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Making climate-ready rice

By reducing the number of stomata that form on rice leaves, it is possible to increase water conservation and drought tolerance in rice.

ROBERT S CAINE | New Delhi |

Rice is a global superfood, eaten daily by half of the world’s seven billion people. Its impact stretches from the wealthiest in society, who enjoy it with delicacies such as sushi, to the very poorest, who depend on rice for day-to-day survival. Cultivation occurs across six of world’s seven continents, with the Food and Agriculture Organisation of the United Nations estimating that, at present, around 510 million metric tonnes of rice are produced annually.

Whilst this level of production is generally meeting the current demand, it’s foreseen that for every additional one billion people, an extra 100 million tonnes of rice will be required. This is a huge challenge considering that as many as three billion extra people will populate the earth by 2050, or four billion by 2100.

As well as human population increases, there are a number of other factors that are predicted to put pressure on future rice yields. A critical factor is the availability of fresh water, a key and fundamental resource for rice cultivation. Rice uses water to maintain vigour, acquire nutrients and regulate internal temperatures when it becomes hot. Currently it takes around 2,500 litres of water to produce one kilogram of paddy rice, and this high water consumption contributes globally to rice using between 25 and 33 per cent of all the developed fresh water reserves. These numbers are clearly unsustainable given that water supplies will come under increasing pressure as the human population continues to expand and the demand for rice continues to increase.

This is especially true given that many people will increase the amount of meat and dairy in their diets, both of which are highly water intensive to produce. To put the water-use of rice into context with animal-based foods, it takes six times as much water to produce one kilogram of beef, and twice as much water to produce a kilogram of butter. Clearly, as pressure on water reserves increase, efforts need to be made to improve the efficiency with which rice uses water.

Because of anthropogenic climate change, water supplies for rice cultivation will be tested further by three additional factors. First, changes in precipitation patterns are predicted to lead to more sporadic incidences of rainfall, which in many cases will lead to increased incidences of severe drought.

Second, because temperatures are forecast to rise, rice leaves will release more water to maintain safe temperatures, thereby reducing the amount of water remaining in the soil. And third, because soil water levels will be reduced due to the first two factors, the concentration of salt in the remaining fresh water will increase. This will be further compounded by more frequent influxes of salt water from the rising oceans, again a factor related to past and present human activities.

Such different environmental factors together suggest we need rice varieties, which are more water-use efficient and salt tolerant, yet at the same time permit enough water loss for rice to stay cool when temperatures are high.

Until August 2019, I was a postdoctoral research associate at the University of Sheffield. The project I worked on involved a multi-national team of researchers from the UK, China, Thailand and the Philippines. Using cutting-edge genetic modification and gene editing technologies our groups collaborated to investigate ways to improve the water-use efficiency of rice.

We focused specifically on manipulating microscopic pores called stomata on the rice leaf surface. Stomata serve two main purposes — first, to enable carbon uptake for photosynthesis, and second, to regulate the release of water. Stomatal regulation over water flow helps to govern the overall water-status of plants, and is crucial for water conservation in the soil and response to drought.

Using GM and GE we generated plants with reduced numbers of stomata per unit area of the leaf. We showed that plants with fewer stomata used less water under normal conditions, resulting in more water being conserved in the soil. This conservation resulted in improved drought tolerance when water was withheld during controlled experiments. We further showed that under higher temperatures plants with fewer stomata could adapt and still regulate plant temperature, yet at the same time survive drought longer than control plants.

Despite the above project coming to a close, we are still working together with one of our partners, the International Rice Research Institute, to undertake field trials using the GM and GE plants we generated together. We hope that our plants will exhibit similarly reduced water usage and improved drought tolerance equivalent to what we have seen during the controlled experiments conducted in Sheffield.

Because our plants take up less water, we have further hypothesised that they might also take up less salt – – therefore being healthier when grown in water with high salinity. We have begun to test whether this is the case under controlled conditions, and preliminary results are looking encouraging.

Given the cultural resistance to GM and GE rice in many rice-growing countries, we acknowledge that our proof-of-concept studies may not be commercialised at this point in time. However, our work clearly shows that by reducing the number of stomata that form on rice leaves, it is possible to increase water conservation and drought tolerance in rice.

My new role job role at The University of Sheffield is a global challenge research fellow. I am now investigating how to optimise rice growth in the future climates of the Mekong Delta in Southern Vietnam. This region has large swathes of land, which already suffer with high salinity and/or drought and this is predicted to worsen with climate change.

At present I’m growing rice varieties from around the world under controlled conditions at the University of Sheffield and am beginning to investigate the stomatal properties associated with the species being grown. I aim to identify rice varieties, which have a natural reduction in the number of stomata.

By early 2020 I will travel to Vietnam to begin working alongside partners at the High Agricultural Technology and Research Institute in the Mekong Delta. We aim to cross varieties identified to have superior stomatal properties with high yielding varieties, thereby generating plants, which will have increased drought and salt tolerance yet still deliver high yield.