Famine has its chips with suicidal potato

Potatoes could soon have an effective defence mechanism against the fungus which caused the Irish famine 150 years ago: self-destruction.

Scientists at the Plant Breeding Institute in Cologne, Germany, are using genetic engineering to give potato plants a "suicide pill" which would be activated when they are infected by the parasitic fungus phytophthora infestans, better known to farmers as Late Blight.

The result would be that although parts of the plant - possibly including some or all of its potatoes - would die, the infection would be contained.

Late Blight is a huge problem for farmers, causing an estimated pounds 10bn crop loss annually and affecting 20 per cent of the world crop. It is also mutating into more aggressive forms, which are being spread internationally by imports to countries which suffer underproduction due to drought.

The new technique adds a gene that produces the enzyme barnase, which is a potent destroyer of essential nucleic acids within cells. "It's lethal if it's inside a cell," said Professor Alan Fersht, of the Cambridge Centre for Protein Engineering. "In nature, there's usually an inhibitor called barstar which prevents it functioning."

Barnase is normally produced by a plant bacterium, which uses it to gather nucleic acid constituents from plants it infects, so that it can reproduce. But the Cologne team is adding the gene for the enzyme to strains of potato plants. Normally when a plant is infected by the Late Blight fungus it starts to fight back in a limited form. The altered plants produce barnase in the cells of affected leaves, killing off those cells and effectively isolating the fungus. However, when used in food and other products they would be indistinguishable from standard potatoes.

"It's really rather clever," said Professor Fersht. "It's like apoptosis, the process of programmed cell death that you get in a normal cell when its DNA is damaged."

Trials of the transgenic potatoes are now under way in Germany, where they are scheduled to last until 1999.