Uh oh.
This is interesting; have a gander:
Recognizing Tomato Problems
Bacterial canker? Ow.

Okay, I'm not sure if Serenade is effective against bacterial disease as it is against fungus, assuming that is even your main problem. I don't know much about bacterial infections of plants; I'll tell you what I personally would do if I saw that set of symptoms in my gardens:
1. Give a treatment of Serenade right away in case it is fungal
2. Give a foliar feed of CalMag Plus and a potassium supplement (PK13/14 adn other high P and K products are meant as a bloom blaster, but I have used them against deficiencies when I don't want to add other stuff to a mix) mixed at half strength
3. Check drainage in all pots; drill extra holes if you even suspect that it is impeded
4. Check soil runoff pH and flush to adjust if it is off. Add some Serenade and a little grow fert to the final flush solution.
This is for all the plants, not just the pot. Tomatoes and peppers like plenty of calcium too to avoid blossom end rot. So do all types of vine vegetables like squashes and zucchinis.
Good luck, sorry I can't be more help.

Edit:
REading the conditions under which blossom end rot (sign of Ca def in fruiting plants) occurs includes very hot weather during blossom set combined with changes in water quality and Ca becoming unavailable. Interesting. No matter what, I would definitely start putting your whole garden on a calmag supplement in their feed, and next year work some extra lime into the soil.