Club root only affects members of the cabbage family, so it's unlikely. Vine weevil is a possibility, but (by God's grace) we don't have that here in the desert, so I wouldn't recognize the damage at sight. One possibility that occurred to me: were the plants planted deeper than in the pots they sprouted in? Burying the stems will do them serious damage. That is true of most plants, except for tomatoes, some cole crops, and marigolds (Tagetes).

I don't think this is vine weevil damage, more likely to be the way they were transplanted.

Once again, it's the old garden saying: "Plant it high, it won't die. Plant it low, it won't grow."

Thanks for your comments. I think that you are all right, I must have planted them too deep. I've been growing them for years though and never had the problem before. I just hope I'm not too late to buy replacement plants.