It looks like lack of nitrogen followed by salt damage, one symptom of which is new flushes dying and older leaves falling. If you gave it 8-3-9 fertilizer, that would have done it.
It could die, but here are some suggestions for the future:
- Don't keep it for a full year in the shade house. Thirty days post graft is normally sufficient. Too long in the shade house causes the leaves to adjust to low light. Moving to sun will then cause leaves to yellow and burn.
- Don't use limestone in potting soil. pH of limestone is generally above 8.0, and many nutrients become unavailable. A sandy mix with some organic matter works great for mangoes.
- Don't use 8-3-9 (quick release) fertilizer on potted plants. Use an osmocote or equivalent slow release product. Mangoes are particularly salt sensitive.
- Water potted trees at least every other day in our area, everyday watering is generally needed in the summer time (make sure your soil is quick draining).
