Keywords: 
• ion beam implantation /
• autotetraploid rice /
• polyembryonic seedling mutant

Abstract: In the present study， the autotetraploid rice IR364X was treated with ion implantation technique by nitrogen ion beams and a polyembryonic seedling mutant(named as the IR36Shuang) was identified in M2 generation. The mutant line was systematically investigated about the location of seedling in polyembryonic seedling, and the cytological initiation of the additional embryo in the IR36Shuang was observed and determined. The results are as follows: The location of seedling in the polyembryonic rice IR36Shuang could be differentiated into 2 types: the uncomplete twin seedlings and the complete twin seedlings. There were 2 types in the uncomplete twin seedlings， i.e. the twin seedlings with single plumule axis and single radicle and the twin seedlings with single radicle and twin plumule axis. The complete twin seedlings also included 2 types， i.e. the normal twin seedlings and the abnormal twin seedlings. The doubleembryo was observed during different embryo development stage of the IR36Shuang. The additional embryo in the IR36Shuang might arise from the double set of embryo sacs in single ovary， multi eggcell egg apparatus， antipodal cells or endosperm cells. The results revealed the practicability of ion beam implantation technique in creating new polyploidy idioplasm， which could provide a new approach for searching the material with apomixis.