are there holes in the cup? look at the roots.. take the plant out of the cup, are they white? root rot from over watering or probably past its time keeping it far too long in the small cup.

I don't think it's Damping Off. Your medium looks very dry. What are you using?

I am having a similar problem (with lower branches dying on 4" seedlings) that I cannot figure out.

Not healthy but not damp-off either. Looks like a good stem injury there on the one side that has allowed the stem below to become infected. Try transplanting it into a deeper container so all that bare stem is buried right up to just below that leaf branch. Assuming the top growth not in the pic is healthy still it may well recover.

Dave

Definitely need to pot up or plant out. Damping off usually occurs very early when seedlings are small.

Just noticed the colour of your leaves. The plant needs some fertilizer.

Linda

Thanks all. I transplanted them into a bigger container, burying them up the first set of leaves. I meant to attach a photo showing the upper leaves are healthy. It's a miracle grow potting mix. It's actually not dry, but I have had a hard time keeping up with the waterings. I've been fertilizing with 1:4 solution of miracle grow.

Its not that noticeable in the pic, but there is a whitish fuzz on parts of the base stem... I think mold. About 30% of tomatos I planted have similar symptoms.

I have one big hole (pinky size) in the bottom of cups for drainage.

I think I really screwed up growing these in my bathroom which is way too humid. I'd try letting the soil dry out because of the mold... But then the plants don't get enough water. Live and learn, I guess. I sprayed some daconil on them.

Next year I will keep them in a different room, add more drainage holes, sterilize seed starter tray (jiffy pods), put some sand on top to help drainage... Anything else?

Yeah one big hole isn't the best. 4 holes around the outside rim of cups and the hole/cuts should be V shaped and include both the bottom and a bit up the cup side. No to Jiffy pellets or pots.

Dave