Understanding environmental modulation of heterosis

Heterosis, which is the superior performance of hybrid offspring relative to the average of their parents, has been exploited in plant and animal breeding for centuries. Understanding the molecular basis of heterosis and variation for the degree of heterosis among different parental combinations has been the focus of many studies. Heterosis within a single parental combination can vary substantial depending on the trait of interest (e.g. high heterosis for plant height, and none or moderate heterosis for yield). The degree of heterosis for a single trait in a single parental combination can also show substantial variation across environments. Here, we summarize the current state of knowledge on variation in heterosis that is driven by environmental modulation. Much of the research in the environmental modulation of heterosis has been conducted under various high stress conditions, with limited studies focusing on environmental modulation under natural field conditions. These investigations have shown that variation in heterosis that is modulated by the environment is largely the product of variability in inbred performance under these high stress conditions. Further understanding of the factors that drive environmental modulation under natural conditions will be important for breeders to further strategize how to exploit this genetic phenomenon for continued crop improvement.