A key part of a complex genetic puzzle that has vexed scientists for years is now solved, with the announcement by researchers at UC Davis and the U.S. Department of Agriculture that the sequencing of the wheat genome is now complete.

The sequencing results, published in the journal Nature, are expected to have a profound effect on the growing of wheat – the world's most important food crop.

"This is a major stepping stone," said Olin Anderson, co-author of the Nature paper and researcher of genomics and gene discovery at the USDA, which participated in the sequencing with eight other institutions.

The sequencing of the genome – the complete set of genetic material of an organism – will likely lead to the breeding of stronger wheat capable of withstanding drought and an onslaught of pests that threaten crops. Locally, Central Valley farmers will someday be able to grow wheat tolerant of the high salt content that is rising in local soils.

The challenge of sequencing the genes was a big undertaking, due to the complexity of wheat genes. Wheat owns the distinction of having the largest genome among all the world's major crops; it is 30 times larger than the rice genome.

Its genomic structure is so complex it is nearly twice the size of the human genome, and its nucleus contains five times as much DNA, said Jan Dvorak, professor of plant biology at UC Davis, and a key member of the multinational research team.

Modern day wheat is derived from three ancient wheat grass species. As a result its DNA is a combination of the three – which made sequencing three times the challenge.

To sequence the genome, new genetic technology had to be created, starting from scratch. The process, called "shotgun sequencing," entailed breaking up the genome into small segments for analysis. Like a jigsaw puzzle those segments are culled with the intention of piecing them together in the right order to complete a genomic picture.

Now that the picture is taking shape, the world's wheat breeders and farmers will be able to grow wheat resistant to drought and pests like stem rust, an airborne fungus that devastates wheat and barley crops in Africa and the Middle East, and is a threat to wheat crops in the United States.

"Knowledge is power, and having this genetic tool will make it possible to breed wheat more efficiently," Dvorak said.

Most wheat breeding in the United States is done by public entities, with UC Davis one of the world leaders.

"In the past the only way you could breed was to take (plants) and expose them to disease and see which ones would survive," said Kent Bradford, director of the seed and biotechnology center at UC Davis. "Now, instead of growing out thousands of plants – and killing 98 percent of them – we can efficiently screen, at a very young stage, those that can resist disease."

Such tailored breeding will have many applications and impacts. In the San Joaquin Valley, farmers will be able to specifically target wheat seeds that can grow in salty soil, Bradford said.

That option is no small matter to farmers given the rising salt content found amid water-hungry farmland areas west of the San Joaquin River. A 2009 UC Davis study reported that if salinity increases at the current rate, by 2030 the direct annual costs to Central Valley agricultural communities and farms will range from $1 billion to $1.5 billion.

With water at a premium, and groundwater levels dropping, Central Valley farmers do not always have the option to flush out salts left in soil once irrigated water evaporates from it, Bradford said.

"If we can increase tolerance in wheat, in even small amounts, we can use poorer quality water, or recycled water, and better manage our water supplies in California," Bradford said.

The sequencing has drawn keen interest from those involved in global food security issues. Wheat is grown on more land than any other commercial crop. The rise in the middle classes in countries like China and Singapore is increasing the demand for wheat, as is overall rising population in the Third World.

"Sequencing the wheat genome has important long-term implications for food security," said Kristin Wedding, deputy director with the Center for Strategic and International Studies.

"This could be especially important for regions in sub-Saharan Africa, south Asia, China, and the Middle East where demand will continue to grow as populations boom in the next 30 years," Wedding said.

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