I'm amaized! I still believe grapes were the first domesticated crop though!
Barley -- 14,000 years before present.
Appropriate FR handle for this topic, BTW.
The original human diet had to be some combination of fruit and shellfish. Elaine Morgan is almost certainly correct in thinking humans originally lived in water and whether a person believes in evolution is pretty much irrelevant to that question. Humans would have eaten shellfish which we could deal with with our hands and which fish can't do anything with, and fruit which they went up on shore for. Things like wheat and greens would be tastes acquired much later and it's far from obvious that anything like that is good for us.