As shown in Figure 1, the following rice cultivars were examined: Koshihikari, Koshihikari Jukkoku_sd1 (Koshihikari∗6//Koshihikari/Jukkoku B6F4), Koshihikari IR8_sd1 (Koshihikari∗3//Koshihikari/Kinuhikari B3F3, Kinuhikari carrying sd1 of IR8 ), Koshihikari d60 (Koshihikari∗3//Koshihikari/Hokuriku 100 B3F3), Koshihikari Jukkoku_sd1 plus d60 (Koshihikari Jukkoku_sd1/Koshihikari d60), and Koshihikari IR8_sd1 plus d60 (Koshihikari IR8_sd1/Koshihikari d60). In each backcross experiment, short-culm BCnF2 plants were backcrossed with Koshihikari as the recurrent female parent in each generation. Each semidwarf phenotype was fixed by the BCnF3 generation. The percentage of genetic materials from Koshihikari in the isogenic semidwarf lines was calculated as follows: For Koshihikari carrying Jukkoku_sd1 (B6F4), (1 − (1/2)6) × 100 ≈ 98.4%. For B3F3, (1 − (1/2)3) × 100 = 87.5%.