Biologists say they have found a potential superweapon in a long-running arms race with bacteria that threaten essential crops.

Tested in a lab, their technique entails inserting a gene kit into a plant so that its immune system recognises and fights germ invaders, they reported in the journal Nature Biotechnology.

Bacteria cause huge losses to crops each year. Farmers usually tackle the foe by dousing their fields with chemicals, but these are expensive and can damage soil biodiversity.

Another way is to shore up the plant's defences by a gene introduced through cross-breeding with a hardier strain.

Yet this can rarely give a plant resistance against a wide range of germs - besides a bacterium may swiftly evolve to sneak around the new defence.

Phytobiologists led by Cyril Zipfel at the Sainsbury Laboratory at Norwich, eastern England, delved into plants' innate defence system, hunting for watchdog genes able to spot a pattern of telltale proteins exuded by a microbial invader.

Like bones and skin in humans, these proteins are essential for the bacteria's core functions and so are less likely to mutate, for to do so could harm the pathogen's survival.

The watchdog genes govern so-called pattern recognition receptors (PRRs).

PRRs were discovered 15 years ago but much is unclear. A PRR can spot essential proteins from quite a range of bacteria but it's uncertain whether the defence is unique to a given family of plants or can be transferred to another.

Exploring this avenue, Zipfel's team took a PRR specific to the Brassica family - the plant group that includes mustard, Brussels sprouts and cabbage - and slotted it into two plants from the Solanaceae family, which includes tomatoes, potatoes, aubergines and tobacco.

The Solanaceae plants showed "drastically enhanced" resistance to many different bacteria, including Ralstonia solanacearum, a major cause of crop wilt.

"The strength of this resistance is because it has come from a different plant family, which the pathogen has not had any chance to adapt to," Zipfel said.

"Through genetic modification, we can now transfer this resistance across plant species boundaries in a way traditional breeding cannot."

The work is proof of principle and there is a long way to go before the technique may enter the public domain.

Zipfel said in the "constant evolutionary arms race" between plant and pathogen, the possibility that a germ could mutate and thus bypass the new weapon will be smaller, but cannot be discounted.

The head of the Sainsbury Laboratory, Sophien Kamoun, said the research was exciting.

"Cyril's work indicates that transfer of genes that contribute to this basic innate immunity from one plant to another can enhance pathogen resistance," said Kamoun.

"The implications for engineering crop plants with enhanced resistance to infectious diseases are very promising."

© 2010 AFP