In article , mike.
buckley writes
I've not grown toms before this year, and am quite happy to treat this
as a learning year and not get much crop. As part of that I think I may
have lost a couple of plants due to blight. Are the symptoms blackening
leaves and the fruits go black from the bottom upwards? I also lost a
couple of plants, but that was my fault for using too small pots :-(
Live and learn. Next year growbags. :-)

You may also have blight, but what you are describing is bottom end rot.
That is not a disease, but an outcome of irregular or erratic watering.
--
Alan & Joan Gould - North Lincs.