I got out of farming in the winter of 2000-01, and became a truck driver, so things have changed a lot since then. However, from 2009 through 2011 I was the ‘farmer’ for a family owned corn and soybean seed company (which included being a truck driver for them).
The production manager told what the biggest genetic changes were for corn: the upright leaves, and improved drought resistance and nutrient uptake.
I asked about the fungicide usage. He said that the elimination of moldboard plow usage was leaving more trash on the surface, causing more fungus growth. That, coupled with the increased populations, shade the ground more, which increases the favorable fungus environment. (They used a disc-chisel plow on everthing, except on some of the previous year’s soybean ground, which we no-tilled.)
A study in 2019 at the Bayer test farm near Monmouth, IL, and mentioned the big reasons for increased corn yields, three of which I mentioned, but also ear plasticity allowing better kernel development. (I lived about 20 north of there until 2016)
What I fear is if the petrochemical industry gets clobbered in a war, there will be a desperate need for moldboard plows and rowcrop cultivators. But only if there is fuel still available. Only the Amish and preppers are ready for such a scenario.
Those are legitimate concerns; even worse would be the unavailability of hybrid seeds.