Genomics the key to knowing the enemy

The American professor likened the confrontation between the world"s farmers and weeds as a "High Noon" face-off between two gunslingers. He projected an image of a western gunfight and apologised for suggesting it is in fact a fair fight: "The gunslinger with his back to us (farmers) needs a ray-gun in his holster."

This was Professor Neal Stewart"s way of impressing on delegates at the 14th Australian Weeds Conference that the fight against weeds needs to get seriously high-tech.

Professor Stewart, from the University of Tennessee, said he was seeking $US12 million to map the genome of a dominant weed species.

"We know nothing about the micro-biology of our enemy," he said. "But if we can understand the genes responsible for "weediness" we have the information needed to fight.

Genomics holds the promise of allowing us to know the enemy as never before."

Professor Stewart has two candidates for his genomics study, and Australian farmers would be heartened by his nomination of wild turnip. However, his prime target is the Amarathus species, the pigweeds which he describes as "the consummate weed".

The team at the University of Tennessee has been working with transgenic canola for 10 years in an effort to try and create the much vaunted "super weed" predicted by anti-GM campaigners. The team has crossed canola, genetically modified to contain the Bt gene, with wild turnip to investigate the impact of a super weed that might be produced naturally in the paddock.

However, instead of a super weed the team has so far only managed to produce a "wimp".

"Our transgenic weed proved to be about as competitive as the canola crop and was certainly less competitive than its unmodified wild turnip parent," Professor Stewart said.

"It seems that we"d managed to "cropify" our new weed.

It"s one of the reasons why it"s important to understand the genomics of our weed species and to identify the genes responsible for their weediness."

Professor Stewart believes that the spontaneous (natural) evolution of new, herbicide resistant weeds is a far greater threat than transgenic super weeds: "We saw the first examples of glyphosate resistance in horseweed, Conyza canadensis, in 2000 and now we have half a million acres of what I call Roundup Ready® horseweed in Tennessee - the effect of overreliance on a single herbicide.

"We don"t understand the mechanism of this resistance, it"s not the same as that used to introduce resistance in the crop plants, and it underlines the need for the development of tools and knowledge in weed genomics."

- Alec Nicol