The rice would be offered for free to developing countries where vitamin A deficiency causes blindness in up to 500,000 children each year, according to World Health Organisation figures. The human body converts beta-carotene in the diet into vitamin A.
The news raises once again the complex issue of genetic modification of plants for the benefit of poor countries. Increasing GM research could also become an issue for the health foods industry.
New biotech capabilities are allowing researchers to develop plants with higher amounts of health nutrients. Last year a team at Bristol University engineered a new strain of Arabidopsis, a relative of the cabbage, which had substantial quantities of they fatty acids arachidonic acid (ARA) and eicosapentaenoic acid (EPA).
Another team, in Germany, designed a linseed plant that accumulates significant levels of PUFA.
Like the new rice, such developments offer cheaper or more plentiful supply of key nutrients than current sources, however they also face safety concerns and consumer resistance to genetic engineering.
Syngenta's original golden rice, developed in Switzerland five years ago, has not yet been grown in field trials in Asia, although the firm says that public rice research institutions in the Philippines, Vietnam, India, Bangladesh, China and Indonesia are in various stages of developing locally adapted varieties.
Greenpeace has criticised the lack of information given on the bioavailability of beta-carotene from the rice in the body, noting that the original variety was also designed to increase intake of this nutrient but children could not get their daily requirement from eating normal quantities of rice.
It adds that several other approaches to solve vitamin A deficiency have been shown to work efficiently and the Golden Rice project is likely to distract the necessary public awareness of solutions like vitamin A supplementation and political efforts against malnutrition.
The Golden Rice Humanitarian Board, chaired by co-inventor of golden rice Professor Ingo Potrykus from the Swiss Federal Institute of Technology and Professor Peter Beyer from the University of Freiburg, noted that the rice "is but one tool in a larger toolbox from which country health officials, farmers and consumers could choose in their efforts to fight vitamin A deficiency" and that it could complement existing efforts to eradicate deficiency of the vitamin.
In Asia, the average person eats rice two or three times a day and it has also has become a staple food in many African countries. Milled white rice contains essentially no beta-carotene and unmilled brown rice contains a very small amount.
Rachel Drake and colleagues from Syngenta discuss the new development in a letter to Nature Biotechnology (doi:10.1038/nbt1082). "We hypothesized that the daffodil gene encoding phytoene synthase (psy), one of the two genes used to develop Golden Rice, was the limiting step in beta-carotene accumulation. Through systematic testing of other plant psys, we identified a psy from maize that substantially increased carotenoid accumulation in a model plant system."
This increased total carotenoids up to 23-fold, giving the rice a maximum carotenoid level of 37 micrograms per gram of rice and a preferential accumulation of beta-carotene.