Extreme heat, especially without overnight relief, and low soil moisture during pollination are very stressful to corn plants in particular. In 2012, an extreme drought enveloped more than 70 percent of the United States including my own farm, but the crop losses were less than feared due in large part to new traits and improved seeds. The most obvious benefit were seeds that allowed crops to use water more efficiently so they could maintain decent yields with less water. Most of these seeds were developed using breeding, but there was a limited amount of a genetically modified drought corn on acres last year as well.
I wrote a piece recently for CNN's Eatocracy (http://bit.ly/1a5js2c) highlighting how far we've come since the days of my great grandfather. I did not have any corn marketed as drought tolerant on my farm last year, but a myriad of factors, not the least of which is breeding, gave us a crop in the extreme drought of 2012 comparable to our state's corn yield contest winner in 1940. Therefore, it's quite possible that the worst corn crop I'll ever raise is equivalent to the best of the best raised by past generations. Compared to other row crops corn has a relatively short window of pollination. I can speak to corn crops since corn is a crop we grow on our farm. Soybeans have a much longer pollination period and generally can withstand heat and water stress conditions more favorably than corn can.
But “drought tolerance” was only one of a number of breeding and genetic improvements that protected crops and sustained yields throughout the drought. The new herbicide-tolerant crops developed with biotechnology have significantly increased the use of no-till agriculture, preserving precious soil moisture. Some conventional farmers like myself are now turning to cover crops in order to keep living plants on our soils between cash crops. These covers have many benefits including improve water infiltration and retention. In addition some GM corn varieties resist root-eating insects, thus keeping their root systems intact and allowing the plants to better access what little water was available.