What kind of pots are they? It is possible that plant roots are getting too hot because the pots are getting too hot. Try slipping yours into another larger pot that will help keep the pot the plant is in cooler.

Only the tomato plants in the pots are showing this problem. The ones planted in the ground look fine and healthy.

And therein lies the problem.

Growing in containers, especially in your hot area, is a challenge. You really need to sometimes water them a couple of times a day. Since you said BIG pots I assume that crowding is not a problem.

Even if you could shade them as several of my friends in NM do, might help. They use those shade cloths you can buy there locally.

Carolyn

SirZoltan, I have never seen necrotic edges like that in pictures of diseases, etc so I did not hazard a guess. Did you find out anything? Did it progress?

I have read that potassium def. can effect leaf margins but again I have not seen anything quite like that at reference sites.