I have been trying for 30 years! I’ve selected varieties resistant to everything! I’ve planted them in sterile containers, different garden soils, different parts of property. Worked on soil improvement, sprayed with serenade fungicide, but every year leaves start turning yellow at bottom of plant just when flowers are beginning to emerge. Then the leaves start curling slightly higher up and yellowing progresses upward. No spots, no greasy areas; fruit that does make it looks fine. Plants are stunted and bear poorly. Squash, and eggplant also are stunted. Beans may be stunted one year and not the next. Help!!!
Certified GKH Gardening Expert
Unfortunately, without photos it will be very hard to say!
There are several viral infections of tomatoes, one being Tomato Mosaic Virus, but it would show very definite signs of infection. Viral infections of plants are, usually, permanent and unable to be removed from an area.
The next thing to consider will be that one or more of their environmental needs are not met. This article will give you a thorough run-down of growing tomato plants: https://www.gardeningknowhow.com/edible/vegetables/tomato/growing-tomatoes-guide.htm
Testing soil pH and nutrient content of soil will be very important to the success of most garden plants. These articles will help: