17. Tight linkage of gene sd-7(t) and d\1\ found in a cross of Taichung 65 isogenic lines

Kuo-Hai TSAI

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 T65d\1\(8) or E- 17 showed that gene d\1\ was closely linked with sd-7 (7). Gene d\1\ is known to be located on chromosome 5.

Line T65d, (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 T65d\1\(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 d\1\ are tightly linked in repulsion. 

Table 1. F2 segregation pattern observed in a cross between T65sd-1(7) and
T65d\1\(8)
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                     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
==============================================================================
Reference

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