Genetic dissection of heading time and its components in rice

Heading time (HT, days from sowing to heading) is an important agronomic tr ait in rice. Physiologically, HT can be divided into two stages: vegetative growth time (VGT) and reproductive growth time (RGT). A number of studies for mapping QTLs conferring HT in rice have been reported, but none of them has tried to map MT-related QTLs based on their component traits (VGT and RGT). The present study aims to map MT-related QTLs in rice according not o nly to the performance of HT, but also the performances of VGT and RGT. A m ethod based on an empirical equation of leaf age growth was developed to pa rtition HT into VGT and RGT. An indica/japonica DH population and a corresp onding RFLP map were constructed for the study. The methods of composite in terval mapping and multiple-trait composite interval mapping were used to m ap QTLs. A total of 19 QTLs were mapped on all 12 rice chromosomes with the exception of chromosomes 1 and 4. Results showed that: (1)more QTLs could be detected by partitioning HT into VGT and RGT; (2) the genetic variation of HT was largely attributed to VGT; and (3) the two component stages were relatively independent in terms of QTL effects, suggesting that the ratio b etween VGT and RGT could be genetically adjusted without apparently alterin g HT.