I've had a Mattson in my inventory with the tubers for weeks now, and it still hasn't bred into a cryo. I've hit my ding on the ground numerous times, but still no hit on it. Would this be a problem with the tubers, perhaps, a bugged instance of the item?
are the tubers still in the box? if so right click and equip/use (unbox them) them and then breed
these links i use to breed, breeding is simple put food with a tribble in your inventory and let alone for about an hour and new tribble different food and tribble make new tribbles, as for rare tribble not sure i havent found any other than the c-store ones