Beginner Gardening: root rot on cauliflower, 0 by hayn

hayn wrote:
Hi,

I bought some cauliflower seedlings and they grew really nicely. But then they suddenly started to look wilted (outer leaves first) and one after another died. I pulled out the plant (see picture) to see what killed it but am not really sure. It is definitelly caused by a problem in the root since I can't see any insects and the dead plants have completely rotten roots. I thought about clubroot but the roots doen't really look like it. Could it be Rhizoctonia? I am not sure if I can see the wirestem and the leaves are not turning purple either.

I have red cabbages planted right next to the cauliflowers and radishes fairly close as well. None of them seem to be affected.

Does anybody have an idea what disease it is and what I can do to save the last cauliflowers (and cabbages and radishes) or prevent it next year?

Thanks. Manuela