Knobbly swedes - quick q

Pulled my last 6 swedes up for the Christmas period and they look awesome. A couple do have some minor knobbly growth on the sides (from parts that would have been underground) and wondered what had caused this? Minor clubroot? Soil too wet?

The swede was Marian and soil type clay/heavy.

Cheers. (",)

I don't know, but never considered it a problem  I mean, if you buy them some of them have been sliced on the sides. 

Never noticed the sliced sides on bought ones... fair enough!