When humans first domesticated maize about 9,000 years ago, these early breeding efforts resulted in an increase in harmful mutations in the culture's genome compared to their wild relatives, which has been corrected by newer modern breeding.
A new comparative study examines whether the same patterns as corn appear in sorghum, a gluten-free grain grown for both livestock and human consumption. Researchers were surprised to find the opposite is true: harmful mutations in sorghum landraces (early domesticated plants) actually decreased compared to their wild relatives.
The study "Comparative evolutionary genetics of harmful loads in sorghum and maize" was published on January 15 in Natural plants. The lead author is Michael Gore, Professor of Molecular Breeding and Genetics at the College of Agriculture and Life Sciences (CALS).
The research could influence future breeding efforts in both sorghum and maize.
"We assumed that maize and sorghum would have complementary patterns of deleterious mutations, as all work up to this point on crops showed an increase in deleterious exposure in domesticated individuals compared to wild relatives from whom crops were derived." said Gore. "But sorghum doesn't follow that pattern, and it's very surprising."
These "harmful mutations", which may negatively affect an organism's fitness, result from random genetic errors that occur every generation and from ancient mutations that can be associated with useful genetic variants that occur during domestication and improvement of the crops selected.
In the study, researchers performed population genetic simulations to explain why sorghum didn't follow the same pattern as corn.
A key difference between maize and sorghum is that maize (wild and domesticated) is an "outcruiser", meaning that its female flowers (ear shoots) are predominantly pollinated by other maize plants. Domesticated sorghum is a "selfer", which means that the flowers of its panicles (heads) are largely fertilized by each plant's own pollen.
It turns out that the wild relatives of sorghum have more open seed heads that make outcrossing easier. In the course of the domestication of sorghum, the panicles in which these flower clusters are located became more compact, which increased the "selfing" rates.
"We believe that the change in panicle morphology affects harmful mutation patterns in sorghum," said Gore. "The resulting increase in selfing likely helped eradicate harmful mutations after domestication."
By understanding the historical patterns of harmful mutations, breeders can use this knowledge to better remove harmful mutations from sorghum plants. "What we learn in sorghum could be applied to corn and vice versa," said Gore.
The study was funded by the US Department of Energy.