Introduction Ever since the epoch-making discoveries made by Muller[1] and Stadler [2] eighty years ago, a large amount of genetic variability has been induced by various mutagens and contributed to modern plant breeding. The use of induced mutations over the past five decades has played a major role in the development of superior plant varieties all over the world (Fig. 1a). Among the mutant varieties, the majority are food crops (Fig. 1b).