current (mA), large beam spot (10 cm) and simple beam line structure without ion mass analysis so that it could deliver mixed molecular and atomic nitrogen ions (Nþ2 þNþ) which would have a broad ion range in the target material. The sample holder stage was water-cooled to prevent the sample temperature from rising. The stage could house four sample holders at four sides and it rotated during ion beam bombardment so that the four sample holders could be exposed to ion beam sequentially to realize an interrupted beam bombardment mode. Each sample holder could hold hundreds of the rice seeds (Fig. 1C). The seeds were bombarded in vacuum by nitrogen ion beam at energy of 60–80keV to a beam fluence range of 21016–21017ions/cm2. An additional sample holder holding the same number of the seeds was placed in the chamber but away from the ion beam to be as a vacuumcontrol. After ion bombardment, the seeds were grown in soil for 2 weeks as transplanted rice in plastic pots at 1 seedling/pot for phenotype and genotype analyses (Fig. 2).