Vegitable plants leafs are tuning yellow and dying. | Vegetable gardening | Urban Gardening, Terrace gardening and Hydroponics

Hi,
I have started doing terrace vegetable garden since June 2016.
Kindly suggest me to save my plants.
Issues as below:
Tomato: Plants were grown healthy but leafs are turning yellow and dying. i have spray neem oil weekly even though No use can you please suggest me
Bitter guard: Plant grown up very healthy and lot many flowers but no single fruit. the plant looks very healthy but the leafs from bottom are turning yellow and Dying, the newly grown branch only in green rest of all dead.
Bottle Guard: The plant started growing but the leafs from bottom are turning yellow and Dying, the newly grown branch only in green rest of all dead (no leafs from bottom).

What would be the reason for it