[AngryData]

Many yield increases are due more to increased fertilizer availability. You don't want to grow ulta-large-super-crop if it means you suck 95% of the fertilizer from the soil and can't replace it. Even if you could breed the plant 100 years ago, nobody would want to use it if it sucked their topsoil layer away in a few years. Or if it was nutrient limited already, those plants would simply not grow as large or have as much yield.