Ricing to the challenge of climate change

There’s a nice feature on the BBC on preparing rice cultivation for climate change. I’ve taken the liberty of dissecting out the bit about the IRRI genebank and the breeding work of Haiyan Xiong. Mainly because I found all the scrolling so annoying.

Farmers in China are acutely aware of the impact of water shortages. Population growth, increasing urbanisation and industrial water use are all making water shortages more common in China, says Haiyan Xiong, a postdoctoral researcher in plant sciences at the University of Cambridge. Water distribution is geographically uneven, with limited rainfall in northern China and seasonal droughts in southern China.

Much of China’s variable water supply is going to a single crop: rice. About 4,000 litres of water are needed to produce just one kilogram of rice, according to Xiong. Other estimates vary between about 2,500 and 5,000 litres. In China, irrigation for the crop accounts for about 70% of the total agricultural water use.

One response to this problem has been to look for types of rice that use less water. To this end, thousands of rice varieties are being preserved at the world’s largest rice gene bank, in the Philippines. These include enhanced varieties such as ‘scuba rice’, which can withstand flooding, and the drought-tolerant Sahod Ulan varieties being used by some Filipino farmers.

Xiong and her colleagues hope to combine genome editing with traditional breeding methods to create new drought-resistant varieties. But this is a challenge. “Due to the complexity of the genetic mechanism…not much progress has been made in improving rice drought resistance in China,” she says. “Very few genes can be used in actual production to improve the rice drought resistance.”

Yet the team have identified a single gene in upland rice, known as OsLG3, that’s linked to the length of rice grains as well as drought tolerance. Upland regions, which are dry and hilly, are a much harder environment to grow rice in than lowland paddy fields, and upland rice is usually of lower quality. So introducing the upland drought-tolerance gene into the more widely cultivated lowland rice could allow for the best of both worlds.

Another new type of rice bred for challenging conditions is known as Green Super Rice.

Chinese soil, especially in coastal provinces, naturally contains high amounts of salt, which can become even more concentrated in areas with low rainfall and high evaporation. When there’s too much salt in the soil, plants experience something known as osmotic stress. A large amount of water exits the plant’s cells, causing them to shrink suddenly. The process limits plant growth and productivity.

As with Xiong’s drought-tolerant upland-lowland rice, researchers have found genetic traits in rice varieties that can help Green Super Rice withstand high salt levels and osmotic stress. This often involves backcross breeding, in which genes associated with a desirable trait are bred into a second variety by hybridisation. So far, Green Super Rice appears to produce a high yield in addition to having a high salt tolerance. The hope is that this could open up coastal or other high-salt areas to rice growing.

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