problem with tomatos

Hi all.
I seem to have a bit of a problem with my tomato plants. This is my first year of trying to grow them. They live in the greenhouse. The leaves at the bottom of the plants have black and yellow patches. I have tryed to attach a photo. (not sure if its attached, this is my first post:dh.
if anyone has any clue as to the problem with my plants and any way to fix the problem it would be a big help.
Thanks

 

Thanks John.
The leaves look ok further up the plant.