Seedlings wilting

[Southbound]

My seedlings had been looking pretty good for the last few weeks, but then here came the dreaded problem that I had last year. The leaves are suddenly turning under and curling up and the stems are drooping. It is not all the plants, but seems to be spreading. This happened last year, and I don't know if it was related, but after the plants were planted in the garden, we had a lot of blight and maybe other disease.
Anyone know how I might nip this in the bud? Thanks very much. I hope I have uploaded the pictures correctly!