Multiple barriers also make it harder for Ug99 to overcome them all.

ECONOMIST: Wheat rust and world farming

Only a handful of wheat varieties have any resistance to Ug99, implying that harvests could fail even more completely than during earlier epidemics.

ECONOMIST: Wheat rust and world farming

If the wheat can learn to recognise this as it is happening, it might also be engineered to generate its own Ug99- resistant proteins.

ECONOMIST: Wheat rust and world farming

The new approach uses four or five weaker defences, for example reducing the area of the wheat plant that Ug99 destroys, or slowing down the spread of the fungus.

ECONOMIST: Wheat rust and world farming