it's look like fungus diseases and i don't know what is the solution for this

Hi Kiran, Your idea is quite right that it might be a fungal infestation. I've good research on the most commonly available diseases on mango, but the disease like it could be also of bacteria, for example, Bacterial Black Spot of Mango. Unfortunately, i found this disease only on leaves and fruits. There are few other scientists in this community, i hope that somebody else will definitely come forward to solving your this trouble, please wait.... Thank you!