Orange string like thing on my eggplant?

Well this sounds very interesting! It might have been some kind of fungus - mycology is something I'm quite interested in and I know there are several species that match your description in one way or another. However, I am not aware of any that would attack a seedling and kill it - they mostly live by decomposing dead organic matter. If I was to guess, then I would say that it was a fungus that was present in your compost that then grew a fruiting body alongside your seedling - Possibly out-competing it for resources. It's just a guess, but I wonder? Maybe someone else can make other suggestions???

You need to get rid of this thing now! We bought a farm in 1985. The first year, we noticed an alfalfa plant with a strange color. Looked close and found it to be covered with a yellowish/orange string looking stuff. We were lucky to have a neighbor who was a homesteader and had seen it all. He told us to remove the plant if possible or remove all the plant twining on it. It is a parasitic plant called dodder. It has no roots. Lives on the host and makes seeds which fall off and grow onto another plant. You can go on google or any site and look it up. Interesting plant. Happy Gardening!!

Yes, I had a response from Sid and he thought it might be a fungus so I started searching and found that it was dodder. We had been hauling in lots and lots of horse manure and I understand that if an animal eats alfalfa infested with dodder that it can then spread through the manure. This was so interesting to me as I had never seen or heard of such a thing. I haven't seen anymore which seems unusual because our whole garden was covered in manure. Maybe we got lucky although I'm out there everyday checking for it. Thanks so much for your response and also thank-you Sid!