A new type of rice that can survive total submersion for more than two weeks has passed its field tests with "flying colours," say researchers, and is now close to official release.

Scientists hope that the rice can make a major difference in Bangladesh and India where up to four million tons of rice per year — enough to feed 30 million people — are lost because of flooding.

'Sub1' rice is identical to the high-yielding varieties popular with both farmers and consumers across Asia, except that it contains a single gene that gives it 'waterproof' qualities.

The enabling gene, 'sub1A', was discovered 13 years ago in a traditional Indian rice variety by David Mackill — now head of the plant breeding, genetics and biotechnology division of the International Rice Research Institute in the Philippines — and Xu Kenong, his then graduate student.

Scientists inserted the gene into other rice varieties and found that it became switched on when a plant was submerged. It acts to make the plant dormant, allowing it to conserve energy until the floodwaters recede.

It also countermands the rice plant's normal strategy when submerged — to extend its stem and leaves in an attempt to escape the water.

"The potential for impact is huge," said Mackill, who collaborated on the project with the Bangladesh Rice Research Institute, India's Central Rice Research Institute and Narendra Dev University of Agriculture and Technology, also in India.

"Submergence-tolerant varieties could make major inroads into Bangladesh's annual rice shortfall and substantially reduce its import needs."

Crop scientists estimate that annual flooding leads to losses worth US$1 billion across South and South-East Asia.

Mackill said flooding is even beneficial to the rice, which produces five tons for each hectare submerged for up to two weeks. He added that an ordinary rice variety without the 'sub1A' gene produces less than one ton per hectare.

"Climate change will most likely result in more extreme weather events, including storms or heavy rainfall that causes flooding. We are continuing our research to increase the level of tolerance to flooding to a higher level," he said.

"Within the next two years, the varieties will be disseminated to small farmers in flood-prone areas."

The field trials mark the completion of a project funded for the past five years by the German Federal Ministry for Economic Cooperation and Development.