Mapping of Hd-6-2 for Heading Date Using Two Secondary Segregation Populations in Rice

Heading date is one of the most important traits for rice adaption to different cultivation areas and crop seasons. In this study, two single segment substitution lines (SSSLs), W31-41-61-3-11-3-6-7 (W31-SSSL) and W32-59-80-2-11-1-10 (W32-SSSL) with substituted intervals derived from the donor parents IR66897B (W31) and IR66167-27-5-1-6 (W32), respectively, with Huajingxian 74 (HTX74) were found to comprise a gene for extremely late-heading date, and the gene was tentatively designated as Hd-6-2. Two secondary F2 segregating populations were developed by crossing the two heterozygous SSSLs with HJX74 to map Hd-6-2 gene. According to phenotype analysis of the two mapping populations, the late heading date trait was controlled by a major recessive gene. In the segregation population derived from W31-SSSL, Hd-6-2 was mapped on chromosome 6 between PSM677 and RM204 with the genetic distances of 1.3 and 2.7 cM, respectively. In the population of W32-SSSL, the gene for heading date was mapped to the similar region as Hd-6-2 and co-segregated with PSM672. The sequence alignment of Hd3a in the coding domains and promoter regions of HJX74 and W31-SSSL are completely consistent, whereas there was a great difference between W32-SSSL and HJX74, suggesting that Hd3a could hardly be the main cause of the heading date variation in W31-SSSL, but it was probably the main reason for the change of heading stage in W32-SSSL.