A chimeric citrus that should have greatly improved hardiness. Are there other fruits where this could have merit? They will need to be graft compatible and have species with differing hardiness. Also, they would need to have fruit that develop from different parts of the meristem than the rest of the plant. This is true with citrus but I have no idea for other plant groups.
I haven’t checked graft compatibility for all of these but here are some preliminary ideas of species that could have their cold hardiness improved with this technique:
Peaches: apparently only minor hardiness differences for some varieties, so likely not with the effort.
Almonds: early blooming might be problematic. Hardiness difference with other stone fruit is about 10F, so there is some benefit here.
Avocados: apparently quite narrow graft compatibility, only grafts with closely related species from similar environments. I couldn’t find much information on their environmental tolerances but it does not seem promising.
Black sapote or other tropical Diospyros: so many species here and most are not well tested, but apparently black sapote (hardy to 28F) is graft compatible with the very hardy American persimmon (-25F). This is a stunning 50 degree difference although it seems unlikely a chimera would be quite this hardy. What would happen with a chimera between an evergreen and deciduous species? Would dormancy, important for frost protection, be disrupted? American persimmon is also fairly heat and drought tolerant. This is the most promising yet, though having never tried black sapote, I don’t know if it’s worth the effort.
Tropical figs? Are any worth eating?
Mulberries—a few more tropical varieties exist
Any others that come to mind?
Could this technique also improve drought and heat tolerance?