This likely to be Alternaria leaf spot. Concentric rings are mostly associated with Alternaria leaf spot. You could equally isolate the pathogen and if possible establish pathogencity.
I recommend the answer of Osabutey Samuel of course it is Alternaria leaf spot with its typical characteristics symptoms (concentric rings) escpcially the upper two images. For a simple identification you can put an adhesive tape on top of the spot and press for seconds then put the tape on microscpic slide with a drop of water on it you can see the conidia of the fungus
Based on the two images on top, I also would go with Alternaria sp.. Those lesions, which do have a dark grey growth on them are most likely showing the presence of Alternaria sp. conidia (spores) on the leaf surface. Under high magnification using a dissecting microscope you should at least be able to see their club-shaped form.
Ascochyta spp. produced lesions do have small, spherical fruit bodies, which do contain the spores internally, until they are expelled from the pycnidia.