Looks to me like the roots are getting too hot.

Perhaps the sun is beating down on the pot too hard...

Wrap the outside of the pot with foil or something white to reflect the heat off the soil bed.

Something is definately wrong with your plant. Its 6 weeks old and it only has 4 sets of leaves?

It either the heat on the soil or the soil itself.

You might wanna try again. You should have a plant like that in one week - ten days after germination....

Good luck.