Scientists said the breakthrough is a critical step towards developing barley varieties able to cope with the demands of climate change.
It should also help in the fight against cereal crop diseases which cause millions of pounds of losses annually.
Researchers said barley is the second most important crop in UK agriculture, and malting barley, some 30% of the total, underpins the beer and whisky sector which is worth around £20 billion to the UK economy.
The UK team behind the international research was led by Professor Robbie Waugh, of Scotland's James Hutton Institute, who worked with researchers at the Genome Analysis Centre in Norwich.
He said: "Access to the assembled catalogue of gene sequences will streamline efforts to improve barley production through breeding for varieties better able to withstand pests and disease, and deal with adverse environmental conditions such as drought and heat stress.
"It will accelerate research in barley, and its close relative, wheat. Armed with this information, breeders and scientists will be much better placed to deal with the challenge of effectively addressing the food security agenda under the constraints of a rapidly changing environment."
As well as being used in the beer and whisky industry, barley is also a major component of the animal feed for the meat and dairy industries, while barley straw is used for animal bedding in the winter, and for frost protection in horticulture.
Unravelling the sequence of barley's DNA has proved a major challenge for scientists as the barley genome is almost twice the size of that of humans.
Its genome contains a large proportion of closely related sequences that are difficult to piece together into a true linear order.
However, scientists from the International Barley Genome Sequencing Consortium (IBSC), including UK researchers in Dundee and Norwich, managed to construct a high-resolution draft DNA sequence assembly which contains the majority of barley genes in linear order.
Published in the journal Nature, the sequence provides a detailed overview of the functional portions of the barley genome, revealing the order and structure of most of its 32,000 genes and a detailed analysis of where and when genes are switched on in different tissues and at different stages of development.
Scientists said the research will provide a far better understanding of the crop's immune system.
It has been funded by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Scottish Government.
Professor Douglas Kell, BBSRC chief executive, said: "This provides a timely and important new tool for unlocking the potential of better varieties of barley that are able to cope with environmental stresses or produce higher yields.
"It is an exceptionally valuable step for UK agriculture at a time when we have seen huge losses in the field due to wet weather and price-rise predictions for the consumer."
The IBSC was founded in 2006, and includes scientists from Germany, Japan, Finland, Australia, the United Kingdom, the United States and China.
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