[hga]

To amply on jeena's point, we used to do this by exposing seeds to e.g. cobalt 60 gamma rays, and breeding the surviving mutants that seemed promising. If you eat all but I assume the very best sushi in the US, the rice is probably a Calrose, do a search on calrose radiation (funny, the Wikipedia article doesn't mention this at all, then again I'm not 100% sure current day Calrose is derived from those earlier varieties).

[moens]

Yeah... I was not aware of this. Another food source I will have to investigate. Chickens, I have found, love rice.

[hga]

Look into the Green Revolution, e.g. start with https://en.wikipedia.org/wiki/Green_Revolution ; if you're growing or using a cereal that's from a dwarf/semi-dwarf plant variety, before modern genetic engineering it probably had untold horrors committed on it to achieve higher yields.