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

In previous studies, quantitative trait loci (QTL) conditioning yield components were detected in the short arm of chromosome 6 by using the RIL population from Zhenshan 97B/ Milyang 46. In this study, the short arm of chromosome 6 and other chromosomes of one plant in each line of 461 F₇ RIL lines was screened using 26 SSR markers, a plant was found to have a heterozygous interval between RM587 and RM402(about 4.1 Mb), and almost homozygous in other intervals, we call the plant residual heterozygous line(RHL). The target interval and other chromosomes were detected using other 208 SSR markers and found that the RHL plant is heterozygous in the interval of RM587-RM19784 (about 7.3Mb, and containing 27 markers), homozygous in other intervals of chromosome 6. Moreover, the plant has heterozygous segments between the interval of RM488-RM3336 (about 3.8Mb) on the long arm of chromosome 1, the interval of RM5916-RM208 (about 1.1Mb) on the long arm of chromosome 2, the interval of RM16252-RM1635 (about 2.0Mb) on the short arm of chromosome 4, and the interval of RM267-RM5874 (about 0.6Mb) on the short arm of chromosome 5. But according to the previous studies using the same combination, no QTL was detected in the segregating regions of background regions, which indicated that the regions of background were little effects to the target region for QTL mapping of yield trait. Using the plant, an F_2:3 populations consisted of 221 lines was consequently developed, from which a SSR-marker linkage map was constructed and then four secondary F_2:3 populations were developed by further selfing the RHLs selected from 221 lines F_2:3 populations. These populations were used in dissection and validation of QTLs controlling yield traits on the short arm of rice chromosome 6. The main results are summarized as following:1. QTLs controlling yield traits in the target region (RM587-RM19784) were dissected to three or more narrow intervals using a F_2:3 population of 221 lines derived from a selfing of RHL selected from F₇ RIL lines.The 221 F₃ lines was planted in Hainan Province and Zhejiang Province, respectively, and mapping tool Windows QTL Cartographer 2.5 was applied to detect QTLs for yield components, including number of panicles per plant (NP), number of filled grains per panicle (NFGP), total number of spikelets per panicle (TNSP), 1000-grain weight (TGWT), spikelet fertility (SF), and grain yield per plant (GYD). Dissect QTLs for yield traits on the short arm of rice chromosome 6. QTLs were detected for each of the traits except panicle number, with phenotypic variance explained by single QTL ranging as 6.3～35.2%. Most of QTLs for yield components acted as additive QTLs. Three or more QTLs for yield traits were located in the target region. The genetic action mode, the direction of QTL effect and the magnitude of QTL effect sometimes varied among different QTLs for a given trait, and among QTLs for different traits that were located in a same interval.2. Three QTLs for yield traits were dissected to intervals ranging from 0.66Mb to 2.49Mb using three sets of near isogenic lines (NILs) which just differed with each other in the interval RM587-RM402.Three sets of secondary NILs which just differed with each other in the target interval RM587-RM402 were derived from the progeny of the 221 F₃ lines. With analysis on the phenotype differences among the three genotype groups in each NIL set and that among overlapping chromosome segment substitution lines, three QTLs for grain number and two QTLs for grain yield were resolved. They were located in intervals ranging from 0.66Mb to 2.49Mb. The additive effect was higher than the dominance effect at each locus. The allele for increasing the trait value was derived from the paternal parent at qNFGP6-1, and from the maternal alleles at other QTLs. Following the present study, an approach for the construction of new genetic resource to facilitate QTL fine-mapping in rice was proposed.3. Using a secondary population which covered the interval RM111-RM19784, the QTLs for yield traits located in the bottom of target interval were verified.A RHL which has a heterozygous interval between RM111 and RM19784, and homozygous in other intervals was selected From the 221 F₃ lines. A total of 484 individuals derived by selfing this individual were genotyed and 134 recombinants and 20 individuals which no recombinants in target interval were selected. Plant the 154 F₃ lines for QTL mapping. With analysis by with Windows QTL Cartographer 2.5, all the six yield traits were detected with significant effect. All of QTLs for yield traits acted as additive QTLs with phenotypic variance explained by a single QTL ranging as 11.93%～76.38%. qGYD6, qNP6 and qNFGP6 were located in the interval between 7.68Mb to 7.87Mb on the short arm of rice chromosome 6, qTNSP6, qSF6 and qTGWT6 were located in the interval between 7.87Mb to 9.45Mb on the short arm of rice chromosome 6.