Study of Genetics and Embryology of Polyembryonic Mutant of Autotetraploid Rice Induced by N^＋ Beam Implantation

In the present study autotetraploid rice IR36-4X was treated by an ion implantation technique with nitrogen ion beams. A polyembryonic mutant （named IR36-Shuang） was identified in the M2 generation. The mutant line and its offspring were systematically investigated in regard to their major agronomic properties and the rate of polyembryonic seedling in the M3-M6 generation. The abnormal phenomena in the embryo sac development and the cytological mechanism of the initiation of additional embryo in IR36-Shuang were observed by Laser Scanning Confocal Microscopy. The results were as follows. 1） The plant height, the panicle length and 1000 grain weight of IRB6-Shuang were lower than that of its control by 35.41%, 5.08% and 15.72% respectively, Moreover, the setting percentage decreased 12.39% compared with that in normal IRB6-4X plants. 2） The polyembryonic trait of IRB6-Shuang was genetically stable and the frequency of the polyembryonic seedlings in the IR36-Shuang line was also relatively stable. 3） The rate of abnormal embryo sacs in IR36-Shuang was significantly higher than that in the control IR36-4X. 4） The additional embryo in IR36-Shuang might arise from the double Jet of embryo sacs in a single owry, antipodal cells or endosperm cells. These results suggest that IRB6-Shuang is a polyembryonic mutant and a new apomixis rice line induced by low energy ion implantation. The prospects for the application in production of the IR36-Shuang line are also discussed. The present study may provide a basis for future investigations of apomixis rice breeding via the ion implantation biotechnology.