Comparison between heterosis for yield exhibited by elite maize hybrids and contribution from dominance

Heterosis in plants refers to the superiority of F1 hybrid over its inbred parents. Heterosis has contributed to reducing hunger and malnutrition over the past 100 years. To unlock the full potential of heterosis for use in crop production, efforts have been devoted to the investigations of its genetic basis. The dominance hypothesis mostly held sway before the modern techniques of genomics were initially employed in this field. The current view is that the dominance hypothesis is one of the non-mutually exclusive hypotheses and is even questioned. Here we perform a combined theoretical and experimental study to assess the contribution of dominance to heterosis. With the consideration that dominance alone contributes to heterosis, we derive the expression for calculating the ratio of heterosis to midparent value, and determine the maximum ratio. Using the maximum ratio as a standard of comparison, we compare the contribution from dominance with heterosis for yield exhibited by the elite maize hybrids and their parents. Our study indicates that dominance partially contributes to heterosis or is not a contributor. In other words, the contributions of other factors to heterosis are essential. For the last two decades, a few new mechanisms underlying heterosis have been proposed coupled with advances in genomics technologies. Because our knowledge regarding the genetic basis of heterosis still needs to be enriched, developing efficient strategies for hybrid breeding would be considerable challenges.