Innovation: Genetic alteration of plants aims to stop the rot: A slowed-down tomato is the first fruit of a process to make food crops last longer and cut waste

UP TO 50 per cent of the world's food crops are wasted because they rot before they can be consumed. Now genetic engineering is promising to stop the rot - which would sharply increase food supplies, writes Nuala Moran.

Trials of the first slow-rotting fruit, a tomato, have shown a yield increase of between 21 and 39 per cent. One key to preventing rotting is to control the production of ethylene, a plant hormone that causes ripening by triggering the expression of a series of ripening genes.

More subtle effects are achieved by turning off individual ripening genes. The first whole genetically engineered food to be marketed in the US, the Flavr Savr tomato, is an example. In this tomato, the gene that controls production of an enzyme called polygalacturonase is turned off.

This enzyme chops up pectin, a structural molecule in the cell wall, making the tomato go soft: without the enzyme the tomato stays firm for longer.

Ethylene is also responsible for leaf senescence, in which a plant withdraws its food reserves from its leaves, causing them to wither and fall off.

Controlling ethylene production could extend the storage life of fruit including apples, pears, melons, avocados, peaches and bananas, and of leafy vegetables such as lettuce, cauliflower and Brussels sprouts. The technique is also being applied to prolong the life of cut flowers.

Most work on the genetics of ethylene production has been done in the tomato. Apart from being easy to work with, the tomato market is worth dollars 3.6bn (pounds 2.3bn) per annum. Reducing ethylene production to 5 per cent of normal still allows the tomato to ripen to the point where it is ready to eat, but prevents ripening continuing, to make the tomato wrinkly and more prone to the damage that leads to rotting.

This is done by inserting man-made antisense genes - reverse copies of genes known to be responsible for ethylene production. Antisense genes interfere with the expression of their natural counterparts and hence the production of ethylene.

'What we are doing is understanding how the plant is working, and redesigning it using its own genes,' said Don Grierson of Nottigham University, who has pioneered tomato-ripening research in collaboration with Zeneca.

Professor Grierson said the technology was now ready to be applied more widely and had the potential to lengthen the post-harvest life of a range of fruit and vegetables.

Genetically engineered Ailsa Craig tomatoes raised at Nottingham University, which produce only 5 per cent of normal ethylene levels, last about two weeks longer than their unaltered counterparts.

The Flavr Savr tomato was launched in the US in May by Calgene, the biotechnology company, and Campbell, the food company (of soup fame), following a long patent dispute with Zeneca. By coincidence the two parties produced the same genetically engineered tomato at the same time.

Zeneca has applied to the US Federal Drugs Administration and the UK Advisory Committee on Novel Foods and Processes for permission to market puree made from tomatoes. The company expects first sales to be next year.

Zeneca also intends to apply the technique in other fruits. In July it announced an agreement to work on bananas with DNA Plant Technology of California. Professor Grierson wants to improve plants in other ways. For example, he says plants could be engineered to improve nutritional qualities.

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