The cereal plants grow up forward on the ground. The rice lazy(la) mutant was characterized as a spreading or prostrate growth by an inability to respond or reduced responsiveness to gravity (Fig. 1. Jones and Adair, 1938; Abe and Suge, 1993). This characteristic was also identified in other cereals such as maize (Overbeek, 1936) and barely (Suge and Turkan, 1991). The rice la gene was assigned to the long arm of chromosome 11by the linkage analysis using telotrisomics (Singh et al., 1996), and was mapped at 13.1 cM from XNpb202 (Kishimoto et al., 1993) or 28.8 cM from RG118 (Yu et al., 1995). Abenes et al. (1994) also mapped la to be near the middle of chromosome 11 and in between RG1094 and RG247. On the other hand, Wu et al. (2002) estimated the distance between la and RG247 to be 16 cM instead of 6.2 cM, which was previously reported by Abenes et al. (1994), and therefore the precise map position of la has not been clarified yet.

In order to map the la locus, we crossed the la mutant of japonica rice cv. Taichung 65 with an indica rice cv. Kasalath containing the wild-type allele (La/La). The F₁ plants were then cultivated and self-pollinated to obtain F₂ seeds. In the F₂ seedlings, we screened homozygous seedlings for la by the agravitropism habit and isolated the genomic DNAs for the linkage analysis. We collected about 2,300 F₂ la homozygous plants, and investigated the linkage between the la locus and three molecular markers, R728, C459B and T57, located near the La locus. Linkage analysis revealed that La was located between R728 and C459B, with distance of 1.0 cM and 0.4 cM, respectively (Fig. 2). We are now performing fine map analysis of La using several new markers located between R728 and C459B to isolate and character-

ize the La gene.

References

Abe, K. and H. Suge, 1993. Role of gravitropic response in the dry matter production of rice (Oryza sativa L.): An experiment with a line having lazy gene. J. Plant Res. 106: 337-343.

Abenes, M.L.P., R.E. Tabien, S.R. McCouch, R. Ikeda, P. Ronald, G.S. Khush and N. Huang, 1994. Orientation and integration of the classical and molecular genetic maps of chromosome 11 in rice. Euphytica 76: 81-87.

Jones, J.W. and C.R. Adair, 1938. A "lazy" mutation in rice. J. Heredity 28: 315-318.

Kishimoto, N., M.R. Foolad, E. Shimosaka, S. Matsuura and A. Saito, 1993. Alignment of molecular and classical linkage maps of rice, Oryz sativa. Plant Cell Rep. 12: 457-461.

Overbeek, J. van, 1936. "Lazy", an a-geotropic form of maize. J. Heredity 27: 93-96.

Singh, K., S.D. Multani and G.S. K hush, 1996. Secondary trisomic and telotrisomics of rice: origin, characterization, and use in determining the orientation of chromosome map. Genetics 143: 517-529.

Suge, H. and I. Turkan, 1991. Can plants normally produce seeds under microgravity in space? Japan. J. Crop Sci. 60: 427-433.

Wu, J.Y., H.K. Wu and M.C. Chung, 2002. Co-dominant RAPD markers closely linked with two morphological genes in rice (Oryza sativa L.). Bot. Bull. Acad. Sin. 43: 171-180.

Yu, Z.H., S.R. McCouch, T. Kinoshita, S. Sato and S.D. Tanksley, 1995. Association of morphological and RFLP markers in rice (Oryza sativa L.). Genome 38: 566-574.