Rotten tomatoes

What is happening with my tomatoes? Brown patches on the leaves, wilted tops that don't revive with watering. Only half the plants are affected: those in pots outside. A look through Dr D G Hessayon's Vegetable & Herb Expert suggests it's a root rot, caused by poor drainage, which could fit in with the massive deluges of rain we got last month after the dry spell. There doesn't seem to be a cure, apart from mulching around the stems to encourage new root growth. Any ideas? Hope fully the plants won't keel over completely and we'll get a crop of some kind.