Here is a photo of some potato plants:
As you can see, the plants on either side are doing fine, but the plant in the middle is wilting. They're all watered at the same time, so that plant can't be thirstier than the others (and it rained overnight, anyway); it seems too early for the potatoes to be ready to harvest; it doesn't seem to have any fungus or disease (and, in any case, such a thing would probably have spread to the other plants). What could be going on here?
In case it's relevant, the two pots planted in March are unknown potato varieties (i.e. supermarket potatoes). The pot planted in April contains Pinto Gold from a seed potato dealer.