Should I be worried?

[JetStar1]

I have planted from seed for a number of years. This winter, I decided to try grafting. I received some rootstock for Christmas and decided that I should practice before "go" time. I set the seeds on New Year's Day, grafted ~ three weeks later. Although I lost a few, the plants that did take looked pretty good, until I transplanted them. Shortly after the transplant, the lower leaves started to turn yellow (see picture)

The scion seed came from my recent harvest and while I did spray (daconil) as a preventative measure. The plants that these seeds came from did not appear to have any issues. My rootstock was purchased, so I am assuming it was disease free. The transplanting potting mix was previously used in my flower boxes. I am using 6500K fluorescent lights @ 16 hours each day in my basement.

I am trying to determine if I should be concerned, or if this is a nutrient issue. I don't normally keep my seedlings this ling before they are in their permanent homes. This was just a test run, but any advice or suggestions would be greatly appreciated.