It's called blossom end rot. It is a calcium deficiency and is often brought about by insufficient watering. Once the plants mature a little and get their roots down deeper into the soil, the problem should largely disappear.
Water your tommies deeply and this will encourage a deeper root sysytem where they can access the nutrients they need.
I only water mine about once a week but i give them a good flooding so the soil becomes wet at least 8 inches down.

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The secret is the soil.