[BobandJack]

I really need some help here, I've dug up a very skanky spud & want to know if it's blight
  The spud is disgutlingly soft & weird looking on the inside surrounded by a thin black line all around the skanky bit.  Only one spud was affected & the foliage was fine so any ideas?

[DD.]

It's not blight.

Could be potato soft rot.....

Soft Rot

[BobandJack]

Yeah that looks like the skank all right, luckily it was only one & that was the last of the few I'd pulled.  thanks for that DD

[Iain@JBA]

Its not the mother spud you planted is it?

[peterjf]

potato black leg

[Howard]

Its not the mother spud you planted is it?

That was my immediate thought too, before I read Iain's post.

[BobandJack]

No I don't think it was the seed unless they grow to 3 times their original size whilst in the ground, but no I don't think so.  I've pulled other original seeds & they looked nothing like this, it looked ok on the outside & it wasn't till I cut into it a few days later that I realised it was 'orrible.