By Jonathan Amos BBC News Online science staff

Two groups of researchers report a draft DNA sequence of the plant - a staple for more than half the world's population - in the journal Science.

The genetic information should speed up the breeding of tougher and higher-yielding varieties that can help feed the world's burgeoning population.

The journal has drawn fire for the deal it has struck with Syngenta

The genomic data will also prove invaluable in boosting the productivity of the other grasses on which humans depend, such as maize (corn) and wheat.

The research shows that a rice plant probably has more genes than a human - perhaps as many as 50-60,000 genes, compared with our 30-40,000.

But the rice genome, like the gene sets of all plants, contains tremendous duplication. Something like three-quarters of all rice genes are repeated in the code.

Much duplication

Scientists think plants copy their genes and then modify them as a strategy for coping with the selective pressures associated with evolution.

The Beijing Genomics Institute and the University of Washington Genome Center, with colleagues at 11 Chinese institutions, read the code of the rice strain known as indica, the predominant subspecies in China and other Asian-Pacific countries.

The second team, fronted by the Swiss-based Syngenta company, decoded the japonica, or Nipponbare, subspecies, which is popular in more arid regions and, in particular, Japan.

The genetic difference between the two is small but significant - about a half to one percent variation in the code. This is about 10 times the variation you would find in the genetic codes of two humans.

Rice, known scientifically as Oryza sativa, is the second plant to be decoded. The first was the tiny mustard plant, Arabidopsis thaliana, used as a laboratory model to investigate plant biology.

Rice, however, is the first food crop to be sequenced.

Another method

Both teams used the Whole-Genome Shotgun technique, the same method employed by the private company Celera to read the human "code of life".

And just like Celera, Syngenta has struck a deal with the Science journal editors that ensures it keeps proprietorial control over the japonica sequence.

Rice

Type of grass that grows from about 60 to 180 cm tall Edible grain is the primary food for over half the world's population World rice production totals nearly 600 million tonnes China (including Taiwan) and India produce more than 50% of the total crop

The code has not been deposited in a public database, GenBank, as is customary, but in an escrow account held by Science and a separate system run by Syngenta.

Researchers wanting to work on the sequence will have to sign usage agreements with the Swiss company. Critics claim the access restrictions go against the spirit of open research and will slow the advance of new knowledge.

A consortium of public laboratories, known as the International Rice Genome Sequencing Project (IRGSP), financed by Japan, is also sequencing the Nipponbare subspecies.

The consortium has opted to use a more systematic, traditional route to decryption which, though more precise, can take longer. The IRGSP is expected to publish its results later this year.