20. Chromosomal location of gene sd-1 examined with isogenic translocation lines of Taichung 65

Kuo-Hai TSAI

Agronomy Department, National Chung Hsing University, Taichung, Taiwan 40227, ROC

The rice variety, Taichung Native 1 is known to carry the Dee-geo-woo-gen dwarfing gene, sd-1 (Suh and Heu 1978) in chromosome 1, which corresponds to former linkage group III (RGN 7, 1990, p. 21-35; Kikuchi and Ikehashi 1984). Gene sd-1 was introduced into Taichung 65 (T65) by 8 backcrosses using Taichung Native 1 as donor and an isogenic line T65sd-1(8) was established. The sd-1 gene is recessive in Indica crosses, but it is incompletely dominant in the T65 X T65sd-1 cross. The F1 plants were only about 15 cm shorter than T65, and the F2 segregated into 1 tall: 2 intermediate: 1 dwarf type (Tsai 1989).

To determine the chromosomal location of sd-1, T65sd-1(8) was crossed with isogenic translocation lines of T65, E-22, E-23, and E-24, which involve chromosome 5 and chromosome 1 (RGN 1, 1984, p. 49). Each of the E lines has an interchange point on the long arm of chromosome 5 and a segment of chromo- some 1 (Sato et al. 1980). The F2 segregation patterns observed in these crosses and recombination values estimated between sd-1 and respective interchange points are given in Table 1, and the results are mapped in Fig. 1. The present experiment confirmed that sd-1 is located on chromosome 1, although the order of locations of interchange points 5-lb and 5-ld is different from that given in RGN 1 (1984, p. 49).

Table 1. F2 segregation for gene sd-1 and point of interchange in crosses
between isogenic T65 lines with sd-1 and reciprocal translocations
===============================================================================
                      Normal   Intermediate     Dwarf     Total X2   Recombi-
Cross       Stature  ========  ============  ===========
                     F     S     F     S       F     S     no.       nation(%)
===============================================================================
T65sd-1 x
 5-lb(E-22) Obs.     24    21    43    49      33    20   190   1.3  33.4+-5.41
            Exp.a    25.0  20.0  40.9  51.1    29.4  23.6

5-lc(E-23)  Obs.     24     6    10   101      46     6   193   2.8   6.1+-1.31
            Exp.a    26.6   3.4  12.7  98.3    46.0   6.0

5-Id(E-24)  Obs.     42    12    22    57      29    14   176   5.5  22.4+-3.20
            Exp.a    35.2  18.8  27.5  51.5    28.7  15.0
===============================================================================
F-fertile, S-Semi-sterile.
a-calculated from estimate of recombination value. All chi-square values were
not significant.


Fig. 1. Mapping of interchange points between chromosomes 1 and 5 and gene sd-1 in reciprocal translocation lines of T65.

References

Kikuchi, F. and H. Ikehashi, 1984. Semidwarfing genes of high-yielding rice varieties in Japan. RGN 1: 93-94.

Sato, S., T. Kinoshita and M. Takahashi, 1980. Location of centromere and interchange break-points in the pachytene chromosome of rice. Genetical studies on the rice plant, 71. Jpn. J. Breed. 30: 387-398.

Shu, H. S. and M. H. Heu, 1978. The segregation mode of plant heioht in the cross of rice varieties, 11. Linkage analysis of the semidwarfness of rice variety "Tongil". Korean J. Breed. 10: 1-6.

Tsai, K. H., 1989. An introduced dwarfing gene, sd-7(t), obtained in Taichung 65. RGN 6: 99- 101.