Hello,

recently I've been having a problem with my begonia maculata (indoors). The problem is that its leaves start to kind of "rot" in the area near the leaf stem and some of them also have brown spots. I' ve attached pictures for you to see what I'm talking about. The air humidity in my flat is usually around 60% (stable, I have a humidifier), its placed near the window but not close to heating. It is getting less light than during the summer, but I've had it for a longer time and it didn't mind it last winter.

Im pretty sure this must be some kind of a disease since the plant is losing leaves in a matter of hours, for example I go to sleep, when I check the leaves they all look sort of OK but then I wake up and suddenly there is another fallen leaf. Some of the fallen leaves look totally okay and it even loses its youngest leaves.

I really don't want to lose this one particular plant, can you help me identify the problem please?

Thank you!