GM walnuts could soon hit the supermarket shelves, after scientists at the University of California developed a way to modify the roots of the walnut tree to enable them to fight infection from a bug called Agrobacterium.

Agrobacterium causes cancerous growth that invades the plants' DNA.

Abhaya Dandekar, who headed the team of researchers, developed tree roots that contained versions of the tumour-causing genes, which acted as a kind of built in vaccine to Agrobacterium.

The team employed a standard cultivation technique to ensure that the nuts produced by the tree are not themselves genetically altered. New Scientist explained: "In this case, non-GM plants would be grafted onto modified roots without the two sets of genes mixing."