For a couple of decades corn dramatically responded to an increase in nitrogen fertilizer. At least this was the language of the breeder, and understandably so. But what was happening at a biological level was the elimination or neutralization of the genes responsible for the plant's ability to discriminate in the rate of fertilizer uptake. That era of fertilizer-response flattened, but now it is climbing again. I suspect that it is climbing because breeders are working with a different genetic ensemble responsible for that response.
All genes interact.
And as selection pressure is applied, as when we seek an improved wheat variety or corn variety or improved beef cow or sheep, we are restructuring the genome of this miniature ecosystem. We can get away with this, for awhile. We have gotten away with it for a long time now just as we have with farm pesticides. With gene splicing it is the other way around. With alteration came a degree of dependency on the species responsible for the alteration, Homo sapiens .