A rice hybrid is the product of a cross between two genetically distinct inbred lines. Owing to yield heterosis in rice hybrids, hybrid rice breeding has been developed and widely used in agriculture. In some cases, the hybrid F₁ lines show extremely late flowering. However, the genetic basis of the phenomenon is not very clear. In this study, two hybrids were found to have heading date of ~ 130 days, which was much later than their inbred parents. To elucidate the underlying mechanism, mapping populations consisting ~ 2000 F₂ individuals were developed, and eight pools were created based on the flowering time of the F₂ individuals. Whole genome deep sequencing of the parental lines and the eight pools enabled the identification of two major loci underlying heading date, on chromosome 6 and 8, respectively. Follow-up PCR amplification and Sanger sequencing showed Hd1 (Heading date1) and Ghd8/DTH8 (Grain number, plant height and heading date 8) were probably the causal genes on the two loci. The female parent had the genotype Hd1^WTghd8^1bp-del while the male parents had the genotype hd1^4bp-delGhd8^WT. Furthermore, genotypes of F₂ individuals at Hd1 and Ghd8 were investigated to estimate the genetic effects of different genotype combinations. The result showed that dominance complementation effects of the two genes leaded to extremely late flowering in the F₁ hybrid crosses with the genotype Hd1^WT/4bp-delGhd8^WT/1bp-del. Taken together, this study lays a foundation for further functional validation and breeding utilization of important flowering genes in genetic improvements of hybrid rice.

水稻杂种是两个遗传上不同的近交系杂交的产物。由于水稻杂交种产生杂种优势，杂交水稻育种已得到发展并广泛用于农业。在某些情况下，杂种F ₁系表现出极晚的开花。但是，这种现象的遗传基础不是很清楚。在这项研究中，发现两个杂种的抽穗期约为130天，这比其近交父母晚得多。为了阐明潜在的机制，开发了约2000个F ₂个体的作图种群，并根据F ₂的开花时间创建了8个库。个人。亲本系和八个库的全基因组深度测序使得能够鉴定出分别位于第6号染色体和第8号染色体上的两个主要基因座潜在的抽穗期。后续PCR扩增和Sanger测序表明HD1（标题日期1）和Ghd8 / DTH8（粒数，株高和抽穗期8）很可能在两个位点的因果基因。女性父母的基因型为Hd1 ^WT ghd8 ^1bp-del，而男性父母的基因型为hd1 ^4bp-del Ghd8 ^WT。此外，F ₂个体的基因型研究了Hd1和Ghd8以估计不同基因型组合的遗传效应。结果表明，这两个基因的优势互补效应导致F ₁杂种与Hd1 ^{WT / 4bp-del} Ghd8 ^{WT / 1bp-del}基因型杂交后的开花极度晚。综上所述，这项研究为进一步的功能验证和杂交水稻遗传改良中重要开花基因的育种利用奠定了基础。