Genetic dissection of QTL for Important Agronomic Traits and Fine Mapping of qGL4 and qGW6 based on a Short-Width Grain Rice CSSL-Z691

Zhaopeng Yu Guangyi Xu Keying Xie Zhuang Xie Dachuan Wang Linlu Tan Yinghua Ling Guanghua He Fangming Zhao ^*

• Rice Research Institute, Academy of Agricultural Science, Southwest University, Chongqing, China

Rice chromosome segment substitution lines (CSSLs) are ideal for creating natural variation and dissecting complex quantitative traits. In addition, it builds a bridge for molecular breeding and accurate identification of quantitative trait loci (QTL). In this study, to construct an indica rice library of single-segment substitution lines (SSSLs) spanning the whole genome, a rice CSSL-Z691 carrying four substitution segments (4.07 Mb of average length) was identified by marker-associated selection (MAS) from indica restorer line "Jinhui 35" in the "Xihui 18" genetic background. Compared with large panicle type Xihui18, seed setting ratio, grain width, and 1000-grain weight were increased in Z691. In contrast, the number of primary branches, spikelet number per panicle, grains number per panicle, grain length, rate of length to width, and yield per plant were decreased in Z691. Then, eleven QTLs were identified in the secondary F2 population from Xihui18/Z691. Again, four QTLs (qGW6, qGL4, qRLW4, and qGWT4) were validated by three SSSLs (S1-S3) developed in F3. In addition, eleven new QTLs were detected by the three SSSLs that were not identified in the F2 population. Moreover, the different QTLs in D1-D3 showed various genetic models. Some, qGWT6 (a=0.96g) and qGWT7 (a=-0.29g), displayed independent inheritance, others exhibited various epistatic interactions. Thus, it is vital to identify different QTLs and their genetic models. Resolving the epistasis effects among different QTLs is crucial for screening QTLs for breeding by design. Finally, qGL4 and qGW6 were fine-mapped to 160 Kb and 240 Kb intervals on chromosomes 4 and 6, and two candidate genes have been determined by DNA sequencing. These results provide valuable genetic and breeding materials for cloning qGL4 and qGW6 and for future molecular breeding by design.