Has anyone ever heard of Yuzu used as a rootstock? I know that it's not ideal in terms of fruit quality for the sweetest citrus, but it's used in areas of Japan where disease (tristeza) pressure is high and a more robust stock is required. Since Yuzu, of all of my citrus, is the most well-adapted to my climate, I may try and experiment with grafting some other varieties to it next year as a science experiment.

For those who aren't familiar with why Yuzu is so good at cold tolerance, it is similar to kumquat in that it induces a deep, deep dormancy during cooler and darker seasons. Unlike Trifoliate, which tends to wake up rapidly as temperatures warm and can be caught off-guard by a sudden reversion to cold, the Yuzu is very sluggish to come out of dormancy and really only wakes up 'when the coast is clear', i.e. after all risk of frost or cold shock has passed. The result is no sugars are wasted on growth that can be killed by a sudden chill and the plant wakes up in the late Spring ready to give everything to growth and flowering. Negative characteristics include slightly thicker peels, lower yields, and lower sugars than something like trifoliate or its hybrids. Still, I think it'd be a fun experiment as I'm always looking for ways to make citrus growing easier.

From what I've been able to gather, it's definitely compatible with Mandarins, but I haven't been able to find much else. I wonder if you could graft lime or lemon to it?