You're correct. Rice and corn are almost tied as staple crops. Wheat, potatoes and bananas trail those two relatively closely. There may be little genetic diversity inside any particular staple food, but there are nevertheless several unrelated staple foods that feed the world.

If blight were to wipe out one or two, things would get bad but I'm confident we'd pull through as a species.

There will be no famine as a result of a single type of crop in a local area getting killed. It still takes at least weeks for the virus to spread around to other crops which is plenty of time to become aware of it and stop its spread. There is also nothing preventing imports of healthy foods over the border.

There is also no real incentive to bring bad crops over the border to a safe area.

That's an extremely naive attitude. No famine looks that serious until it is already too late.

Assuming it's spread naturally of course. If it was a deliberate attack it wouldn't be quite so straightforward.

Fortunately the subset of People that are chaotic, bad, smart, and organized enought to pull this though is emptt

I assume you're joking?

USPS operates through rain, sleet, snow, etc, but not famine.