Root initials are not very significant, but they might indicate that fine-tuning of cultivation, especially watering methods might be needed. Keeping the stems and foliage dry when watering should remedy the problem, and will also help to prevent tomato blight.
Some of the diseases that affect tomato stems can persist in the soil. Changing to a system of growing in grow-bags or in pots will prevent these diseases. There are no soil fungicides or soil sterilisers available to home gardeners. Removal and destruction of all infected material is also a wise precaution.