Researchers have genetically engineered a more nutritious type of rice which could help alleviate the serious problem of vitamin A deficiency.

It is estimated 124 million children worldwide lack vitamin A, putting them at risk of permanent blindness and other serious ailments.

The scientists, based at the Swiss Federal Institute of Technology in Zurich, inserted three genes into rice that make the plant produce beta-carotene.

This is the substance all mammals, including humans, must take into their bodies to make vitamin A.

Beta-carotene, or provitamin A as it is known, gives the new rice a golden colour.

The team, whose research is reported in the journal Science, says breeding lines of the plant are now being established and the seeds will be made freely available to farmers in developing countries.

This will please aid organisations who have expressed concern that the new plant technologies will be priced beyond the reach of the world's poorest farmers.

Biochemical pathway

Commentators say the science represents a "technical tour de force" as it is the first time a plant has been engineered with a complete biochemical pathway - that is to say, all the different steps an organism must complete to make a particular product.

Professor Ingo Potrykus, one of the rice researchers, told the BBC many scientists did not believe it would be possible when work began on the project eight years ago.

He said: "When we started the project, and throughout the progress of this project, the scientific community was convinced that it could not work because nobody previously had been able to engineer a complete biochemical pathway."

The technology is being given to a number of rice institutes around the world, where traditional breeding methods will be used to integrate the beta-carotene genes into local varieties.

Professor Potrykus said: "We are already starting to do the same with wheat. We are close to doing the same with cassava.

"We will probably also introduce it to barley. We have initiated collaborations to put the same genes into banana and sweet potato. The number of important core plants which don't have enough or any provitamin A can be engineered now to achieve the same."

Iron-rich

The team has also managed to insert two genes into rice which make it iron-rich, something that could have serious impact on tackling anaemia around the world.

But this has not been as successful as the beta-carotene project as rice naturally prevents iron absorption in the gut.

Dr Manju Sharma, secretary of the Indian Government's Department of Biotechnolgy, told the BBC the new rice could have very important implications.

He said: "Rice is a strategic crop. A very large population of India is dependent on rice.

"We would like to improve the nutritional quality of rice so as to combat a number of deficiencies like the vitamin A deficiency, which causes blindness to millions of children."

Roughly half of the world's population, including virtually all of East and Southeast Asia, is wholly dependent upon rice as a staple food.

This compounds health problems because the edible part of rice grains, the endosperm, lacks several essential nutrients.