The movie claims that "okra" has just gone down to the blight, that wheat went seven years earlier, and that corn was the last one standing. But that's beyond stupid, first because there are literally thousands of different kinds of food crops and no one disease would check out all of them, and second because if something did get diseased, the omnipresent monocrops like corn and wheat would be the FIRST to go.
If you started losing things like rice and wheat to a blight and you were worried it was going to spread more, you would respond by rapidly diversifying. Giant fields of corn would NEVER exist again - instead, you'd plant a row of corn, with some sort of squash mixed into it, beans on the side, then some potatoes, maybe a row of trees to block the wind, and so on. Even if corn was the only thing left to eat on the planet, you wouldn't grow giant fields of it, you would be growing all sorts of diverse fields spread out on different sides of different hills and shyt, to lower potential contamination.
And even if you lost every major crop - wheat, rice, corn, soybeans, oats, etc. - there are so many thousands of minor crops all over the world that would take far longer to succumb. People would start growing weird shyt like paw-paw and bitter goards and watercress and stuff that don't even have English names. And they would never grow it in monocrop fields again.