I'm wondering if sweet potatoes as such are just a dead end for my project. They have very limited ability to cross with other Ipomoea species, and I can hardly grow them here.
But there are wild relatives, such as Ipomoea leptophylla and I. pandurata, that have edible roots and are hardy here. Are there other tropic species besides sweet potatoes that have more or less edible roots and could be crossed with them?
I'm also becoming more and more interested in the idea of perennial squash; all the advantages of perennial tubers, without the digging. (Though probably with lower yields.)