brown ring around base of stem

hi there
a friend sent me a few pics of some plants he's growing that have developed a brown ring around the base of the stem about 2 weeks before the chop. i asked what they were and he says easy rider auto...
he also said that 1 plant did the same thing early on and actually broke off at the stem base under it's own weight when the stem was as thick as a pencil.
Anyone got any ideas??

thanks in advance

Pone

The base may be too wet and thus may be rotting, but I have no real idea.