An international team of researchers, representing research institutes in China and the United States, have found that ancient farmers had a stronger impact on the evolution of maize than modern plant breeders. Maize, now the world’s most widely produced grain, was domesticated around 10,000 years ago.

Two studies, one on the evolution of maize and a companion study on maize diversity, were produced with contributions from scientists at 17 international institutions. Commenting on the study’s impact, plant geneticist Jeffrey Ross-Ibarra, lead researcher from University of California Davis, said, "These two studies provide a new and more comprehensive understanding of genomic variation in maize, which will be critically important to plant breeders as they work to increase corn yield in the face of global population growth and climate change."

The study led by Ross-Ibarra analysed the evolution of maize during the period when it was domesticated 10,000 years ago, as well as during subsequent breeding. The study looked at 75 genomes of maize and its relatives, including wild strains, traditional cultivated varieties and improved modern inbred lines. The study revealed that, whilst diversity was initially lost during domestication, new diversities have arisen since domestication in the form of novel mutations.

The researchers also found that selection applied during initial domestication appears to have been much stronger than selection applied more recently during maize breeding, meaning initial changes during the domestication of maize wrought greater changes than subsequent breeding.

In looking at maize’s transition from wild plant to major staple food, the UC Davis team also found that most of the modern variations on maize are centred on genes selected for hybrid vigor, however, the most significant changes were brought about by ancient farmers who domesticated the crop. Hybrid vigor is a phenomenon identified in 1908, whereby superior offspring is produced from mixing the genetic contributions of its parents; this can include greater resistance to disease or increased fertility.

Another companion study, also examining the maize genome, revealed that the presence or absence of certain genes is common in both wild and domesticated maize, and these variations are associated with important agricultural traits, such as disease resistance. The second study, led by Doreen Ware, a U.S. Department of Agriculture-Agricultural Research Service biologist, found that there is substantial continuity of gene content between maize relatives, suggesting that environmental adaptations such as perennialism, and frost and drought tolerance might be transferred from wild relatives into domesticated maize. The researchers said the maize gene is “essentially still in flux.”

Both teams of researchers suggested their studies, published in Nature Genetics this month, have implications for addressing food security issues; as the world's population is expected to climb from 7 billion people this year to an estimated 9 billion by 2050, experts have suggested that food production needs to increase globally by a significant amount, and that due to environmental constraints, much of this rise in production will have to be realised by increasing crop yield on existing farmland rather than by bringing new land into agricultural production.

The researchers from UC Davis said their research will go towards breeding healthier more resilient maize, which may raise yields and increase the crops’ range further still, and that they believe the maize studies will serve as the basis for future research in crop evolution.

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