A drought-screening facility for transgenic plants promises further gains as drought-tolerant rice varieties begin to emerge.

Since the dawn of agriculture, drought has been the bane of farmers, especially those who grow rice, a crop with special water requirements. Most rainfed areas receive a reasonable amount of rain during the growing season, but its erratic distribution and deficits at such critical stages as flowering and grain-filling can seriously curtail productivity. In Asia alone, 23 million hectares, or 20% of the continent’s rice land total, are prone to drought under current climatic conditions. Climate change is likely to worsen water scarcity in many rice-growing areas.

IRRI scientists intend to find more ways to help rice farmers cope with drought. Photo: IRRI.

Most farmers in drought-prone rainfed areas grow varieties bred for irrigated conditions. As irrigated varieties are highly susceptible to drought, farmers are lucky to harvest even half a ton per hectare when droughts occur.

To help farmers cope with water scarcity, the International Rice Research Institute (IRRI) has developed several new breeding lines that yield as well as other varieties under normal conditions and have a yield advantage of up to 1 ton per hectare under drought. Two of these drought-tolerant lines have been recommended for official release, one in India and the other in the Philippines.

“IRRI has intensified efforts to develop drought-tolerant and aerobic cultivars to cope with the looming water shortage,” says David Mackill, leader of IRRI’s rainfed program. (Aerobic rice is cultivated intensely in the lowlands for high yield but in dry paddies, not flooded ones, to save water.) “Drought-tolerance has been a complex trait to improve, and I’m very happy to see recent progress in developing drought-tolerant lines at IRRI.”

With advances in technology, both farmers and scientists can look foward to more climate-resilient varieties of rice. Photo: IRRI.

To support and expand scientists’ development of drought-tolerant rice varieties using genetic modification, IRRI established a drought-screening facility and a protocol that mimics drought conditions in lowland rice fields. In the past, genetically modified drought-tolerant breeding lines were tested mostly under artificial conditions using pots, as field trials would violate biosafety requirements. The drought-screening facility allows scientists to better predict the yield these lines would have in the field. The facility has a flooded control plot of genetically modified rice to allow scientists to compare the performance of the tested varieties under different conditions and ensure that any selected material would perform well under a variety of conditions.

During the dry season of 2007, the first drought-screening experiment using the facility was carried out to test the effects of a gene for drought tolerance provided by the Japan International Research Center for Agricultural Sciences. Scientists were pleased to observe that the data on yield under irrigated and drought conditions inside the drought-screening facility were similar to those obtained from non-transgenic field experiments at IRRI. The drought-screening facility was thus found to succeed in creating realistic drought conditions.

“The facility allows us to assess a large population of plants to take into account possible variation in the effects of a transgene on plant growth and yield performance,” explains crop physiologist Rachid Serraj. “IRRI is able to generate large numbers of transgenic lines, so it is more efficient to select and discard plants early on, keeping only those that show promise.

“We assess the impact of water deficit on plant growth and use non-destructive measurements to analyze crop performance,” Serraj continues, adding that plants’ flowering, tillering, grain formation, transpiration, canopy temperature, photosynthesis, leaf rolling, tillering ability, root biomass, and spikelet fertility are other parameters that are measured.

Sometimes a transgenic plant performs better than others under drought but yields less under normal conditions. IRRI looks for candidate genes that are activated by drought to avoid any yield penalty under normal conditions.  

“The drought-screening facility has greatly helped in our transgenic research, so we plan to establish a similar and bigger facility in the future,” states Serraj. “This will allow us to test more candidate genes.”