*2.1. Plant Materials*

Two introgression lines, CR1517 and CR1518, which were derived from crossing between Hwaseong and *O. rufipogon*, were used as parents. We selected the two parental lines from an interspecific cross population, BC4F8 [27]. CR1517 has *O. rufipogon* chromosomal segments on chromosomes 8 and 10, and CR1518 has *O. rufipogon* segments on chromosomes 1, 3, 9, and 10 (Figure 1). Two introgression lines were crossed to produce F1 seeds. During the winter season of 2018–2019, F1 seeds were sown in a greenhouse to produce F2 seeds. In the middle of April 2019, F2 seeds were sown in a greenhouse and 30-day-old seedlings were transplanted into the experimental paddy field. The F2 population (154 plants) was grown in a field belonging to Chungnam National University, Daejeon, South Korea. The plants were used for further phenotypic and genotypic analyses. To verify minor QTLs, two F2 plants (CR8017-4 and CR8020-6) were selected based on the genotypes to verify *qLTG10.1* and *qLTG10.2*, respectively. CR8017-4 is heterozygous at *qLTG10.1* and *qLTG8*, while *O. rufipogon* homozygous for *qLTG3*, and Hwaseong homozygous for *qLTG1* and *qLTG10.2*. CR8020-6 is heterozygous at *qLTG10.2*, while *O. rufipogon* homozygous for *qLTG1* and Hwaseong homozygous for *qLTG3* and *qLTG10.1*. The F3 plants were grown in the 2019/2020 winter season and dormancy was broken for seeds harvested from each F3 plant.

**Figure 1.** Graphical genotypes of two parental lines (CR1517 and CR1518) with the locations of five and three QTLs for low-temperature (*qLTG* in filled triangle) and coleoptile length (*qCCL* in filled box), respectively, on the left of the chromosomes. Black and white bars represent *O. rufipogon* and Hwaseong chromosome segments, respectively.
