Fine Mapping Of QFL-Chr1, A Fiber Length QTL On Chromosome1in Cotton And Development Of Single QTL Near-Isogenic Lines

Cotton fiber is the world’s most important raw materials of natural textile. It is a single cell villi developed from the ovule epidermal cell. Due to the continuous accelerating of the textile industry and the continuous improvement of people’s living standards; the people’s demands for natural, environmental textiles are higher and higher. Cotton fiber quality is defined by many physical properties, such as fiber length, fiber strength, fiber fineness and uniformity. Fiber length is one of the most important aspects of fiber quality and also the initial property used to evaluate cotton quality, finally affecting the quality of the terminal products. However, as the fiber length is a quantitative trait controlled by multiple genes, its genetic mechanisms are very complex. More importantly, there are significant negative correlation between fiber length, strength and other important quality indicators and yield, yield components. These factors constrain genetic improvement of cotton fiber quality. The negative correlations had been still exsisted for decades of efforts,In this study, the introgression line RO1-40-08was employed for fine mapping of the fiber length QTL, qFL-chrland developing a set of single segment introgression lines. The results will facilitate cloning of the gene underlying this QTL and lay a foundation of materials for further research on fiber development.1. Construction of a high-density genetic linkage mapOn the basis of the previous study, a single NIIL, R01-40-08, which had about94.3%of recurrent genome composition and significantly longer fiber than the recurrent parent, was selected to develop a large population (1672individuals) segregating for the target region. A totalof88SSR and19STS markers from the chromosome1were selected for analysis of RO1-40-08and the recurrent parent; finally,23polymorphic markers are obtained to genotype F2population with1672individuals. Linkage analysis was conducted by MAPMAKER/EXP version3.0b software. Finally, a linkage map located between the marker interval NAU3384-BNL3090was constructed that spanned a distance of13.1cM, with an average distance of0.6cM.2. Fine mapping of QTLs for fiber length (qFL-chrl) by substitution mapping method:Twenty three markers were used to refine the target QTL region in F2population with1672individuals. A total of432recombinants representing different recombination breakpoints were identified. Only143informative recombinants which contained breakpoints between homologous Tamcott2111segment and homologous Pima S-6segment or PimaS-6/Tamcott2111heterozygous segment were considered for substitution mapping. These143recombinants were classified into29groups based on different recombinant breakpoints within the introgression region through replicated determination of fiber length in multiple years. From substitution mapping results, it can be speculated that qFL-chrl was mapped at1.0cM interval of MUSS084-CIR018.3. Construction of single segment introgression line on target region and further validation of the position and effect of the qFL-chrl:Five recombinant individuals,5674-3,5676-8,5680-4,5689-4, and5694-6, with shorter introgression segments near target region and longer fiber were selected in F3population. Their recombinant intervals were NAU3384-MGHES10, NAU3384-MUSS84, NAU3384-CGR5144, NAU3384-MUSS422and NAU3384-CIR018, respectively. Five backcross populations were constructed using above5recombinant individuals and the recurrent parent Tamcot2111. A set of single segment introgression lines with homozygous Tamcot2111genetic background was obtained by forground and background selection. After comparison of their phenotype difference, the refined position of qFL-chrl was confirmed and further delimited to0.9cM interval flanked by two SSR markers MUSS422and CIR018. The presence of qFL-chrl locus could increase fiber length by about lmm. In our study, the fiber length QTLqFL-chrl was fine mappedat1.0cM interval of MUSS084-CIR018, and a set of single near isogenic introgression lineswithtarget QTL were obtained.This research would lay a foundation for futher map-based cloning reseach.