The publication today of the full genetic recipe for the world's most important food crop – otherwise known as the rice genome – has thrown the spotlight on the difficulties facing global agriculture. The production of rice, like many staple crops in the developing world, is failing to keep pace with the growth in the human population. Already, in many parts of the world, there is not enough rice to meet demand. Could the manipulation of rice genes using DNA technology provide the answer?
Half of the people alive today rely on rice to provide them with 80 per cent of their dietary needs. For a third of the world's population, rice is the principle, or indeed the sole source of vital calories. At the same time, some 24,000 people die each day of hunger and its related causes, and another 800 million, many of them children, go to bed each night hungry and malnourished.
Since the "green revolution" of the late 20th century, when increased agricultural production banished many, but not all, famines, rice has been at the centre of the improvements in cereal crop yields. Between the 1960s and 1980s, the rate of increase in rice production just about matched the rate at which human numbers were also increasing. We were, by and large, able to believe that we could feed the new mouths that appeared each year.
However, something happened in the 1990s to cast new doubts over this assumption. Scientists first began to detect the decline in rice production in Thailand and India, and then confirmed it by long-term field trials in the Philippines. The problem seemed complex. Intensive rice cropping damaged the delicate soils of the rice paddies; overwatering boosted production but led to a rise in salinity levels; and some new rice varieties simply reached their highest possible yields.
The rate of increase in rice production fell to less than half of what it was in the previous three decades. Over the last decade, for the first time in a generation, the rate of increase in the population exceeded that for the rate of increase in rice production. The Food and Agriculture Organisation wanted to find out why, so they set up a task force with the unwieldy name of the Expert Consultation on Yield Gap and Productivity Decline in Rice Production.
It was a straightforward, almost Malthusian problem. Unless rice production could be boosted, we were heading for a global famine on a scale that no-one could predict. "We'll need to increase current rice production from nearly 600 million tons annually to almost 800 million tons by the year 2025," says Nguu Nguyen, an agricultural officer at the FAO. And just to make things more difficult, it will have to be done using less land, labour, water and pesticides, or the increased yield will be unsustainable, says Nguyen.
If this sounds like mission-near-impossible, you'd be right. Past experience suggests that boosting yields can only be achieved by using more land, water, and pesticides. Combined with the clever creation of high-yielding hybrid crops, this was essentially how the green revolution managed to increase production to feed a growing world. Many agriculturalists, however, say that although this worked once before, we have to think of some new tricks – which is where the rice genome comes in.
Donald Kennedy, the editor of the journal Science, which publishes the genome studies today, believes that rice could prove more important even than the deciphering of the human genome. The genetic code for rice "will speed improvements in nutritional quality, crop yield and sustainable agriculture to meet the world's growing needs", he says.
The sentiment is matched by Gane Ka-Shu Wong, senior research scientist at the University of Washington's Genome Center, and a lead author on the Science study. "Rice is considered the model genome for all the cereal crops, such as maize, oats, wheat and barley. If you put all these cereal crops together, something like 80 per cent of all the calories consumed in the world come from genomes that are very similar to rice," explains Dr Wong.
Steven Briggs, from the Swiss-based agrochemicals firm Syngenta, agrees: "The genome map of rice is directly related to corn, wheat and barley and provides commercial opportunities for the improvement of all cereal crops – the foundation for the world's food supply."
Dr Briggs was part of the Syngenta team that sequenced the japonica variety of rice, whereas Dr Wong worked alongside the Chinese scientists who decoded the DNA sequence of the indica strain. Combining the results of the two studies suggests that the rice plant possesses between 45,000 and 56,000 genes – perhaps more than the estimated 30,000-40,000 human genes.
The apparent dearth of genes in the human genome belies its hidden complexity. Whereas most rice genes appear to be involved in producing a single protein, many human genes appear to be able to produce more than one by a genetic trick known as "alternate splicing".
"What is interesting about rice and other plants is that there is relatively little alternate splicing," says Dr Wong. "In the case of humans, it's like each gene is a Swiss army knife and you can do a lot of things with one knife. If you do not use a Swiss army knife, you have to carry a separate tool for everything."
A direct comparison between the human and rice genomes has resulted in another finding. "We have compared the genome map of rice to that of humans, and despite having eaten plants for millions of years, there is no evidence that dietary DNA from plants can be taken up into the DNA of humans. So a crop gene produced by biotechnology is unlikely to be acquired by livestock or humans," says Dr Briggs.
Comparing the rice genome with that of arabidopsis, a weed-like plant that has become a genetic model for the botanist, reveals that they share about 8,000 genes, a legacy of a common ancestor dating back to about 200 million years ago when the two major branches of plants (monocots and dicots) diverged.
More interestingly, rice appears to share much in common with the other cereal crops, which had a common ancestor some 50 to 70 million years ago. Dr Briggs says that this is why Syngenta spent about $30m (£21m) decoding the rice genome. "We are working to improve mainly our varieties of maize and wheat using the rice genome," Dr Briggs says. "Because the organisation of the rice genome and the sequence of its genes is directly related to that of the other cereals, we are using it primarily for the purpose of improving those other cereals. We expect to see improvements both in yield and in quality of the grain produced by the application of the rice genome."
By decoding the genes of rice and other staple crops, scientists hope to find new ways of improving productivity by increasing, for instance, resistance of the plants to drought and pests. With rice in particular, there are great hopes of improving its nutritional content – "golden" rice, genetically engineered with a gene for enriching vitamin A, is an example of what could be done in the future. As the authors of the Science paper conclude: "Continued application of genomic and biotechnology tools to crop improvement will be necessary to meet future food, health and material challenges."
The "high-tech" solution to global food shortages is not, however, universally accepted. Environmental groups such as Greenpeace are opposed to genetic modification of crops, arguing that it is about maximising profits for multinational companies rather than helping the poor. Greenpeace cites other ways of boosting rice production that do not rely on increased agrochemicals or gene technology. Planting different rice varieties in fields affected by fungal disease has increased some yields in China by 89 per cent, it says. But Greenpeace also says that it is not yields alone that matter. "The ghost of Malthus still haunts debates about food security, despite widespread recognition that it is not food production per se that determines whether the world is fed or not," says a report by Greenpeace called The Real Green Revolution.
"In this sense, arguments as to whether different forms of agriculture can 'feed the world' are simplistic," it says. "Other significant intermediary factors influence access to and distribution of food on the global and regional scales and within communities."
Comments