Aid workers in Africa are familiar with the sight: children with orange-tinted hair and distended bellies, lying listless in villages seemingly blessed with abundant food.

Victims of malnutrition rather than hunger, the children are dying because they have been weaned early from their mother's milk and placed on gruel diets that lack the protein needed to build muscle and bone.

So when scientists came up with a maize variety that boasted higher levels of essential amino acids - a maize, incidentally, that was produced by conventional breeding, not genetic engineering - you might have expected universal rejoicing.

But while the two researchers who played a large role developing Quality Protein Maize, known as QPM, were yesterday named winners of this year's World Food Prize, some promoters of economic development in poor countries regard the breakthrough with something bordering on suspicion.

Their caution sheds light on why the debate over the rights and wrong of genetically modified crops has become so heated. Wrapped up within the anti-GM stance adopted by environmental groups and development agencies are issues unconnected to fears of horizontal gene-transfer or pollen contamination.

Rather, they concern what are perceived as top-down approaches, or "technofixes", and they date further back than the recent furore over genetic engineering - back, indeed, to the Green Revolution itself.

"GM has become a lightning rod for other worries about agro-industrial complexes, corporate control and the undermining of local knowledge," says Professor Jules Pretty, an agricultural specialist at the University of Essex. "A lot of these concerns are not directly related to GM, but they are being expressed in that form."

Many of these issues got a recent public airing with the invention of Golden Rice, which was genetically engineered to contain beta-carotene, a yellow compound that the body converts into vitamin A. Its nutritional absence kills or blinds millions each year.

Although QPM comes free of the GM tag - a label that raises the prospect of regulatory hurdles and legal wrangling over intellectual property rights - it shares several charac- teristics with Golden Rice.

The maize traces its roots back to the 1960s, when a PhD student at Purdue University in the US discovered that two maize varieties from the Andean highlands, characterised by opaque kernels, contained large amounts of the amino acids lysine and tryptophan.

Traced to the gene opaque-2, the improved protein quotient was seized on as a weapon against kwashiorkor, a condition which distends the belly, and marasmus, a wasting disease.

But initial enthusiasm was short-lived. In the field, opaque-2's yields were 20 per cent lower than those of conventional varieties. The maize was soft and chalky, making it susceptible to insects and viruses. Kernels rotted in storage.

Opaque-2 lost its lustre and research was largely abandoned, with the notable exception of Mexico's International Maize and Wheat Improvement Centre (CIMMYT). There, Dr Surinder Vasal and Dr Evangelina Villegas - the winners of yesterday's prize - began cross-breeding Opaque-2 maize. It took funds from the UN Development Programme and 14 years of painstaking work, but they finally perfected a maize that looked and tasted like its conventional equivalent, gave high yields and boasted the extra protein content of its Peruvian ancestors.

For a while, it looked as though the breakthrough had come too late. Despairing of the project, the UNDP suspended funding and in 1992 the Mexican institute put its research materials into cold storage.

The maize was saved from obscurity by Norman Borlaug, a veteran US agricultural scientist, working with the backing of Sasakawa Global 2000, a joint venture between Jimmy Carter's centre in Atlanta and a Japanese foundation running agricultural programmes in a score of African countries.

Reviving the project and working alongside breeders in Ghana, SG 2000 developed a strain adapted to the tropics. Thanks in large part to SG 2000 and CIMMYT's efforts, QPM varieties are now being tested and grown commercially in Ghana, Togo, Mozambique, Ethiopia, Mexico, Brazil, central America and China.

It is apt that QPM's highest-profile promoter should be Mr Borlaug. The 86-year-old Nobel Peace prize winner is regarded as leader of the Green Revolution, which launched high-yielding crop hybrids on the developing world in the 1960s. Criticisms of QPM are essentially critiques of the Green Revolution's legacy.

Many development groups argue that while the new crops undoubtedly saved lives, trebling and quadrupling harvests, the revolution encouraged farmers to abandon traditional, often vitamin-rich crop strains.

With abundant carbohydrate available, peasants stopped using wild plants or vegetable plots to supplement their diets, thereby losing precious minerals.

"Two billion people now have diets less diverse than 30 years ago. The Green Revolution stripped out the micronutrients and encouraged monocropping," says Alex Wijeratna of ActionAid, the development agency.

To its critics, QPM represents an overly simplistic attempt to solve the highly complex problem of malnutrition, into which education, cultural self-confidence and overall wealth must all be factored.

"We don't reject QPM per se, but we feel it misses the point in the same way as Golden Rice. It revives the issue of 'silver bullet' solutions which often prove to have unforeseen long-term implications," says Mr Wijeratna.

The backers of QPM reject such objections as dangerously pie-in-the-sky, rooted in an unacknowledged distrust of science.

"All attempts to improve nutrition through education or supplementing diets with an egg or a piece of meat have failed, because they require complicated delivery systems or imply a degree of wealth," argues Chris Dowswell, programme director at Sasakawa. "QPM's beauty is its simplicity."

The debate seems certain to become more polarised.

SG 2000 now wants to take the project to a higher level, arguing there is only so much one foundation can do. It would like its new crop to be promoted by the UN, with agencies such as the World Health Organisation and UNICEF playing a lead role.

Looking back on the laborious years of traditional breeding, the organisation also believes genetic engineering is needed to speed up the development of QPM varieties that are adapted to different climates and conditions.

"If Sasakawa go down that route they will be highly criticised," predicts Michael Hansen, of the US Consumer Policy Institute. "Genetic engineering today is the equivalent of nuclear energy in the 1960s. My advice would be to steer well clear."

QPM's proponents admit to a degree of nervousness unimaginable before the controversy surrounding GM crops erupted a few years ago, when the launch of a new maize variety would have passed unnoticed by the public at large.

The new climate has its merits, however. On both sides of the debate, the protagonists welcome that the GM controversy has brought the issue of world hunger and food security to the attention of a wider audience.

"The one benefit of the GM debate is that your average Joe is now talking about food security. World hunger is a big issue and this is a debate we should be having," says Mr Wijeratna.

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