| Pericarp tenderness indicates the ability of pericarp resistant to the chew, which is always one of the most important index for quality and taste in sweet corn and is negative correlative with the pericarp thickness. In recent years, sweet cron has been popular as a nutritional and healthful food. The research on pericarp thickness of sweet corn has been growing, but the studies of gene mapping are still few. In this study, we selected two sweet cron inbred lines with big differences in pericarp tenderness and any other traits as the parent lines to build the chromosome segment substitution Lines, and the QTL mapping for the percarp thickness had been carried out using these lines. In the study, we validated the chromosome introgression in BC4F3 segregation populations by Specific-Locus Amplified Fragment Sequencing(SLAF). Three methods including frozen section method, spiral micrometer method and the fruit hardness tester method had been using to identify the pericarp thickness at the same time, the QTLs cotrolling the pericarp thickness had been detected by the combination genotype data with phonotype data. The study will provide important basis for subsequent research on pericarp thickness of sweet corn and build the foundation for cloning these genes. Moreover, these lines also provided the materials for sweet corn breeding with thin pericarp thicknes. The main results obtained in this study are as follows:1. Three different methods to measure the pericarp thickness had been evaluated in sweet corn. The result by spiral micrometer method in the autumn of 2015 is positive correlated with the result by fruit firmness meter in the autumn of 2015, and the correlation coefficient is 0.226. The result by fruit firmness meter in the spring of 2015 is positive correlated with both the result by frozen section in the spring of 2015 and the result by spiral micrometer in the spring of 2015, and the correlation coefficients are 0.149 and 0.188,respectively. No correlationship had been detected between the different seasons by the same methods.2. This is the first application of SLAF to the construction of genetic mapping in sweet corn. The total of 2964 markers had been selected and located on the genetic linkage map.The total distance of linkage map was 3394.9 cM with the average distance of <5 cM. The evaluation of cover depth, collinearity and chain depth showed that this linkage map was enough to map QTLs.3. 135 sweet maize CSSLs had been built from these two excellent sweet corn inbred lines. The total genetic distance covered by these CSSLs was 18865.5 cM, which was equivalent to 7 times of the maize whole genome. The number of the total introgression fragments was 444, which were distributed evenly on each chromosome. Among them,62.9 % of the CSSLs were less than 3 introgressive fragments, and the average length of these introgressive fragments was 35.9 cM with the average background recovery genome ratio of 95.91 %.4. The linkage analysis between the genotype data and the phenotype data has been done and the LOD threshold value was 3. The number of markers linked with pericarp thickness was 119, and 9 QTLs for pericarp thickness by three methods in two seasons were detected after combining the adjacent markers. Among of them, there were 2 QTLs, 1QTL, 2 QTLs, 1 QTL and 3 QTLs were located on chromosome 1, 3, 4, 8 and 10,respectively. The average contribution rate is 9.66 %, and additive effect values were mostly negative that means the pericarp thickness of F1 hybrids were tend to the thin parent lines... |
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