Dual genetic mechanisms of heterosis: population structure and gene action

Authors: AGUILAR, FERNANDO - Iowa State University; LAMKEY, KENDALL - Iowa State University; Edwards, Jode

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2025
Publication Date: 1/27/2026
Citation: Aguilar, F.S., Lamkey, K.R., Edwards, J.W. 2026. Dual genetic mechanisms of heterosis: population structure and gene action. Frontiers in Plant Science. 16. Article 1715826. https://doi.org/10.3389/fpls.2025.1715826.
DOI: https://doi.org/10.3389/fpls.2025.1715826

Interpretive Summary: Producing and marketing successful hybrid corn varieties requires identifying high performing hybrids and managing the cost of producing seed of those varieties. Corn varieties, or hybrids, sold to farmers are produced by crossing two seed parent lines to produce the hybrid seed that is sold to farmers. Seed parent yield in corn tends to be very low, which makes production of seed corn very expensive. The difference between seed parent productivity and the productivity of the hybrid variety sold to farmers is referred to as hybrid vigor. Scientists in Ames, Iowa, have developed and tested new genetic models for hybrid vigor that improve our understanding of the genetic basis for the difference in yield between seed parents and hybrid varieties grown by farmers. The new models indicate more clearly that hybrid vigor is mostly a function of seed parent yield and has little effect on hybrid variety performance, which is in contrast to previous work suggesting a need to increase hybrid vigor in order to increase on-farm yields of hybrid varieties. The work supports growing evidence that seed parent yields can be increased to reduce seed-production costs without negatively impacting on-farm hybrid variety grain yield. The work also provides new insights for scientists on how to design experiments to study hybrid vigor. This work will directly impact seed producers and farmers which will benefit on farm profitability.

Technical Abstract: Introduction: Heterosis refers to the superiority of a hybrid over its parents. Existing heterosis theory has not sufficiently addressed the contribution of inbreeding at both population level and the level of individual lines within populations. The objectives of the present paper were to formalize theoretical extensions of heterosis theory to address inbreeding at multiple levels, to empirically test the theory in maize, and to provide greater clarity in the quantitative genetic interpretation of heterosis as a function of independent genetic principles of population structure and gene action. Methods: Existing heterosis theory for biparental crosses was extended by adding terms for inbreeding within panmictic parent populations. The theory was tested with an experiment in maize with a diverse set of panmictic and inbred parents. Results: Extended theory demonstrated that both heterosis and inbreeding depression are linear functions of inbreeding, FST at the population level, and f at the individual level, under a model of directional dominance. The model demonstrates that heterosis is expected to be negatively related to both midparent value and inbreeding depression within parent populations, i.e., heterosis increases as midparent value decreases and as inbreeding depression within parent populations decreases. Consistent with theoretical predictions we found that that for maize grain yield midparent value predicted 86% of heterosis in a set of crosses and parental inbreeding depression predicted 70% of variation in heterosis among crosses. Discussion: Model extensions presented here illustrate the excess and transient nature of heterozygosity in the F1 generation that is partially responsible for the unique performance benefit of F1 hybrids. Mechanistically, the theory illustrates that heterosis is a function of two separate and independent mechanisms, population structure and gene action, both of which need to be considered in understanding the mechanisms of heterosis.