Human Aspects of Technical Risk Management

Abstract

Technology has never been accepted as broadly as it is today. There are three exceptions, however: Nuclear, bio and gene technology. Whether a technology is accepted or not depends less on rational arguments and more on whether we trust the people who run and supervise the technology. As new technology has increased manifold, there is no time to test everything in detail and science does not give us the answers about threshold levels and safety limits. Risk acceptance cannot be calculated. Instead, it has to be discussed in a democratic dispute.

Bounded rationality makes risk management possible; we are able to convince, to lead a risk dialogue, to overcome complex situations.

Herbert Simon (1916–2001), American economist

The Economist: Genetic modification: Filling tomorrow’s rice bowl

Genetic engineers are applying their skills to tropical crops

© The Economist Newspaper Limited, London (Dec 7th 2006)

EVERY hectare of paddy fields in Asia provides enough rice to feed 27 people. Fifty years from now, according to some projections, each hectare will have to cater for 43. Converting more land to paddy is not an option, since suitable plots are already in short supply. In fact, in many of the continent’s most fertile river basins, urban sprawl is consuming growing quantities of prime rice-farming land. Moreover, global warming is likely to make farmers’ lives increasingly difficult, by causing more frequent droughts in some places and worse flooding in others. Scientists at the International Rice Research Institute (IRRI) doubt it is possible to improve productivity as much as is needed through better farming practices or the adoption of new strains derived from conventional cross-breeding. Instead, they aim to improve rice yields by 50% using modern genetic techniques.

On December 4th the Consultative Group on International Agricultural Research (CGIAR), a network of research institutes of which IRRI is a member, unveiled a series of schemes intended to protect crop yields against the ill effects of global warming. Many involve genetic engineering—which is generally embraced by farmers in poor countries even if some Western consumers turn their noses up at it. Some, though, only use genetics to identify useful genes. For example, IRRI’s scientists have found a gene that allows an Indian rice strain to survive total immersion for several weeks, and have cross-bred it into a strain favoured by farmers in flood-prone Bangladesh. In trials, the new plant produced as much rice as the original under normal conditions, but over twice as much after prolonged flooding. This trait could increase the world’s rice harvest dramatically, since flooding damages some 20m hectares (50m acres) of rice each year out of a total crop of 150m hectares.

By far the most ambitious project on CGIAR’s list, though, involves transforming the way in which rice photosynthesises. That will require some serious genetic restructuring.

Three into four will go

Most plants use an enzyme called rubisco to convert carbon dioxide (CO₂) into sugars containing three carbon atoms—a process known as C3 photosynthesis. But at temperatures above 25°C, rubisco begins to bond with oxygen instead of CO₂, reducing the efficiency of the reaction. As a result, certain plants in warm climates have evolved a different mechanism, called C4 photosynthesis, in which other enzymes help to concentrate CO₂ around the rubisco, and the initial result is a four-carbon sugar. In hot, sunny climes, these C4 plants are half as efficient again as their C3 counterparts. They also use less water and nitrogen. The result, in the case of staple crops, is higher yields in tougher conditions: a hectare of rice, a C3 plant, produces a harvest of no more than eight tonnes, whereas maize, a C4 plant, yields as much as 12 tonnes.

Turning a C3 plant into a C4 one, though, is trickier than conferring flood resistance, since it involves wholesale changes in anatomy. C4 plants often absorb CO₂ from the air in one type of cell and then convert it to sugars through photosynthesis in another. C3 plants, by contrast, do both jobs in the same place.

On the other hand, C4 photosynthesis seems to have evolved more than 50 times, in 19 families of plant. That variety suggests the shift from one form of photosynthesis to the other is not as radical as might appear at first sight. It also gives researchers a number of starting points for the project. Some C4 plants, for example, absorb CO₂ and photosynthesise it at either end of special elongated cells, instead of separating the functions out into two different types of cell. Many C3 plants, meanwhile, have several of the genes needed for C4 photosynthesis, but do not use them in the same way. In fact, the distinction between C3 and C4 plants is not always clear-cut. Some species use one method in their leaves and the other in their stems.

John Sheehy, one of IRRI’s crop scientists, plans to screen the institute’s collection of 6,000 varieties of wild rice to see if any of them display a predisposition for C4 photosynthesis. Other researchers, meanwhile, are trying to isolate the genes responsible for C4 plants’ unusual anatomy and biochemistry. A few years ago, geneticists managed to get rice to produce one of the enzymes needed for C4 photosynthesis by transplanting the relevant gene from maize.

The task, admits Robert Zeigler, IRRI’s director, is daunting, and will take ten years or more. But the potential is enormous. Success would not only increase yields, but also reduce the need for water and fertilisers, since C4 plants make more efficient use of both. Other important C3 crops, such as wheat, sweet potatoes and cassava, could also benefit. If it all works, a second green revolution beckons.