| Rice（Oryza sativa L.）is one of the most important crops all over the world.Spikelets number per panicle is one of the important factors for the formation of rice yield,and is an important agronomic trait.In addition,grain shape not only affects the grain weight of rice,but also affects quality,so it is an important agronomic trait of rice.In this paper,chromosome segment substitution lines Z744 and Z1364 were identified using Nipponbare as the recipient parent and Xihui 18 as the donor parent.The main results are as follows:1.Identification of long-grain chromosome segment substitution line Z744 and QTL analysis for agronomic traits in rice1.1 Identification the chromosome substitution segment and analysis of the phenotype of Z744Z744 was selected and bred with Nipponbare as the recipient parent and Xihui 18 as the donor parent.Z744 contains 6 substitution segments from Xihui 18.The average substitution length was 3.01Mb.Compared with Nipponbare,the grain length,length-width ratio and 1000-grain weight of Z744 significantly increased.1.2 Cytological analysis of grain glume of Z744The glume cells of Z744 were 33.49μm longer than that of Nipponbare.There was no significant difference in cell width.The cell number with the same squares of Z744glume are less than that of Nipponbare.Therefore,the phenotype of long-grain was mainly caused by the length of glume cells.1.3 Genetic analysis of Z744 with long grainZ744 was controlled by a single gene.Indicating the grain length are mainly controlled by a major QTL.1.4 QTL mapping for important agronomic traits from Z744The F2 population constructed by Nipponbare and Z744 hybridization was used as a QTL mapping population,and a total of eight QTL were identified.Among them,two QTL（qGL1 and qGL7-3）that affect grain length.1.5 Breeding of secondary substitution segment lines from Z744Based on QTL mapping,four single-segment substitution lines（SSSL,S1-S4）and three double segment substitution lines（D1,D2 and D3）were bred by MAS.1.6 Analysis of additive effects of QTL based on SSSLsFour QTL-qGL1,qGWT1,qGWT6,and qGWT7 were verified by according SSSL S1-S4.2.Identification of QTL for grain number related traits based on a rice chromosome segment substitution line and qSP1 fine mapping2.1 Identification the chromosome substitution segment and phenotype analysis of Z1364The substitution segments of Z1364 were distributed on chromosomes 1,6,and 8,and the average substitution length was 1.19Mb.Compared with Nipponbare,grains per panicle,spikelets per panicle,panicle length,number of primary branches,number of secondary branches,seed-set density,plant height,grain length,and grain width were significantly increased.2.2 Genetic analysis of Z1364the increase in spikelets per panicle of Z1364 was controlled by a single gene.2.3 QTL detection of important agronomic traits from Z1364QTL mapping was performed using the secondary F2 population constructed byNipponbare and Z1364,and a total of 17 QTL are detected.Increasing in the total number of grains in Z1364 was mainly caused by the increase of number of secondary branches and the increase of seed-set density.2.4 Breeding of Substitution Substitution Lines from Z1364Based on QTL mapping,two SSSLs（S5 and S6）and a double segment substitution line（D4）were further bred by MAS method.2.5 Analysis the additive effects of QTL based on S5 and S6 and the epistatic effects between QTL based on D4The SSSL-S5 carried QTL-q PN1,qNSB1,qGW1,qSSD1,qGP1,and qSP1.Three QTL（qNSB6,qGP6,and qSP6）were carried by the single-segment substitution line S6.After pyramiding of qSP1 and qSP6,D4 produced more spikelets per panicle than the single fragment substitution line（S5 or S6）.2.6 Fine Mapping of qSP1 and Analysis of Candidate GenesOn the basis of QTL mapping,the main QTL-qSP1 for spikelets per panicle was further finely located in the 50kb region of the short arm of the first chromosome.Candidate gene prediction and sequencing analysis reveals that the candidate gene of qSP1 is a homologous gene of Arabidopsis AT4G32551 gene that has not been reported in rice.2.7 Analysis of expression patterns of qSP1 and other grain number related genesqSP1 are expressed in all tissues,especially in 1 cm panicle.Os MADS22,GN1A and DST are down-regulated in Z1364 while LAX2,GNP1 and GHD7 in Z1364 are up-regulated when compared with Nipponbare. |
