Three loci, Rc (brown pericarp and seed coat), slg (slender glume) and rfs (rolled fine stripe leaf), are located on rice chromosome 7. Rc co-segregates with RFLP marker C67A (Lin et al. 1994); slg is located between two RFLP markers XNpb33 and XNpb20 (Teraishi et al. 1999); rfs is located between two RFLP markers XNpb20 and XNpb152 (Kishimoto et al. 1992). These RFLP markers are arranged in the following order, C67A - XNpb33 - XNpb20 - XNpb152 (Kishimoto et al. 1992, Kurata et al. 1994). Based on these reports, we arranged the three loci in the following order, Rc - slg - rfs (Ichitani et al. 1998). According to Kinoshita (1998), however, the three genes are arranged in the following order, Rc - rfs - slg. In the present study, a linkage analysis was conducted to investigate which order is correct.

A line SR1 with genotype Rc⁺Rc⁺ slgslg rfsrfs was crossed with indica variety Kasalath with genotype RcRc slg⁺slg⁺ rfs⁺rfs⁺. The F₁ plant was backcrossed with SR1. In BC₁F₁ population, we selected a plant having round grains, normal green leaves, and brown pericarps and seed coats. The plant genotype at Rc, rfs and slg loci was RcRc⁺rfs⁺rfs slg⁺slg. Selfedprogenies of the plant were grown in a paddy field. Three characteristics, glume shape (round or slender glume), leaf character (normal or rolled fine stripe leaf), and pericarp and seed coat color (brown or white), were examined for each plant. The linkage analysis was conducted using Mapmaker/Exp 3.0.

The results are summarized in Table 1. The selfed-progeny of RcRc⁺ rfs⁺rfs slg⁺slg is supposed to produce eight kinds of genotypes, but there were no Rc⁺Rc⁺slg⁺_rfsrfs plants. Therefore, we concluded that the three genes are arranged in the following order, Rc - slg - rfs. The genetic distances of Rc - slg and slg - rfs were estimated to be 12.7 and 7.1 cM, respectively (Fig. 1).

We are undertaking the relationships between these genes and DNA markers using a mapping population.

References

Ichitani, K., Y. Okumoto and T. Tanisaka, 1998. Genetic analysis of the rice cultivar Kasalath with special reference to two photoperiod sensitivity loci, E₁ and Se-1. Breed. Sci. 48: 51-57.

Kinoshita, T., 1998. Linkage mapping using mutant genes in rice. RGN 15 : 13-74.

Kishimoto, N., E. Shimaoka, S. Matsuura and A. Saito, 1992. A current RFLP linkage map of rice : Alignment of the molecular map with classical map. RGN 9: 118-124.

Kurata, N., Y. Nagamura, K. Yamamoto, Y. Harushima, N. Sue, J. Wu, B. A. Antonio, A. Shomura, T. Shimizu, S-Y. Lin, T. Inoue, A. Fukuda, T. Shimano, Y. Kuboki, T. Toyama, Y. Miyamoto, T. Kirihara, K. Hayasaka, A. Miyao, L. Monna,H. S. Zhong, Y. Tamura, Z-X. Wang, T. Momma, Y. Umehara, M. Yano, T. Sasaki and Y. Minobe, 1994: A 300 kilobase interval genetic map of rice including 883 expressed sequences. Nature Genet. 8: 365-372.

Lin, S. Y., Y. Nagamura, N. Kurata, M. Yano, T. Sasaki and Y. Minobe, 1994. DNA markers tightly linked to genes, Ph, alk and Rc. RGN 11: 108-109.

Teraishi, M., Y. Okumoto, H. Hirochika, A. Horibata, H. Yamagata, T. Tanisaka, 1999. Identification of a mutable slender glume gene in rice (Oryza sativa L.). Mol. Gen. Genet. 261: 487-494.