Confused about this deficiency .. Potassium or Iron?

Hi I am confused what kind of deficiency it is. This plant like 70cm height. This plant has two branch of fruits now (about 5 fruits). It has only three branches of leaves in the top .. each leaf attached belongs to one branch .. There are other 3 or 4 young branches are growing in the very top of the plant and they donot have this issue yet. but this issue is there before these young branches appear. This plant was suffering early blight anf I had to cut many branches of leaves and I think it is fine now, will recheck the next days to assure. I thought to mention these details if important. Btw, I am beginner in simple gardening. This plant is growing in pot of 30cm height and 25 width.