棉花是重要的天然纤维作物，精细定位纤维品质性状QTL和鉴定QTL 候选基因对棉花育种意义重大。项目组前期利用（T586×渝棉1号）RIL群体，在第21染色体检测到环境稳定的纤维品质性状QTL。为进一步精细定位第21染色体纤维品质性状QTL和鉴定QTL候选基因，本项目选择第21染色体QTL区域来源T586（其他区域来源渝棉1号）的株系RIL020与渝棉1号杂交，建立包括5000株左右的F2群体。利用QTL区域对应的雷蒙德氏棉序列设计SSR引物，构建QTL区域饱和图谱，筛选重组单株。结合（RIL020×渝棉1号）F3、F4和F5重组系的纤维品质鉴定结果，采用QTL近等基因重组系分析法精细定位纤维品质性状QTL。利用QTL区域标记筛选T586基因组BAC库，并对阳性克隆测序。根据BAC序列推测QTL初步候选基因。利用RT-PCR和QPCR技术分析初步候选基因的组织表达特性，确定并克隆候选基因。

Cotton is important natural fiber crop in the world. It is essential to fine-map QTL affecting fiber quality traits and identify QTL candidate gene for cotton molecular breeding. In our previous study, the environment-stable QTL for fiber quality trait was mapped on chromosome 21 in upland cotton recombinant inbred line population (T586 × Yumian 1). To fine-map the fiber quality QTL and identify QTL candidate gene on chromosome 21, the present study selects a recombinant line RIL020 from upland cotton recombinant inbred line population (T586 × Yumian 1) to cross with Yumian 1 and develop a (RIL020 × Yumian 1) F2 population with about 5000 individuals. For RIL020, the fiber quality trait QTL region on chromosome 21 originated from T586 whereas the other chromosome regions originated from Yumian 1. The new SSR primers designed from the G. raimondii sequence, which responds to the QTL region, are used to construct a saturated QTL region map on chromosome 21. Based on the fiber quality identified from F2, F3,F4 and F5 recombinant lines, QTL isogenic recombinant analysis will be used to fine-map the fiber quality QTL on chromosome 21. Markers within the QTL region will be used to screen the BAC bank, which was developded from T586 genome, and the positive BAC clones will be sequenced. The putative QTL candidate genes are confered from BAC sequences according to bioinformatics. The RT-PCR and QPCR will be used to analyze the tissue expression patterns of putative candidate genes, and the candidate genes of variety Yumian 1 and T586 will be cloned. The result will pave a way for marker breeding in cotton.