By: James A. Birchler, Donald L. Auger and Nicole C. Riddle
Heterosis, or hybrid vigor, refers to the phenomenon that progeny of diverse inbred varieties exhibit greater biomass, speed of development, and fertility than the better of the two parents. This phenomenon has been exploited extensively in crop production and has been a powerful force in the evolution of plants. The genetic basis has been discussed for nearly a century but little consensus has emerged. With the advent of the genomic era, the tools to establish a molecular basis for heterosis are at hand. In the past, there has been a tendency to attribute any molecular differences between the parents and progeny as contributing to the basis of heterosis. Some individuals dismiss the phenomenon as hopelessly complex. It seems likely, however, that the complexity derives from its multigenic nature and that eventually a unifying principle will emerge. In this article, we summarize some of the salient features of heterosis that a viable molecular model must explain.