Agronomy Department, National Chung Hsing University, Taichung, Taiwan 40227, ROC
A semidwarf mutant (coded D65-31) was induced by X-ray irradiation of seed of Taichung 65 (T65), which had a recessive dwarfing gene, sd-7(t) and was about 21 cm shorter in height and 7 days earlier-heading than T65. It was backcrossed with T65 twice and a near-isogenic line T65sd-7(2) was fixed, which was about 16 cm shorter and 3 days earlier-heading than T65 (Tsai 1989). To find out the chromosome location of sd-7(t), this line was crossed with isogenic translocation lines of T65 carrying different interchanges of chromosomes (E lines, RGN 1, 1984, p. 49-52). But, none of the crosses showed linkage of sd-7(t) with interchange points carried by those translocation lines. It was also crossed with isogenic lines of T65 carrying different marker genes (RGN 1, 1984, p. 54-55). Line T65d1(8) or E- 17 showed that gene d1 was closely linked with sd-7 (7). Gene d1 is known to be located on chromosome 5.
Line T65d1 (Daikoku dwarf) had a height of 39 cm and T65sd-7(2) 87 cm, while the height of T65 was 104 cm. The F1 plants from T65d1(8) X T65sd-7(2) showed the stature of T65, and the F2 Segregated into normal, sd-7 and Daikoku type in a 2: 1: 1 ratio. No double recessive plants, expectedly very short, were found (Table 1). This suggests that genes sd-7(t) and d1 are tightly linked in repulsion.
Table 1. F2 segregation pattern observed in a cross between T65sd-1(7) and T65d1(8) =============================================================================== Plant type Double X2 Recombi- Observation ========================= dwarf Total nation(%) Normal sd-7 Daikoku =============================================================================== Mean height(cm) 104 84 37 - Observed no. 112 42 41 2 195 4.35ns 0 Expected ratio 2+p2 1-p2 1-p2 p2 If p=0 2 1 1 0 Expected no. 97.5 48.8 48.8 0 ==============================================================================
Tsai, K. H., 1989. An induced dwarfing gene, sd-7(t), obtained in Taichung 65. RGN 6: 99-101.