I found a great link with close-up color photos that I didn't see listed here. http://www.maine.gov/agriculture/pesticides/gotpests/diseases/tomato-problems.htm

IâÂÂll try to answer some of your questions: >I don't know where you are⦠IâÂÂm in Long Island. >You didn't mention if there are any other symptoms on the plants in addition to the stem lesions and if so, key those into the plant parts affected as well. No, there are no other symptoms. Actually one seedling has some curly leaves, but probably is the variety. >I agree that it looks like it started out as a scrape or injury of some kind that then got infected. I start seriously thinking that maybe it started as a scrape or injury. >Did you happen to prune off a leaf or branch? I pruned off a few leaves but not close to those wilted area. >Any sign of pests? No. >Are they indoors or outside? Indoor. >Did you buy these plants or grow them yourself? I bought the seedlings. >If you purchased them they could have been exposed to all sorts of injuries. Could they have rubbed on something - stake, cage, wire, etc.? Oh, poor plants; over 70 seedlings in a small box on two levels. Packed like sardines. IâÂÂm sure it was a lot of rubbing. >Disease-wise it most closely resembles Early Blight of the stem which would be very unusual on indoor plants unless contaminated material was brought indoors. I also thought of Early Blight, which in mid-April would be pretty ⦠early. IâÂÂll wait 1-2 days to see what will happen. Tx for your comments. And tx Carolyn for the links. I wanted to make the links live links for others, but I was only able to find this one: Cornell Tomato Disease Identification Key by Affected Plant Part.

Doesn't look nutritional to me, nor like a bug infestation. Could be fungal, but I don't get that much where I live in California. There must be a "my tomato leaves have yellow spots" FAQ somewhere, because it's common, and there are clues. Stuff like "wedge shaped", and "halos', and "bottom to top" vs "top to bottom". Maybe the tomato disease form?

IMO it's either fusarium or verticillium wilt. Fairly common and most of us have had it. The bad news is that yes, it does move fairly quickly up the plant. You might be able to stop it by removing the affected foilage and spraying with a fungicide like Daconil. Sometimes it stops and sometimes it doesn't. If you can save most of the plant, the tomatoes should be ok. Like you said, they don't appear to be affected. The little tomatoes that don't appear to be growing is just normal, the plant sometimes aborts them with or without wilt. Not every blossom becomes a tomato.