It will be helpful if you provide more information about weather conditions, the presence of symptoms other than leaves (on the stem, petiole or fruit), application of any chemicals etc.
The gummy stem blight disease causes similar symptoms like
- The earliest symptoms are appearance of light brown indefinite-shaped lesion on the leaf/stem
- Normally these lesions may be surrounded by areas of chlorosis (yellow tissue).
- In the later stage, the infected tissue may appear woody. Closer inspection (using a 10X hand lens) of diseased leaves at this stage may reveal the dark fungal structures (pycnidia).