One of my toms was wilting terminally so I dug it out to see what was going on. ##The roots had died and the base of the stem was rotting. Any idea what this could have been?
short of a drainage issue - i assume they get the same diseases at potatoes? blackleg, for instance?
Try here
http://aggie-horticulture.tamu.edu/tomatoproblemsolver/
I'm inclined to think phytophthora, but that's associated with waterlogging. My soil dries out well, and the other 47 plants all look perfectly heathy.