They are modified to have a suicide gene in them which wont let them produce viable seed. Its starting to become clearer why they built this thing now. Bet nothing in here is GM
http://news.nationalgeographic.co.u...702-svalbard-doomsday-seed-vault-food-supply/
That's a good idea (protecting older or alternate seed sources)
But TBH the compamies have been supplying seeds which grow sterile crops for decades without using GM (just old fashioned husbandry) All they have to do is cross pollinate the old fashioned way and the result is sterile the vast majority of the time; just like crossing animal species (think how a mule resulting from crossing a horse and burrow is usuaaly sterile)