Fine Mapping of qHD8-1, a QTL Controlling the Heading Date, to a 26-kb DNA Fragment in Rice (Oryza sativa L.)

Heading date is one of the importance agronomic traits. A library consisting of 1,123 single segment substitution lines (SSSLs) in the same genetic background of an elite rice variety Huajingxian 74 (HJX74) was evaluated for heading date (HD). From this library, the SSSL W06-26-35-1-5-2 with the substituted interval of PSM152-PSM154-PSM155-RM25-RM547-RM72-RM404 was found having a gene, which performed stable and late heading in the different environments of Shandong and Hainan provinces. To map the gene governing heading date, the SSSL W06-26-35-1-5-2 was crossed with the recipient HJX74 to develop an F-2 segregating population. The distribution of late and early heading plants in this population fitted a segregation ratio of 3:1, indicating the late heading was controlled by a dominant gene. The gene locus for heading date was tentatively designated as qHD8-1. Using a random sample of 460 individuals from the F-2 population, the qHD8-1 was narrowed down to a region flanking by two SSR markers PSM155 and RM547. For fine mapping of qHD8-1, a large F-2:3 segregating population of 3,000 individuals were developed from F-2 plants heterozygous in the PSM155-RM547 region. Recombinants analysis further mapped qHD8-1 to an interval of region 26 kb with markers RM22492 and P23 bounded on the left and right sides, respectively. Sequence analysis of this 26-kb fragment revealed that it contains five putative open reading frames, which were regarded as candidates of qHD8-1. These results will be useful in cloning of the qHD8-1 gene.