carrying recombinanat segments in the heterozygous region, in spite of the decrease of LOD score and increase of the proportion of phenotypic variance explained.On comparison of the QTLs detected in the three populations, the interval RM6917-RM402 was verified to contain genes controlling NFGP, SF and GYD. By using overlapping recombinants from CH6-3, the QTL interval was further delimited to RM6119-RM276 that covers a physical distance of 1.8Mb.Distorted segregation was found in each of the RHL-derived F₂ populations, inferring the existence of gamete abortion (ga) gene in the genomic regions under study. Recombinants that contain different heterozygous segments in the target region were selected from populations CH6-1, CH6-4 and CH6-5. Ten to twenty F₂ progenies of each recombinant were genotyped and tested against the expected ratio of 1:2:1. Taking distorted segregation as the indication for the presence of ga gene and expected segregation for the absence, the gene ga was located in a 1.6Mb region flanked by markers RM510 to RM6119.