Kernel weight contribution to yield genetic gain of maize: A global review and US case studies

Over the past century of maize (Zea mays L.) breeding, grain yield progress has been the result of improvements in several other intrinsic physiological and morphological traits. In this study, we describe (i) the contribution of kernel weight (KW) on yield genetic gain across multiple agronomic settings and breeding programs, and (ii) the physiological bases for improvements in KW for US hybrids. A global-scale literature review concludes that rates of KW improvement in US hybrids were comparatively similar to those of other commercial breeding programs but extended over a longer period of time. There is room for a continued increase of kernel size in maize for most of the genetic materials analyzed, but the trade-off between kernel number and KW poses a challenge for future yield progress. Through phenotypic characterization of Pioneer Hi-Bred ERA hybrids in the US, we determine that improvements in KW have been predominantly related to an extended kernel-filling duration. Likewise, crop improvement has conferred modern hybrids with greater KW plasticity, expressed as a better ability to respond to changes in assimilate availability. Our analysis of past trends and the current state of development helps to identify candidate targets for future improvements in maize.

Automated summary

This study describes the impact of kernel weight on maize yield and the physiological basis for kernel weight improvements. The rate of kernel weight improvement in US hybrids is similar to that of other breeding programs, but it has taken a longer period of time. Phenotypic analysis of US hybrids reveals that improvements in kernel weight are primarily related to an extended kernel-filling duration. Modern hybrids have greater plasticity in kernel weight, meaning they have a better ability to respond to changes in assimilate availability.