Poorly armed for the showdown with weeds

By Alec Nicol

The presentation opened with an illustration of two gunslingers facing off at high noon with the caption "new weapons to fight new battles".

For Professor Neal Stewart, from the University of Tennessee, the face-off is against weeds, but without the right weapons - revolvers, when a futuristic raygun is needed.

Having spent 10 years trying, and failing, to deliberately breed a "super weed" incorporating the herbicide-resistant traits of GM canola, Professor Stewart said there was a lot to be learned about the genes responsible for "weediness".

"This is what we need to understand if we are going to get the information necessary to fight this enemy," he said. Speaking to more than 200 delegates at the 14th Australian Weeds Conference at Wagga in September, Professor Stewart said he was seeking $US12 million ($A17 million) to map the genome of a dominant weed species.

"We know nothing about the microbiology of our enemy, but genomics holds the promise of allowing us to know the enemy as never before," he said.

He had a couple of candidates for his genomics study, including wild turnip, but his prime target was the Amarathus species, the pigweeds that he described as "the consummate weed".

The team at the University of Tennessee has been working with transgenic canola for 10 years.

Researchers have crossed canola - genetically modified to contain the Bt gene - with wild turnip to investigate the impact of a "super weed" produced naturally in the paddock by such a cross.

But instead of a super weed, he said, they had only managed to produce a "wimpy weed".

"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 said his research had convinced him that the spontaneous evolution of new, herbicide-resistant weeds was a far greater threat than the possibility of a transgenic super weed.

"We saw the first examples of glyphosate resistance in horseweed, Conyza canadensis, in 2000," he said. "Now we have half a million acres of what I call Roundup Ready horseweed in the state - the effect of over-reliance 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."

GRDC Program 6