Hi! I know it's way late, but for anyone else, that's an example of magnesium deficiency.

It does not look like the examples of Mg deficiency that I found on the Internet. I found pics like this:

That's odd. The picture there looks like a plant virus to me. The options in the posts photos to me would be Magnesium or Potassium deficiency. But I'm definitely not an expert.... :) His/her plant is much too young to be positive, though.

It's tough with such few leaves. The first almost looks like sunburn to me.

It looks more like fertilizer or some other chemical burn to me.

Yes, I agree about the dead parts of the leaves but that doesn't explain the discoloration of the leaves... Like I said, the plant is too young to really tell what happened.

Discoloration is due to chemical/fertilizer burn.

Jeez, I must seem like a stuck-up idiot again, but fertilizer or chemical burns would affect all the leaves, right? Same with a vitamin deficiency. But with Magnesium deficiency, it makes sense- older leaves always yellow or discolor first- the leaves affected are larger. Magnesium deficiency can be caused by heavy rain as well- aka overwatering, which is entirely possible as only 1 plant was affected. I guess it could also be a magnesium deficiency caused by high potash fertilizers.... So Potassium may also be a problem.... See where I'm getting here? As i must repeat each time, this plant is far too young for us to know for sure. The leaves are too small. And wouldn't all of the plants get the same amount of the same fertilizer? Leaf sunscald COULD be the problem, but generally that doesn't change leaf coloration. That's just my opinion as to what happened here.

The reason one plant got chemical burn and the other did not is due to the shape of the leaves with the burned plant's leaves retaining the chemical while ,the other shedding it.