BC_1F_1 and BC2 F1 generations was obtained through continuous backcrossing,ddopting heterotic ecotype of Taiwan japonica 'Jianong 428' and 'Jianongyu 251' as acceptor materials and elite restorer line of japonica rice 'C418' as donor material,and selecting plants containing restoring gene to make crosses with sterile lines including 'Qiuguang A','Ningjing16A','216A','552A','Ningjing 3A' 'Ningjing 4A' and 'Hua 43A'.Yield of F1 generation shows heterosis to a certain extent,the percentage of over-contrast is...