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Researchers in China and Japan have combined molecular genetics with traditional plant breeding to create high-yielding rice plants.

They say their approach, which greatly reduces the time needed to develop new crop varieties, could be applied to a range of cereal crops and trigger "a new green revolution".

The original green revolution of the 1960s developed high-yielding varieties of crops such as rice and wheat by crossing existing strains to find hybrid offspring with desirable traits. It is credited with saving millions of people from starvation.

But the success relied on years of painstaking work.

"Usually, it takes more than ten years to produce a new variety," says Moto Ashikari, one of the authors of the new study, published online last week by Science.

Ashikari and colleagues wanted to develop a large number of seeds per plant. The researchers wanted their new variety to be short because tall plants with heavy seed heads tend to fall over in strong wind and rain. Short rice plants also invest more of their energy into producing seeds rather than growing taller.

The researchers began by selecting two varieties with desirable traits. One is Japan's most popular rice, Koshihikari; the other, a shorter, more productive variant called Habataki.

They identified regions of the plants' genetic code that had to be present to increase plant yields.

One DNA region was a gene that makes an enzyme called cytokinin oxidase, which breaks down a hormone cytokinin that affects plant reproduction and growth.

Habataki plants, which make less of the enzyme, produce more seeds; 306 per branch compared with Koshihikari's 164.

Using a form of cloning, the researchers produced Habataki plants containing only the DNA region of interest. They then used conventional plant breeding to create hybrids with Koshikari plants. These hybrids had 45 per cent more rice grains the normal Koshikari plants.

But they were too tall. So using another set of clones, whose Habataki genes make plants shorter than Koshikari, the researchers used conventional methods to breed a new, stout variety with 26 per cent more seeds than normal Koshikari and short enough to resist bad weather.

The researchers believe that wild varieties of rice and other crops could have particular DNA regions "not only for yield, but also for disease resistance, stress tolerance and other desired traits".

Ashikari told SciDev.Net that identifying the regions that affect important agricultural traits is difficult because environmental conditions have a big effect on how plants develop.

"Strict control of growth and climatic conditions is necessary," says the researcher. "Molecular biologists tend not to do such research, so it is essential to collaborate with excellent agronomists."

Ashikari and colleagues at Nagoya University, Japan, worked together on the research with Japanese scientists at the RIKEN Plant Science Center in Yokohama and the Honda Research Institute in Chiba, and with researchers at the China National Rice Research Institute, in Hangzhou, China.

Link to full paper by Ashikari et al.