Characterization of Quantitative Trait Loci for Germination and Coleoptile Length under Low-Temperature Condition Using Introgression Lines Derived from an Interspecific Cross in Rice

Abstract

Previously, five putative quantitative trait loci (QTLs) for low-temperature germination (LTG) have been detected using 96 BC₃F₈ lines derived from an interspecific cross between the Korean japonica cultivar "Hwaseong" and Oryza rufipogon. In the present study, two introgression lines, CR1517 and CR1518, were used as parents to detect additional QTLs and analyze interactions among QTLs for LTG. The F₂ population (154 plants) along with parental lines, Hwaseong and O. rufipogon, were evaluated for LTG and coleoptile length under low-temperature conditions (13 °C). Among five QTLs for LTG, two major QTLs, qLTG1 and qLTG3, were consistently detected at 6 and 7 days after incubation. Three minor QTLs were detected on chromosomes 8 and 10. Two QTLs, qLTG10.1 and qLTG10.2, showing linkage on chromosome 10, exerted opposite effects with the Hwaseong allele at qLTG10.2 and the O. rufipogon allele at qLTG10.1 respectively, in turn, increasing LTG. Interactions among QTLs were not significant, implying that the QTLs act in an additive manner. Near-isogenic line plants with the combination of favorable alleles from O. rufipogon and Hwaseong exhibited higher LTG than two introgression lines. With regard to coleoptile length, three QTLs observed on chromosomes 1, 3, and 8 were colocalized with QTLs for LTG, suggesting the pleiotropy of the single gene at each locus. According to the results, the introgression of favorable O. rufipogon alleles could hasten the development of rice with high LTG and high coleoptile elongation in japonica cultivars.

Keywords: QTL; interaction; interspecific cross; low-temperature germinability; rice.

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.

Figure 2

Frequency distribution of germination rate in 154 F₂ plants at 6 and 7 days after incubation (DAI) at 13 °C. Germination rate was measured at 4–8 (DAI). Arrows indicate mean germination rate of CR1517 and CR1518 lines.

Figure 3

Frequency distribution of LTG at 7 days after incubation in the two F₃ population. Plants in each population are segregating in (A) RM25633 for qLTG10.1 and (B) RM333 for qLTG10.2 in the different genetic background. The numbers in parenthesis indicate plants number followed by mean germination rate ± standard deviation of genotype group. p-value and R² were determined by one-way ANOVA. HH: Hwaseong homozygoutes, RR: O. rufipogon homozygotes, HR: heterozygotes.

Figure 4

Frequency distribution of coleoptile length in 149 F₂ plants at 13 °C at 9 and 10 DAI. Arrows indicate mean coleoptile length of CR1517 and CR1518 lines.