Yellow dying leaves is due to a nitrogen deficiency.
White spots on the stem are normal and not an issue.........they are where roots grow from if conditions allow.
You do not have fusarium wilt and do not have anything to worry about in that regard.
Oh shit, Fusarium is like cancer but for plants. And i think thats Fusarium i can see on the stem.
Don't forget to always disinfect your tools after working on a contaminated plant.
F