**Characterization of QTLs and Candidate Genes for Days to Heading in Rice Recombinant Inbred Lines**

**Youngjun Mo 1, Jong-Min Jeong 1, Su-Kyung Ha 1, Jinhee Kim 1, Changmin Lee 1, Gung Pyo Lee 2 and Ji-Ung Jeung 1,\***


Received: 10 July 2020; Accepted: 17 August 2020; Published: 19 August 2020

**Abstract:** Understanding the gene mechanisms controlling days to heading (DH) is important in rice breeding for adaption in the target environment. Using a recombinant inbred line population derived from the cross between two *japonica* rice cultivars, Koshihikari and Baegilmi, we identified three consistent quantitative trait loci (QTLs) for DH for two years, *qDH3*, *qDH6*, and *qDH7* on chromosomes 3, 6, and 7, respectively. While Baegilmi contributed the allele for early heading at *qDH6* and *qDH7* with the additive effect of five days each, Koshihikari contributed the allele for early heading at *qDH3* with the additive effect of three days. Notably, pyramiding two or more alleles for early heading at these QTLs accelerated heading effectively. Sequencing of *Hd16*, *Hd1*, and *Ghd7*, the previously known heading date genes underlying *qDH3*, *qDH6*, and *qDH7*, respectively, revealed that Baegilmi and Koshihikari carry different alleles at the three genes. Molecular markers were developed to screen the allelic compositions of the three genes among 295 Korean commercial rice cultivars. The results showed that few cultivars carry alleles for early heading at the three genes, highlighting that DH can be further accelerated and fine-tuned in breeding programs by combining the desirable alleles of *Hd16*, *Hd1*, and *Ghd7*.

**Keywords:** rice; days to heading; QTL; *Hd1*; *Ghd7*; *Hd16*
