Identification of QTLs for rice flower opening time in two environments

Flower opening time (FT) is a critical factor for seed production in hybrid rice. To unravel the genetic basis of FT, a recombinant inbred (RI) line population including 184 lines was developed from the cross between a japonica variety Nipponbare and an early FT mutant (eft). A genetic linkage map was constructed using 70 SSR and 123 InDel markers, covering a total length of 1753.3 cM of the genome. The FT of both parents and RI lines was measured by the traditional grading scale method and a new time-interval method in two environments, i.e., Hainan (HN) and Hangzhou (HZ). A total of seven FT-related quantitative trait loci (QTLs) distributing on 4 chromosomes were detected in HN and HZ. qFT1b and qFT12 could be detected in both environments. The time-interval FT in Hangzhou allowed us to detect one more QTL (qFT-9) than the grading scale method. qFT1a is a major QTL explaining more than 60% of the total phenotypic variations in FT. Although FT had a positive correlation with heading date in Hangzhou (r = 0.16), no common QTL was detected for them, suggesting that FT and heading date are under different genetic controls. These discoveries may help to understand the genetics of flower opening time in rice and be useful for breeding early FT rice to facilitate hybrid seed production in the near future.