Do you have a disease diagnostic facility in your area? Since the symptoms look different, we recommend getting it diagnosed in the laboratory. Meanwhile, you can do small testing like

1. Ooze test: To confirm if it's bacterial diseases (like angular leaf spot) cut the diseased part of the leaves and place in a clean glass of water and check for any white ooze from this part.
https://www.lsu.edu/agriculture/plant...

The main symptoms are small, water-soaked spots that develop on the undersides of leaves. These lesions expand until they become limited by the larger secondary veins in the leaf, giving the spots an angular shape.

2. If it is downy mildew the infected plants develop a gray mold on the lower leaf surface.
"Typically, symptoms begin as small yellow areas on the upper leaf surface. As the lesions expand, they may become brown with irregular margins. Affected areas may grow together, and the entire leaf may wither and die."
http://www.clemson.edu/extension/hgic...