How would crops that don't reproduce on their own crowd out crops that do? That doesn't really sound like a realistic scenario.
There could be GMO crops that don't need anything manmade at all, but that'd be a waste of calories in plant growth.
There are actually plant lines which are more or less sterile and can't really reproduce sexually any more, because they have been (naturally) cloned.
The point is that modern breeding schemes and technology is necessary to feed the growing world population. There is no margin to reduce agricultural performance. You will feel any loss in performance immediately through price hikes.
I don't know enough about plant seeds to transfer that, but I guess it's the same principle.