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Two corncobs are seen in a corn field ready to be harvested
A team of US scientists has uncovered the complete genetic code of corn, a discovery that promises to speed development of higher yielding varieties of one of the world's most important food crops.

Corn is the third most abundant cereal crop, after rice and sorghum, researchers said. Advances in corn production could mean major steps toward feeding the world's growing population as it struggles with climate change.

The team of 150 experts, led by Washington University in St. Louis, Missouri, said Thursday they had identified some 32,000 DNA sequences, or genes, in the 10 chromosomes that make up the genome of maize, the largest of any plant examined so far.

By comparison, the human genome includes 20,000 genes distributed in 23 chromosomes.

"Having the complete genome in hand will make it easier to breed new varieties of corn that produce higher yields or are more tolerant to extreme heat, drought, or other conditions," said senior author Richard Wilson, director of Washington University's Genome Center.

"Seed companies and maize geneticists will pounce on this data to find their favorite genes," he said. "Now they'll know exactly where those genes are."

The study is published in the November 20 issues of Science, PLoS Genetics and the Proceedings of the National Academy of Sciences.

Corn's genetic code contains about 2.3 billion bases of DNA, represented by the letters T, C, G and A. Human genetic code is not far off with 2.9 billion.

After having great difficulty establishing the exact order of the letters, the researchers found that about 85 percent of the sequences are repetitive. Their function -- if the repetitive sequences have a function -- is unknown, researchers said.

"Sequencing the corn genome was like driving down miles and miles of desolate highway with only sporadically placed sign posts," said researcher Sandra Clifton of Washington University.

"We had a rudimentary map to guide us, but because of the repetitive nature of the genome, some of the landmarks were erroneous. It took the dedicated efforts of many scientists to identify the correct placement of the genes."

The project, which began in 2005, cost 29.5 million dollars and was funded by the National Science Foundation and the US departments of agriculture and energy.

Scientists at the University of Arizona in Tucson, Cold Spring Harbor Laboratory in New York and Iowa State University in Ames were key to the mapping of the corn genome, the researchers said.

As is often the case in plants, corn's genetic code is made up of two separate but intertwined genomes, reflecting its evolution over millions of years.

The United Nations predicts that world food output must grow by 70 percent over the next four decades to feed a projected extra 2.3 billion people by 2050.

The United States is the world's top producer of corn with 200 million tons a year, or 44 percent of the world's output.

Researchers Fusheng Wei and Jianwei Zhang of the Arizona Genomics Institute said the corn genome project should help food-growers face the challenges of growing more crops on less land with less water and poorer soil.

"Contemporary society is now faced with growing demands for food and fuel in the face of global climate change and the potential for increased disease pressure," Wei and Zhang wrote.

The genome projects aims "to provide a comprehensive foundation to systematically understand maize biology with the goal of breeding higher yielding, disease-resistant and drought-tolerant cultivars."