It looks like diplodia fruit rot caused by Botryodiplodia theobromae. The main symptoms are the epicarp of fruit turn dark near the pedicel in the beginning. This area extends to form a black round patch and which later covers the whole fruit. The pulp of fruits become brown and soft. High humid condition favors the disease.

Generally the infection is carried from the dead twigs and bark of the trees which harbors the fungus. With the beginning of rain the whole orchard get contaminated with this pathogen.

Management:
1. Remove the dead twig and barks from the tree and burn them. Also remove the infected fruits and destroy them.
2. Spraying fungicides like Bavistin (0.1%) or Topsin-M (0.1%) or chlorothalonil (0.2%) controls the disease.