it always helps to tell us where you are located. There are hardly any garden questions that can be discussed without regard to location/ climate.
The tomato plant has at least a couple problems. As applestar suggested the tomato fruit is showing blossom end rot. That is not a disease, it is a physiological response to conditions. Most often it is a response to inconsistent watering and too much wet/ dry cycles. But the leaves are showing some yellowing/ spotting etc indicating some fungal disease, perhaps septoria leaf spot. If you type septoria into the search box at top left, you will find a lot here about it.
The soil looks quite dry. Are you watering enough? Tomato plants in containers in hot dry conditions may need to be watered twice a day. Has it been fertilized? With what? How many hours of sun a day does it get?