Genetic Contributions to Yield of Maize in the US Central Corn Belt 1930-2011.

Studies measuring genetic gain for hybrids widely used in the central Corn Belt of the US during the 1930s and thereafter were initiated at Pioneer in 1977. Here we report data for the release period 1930-2011. Previous reports of genetic gain at optimum planting density were 92 kg ha^–1 yr^–1  (1930-1980) and 77 kg ha^–1 yr^–1 for 1930-2001. We report genetic gain of 88 kg ha^–1 yr^–1 for hybrids released 1930-2011 when planted at optimum density. Estimated effects of weather on the 35 year period during which era hybrids have been yield tested are minimal contributing a slight upward bias. Genetic gain contributes 71% of annual yield gain on Iowa farms. Tassel size has continued to decrease but erectness of leaves has plateaued. Trends toward shorter anther silk interval, improved stalk lodging, and root lodging have continued while resistance to barrenness and improvement in stay green have plateaued. From yield studies of isohybrids (+- Cry1Ab) during 200-2007 we estimate a mean contribution to yield from resistance to attack by European Corn Borer of 565  kg ha^–1. Over a 20 year period the contribution to yield by insect resistance is approx. 23% while 77% is contributed by improvements in the well-adapted native maize germplasm base. Further improvements will be hardest to achieve for maize grown in low stress (e.g. irrigated) environments. We anticipate a further increase in the rate of genetic gain, especially in rain-fed environments as the impact of recently adopted new breeding technologies exert their full impact during the next 10 years.