Thats mold man... plant only looks a few weeks old... IMO Id cut my losses, uproot, and do a SERIOUS cleaning of the grow area. Disinfect EVERYTHING. Not worth the risk of this sprouting back up again further down the line. Whats your humidity at? Sent from my SCH-I535 using Grasscity Forum mobile app
Yeah that's mould. The mould isn't going to cause you problems, but it's a sure sign that your stem is rotting and that's a pretty serious problem. You need to sort out air flow right away, get some fans in there and sort out your ventilation. What is your humidity? And do you know why that part is staying wet?