This narrow genetic base of current semidwarf rice cultivars has led to reduced genetic diversity in rice [20–22]. Thus, it is necessary to identify a novel semidwarf gene alternative to sd1 and to utilize it to extend genetic diversity in semidwarf cultivars. A novel dwarf gene, d60, which was found in the semidwarf mutant Hokuriku 100, developed by exposing Koshihikari to 20 kR of gamma radiation [23, 24], is thus of particular importance. Unlike sd1, which is inherited as a single recessive gene, d60 complements the gametic lethal gene gal, which is carried by many rice varieties. Consequently, the cross between Hokuriku 100 and Koshihikari exhibits a unique genotype ratio of 4D60D60 : 4D60d60 : 1d60d60 [23–25].