Will Rate of Maize Yield Improvement That Has Occurred in the Past Extend into the Future?.

US maize yield has increased eightfold over the past eight decades and approximately 75% of the improvement is attributable to genetic gain. The physiological mechanisms that have contributed most to the genetic improvement have been (i) increased functional stay-green and abiotic stress tolerance, on the source side, and (ii) increased partitioning of dry matter to ears and florets/kernels during early ear development, on the sink size. Functional stay-green and tolerance to abiotic stresses appear to be associated and the potential for future improvement in those traits is large. Harvest index (i.e., proportion of dry matter partitioned to the grain at maturity) has remained constant during the past 8 decades, but we speculate that harvest index will start to increase in the near future thereby accelerating yield improvement beyond the rate of improvement in source traits.