I have an 18 yo desert rose I grew from a seed, so I'm quite attached to it. Some time back, it got a little spot of yellow on one of the roots, and I figured it was sunburn, so I watched it. The yellow started to spread, and it blistered on the largest root, exposing a black fungus underneath. I scraped all that away, treated it with sulfur, and it scabbed over. Now the yellow has spread to all the roots on that side, and up into the caudex.

The large yellow spot on the caudex was a little soft, but hardened up when I let it dry out for a few weeks. We had a very wet summer, and it was hard keeping it dry, but I finally brought it indoors to control the water. The yellow spot seems to be growing, and I fear it's a lot more serious than sunburn.

I'm willing to sacrifice most of the plant to save it. The yellow is only on one side of the plant now. I have two questions:

1) If I root prune it and just bury the whole thing up past the yellow spot on the caudex, will it grow roots around the caudex? I've seen some that have roots growing all over the plant, so I'm guessing that is a yes. It seems to have bumps on the caudex now like it's trying to put out roots to save itself.

2) Can I just cut off the top of the plant and re-root it? I know it will lose its caudex if I do that, but I don't mind that. I just want to save it.

Also, I tried cutting back the limbs so they would branch, but so far, no branching. I know it's getting to be fall, but here in FL, this is out growing season, so I don't really understand why it isn't branching.

Pictures - scroll down to see closeup of caudex

https://imgur.com/a/AdjhS