I grew a mango tree last summer from seed in a pot. In the beginning it was extremely healthy looking and fast-growing. When the summer was over, as it gets very cold here in Canada, I took it indoors and placed it in the window frame. I fertilized it once or twice only during summer. Indoors, the lighting was less than ideal during the winter but it could get some sun light for a few hours per day.
However, after some time, I saw that leaves started to get brown, dry and fall off. Curiously, the browning pattern was quite peculiar as in many leaves it first starts as an isolated regular-shaped segment that then spreads to the whole leaf. Sometimes only the segment that has gotten brown gets dry while the other parts are still green and soft. In some leaves the browning is less regular and can come like an overall shade of brown. This second type starts with a tint of brown more or less everywhere and then it gets darker and darker all over the leaf. In both cases, the browning can exist in a segment, in very tip of the leaf or at the base.
The plant has lost many leaves. Even new coming leaves can be affected and fall off. It seems that some of them can be diseased even before unfolding. I water it somewhat regularly, only when the soil is dry. I also gently transplanted it into a bigger pot. I thought it may help but it didn't. When changing the pot, I saw some kind of yellowish powder near the root. I'm not sure if it was fungus or some color that had come off the pot.
Now it's summer and I can put it outside but it seems that it is dying. Is there any way that I can save this lovely thing?
I love plants but I am not very knowledgeable in caring for various plants. I really appreciate your comments.