Hello, i noticed one of my cacti was wrinkeling and getting black spots on the sides. I unpotted it and examined the roots. Some of the roots seemed to be black and broken.
The cactus does not seem to be squishy.
Is this rot? Can it be saved? Should i take a cutting to salvage what i can?
Also the species is unknown, so if anyone knows it off the top of their head, i would be grateful
I am an amateur, so any and all information is appreciated
(The second photo is torch-lit - The cactus is not actually as white as the photo suggests)
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If I were you, I would prune off the dead roots, those that are discolored, blackened, or have lost the external covering. It also looks, like your growing medium is too rich in organic matter for the kind of cactus you are growing. You should replace it with a mostly mineral substance, which may contain pumice, weathered granite, grit or some other substance, including unscented cat litter and perhaps some garden soil. You can locate some mixes when clicking on the tab "growing help" here on the CactiGuide page.
Now to the black spots that I believe I can spot along the ribs in image two. They could have been caused by perhaps a sunburn or dehydration of your plant. Then, only the discoloration will be a cosmetic thing. They could also be caused by a pathogen. However, it seems, that the black discoloration only extends to slightly above the midlevel of the plant, with the top looking fine. Make sure, that these blotches do not spread upwards. If they do, then you do have a real problem. It could either be a disease or perhaps some kind of insect or mite infestation. The latter will most likely prefer the new growth, however, and not remain on the lower part of your plant.
In short, your plant may be OK, once it is planted in a better growing medium and the blemishes are a thing of the past. I do not believe, that a rot has set in, because the discoloration is limited to the ribs and you state, that the plant has not become soft. Just to ensure, that there is no disease present, you should be watching the plant for any changes, e.g. enlarging of the discolored areas, formation of new lesions, etc..
