One of agriculture's major challenges to poor rice farmers, especially those in developing countries, is damage to rice crops from flooding.

Rice thrives in standing water but, like other crops, will succumb if completely submerged for more than a few days. Any measures helping rice plants to survive periods of flooding would clearly be of immense value to rice farmers and those who depend on their products – increasing food security for tens of millions of people as well as reducing weed losses where, as in the US, rice is planted in flooded fields.

So it is encouraging to learn that a gene enabling rice to survive complete submergence has been identified in a collaboration between the International Rice Research Institute in the Philippines and the Davis and Riverside campuses of the University of California. The discovery allows for development of new rice varieties able to withstand flooding, thus overcoming one of agriculture's oldest challenges and offering relief to millions of poor rice farmers around the world.

The announcement of the discovery points out that 25% of the global rice crop, the primary food for more than 3 billion people, is grown in rain-fed, lowland plots at risk from unpredictable seasonal flooding which may occur at any growth stage of the rice crop.

Rice is the only cereal crop able withstand submergence at any time but most varieties die if fully submerged for too long because oxygen and carbon dioxide exchange are hampered, so interfering with photosynthesis and respiration. Four days of total submergence is about the limit.

Annual crop losses have been estimated at more than $1 billion, while in any given year, yield losses from lowland flooding may range from 10% to total destruction, depending on the severity of flooding as well as the age and nutritional state of the plants.

A cluster of three genes appear to be linked to either making rice plants vulnerable to flooding or enabling them to withstand total submergence. Over-expression of one of these genes confers tolerance to flooding.

Transferring that gene into a rice variety suitable for cultivation in India has already yielded plants both tolerant to flooding and generating high yields. Development of submergence-tolerant varieties for commercial production in Laos, Bangladesh and India is now under way.

Sources:

1. Flood-tolerant rice offers relief for world's poorest farmers. UC David News & Information
(9.11.06) (http://www.news.ucdavis.edu/search/news_detail.lasso?id=7833)

2. Takuji Sasaki. Rice in deep water. Nature, 442, 635-636 (10.8.06) (http://www.nature.com/nature/v442/n7103/full/442635a.html)

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