Overcoming the toughest stress in rice: Drought

 Lanie C. Reyes   |  
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 drought-screening facility. (Photo: William Sta. Clara)

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 drought-screening facility. (Photo: William Sta. Clara)

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), 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 water-adapted 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. In addition, the Nuffield Council on Bioethics concluded in 1999 that genetic engineering could be considered as natural as conventional plant breeding.

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.”

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