Tuesday, August 4, 2009

By Lanie Reyes

Drought brings to mind negative images of wide expanses of dry and parched lands. It is often associated with abject poverty, distraught farmers, hungry children, sickness, and sometimes hopelessness (see Dreams beyond drought, pages 15-21 of Rice Today Vol. 4 No. 2).

According to the International Rice Research Institute (IRRI),1 about 38% of the world area—home to 70% of the total population and source of 70% of global food production— suffers from drought. The effects of this problem are massive and devastating for the rice farmers who need to plant the crop that feeds half the world's people.

Drought is a formidable foe, which IRRI fights untiringly through rice research. Most scientists agree that it is one of the most complex and toughest stresses to overcome when compared with other constraints such as salinity, flooding, pests, and diseases.

Considering that rice is a wateradapted plant grown in flooded fields, helping it cope with water stress and enabling it to produce economically good yields under drought is a great challenge.

But, this does not stop IRRI scientists from finding answers and new solutions for breeding new varieties and from understanding the effects of drought on rice at the genetic and molecular level (see Making rice less thirsty on pages 12-14). For them, the challenge is clear― increase rice yield despite drought.

One potential solution for better understanding drought complexities is through genetic modification (GM, also called transgenics, uses modern biotechnology techniques to change the genes of an organism).

Coincidentally, scientists have been using genetic modification in some forms for years. In fact, all crops have been genetically improved (modified) for millennia by selection by farmers and by breeding in the past hundred years.2 In addition, the Nuffield Council on Bioethics concluded in 1999 that genetic engineering could be considered as natural as conventional plant breeding.3

For farmers, GM crops are no longer a novelty. The International Service for the Acquisition of Agribiotech Applications (ISAAA) reported in 2008 that 25 countries cultivated GM crops, including the developing countries Egypt and Burkina Faso. ISAAA reported that between 2007 and 2008, the area grown to GM crops rose by 9.4% or 10.7 million hectares, totaling more than 120 million hectares. An increasing number of people consider GM as a potential source for more benefits in agriculture, for example, for a rice variety tolerant to drought.

Research groups at IRRI, led by Drs. Rachid Serraj, crop physiologist, and Inez H. Slamet-Loedin, cell biologist, are currently working on drought-tolerant varieties using GM. (For a general idea about this process, see Tool box for making GM rice.). “Current GM technologies at IRRI are very efficient for both indica and japonica rice cultivars, and there is no major technical bottleneck in producing a large number of ‘events’ (independent plants generated from a GM cell) as long as there is space to plant and characterize them,” said Dr. Slamet-Loedin.

A new drought-screening facility and a protocol that mimics drought conditions in the lowland rice ecosystem have been established at IRRI to support, enhance, and expand the scientists’ work on developing a drought-tolerant crop. Unlike in the past, when GM drought-tolerant crops were mostly tested under artificial conditions using pots, the new facility allows scientists to better predict the crop’s yield, which previously was difficult to estimate.

“The new drought-screening facility can assess a bigger population of plants to take into account the possible variation in the effects of a transgene on plant growth and yield performance,” Dr. Serraj said.


“Since IRRI is able to generate large numbers of transgenic events, it is more efficient to select and discard plants from the early steps, and keep only those showing promising responses,” he added. The rice plants can be robustly and comprehensively selected based on their phenotypes (physical attributes) and yield characteristics.

Rice farmers, however, are often not interested in the significance of having a drought-tolerant crop per se, since they are more concerned about whether the crop will produce a good and sustainable yield. An improved crop could survive drought stress, yet not produce a harvestable yield. So, it is crucial for scientists to measure biomass accumulation (weight or total quantity of the plant) and yield performance that would result from modifying a gene.

“At an early step of the evaluation, we assess the impact of water deficit on plant growth and use nondestructive measurements to analyze crop performance,” Dr. Serraj said. “Plant phenology (the plant’s biological stage, that is, flowering, tillering, grain formation, etc.), growth, transpiration, canopy temperature, photosynthesis, leaf rolling, tillering ability, root biomass, and spikelet fertility are among the parameters to be measured for a large number of plants.”4
Nancy Sadi asa, Evelyn Liwanag, and Flor Montecillo, research technicians; Malen Estrada, assistant scientist (front row); Dr. Rachid Serraj, crop physiologist, and Dr. Dong Jin Kang, a postdoctoral fellow (at the back) at IRRI, inside the droughtscreening facility.

Moreover, Dr. Dong Jin Kang, an IRRI postdoctoral fellow, explained (with reference to the samples in the droughtscreening facility), “Plants that grow and produce well in this condition are selected as candidates for drought tolerance.” The facility also contains a flooded control plot of GM rice. Scientists compare the performance of the tested varieties under different conditions, to make sure that any selected material would be able to perform well under a variety of environments.

Dr. Slamet-Loedin said that the performance of GM rice is tested under drought and irrigated conditions to identify transgenic events in both conditions since drought may not occur in each planting season.

Sometimes, the transgenic plant performs better than the wild-type counterpart in drought conditions, but may yield less in normal conditions. This is a crucial factor and the reason candidate genes tested at IRRI are designed to be activated by drought (making the expression of the drought tolerance gene inducible by drought) to avoid any yield penalty in normal conditions.

To further ensure that no uncontrolled water will enter and ruin these experiments, the scientists placed a 1-meter-deep physical barrier around the plots to prevent water seepage and percolation from adjacent flooded plots. The bed under the drought treatment, on the other hand, is equipped with a drainage system in which water gravitationally flows and gradually reduces the soil moisture of the topsoil.

Moreover, to maintain the precision of soil drying, scientists constantly monitor the amount of moisture and water tension in the soil, as well as the air temperature, relative humidity, and vapor-pressure deficit.

“Periods of managed water deficits are imposed with precise parameters of stress timing, duration, and severity,” Dr. Serraj explained. “Soil water is gradually reduced a few weeks after transplanting until the flowering and grain-setting stages, with soil moisture decreasing from fully saturated to minimal,” he added.

The facility also has a doublelayered mesh on the ceiling and the surrounding divider to satisfy biosafety requirements. “Without protection, flying insects could enter the facility,“ Dr. Kang explained.

The drought-screening facility has been successful in creating realistic drought conditions. During the dry season of 2007, the first droughtscreening 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. The scientists were pleased to observe that the data on yield under irrigated and drought conditions inside the drought-screening facility were similar to the ones obtained from non-transgenic field experiments at IRRI.

“We are making progress and we have already identified a few promising lines,” Dr. Serraj confidently stated. “These, however, will need further testing and validation. The drought-screening facility greatly helped in our transgenic research, so we plan to establish a similar and bigger facility in the future. This will allow us to test more gene candidates.”

Not leaving any stone unturned, IRRI scientists intend to find more ways to help farmers cope with drought. With advances in technology, things are definitely looking up for both scientists and farmers. Droughttolerant varieties are developed and enhanced by the integration of GM approaches into breeding programs, as well as the by the use of this new facility that enhances precision and effectiveness in delivering new and improved genetic lines.

1. See Economic costs of drought and rice farmers’ coping mechanisms, edited by S. Pandey, H. Bhandari, and B. Hardy, 2007.
2. See Redesigning rice photosynthesis to increase yield, edited by J.E. Sheehy, P.L. Mitchell, and B. Hardy, 2000.
3. http://www.nuffieldbioethics.org/fileLibrary/pdf/gmcrop.pdf
4. See Drought frontiers in rice: crop improvement for increased rainfed production, edited by R. Serraj, J. Bennett, and B. Hardy, 2008.

© International Rice Research Institute 2009