| Low temperature germination and seed storability are two important aspects of seed vigor. A good seed vigor including both good germinability in low temperature and good seeds storability is required in an excellent variety. Due to the economic development and increasing labor costs, direct seeding rice cultivation becomes more and more popular in many Asian countries because of the low production costs and easy operation. Low temperature and cold water irrigation are encountered in the planting season in the subtropical regions, resulting in irregular germination and seedling deficiency, which are large obstacles to rice direct seeding. A quick and neatly germination ability at low temperatures is a necessary condition to promoting direct seeding rice cultivation. At the same time, good seed storability is a key factor for the protection of seeds and food security, good germination capacity after long storage is also required in rice production. So the breeding and mechanism research of seed vigor (low temperature germinability and seeds storability) gradually become a hot spots.Three populations including two backcross inbred lines derived from Nanjing35(Japonica)/N22(Indica)//Nanjing35 and Koshihikari(Japon-ica)/Kasalath (Indica)//Koshihikari, a recombinant inbred lines derived from USSR5 (.Japonica)/N22 (Indica), were employed to map quantitative trait locis (QTL) relating to low temperature germination in rice. Advanced backcross population and near isogenic lines were built to validate the stablibity and effect of qLTG-9, which was the major QTL detected, then this loci was fine mapped. The main content of this study are as follows:1. QTL detection and stability analysis of low temperature germinationIn this experiment, backcross inbred lines derived from Nanjing35/N22//Nanjing35 were planted in three different environments (Nanjing (2010), Nanjing (2011), Lianyungang (2011)). A total of 15 QTL related to low temperature germination were detected in 3,4,5,6 days after imbibition by using QTL Cartographer version 2.5 software.They were located on chromosome 1,2,3,4,5,7,8,9 and 10, respectively. qLTG-8 was expressed in all three environments, qLTG-5 was expressed in two environments. qLTG-3, qLTG-1-1 and qLTG-1-2 were detected in several days after imbibition in the lines planted in Nanjing in different years. The near markers of the stable loci, qLTG-8 could be used to marker-assisted selection breeding.2. QTL detection of low temperature germination by using recombinant inbred linesIn this experiment, recombinant inbred lines derived from USSR5 and N22 were planted in Nanjing in 2008. QTL related to low temperature germination were detected in 4 and 5 days after imbibition by using QTL Cartographer version 2.5 software. Three QTL are mapped in chromosomes 7,9 and 12, respectively. qLTG-7 and qLTG-9 were expressed in both 4 and 5 days after imbibition, the maximum phenotypic variation explain of qLTG-7 and qLTG-9 were 9.5% and 12.12%, respectively. qLTG-12 was detected only in the fourth day after imbibition. This study provided a theoretical basis for subsequent fine mapping of low temperature germination sites.3. The construction of advanced backcross population and the near-isogenic lines, and subsequent fine mapping of qLTG-9.The low temperature germination of rice is a very important agronomic trait. In this study, advanced backcross population and the near isogenic lines were builted for fine mapping of genes associated to low temperature germination. A hybrid Fi was firstly generated between USSR5 and N22, then the F1 was backcrossed with USSR5 to get BC1F1, progeny lines with weak low temperature germination ability were continually backcrossed with USSR5 until BC4F1.121 polymorphic SSR molecular markers between USSR5 and N22 were used in their genetic background analysis. And qLTG-9 was detected by using of an advanced backcross population W907 (BC4F2) during building process, and the QTL was also detected in Y2469 (BC4F3), Y2288 (BC5F2). Then advanced backcross population and the near-isogenic lines with qLTG-9 (N22) insertion were built. To fine map qLTG-9,7218 individuals of BC6F2 were used, the recombinant individuals with extreme phenotype were selected for progeny validation in all three environments (Nanjing (2010), Hainan (2010-2011), Nanjing (2011)). qLTG-9 was final narrowed to a 72.3kb region in chromosome 9 between markers L9-25D and ID-1. A total of five ORFs were predicted in this map region by using the RAP-DB website, they were Os09g0395600, Os09g0396300, Os09g0396900, Os09g0395700 and Os09g0395800. Furthermore, researches showed that dormancy and the sensitivity of hormone (ABA and GA) were enhanced in the near isogenic lines compared with USSR5.4. QTL analysis of seed storabilityA population comprising 182 backcross recombinant inbred lines (BIL) derived from the Koshihikari/Kasalath//Koshihikari was used for detecting quantitative trait loci (QTL) for seed storability. Germination rate was used as the phenotype of seed storability under room temperature conditions after storage for 32 months (grown only in Nanjing), and 48 months (grown at Nanjing, Jinhu and Lianyungang). Six QTL, named qSS-2, qSS-3, qSS-4, qSS-6, qSS-9 and qSS-11 were detected. qSS-9, which had the largest effect, was detected in seed from all environments and storage times, explaining 10.63-33.10% of the phenotypic variation. The existence of QTL qSS-2, qSS-4, qSS-6 and qSS-9 was confirmed by using Kasalath chromosome segment substitution lines (CSSL) in a Koshihikari genetic background. These results provide an opportunity for map-based cloning of qSS-9, thereby gaining an understanding of seed storability in rice and possibilities for its improvement... |
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