Construction Of Rice SSR Linkage Maps And Comparative Research On Four Mapping Methods Of QTLs

Rice is the most important crop for human consumption, providing staple food for more than half the world's population. Most of rice traits are quantitative for example yield,quality and stress resistent, which are controlled by polygene. It's very important for rice breeding improvement to map quantitative trait loci (QTLs).The genetic map and the method of QTL mapping are the base for QTL mapping .So the method of QTL mapping and the veracity of genetic map are two important factors for the veracity of QTL mapping.Using 180 PA64S X Nipponbare F₂ descendants as mapping population, we constructed rice SSR linkage map and positioned a group of new SSR markers and compared it with the map of Temnykh and the sequence map of Nipponbare. Four mapping methods, the interval mapping(IM) , the composite interval mapping(CIM),the mixed composite interval mapping(MCIM) and the multiple interval mapping(MIM),were employed to detect the quantitative trait locus (QTL) loci of rice plant height with an F₂ data from the intercross PA64SxNipponbare.The results were as the following:1. A F₂ population (180 lines), derived from the cross between two sequenced (or partial sequenced) varieties Pei'ai 64s and Nipponbare, was used for genetic linkage mapping by SSR markers. 156 of the 515 SSR makers had distinct polymorphism between the parents. A molecular linkage map was constructed by 137 of the 156 SSRs markers, and the length of the map was 2046.2 cM with an average interval size of 17.1cM.2. There were 85 identical markers on the present map and the one of Temnykh's (2001), of which, 82 markers were located on the same chromosomes in the two maps. Of the 137 markers, 113 were tagged to the sequence map of Nipponbare. And 111 of the 113 SSR markers, covering 289.7 Mb of genomic length with an average interval size of 2610.0 kb, were located on the same chromosomes on the sequence map, the other two were located on different chromosomes.3. Most of the SSR markers have similar linear order on this map and the sequencemap. The chromosomes 1,2,3 and 8, in particular, are completely identical.4. Four mapping methods, the interval mapping(IM) , the composite interval mapping(CIM),the mixed composite interval mapping(MCIM) and the multiple interval mapping(MIM),were employed to detect the quantitative trait locus (QTL ) loci of rice plant height with an F2 data from the intercross PA64SxNipponbare. The results were as the following:(1) 7 significant QTLs were detected by IM, 10 QTLs by CIM, 3 QTLs by MCIM, 1 QTL by MIM for the trait under the same significant level. So CIM had the highest detective capability among the four methods.The loci detected by IM were also detected by the method of CIM, and aiming at the same QTL, their distance to the left marker is almost coincidence.(2)Only one QTL was detected by the four methods, respectively, and the locus had the biggest contribution to plant height. The differences for average of additive effects (absolute values) or dominant effects(practical values) of QTLs were insignificant among four methods were insignificant effects of the same QTLs had the same direction.(3) A suggestion for mapping QTLs is that multiple methods should be considered, and it is preferential to declare the QTLs detected simultaneously by the four methods.