Why does my Cuor di bue tomatoes have a disfigured bottom?

as with most tomato problems it is probably down to watering/feeding or temp fluctuation. sorry not much help really.

Thanks for your reply. I think that it must be a problem that's unique with growing this particular species as it doesn't occur with Shirley, Ailsa Craig, Alicante, Moneymaker, Sungold or Gardener's Delight which are all grown in the same greenhouse, with the same conditions regarding watering, feeding and shading .
I'll put up with this fault as it is the best variety that I've come across when it comes to slicing for sandwiches or for grilling, due to the superior taste and shortage of seeds.
Hootsmon

now i much prefer ailsa craig for flavour. and i actually like the seedy bits the best. funny that. :o)

Ah well, everyone has their likes and dislikes :-)