Initial materials for mutagenic treatment. Mutagenic treatment is often conducted for elite inbred lines for expanding its genetic basis. The best hybrid АхВ with the highest yield is selected in a competitive examination. If the yield of the hybrid АхВ significantly exceeds others, it indicates that classical recurrent selection has reached this peak potential and the chance for further improvement through cross and backcross programmes is small, while induced mutagenesis may have a chance. The mutagenesis for increasing the genetic variation of the inbred line is conducted at this stage and an effective way for selecting mutants without many test crosses is developed. Mutant lines are selected after testing and included in the list of parent lines for developing new hybrids. Mutation breeding is conducted in parallel for the inbred lines, the parents of hybrid АхВ. For mutants of line A, the tester is the В and vice versa and hybrid АхВ is always used as a control.