We used to have a Gros Michel monoculture, and now we have a Cavendish monoculture. There's not a great candidate for the "next" monoculture, in that TR4 affects all the varieties that ship well.

And bananas, because we want seedless varieties, favor cloning which favors monocultures (both directly because they're, you know, clones; through slow propagation which in turn makes scaling a variety pretty capital intensive, etc.)