Faculty of Agriculture, Hirosaki University, Hirosaki, 036 Japan
Linkage relations were investigated with regard to three isozyme loci and three morphological markers on chromosome 12. As the rl-1 (rolled leaf) locus with a map position of 28 showed linkage with Acp-1 (acid phosphatase) and Sdh-1 (shikimate dehydrogenase) in the F2 from a cross between KL403 with rl-1 and Acc419 with Acp-11 and Sdh-11, the order of these three genes was determined to be Acp-1-rl-1-Sdh-1 (Fig. 1A). The rl-1 gene is identical with rl-3 (Iwata and Omura 1975; Kinoshita 1987). The spl-1 (spotted leaf) locus showed linkage with Acp-1 and Pox-2 (peroxidase) in the F2 between FL58 (spl- 1) and Acc435 (Acp-11 and Pox-21), their order was determined as shown in Fig. 1B. In addition, the linkage relations among Acp-1, Pox-2 and d-33 (bonsaito dwarf) have been known to be in this order (Ishikawa et al. 1991). With these three linkage maps, however, the gene order of Sdh-1, rl-1 and d-33 was still ambiguous, and further investigations were carried out.
The recombination value between Pox-2 and spl-1 and that between Pox-2 and Sdh-1 were obtained from the above F2 population and from another F2 be- tween IR36 and Kagoshima-zairai. The recombination value between the former two loci was 21.8±4.8 and between the latter two was 16.6±3.8. Therefore, it was suggested that the location of spl-1 was more distant from Pox-2 than that of Sdh-1, although the standard error for the former recombination value was higher than the difference between the two recombination values. The linkage relation between d-33 and rl-1 was analyzed by using the cross between FL27 (d-33) and KL403 (rl-1). The F1 plants showed the same morphology as that of KL403 and the F2 segregated into two types of plants like KL403 and FL27 in a ratio of 164:54. This ratio agreed with the expected 3:1 (X2=0.07). No normal plant appeared showing that the two genes are allelic, rl-1 being dominant over d-33.
Based on these findings, the order of three isozyme genes and three morpholo- gical markers was suggested to be spl-1-Sdh-1-rl-1 (d-33)-Pox-2-Acp-1.
Fig. 1. Linkage relations among Acp-1, r1-3 and Sdh-1 (A), and among Acp-1, Pox-2 and spl-1 (B).
Ishikawa, R., H. Morishima, T. Kinoshita, T. Harada, M. Niizeki and K. Saito, 1991. Linkage analysis of nine isozyme genes on the conventional linkage map in rice. Jpn. J. Breed. 41: 265-272.
Iwata, N. and T. Omura, 1975. Studies on the trisomics in rice plants (Oryza sativa L.), III. Relation between trisomics and genetic linkage groups. Jpn. J. Breed. 25: 363-368.
Kinoshita, T., 1987. Report of the committee on gene symbolization, nomenclature and linkage groups. RGN 4: 3-37.