Lower leaf dieback is common in tomatoes and can be reduced by removing the lower-most leaves as the plants mature. Some of the symptoms pictured look like Early Blight, a very common fungal disease of tomato foliage. You can learn more about this can other typical conditions and their management on our page Key to Common Problems of Tomatoes. Some tomato cultivars have more inherent resistance to diseases than others, but disease severity and spread can also depend on weather conditions and how wet the foliage gets from irrigation methods. (Try to keep the leaves dry when watering, as leaf surfaces wet for long periods are easier for disease spores to infect.)

Miri