Looks like Pseudomonas...bacterial infections generally move much faster than most fungal infections with the exception of Black rot which it could also be.
Either way, your plant is in bad shape.
Cut the diseased tissue off with a sterile razor blade leaving at least an inch of healthy tissue.
Treat with Phytan 27 which kills Pseudomonas.
If you have access to Subdue Maxx you can use that as well but for most of us it's way too expensive and hard to get. This is the only thing I have seen which can kill black rot fungus (pythium).
Maybe sprinkle a little cinnamon on the plant for good luck.
Repot.
Hope for the best.
Good luck, I'm hoping for you