Maize Yield Potential and Density Tolerance

Abstract

Maize (Zea mays L.) yield potential has not undergone genetic improvement during the hybrid era, yet substantial genetic improvement has occurred for tolerance to high plant population densities. As many crops including maize are approaching yield plateaus, it may be necessary to exploit other means of increasing grain yields. In this study, we examine potential reasons for why this occurred. Using a four‐way breeding cross representing the commercial germplasm pool, we demonstrate that the lack of genetic improvement in yield potential is not due to the two attributes being antagonistic. We then demonstrate that the lack of genetic improvement in yield potential is not due to density‐tolerant genotypes being higher yielding at modern conventional plant densities. We show that physiological differences in partitioning dry matter to the grain (i.e., harvest index [HI]) are present in a set of genotypes with contrasting yield potential and density tolerance genotypes. However, a higher or a lower HI is not associated with yield potential either. Finally, we show that the density‐tolerant genotypes exhibit a static kernel set efficiency (KSE), meaning that regardless of the plant growth rate at silking (pGRS), the number of kernels formed per unit dry matter fixed is constant. Surprisingly, the hybrids with high yield potential possess a dynamic KSE and are capable of sustaining kernel set at higher levels when pGRS is low. Given our findings, there is no apparent biological or genetic explanation for genetic improvement in only density tolerance during the hybrid era.