I don't know if it's just the angle of the camera but that pot looks awfully small.

Hi, it is a small pot but it’s been in there since a seed, going to transplant to a proper garden bed. do you think the small pot Is causing troubles? Lack of nitrogen?

Lack of all nutrients if the roots are all scrunched up in there. When you plant it out in your garden, dig a fairly deep trench and slope it upward. Take all the leaves off at least 6" up. Put the roots at the deep end and put the plant's stem along the trench up to almost where the leaves are still on the plant and cover it. Tomato plants love to put out as many roots as they can so any part of the stem in the ground will root. Put your support where your trench ends so you don't accidentally cut the plant when putting it in. But don't fertilize for a couple of weeks or so to give it a chance to get established. Do, however, start spraying with an anti-fungal like Daconil. Hope this helps.

I've never seen that before.

Thanks for the great advice ediej I'll transplant as you say and see how they grow!

Never seen it before. The pattern looks as if something - a toxin? a dye? a mystery substance. . . was sucked up through the root system and has damaged the parts of the leaves near the veins. Have you fertilized with anything unusual? Please keep us updated.

Please get it out of that pot asap.

Could be the blue dye in the pottery glaze. Hope the transplanting went well!